Add an option to opt out fieldnorms for indexed fields.

Closes #922

.gitignore

@@ -1,4 +1,5 @@
 tantivy.iml
+proptest-regressions
 *.swp
 target
 target/debug
@@ -11,3 +12,4 @@ cpp/simdcomp/bitpackingbenchmark
 *.bk
 .idea
 trace.dat
+cargo-timing*

CHANGELOG.md

@@ -1,5 +1,33 @@
+Tantivy 0.14.0
+=========================
+- Remove dependency to atomicwrites #833 .Implemented by @pmasurel upon suggestion and research from @asafigan). 
+- Migrated tantivy error from the now deprecated `failure` crate to `thiserror` #760. (@hirevo)
+- API Change. Accessing the typed value off a `Schema::Value` now returns an Option instead of panicking if the type does not match. 
+- Large API Change in the Directory API. Tantivy used to assume that all files could be somehow memory mapped. After this change, Directory return a `FileSlice` that can be reduced and eventually read into an `OwnedBytes` object. Long and blocking io operation are still required by they do not span over the entire file.
+- Added support for Brotli compression in the DocStore. (@ppodolsky)
+- Added helper for building intersections and unions in BooleanQuery (@guilload)
+- Bugfix in `Query::explain`
+- Making it possible to opt out the generation of fieldnorms information for indexed fields. This change breaks compatibility as the meta.json file format is slightly changed. (#922, @pmasurel)
+
+Tantivy 0.13.2
+===================
+Bugfix. Acquiring a facet reader on a segment that does not contain any 
+doc with this facet returns `None`. (#896)
+
+Tantivy 0.13.1
+===================
+Made `Query` and `Collector` `Send + Sync`.
+Updated misc dependency versions.
+
 Tantivy 0.13.0
 ======================
+Tantivy 0.13 introduce a change in the index format that will require
+you to reindex your index (BlockWAND information are added in the skiplist). 
+The index size increase is minor as this information is only added for
+full blocks.
+If you have a massive index for which reindexing is not an option, please contact me
+so that we can discuss possible solutions.
+
 - Bugfix in `FuzzyTermQuery` not matching terms by prefix when it should (@Peachball)
 - Relaxed constraints on the custom/tweak score functions. At the segment level, they can be mut, and they are not required to be Sync + Send.
 - `MMapDirectory::open` does not return a `Result` anymore.
@@ -17,6 +45,8 @@ while doc != TERMINATED {
 The change made it possible to greatly simplify a lot of the docset's code.
 - Misc internal optimization and introduction of the `Scorer::for_each_pruning` function. (@fulmicoton)
 - Added an offset option to the Top(.*)Collectors. (@robyoung)
+- Added Block WAND. Performance on TOP-K on term-unions should be greatly increased. (@fulmicoton, and special thanks 
+to the PISA team for answering all my questions!)
 
 Tantivy 0.12.0
 ======================

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "tantivy"
-version = "0.12.0"
+version = "0.14.0-dev"
 authors = ["Paul Masurel <paul.masurel@gmail.com>"]
 license = "MIT"
 categories = ["database-implementations", "data-structures"]
@@ -13,42 +13,40 @@ keywords = ["search", "information", "retrieval"]
 edition = "2018"
 
 [dependencies]
-base64 = "0.12.0"
+base64 = "0.13"
-byteorder = "1.0"
+byteorder = "1"
-crc32fast = "1.2.0"
+crc32fast = "1"
-once_cell = "1.0"
+once_cell = "1"
-regex ={version = "1.3.0", default-features = false, features = ["std"]}
+regex ={version = "1", default-features = false, features = ["std"]}
 tantivy-fst = "0.3"
 memmap = {version = "0.7", optional=true}
-lz4 = {version="1.20", optional=true}
+lz4 = {version="1", optional=true}
+brotli = {version="3.3.0", optional=true}
 snap = "1"
-atomicwrites = {version="0.2.2", optional=true}
+tempfile = {version="3", optional=true}
-tempfile = "3.0"
 log = "0.4"
-serde = {version="1.0", features=["derive"]}
+serde = {version="1", features=["derive"]}
-serde_json = "1.0"
+serde_json = "1"
-num_cpus = "1.2"
+num_cpus = "1"
 fs2={version="0.4", optional=true}
 levenshtein_automata = "0.2"
 notify = {version="4", optional=true}
 uuid = { version = "0.8", features = ["v4", "serde"] }
-crossbeam = "0.7"
+crossbeam = "0.8"
 futures = {version = "0.3",  features=["thread-pool"] }
-owning_ref = "0.4"
+tantivy-query-grammar = { version="0.14.0-dev", path="./query-grammar" }
-stable_deref_trait = "1.0.0"
+stable_deref_trait = "1"
-rust-stemmers = "1.2"
+rust-stemmers = "1"
-downcast-rs = { version="1.0" }
+downcast-rs = "1"
-tantivy-query-grammar = { version="0.13", path="./query-grammar" }
 bitpacking = {version="0.8", default-features = false, features=["bitpacker4x"]}
 census = "0.4"
-fnv = "1.0.6"
+fnv = "1"
-owned-read = "0.4"
+thiserror = "1.0"
-failure = "0.1"
+htmlescape = "0.3"
-htmlescape = "0.3.1"
 fail = "0.4"
 murmurhash32 = "0.2"
 chrono = "0.4"
-smallvec = "1.0"
+smallvec = "1"
 rayon = "1"
 
 [target.'cfg(windows)'.dependencies]
@@ -58,6 +56,7 @@ winapi = "0.3"
 rand = "0.7"
 maplit = "1"
 matches = "0.1.8"
+proptest = "0.10"
 
 [dev-dependencies.fail]
 version = "0.4"
@@ -74,7 +73,8 @@ overflow-checks = true
 
 [features]
 default = ["mmap"]
-mmap = ["atomicwrites", "fs2", "memmap", "notify"]
+mmap = ["fs2", "tempfile", "memmap", "notify"]
+brotli-compression = ["brotli"]
 lz4-compression = ["lz4"]
 failpoints = ["fail/failpoints"]
 unstable = [] # useful for benches.

README.md

@@ -5,7 +5,6 @@
 [![License: MIT](https://img.shields.io/badge/License-MIT-yellow.svg)](https://opensource.org/licenses/MIT)
 [![Build status](https://ci.appveyor.com/api/projects/status/r7nb13kj23u8m9pj/branch/master?svg=true)](https://ci.appveyor.com/project/fulmicoton/tantivy/branch/master)
 [![Crates.io](https://img.shields.io/crates/v/tantivy.svg)](https://crates.io/crates/tantivy)
-[![Say Thanks!](https://img.shields.io/badge/Say%20Thanks-!-1EAEDB.svg)](https://saythanks.io/to/fulmicoton)
 
 ![Tantivy](https://tantivy-search.github.io/logo/tantivy-logo.png)
 
@@ -34,11 +33,6 @@ Tantivy is, in fact, strongly inspired by Lucene's design.
 The following [benchmark](https://tantivy-search.github.io/bench/) break downs 
 performance for different type of queries / collection.
 
-
-In general, Tantivy tends to be 
-- slower than Lucene on union with a Top-K due to Block-WAND optimization.
-- faster than Lucene on intersection and phrase queries. 
-
 Your mileage WILL vary depending on the nature of queries and their load.
 
 # Features
@@ -90,7 +84,7 @@ There are many ways to support this project.
 - Help with documentation by asking questions or submitting PRs
 - Contribute code (you can join [our Gitter](https://gitter.im/tantivy-search/tantivy))
 - Talk about Tantivy around you
-- Drop a word on on [![Say Thanks!](https://img.shields.io/badge/Say%20Thanks-!-1EAEDB.svg)](https://saythanks.io/to/fulmicoton) or even [![Become a patron](https://c5.patreon.com/external/logo/become_a_patron_button.png)](https://www.patreon.com/fulmicoton)
+- [![Become a patron](https://c5.patreon.com/external/logo/become_a_patron_button.png)](https://www.patreon.com/fulmicoton)
 
 # Contributing code
 

examples/basic_search.rs

@@ -112,18 +112,6 @@ fn main() -> tantivy::Result<()> {
             limbs and branches that arch over the pool"
     ));
 
-    index_writer.add_document(doc!(
-    title => "Of Mice and Men",
-    body => "A few miles south of Soledad, the Salinas River drops in close to the hillside \
-            bank and runs deep and green. The water is warm too, for it has slipped twinkling \
-            over the yellow sands in the sunlight before reaching the narrow pool. On one \
-            side of the river the golden foothill slopes curve up to the strong and rocky \
-            Gabilan Mountains, but on the valley side the water is lined with trees—willows \
-            fresh and green with every spring, carrying in their lower leaf junctures the \
-            debris of the winter’s flooding; and sycamores with mottled, white, recumbent \
-            limbs and branches that arch over the pool"
-    ));
-
     // Multivalued field just need to be repeated.
     index_writer.add_document(doc!(
     title => "Frankenstein",

examples/custom_collector.rs

@@ -14,7 +14,7 @@ use tantivy::fastfield::FastFieldReader;
 use tantivy::query::QueryParser;
 use tantivy::schema::Field;
 use tantivy::schema::{Schema, FAST, INDEXED, TEXT};
-use tantivy::{doc, Index, SegmentReader, TantivyError};
+use tantivy::{doc, Index, Score, SegmentReader, TantivyError};
 
 #[derive(Default)]
 struct Stats {
@@ -114,7 +114,7 @@ struct StatsSegmentCollector {
 impl SegmentCollector for StatsSegmentCollector {
     type Fruit = Option<Stats>;
 
-    fn collect(&mut self, doc: u32, _score: f32) {
+    fn collect(&mut self, doc: u32, _score: Score) {
         let value = self.fast_field_reader.get(doc) as f64;
         self.stats.count += 1;
         self.stats.sum += value;

examples/faceted_search_with_tweaked_score.rs

@@ -56,7 +56,7 @@ fn main() -> tantivy::Result<()> {
         );
         let top_docs_by_custom_score =
             TopDocs::with_limit(2).tweak_score(move |segment_reader: &SegmentReader| {
-                let mut ingredient_reader = segment_reader.facet_reader(ingredient).unwrap();
+                let ingredient_reader = segment_reader.facet_reader(ingredient).unwrap();
                 let facet_dict = ingredient_reader.facet_dict();
 
                 let query_ords: HashSet<u64> = facets

examples/iterating_docs_and_positions.rs

@@ -45,7 +45,7 @@ fn main() -> tantivy::Result<()> {
         // Inverted index stands for the combination of
         // - the term dictionary
         // - the inverted lists associated to each terms and their positions
-        let inverted_index = segment_reader.inverted_index(title);
+        let inverted_index = segment_reader.inverted_index(title)?;
 
         // A `Term` is a text token associated with a field.
         // Let's go through all docs containing the term `title:the` and access their position
@@ -58,7 +58,7 @@ fn main() -> tantivy::Result<()> {
         // If you don't need all this information, you may get better performance by decompressing less
         // information.
         if let Some(mut segment_postings) =
-            inverted_index.read_postings(&term_the, IndexRecordOption::WithFreqsAndPositions)
+            inverted_index.read_postings(&term_the, IndexRecordOption::WithFreqsAndPositions)?
         {
             // this buffer will be used to request for positions
             let mut positions: Vec<u32> = Vec::with_capacity(100);
@@ -106,7 +106,7 @@ fn main() -> tantivy::Result<()> {
         // Inverted index stands for the combination of
         // - the term dictionary
         // - the inverted lists associated to each terms and their positions
-        let inverted_index = segment_reader.inverted_index(title);
+        let inverted_index = segment_reader.inverted_index(title)?;
 
         // This segment posting object is like a cursor over the documents matching the term.
         // The `IndexRecordOption` arguments tells tantivy we will be interested in both term frequencies
@@ -115,13 +115,18 @@ fn main() -> tantivy::Result<()> {
         // If you don't need all this information, you may get better performance by decompressing less
         // information.
         if let Some(mut block_segment_postings) =
-            inverted_index.read_block_postings(&term_the, IndexRecordOption::Basic)
+            inverted_index.read_block_postings(&term_the, IndexRecordOption::Basic)?
         {
-            while block_segment_postings.advance() {
+            loop {
+                let docs = block_segment_postings.docs();
+                if docs.is_empty() {
+                    break;
+                }
                 // Once again these docs MAY contains deleted documents as well.
                 let docs = block_segment_postings.docs();
                 // Prints `Docs [0, 2].`
                 println!("Docs {:?}", docs);
+                block_segment_postings.advance();
             }
         }
     }

query-grammar/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "tantivy-query-grammar"
-version = "0.13.0"
+version = "0.14.0-dev"
 authors = ["Paul Masurel <paul.masurel@gmail.com>"]
 license = "MIT"
 categories = ["database-implementations", "data-structures"]

query-grammar/src/occur.rs

@@ -31,22 +31,12 @@ impl Occur {
 
     /// Compose two occur values.
     pub fn compose(left: Occur, right: Occur) -> Occur {
-        match left {
+        match (left, right) {
-            Occur::Should => right,
+            (Occur::Should, _) => right,
-            Occur::Must => {
+            (Occur::Must, Occur::MustNot) => Occur::MustNot,
-                if right == Occur::MustNot {
+            (Occur::Must, _) => Occur::Must,
-                    Occur::MustNot
+            (Occur::MustNot, Occur::MustNot) => Occur::Must,
-                } else {
+            (Occur::MustNot, _) => Occur::MustNot,
-                    Occur::Must
-                }
-            }
-            Occur::MustNot => {
-                if right == Occur::MustNot {
-                    Occur::Must
-                } else {
-                    Occur::MustNot
-                }
-            }
         }
     }
 }
@@ -56,3 +46,27 @@ impl fmt::Display for Occur {
         f.write_char(self.to_char())
     }
 }
+
+#[cfg(test)]
+mod test {
+    use crate::Occur;
+
+    #[test]
+    fn test_occur_compose() {
+        assert_eq!(Occur::compose(Occur::Should, Occur::Should), Occur::Should);
+        assert_eq!(Occur::compose(Occur::Should, Occur::Must), Occur::Must);
+        assert_eq!(
+            Occur::compose(Occur::Should, Occur::MustNot),
+            Occur::MustNot
+        );
+        assert_eq!(Occur::compose(Occur::Must, Occur::Should), Occur::Must);
+        assert_eq!(Occur::compose(Occur::Must, Occur::Must), Occur::Must);
+        assert_eq!(Occur::compose(Occur::Must, Occur::MustNot), Occur::MustNot);
+        assert_eq!(
+            Occur::compose(Occur::MustNot, Occur::Should),
+            Occur::MustNot
+        );
+        assert_eq!(Occur::compose(Occur::MustNot, Occur::Must), Occur::MustNot);
+        assert_eq!(Occur::compose(Occur::MustNot, Occur::MustNot), Occur::Must);
+    }
+}

query-grammar/src/query_grammar.rs

@@ -9,8 +9,10 @@ use combine::{
 
 fn field<'a>() -> impl Parser<&'a str, Output = String> {
     (
-        letter(),
+        (letter().or(char('_'))),
-        many(satisfy(|c: char| c.is_alphanumeric() || c == '_')),
+        many(satisfy(|c: char| {
+            c.is_alphanumeric() || c == '_' || c == '-'
+        })),
     )
         .skip(char(':'))
         .map(|(s1, s2): (char, String)| format!("{}{}", s1, s2))
@@ -180,7 +182,7 @@ fn occur_leaf<'a>() -> impl Parser<&'a str, Output = (Option<Occur>, UserInputAS
     (optional(occur_symbol()), boosted_leaf())
 }
 
-fn positive_float_number<'a>() -> impl Parser<&'a str, Output = f32> {
+fn positive_float_number<'a>() -> impl Parser<&'a str, Output = f64> {
     (many1(digit()), optional((char('.'), many1(digit())))).map(
         |(int_part, decimal_part_opt): (String, Option<(char, String)>)| {
             let mut float_str = int_part;
@@ -188,18 +190,18 @@ fn positive_float_number<'a>() -> impl Parser<&'a str, Output = f32> {
                 float_str.push(chr);
                 float_str.push_str(&decimal_str);
             }
-            float_str.parse::<f32>().unwrap()
+            float_str.parse::<f64>().unwrap()
         },
     )
 }
 
-fn boost<'a>() -> impl Parser<&'a str, Output = f32> {
+fn boost<'a>() -> impl Parser<&'a str, Output = f64> {
     (char('^'), positive_float_number()).map(|(_, boost)| boost)
 }
 
 fn boosted_leaf<'a>() -> impl Parser<&'a str, Output = UserInputAST> {
     (leaf(), optional(boost())).map(|(leaf, boost_opt)| match boost_opt {
-        Some(boost) if (boost - 1.0).abs() > std::f32::EPSILON => {
+        Some(boost) if (boost - 1.0).abs() > std::f64::EPSILON => {
             UserInputAST::Boost(Box::new(leaf), boost)
         }
         _ => leaf,
@@ -279,14 +281,16 @@ pub fn parse_to_ast<'a>() -> impl Parser<&'a str, Output = UserInputAST> {
 #[cfg(test)]
 mod test {
 
+    type TestParseResult = Result<(), StringStreamError>;
+
     use super::*;
     use combine::parser::Parser;
 
-    pub fn nearly_equals(a: f32, b: f32) -> bool {
+    pub fn nearly_equals(a: f64, b: f64) -> bool {
         (a - b).abs() < 0.0005 * (a + b).abs()
     }
 
-    fn assert_nearly_equals(expected: f32, val: f32) {
+    fn assert_nearly_equals(expected: f64, val: f64) {
         assert!(
             nearly_equals(val, expected),
             "Got {}, expected {}.",
@@ -296,14 +300,15 @@ mod test {
     }
 
     #[test]
-    fn test_occur_symbol() {
+    fn test_occur_symbol() -> TestParseResult {
-        assert_eq!(super::occur_symbol().parse("-"), Ok((Occur::MustNot, "")));
+        assert_eq!(super::occur_symbol().parse("-")?, (Occur::MustNot, ""));
-        assert_eq!(super::occur_symbol().parse("+"), Ok((Occur::Must, "")));
+        assert_eq!(super::occur_symbol().parse("+")?, (Occur::Must, ""));
+        Ok(())
     }
 
     #[test]
     fn test_positive_float_number() {
-        fn valid_parse(float_str: &str, expected_val: f32, expected_remaining: &str) {
+        fn valid_parse(float_str: &str, expected_val: f64, expected_remaining: &str) {
             let (val, remaining) = positive_float_number().parse(float_str).unwrap();
             assert_eq!(remaining, expected_remaining);
             assert_nearly_equals(val, expected_val);
@@ -311,9 +316,9 @@ mod test {
         fn error_parse(float_str: &str) {
             assert!(positive_float_number().parse(float_str).is_err());
         }
-        valid_parse("1.0", 1.0f32, "");
+        valid_parse("1.0", 1.0, "");
-        valid_parse("1", 1.0f32, "");
+        valid_parse("1", 1.0, "");
-        valid_parse("0.234234 aaa", 0.234234f32, " aaa");
+        valid_parse("0.234234 aaa", 0.234234f64, " aaa");
         error_parse(".3332");
         error_parse("1.");
         error_parse("-1.");
@@ -410,6 +415,25 @@ mod test {
         assert_eq!(format!("{:?}", ast), "\"abc\"");
     }
 
+    #[test]
+    fn test_field_name() -> TestParseResult {
+        assert_eq!(
+            super::field().parse("my-field-name:a")?,
+            ("my-field-name".to_string(), "a")
+        );
+        assert_eq!(
+            super::field().parse("my_field_name:a")?,
+            ("my_field_name".to_string(), "a")
+        );
+        assert!(super::field().parse(":a").is_err());
+        assert!(super::field().parse("-my_field:a").is_err());
+        assert_eq!(
+            super::field().parse("_my_field:a")?,
+            ("_my_field".to_string(), "a")
+        );
+        Ok(())
+    }
+
     #[test]
     fn test_range_parser() {
         // testing the range() parser separately

query-grammar/src/user_input_ast.rs

@@ -87,7 +87,7 @@ impl UserInputBound {
 pub enum UserInputAST {
     Clause(Vec<(Option<Occur>, UserInputAST)>),
     Leaf(Box<UserInputLeaf>),
-    Boost(Box<UserInputAST>, f32),
+    Boost(Box<UserInputAST>, f64),
 }
 
 impl UserInputAST {

src/collector/count_collector.rs

@@ -96,18 +96,18 @@ mod tests {
         }
         {
             let mut count_collector = SegmentCountCollector::default();
-            count_collector.collect(0u32, 1f32);
+            count_collector.collect(0u32, 1.0);
             assert_eq!(count_collector.harvest(), 1);
         }
         {
             let mut count_collector = SegmentCountCollector::default();
-            count_collector.collect(0u32, 1f32);
+            count_collector.collect(0u32, 1.0);
             assert_eq!(count_collector.harvest(), 1);
         }
         {
             let mut count_collector = SegmentCountCollector::default();
-            count_collector.collect(0u32, 1f32);
+            count_collector.collect(0u32, 1.0);
-            count_collector.collect(1u32, 1f32);
+            count_collector.collect(1u32, 1.0);
             assert_eq!(count_collector.harvest(), 2);
         }
     }

src/collector/custom_score_top_collector.rs

@@ -46,7 +46,7 @@ pub trait CustomScorer<TScore>: Sync {
 
 impl<TCustomScorer, TScore> Collector for CustomScoreTopCollector<TCustomScorer, TScore>
 where
-    TCustomScorer: CustomScorer<TScore>,
+    TCustomScorer: CustomScorer<TScore> + Send + Sync,
     TScore: 'static + PartialOrd + Clone + Send + Sync,
 {
     type Fruit = Vec<(TScore, DocAddress)>;
@@ -58,10 +58,10 @@ where
         segment_local_id: u32,
         segment_reader: &SegmentReader,
     ) -> crate::Result<Self::Child> {
-        let segment_scorer = self.custom_scorer.segment_scorer(segment_reader)?;
         let segment_collector = self
             .collector
             .for_segment(segment_local_id, segment_reader)?;
+        let segment_scorer = self.custom_scorer.segment_scorer(segment_reader)?;
         Ok(CustomScoreTopSegmentCollector {
             segment_collector,
             segment_scorer,

src/collector/docset_collector.rs

@@ -0,0 +1,61 @@
+use std::collections::HashSet;
+
+use crate::{DocAddress, DocId, Score};
+
+use super::{Collector, SegmentCollector};
+
+/// Collectors that returns the set of DocAddress that matches the query.
+///
+/// This collector is mostly useful for tests.
+pub struct DocSetCollector;
+
+impl Collector for DocSetCollector {
+    type Fruit = HashSet<DocAddress>;
+    type Child = DocSetChildCollector;
+
+    fn for_segment(
+        &self,
+        segment_local_id: crate::SegmentLocalId,
+        _segment: &crate::SegmentReader,
+    ) -> crate::Result<Self::Child> {
+        Ok(DocSetChildCollector {
+            segment_local_id,
+            docs: HashSet::new(),
+        })
+    }
+
+    fn requires_scoring(&self) -> bool {
+        false
+    }
+
+    fn merge_fruits(
+        &self,
+        segment_fruits: Vec<(u32, HashSet<DocId>)>,
+    ) -> crate::Result<Self::Fruit> {
+        let len: usize = segment_fruits.iter().map(|(_, docset)| docset.len()).sum();
+        let mut result = HashSet::with_capacity(len);
+        for (segment_local_id, docs) in segment_fruits {
+            for doc in docs {
+                result.insert(DocAddress(segment_local_id, doc));
+            }
+        }
+        Ok(result)
+    }
+}
+
+pub struct DocSetChildCollector {
+    segment_local_id: u32,
+    docs: HashSet<DocId>,
+}
+
+impl SegmentCollector for DocSetChildCollector {
+    type Fruit = (u32, HashSet<DocId>);
+
+    fn collect(&mut self, doc: crate::DocId, _score: Score) {
+        self.docs.insert(doc);
+    }
+
+    fn harvest(self) -> (u32, HashSet<DocId>) {
+        (self.segment_local_id, self.docs)
+    }
+}

src/collector/facet_collector.rs

@@ -7,7 +7,6 @@ use crate::DocId;
 use crate::Score;
 use crate::SegmentLocalId;
 use crate::SegmentReader;
-use crate::TantivyError;
 use std::cmp::Ordering;
 use std::collections::btree_map;
 use std::collections::BTreeMap;
@@ -266,10 +265,7 @@ impl Collector for FacetCollector {
         _: SegmentLocalId,
         reader: &SegmentReader,
     ) -> crate::Result<FacetSegmentCollector> {
-        let field_name = reader.schema().get_field_name(self.field);
+        let facet_reader = reader.facet_reader(self.field)?;
-        let facet_reader = reader.facet_reader(self.field).ok_or_else(|| {
-            TantivyError::SchemaError(format!("Field {:?} is not a facet field.", field_name))
-        })?;
 
         let mut collapse_mapping = Vec::new();
         let mut counts = Vec::new();
@@ -472,7 +468,7 @@ mod tests {
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
 
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests().unwrap();
         let num_facets: usize = 3 * 4 * 5;
         let facets: Vec<Facet> = (0..num_facets)
             .map(|mut n| {
@@ -531,7 +527,7 @@ mod tests {
         let facet_field = schema_builder.add_facet_field("facets");
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests().unwrap();
         index_writer.add_document(doc!(
             facet_field => Facet::from_text(&"/subjects/A/a"),
             facet_field => Facet::from_text(&"/subjects/B/a"),
@@ -550,12 +546,12 @@ mod tests {
     }
 
     #[test]
-    fn test_doc_search_by_facet() {
+    fn test_doc_search_by_facet() -> crate::Result<()> {
         let mut schema_builder = Schema::builder();
         let facet_field = schema_builder.add_facet_field("facet");
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests()?;
         index_writer.add_document(doc!(
             facet_field => Facet::from_text(&"/A/A"),
         ));
@@ -568,8 +564,8 @@ mod tests {
         index_writer.add_document(doc!(
             facet_field => Facet::from_text(&"/D/C/A"),
         ));
-        index_writer.commit().unwrap();
+        index_writer.commit()?;
-        let reader = index.reader().unwrap();
+        let reader = index.reader()?;
         let searcher = reader.searcher();
         assert_eq!(searcher.num_docs(), 4);
 
@@ -586,17 +582,17 @@ mod tests {
         assert_eq!(count_facet("/A/C"), 1);
         assert_eq!(count_facet("/A/C/A"), 1);
         assert_eq!(count_facet("/C/A"), 0);
+
+        let query_parser = QueryParser::for_index(&index, vec![]);
         {
-            let query_parser = QueryParser::for_index(&index, vec![]);
+            let query = query_parser.parse_query("facet:/A/B")?;
-            {
+            assert_eq!(1, searcher.search(&query, &Count).unwrap());
-                let query = query_parser.parse_query("facet:/A/B").unwrap();
-                assert_eq!(1, searcher.search(&query, &Count).unwrap());
-            }
-            {
-                let query = query_parser.parse_query("facet:/A").unwrap();
-                assert_eq!(3, searcher.search(&query, &Count).unwrap());
-            }
         }
+        {
+            let query = query_parser.parse_query("facet:/A")?;
+            assert_eq!(3, searcher.search(&query, &Count)?);
+        }
+        Ok(())
     }
 
     #[test]
@@ -631,7 +627,7 @@ mod tests {
             .collect();
         docs[..].shuffle(&mut thread_rng());
 
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests().unwrap();
         for doc in docs {
             index_writer.add_document(doc);
         }
@@ -684,7 +680,7 @@ mod bench {
         // 40425 docs
         docs[..].shuffle(&mut thread_rng());
 
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests().unwrap();
         for doc in docs {
             index_writer.add_document(doc);
         }

src/collector/int_facet_collector.rs

@@ -1,127 +0,0 @@
-use std::cmp::Eq;
-use std::collections::HashMap;
-use std::hash::Hash;
-
-use collector::Collector;
-use fastfield::FastFieldReader;
-use schema::Field;
-
-use DocId;
-use Result;
-use Score;
-use SegmentReader;
-use SegmentLocalId;
-
-
-/// Facet collector  for i64/u64 fast field
-pub struct IntFacetCollector<T>
-where
-    T: FastFieldReader,
-    T::ValueType: Eq + Hash,
-{
-    counters: HashMap<T::ValueType, u64>,
-    field: Field,
-    ff_reader: Option<T>,
-}
-
-
-impl<T> IntFacetCollector<T>
-where
-    T: FastFieldReader,
-    T::ValueType: Eq + Hash,
-{
-    /// Creates a new facet collector for aggregating a given field.
-    pub fn new(field: Field) -> IntFacetCollector<T> {
-        IntFacetCollector {
-            counters: HashMap::new(),
-            field: field,
-            ff_reader: None,
-        }
-    }
-}
-
-
-impl<T> Collector for IntFacetCollector<T>
-where
-    T: FastFieldReader,
-    T::ValueType: Eq + Hash,
-{
-    fn set_segment(&mut self, _: SegmentLocalId, reader: &SegmentReader) -> Result<()> {
-        self.ff_reader = Some(reader.get_fast_field_reader(self.field)?);
-        Ok(())
-    }
-
-    fn collect(&mut self, doc: DocId, _: Score) {
-        let val = self.ff_reader
-            .as_ref()
-            .expect(
-                "collect() was called before set_segment. \
-                This should never happen.",
-            )
-            .get(doc);
-        *(self.counters.entry(val).or_insert(0)) += 1;
-    }
-}
-
-
-
-#[cfg(test)]
-mod tests {
-
-    use collector::{chain, IntFacetCollector};
-    use query::QueryParser;
-    use fastfield::{I64FastFieldReader, U64FastFieldReader};
-    use schema::{self, FAST, STRING};
-    use Index;
-
-    #[test]
-    // create 10 documents, set num field value to 0 or 1 for even/odd ones
-    // make sure we have facet counters correctly filled
-    fn test_facet_collector_results() {
-
-        let mut schema_builder = schema::Schema::builder();
-        let num_field_i64 = schema_builder.add_i64_field("num_i64", FAST);
-        let num_field_u64 = schema_builder.add_u64_field("num_u64", FAST);
-        let num_field_f64 = schema_builder.add_f64_field("num_f64", FAST);
-        let text_field = schema_builder.add_text_field("text", STRING);
-        let schema = schema_builder.build();
-
-        let index = Index::create_in_ram(schema.clone());
-
-        {
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
-            {
-                for i in 0u64..10u64 {
-                    index_writer.add_document(doc!(
-                        num_field_i64 => ((i as i64) % 3i64) as i64,
-                        num_field_u64 => (i % 2u64) as u64,
-                        num_field_f64 => (i % 4u64) as f64,
-                        text_field => "text"
-                    ));
-                }
-            }
-            assert_eq!(index_writer.commit().unwrap(), 10u64);
-        }
-
-        let searcher = index.reader().searcher();
-        let mut ffvf_i64: IntFacetCollector<I64FastFieldReader> = IntFacetCollector::new(num_field_i64);
-        let mut ffvf_u64: IntFacetCollector<U64FastFieldReader> = IntFacetCollector::new(num_field_u64);
-        let mut ffvf_f64: IntFacetCollector<F64FastFieldReader> = IntFacetCollector::new(num_field_f64);
-
-        {
-            // perform the query
-            let mut facet_collectors = chain().push(&mut ffvf_i64).push(&mut ffvf_u64).push(&mut ffvf_f64);
-            let mut query_parser = QueryParser::for_index(index, vec![text_field]);
-            let query = query_parser.parse_query("text:text").unwrap();
-            query.search(&searcher, &mut facet_collectors).unwrap();
-        }
-
-        assert_eq!(ffvf_u64.counters[&0], 5);
-        assert_eq!(ffvf_u64.counters[&1], 5);
-        assert_eq!(ffvf_i64.counters[&0], 4);
-        assert_eq!(ffvf_i64.counters[&1], 3);
-        assert_eq!(ffvf_f64.counters[&0.0], 3);
-        assert_eq!(ffvf_f64.counters[&2.0], 2);
-
-    }
-}

src/collector/mod.rs

@@ -111,6 +111,9 @@ mod facet_collector;
 pub use self::facet_collector::FacetCollector;
 use crate::query::Weight;
 
+mod docset_collector;
+pub use self::docset_collector::DocSetCollector;
+
 /// `Fruit` is the type for the result of our collection.
 /// e.g. `usize` for the `Count` collector.
 pub trait Fruit: Send + downcast_rs::Downcast {}
@@ -133,13 +136,13 @@ impl<T> Fruit for T where T: Send + downcast_rs::Downcast {}
 /// The collection logic itself is in the `SegmentCollector`.
 ///
 /// Segments are not guaranteed to be visited in any specific order.
-pub trait Collector: Sync {
+pub trait Collector: Sync + Send {
     /// `Fruit` is the type for the result of our collection.
     /// e.g. `usize` for the `Count` collector.
     type Fruit: Fruit;
 
     /// Type of the `SegmentCollector` associated to this collector.
-    type Child: SegmentCollector<Fruit = Self::Fruit>;
+    type Child: SegmentCollector;
 
     /// `set_segment` is called before beginning to enumerate
     /// on this segment.
@@ -154,7 +157,10 @@ pub trait Collector: Sync {
 
     /// Combines the fruit associated to the collection of each segments
     /// into one fruit.
-    fn merge_fruits(&self, segment_fruits: Vec<Self::Fruit>) -> crate::Result<Self::Fruit>;
+    fn merge_fruits(
+        &self,
+        segment_fruits: Vec<<Self::Child as SegmentCollector>::Fruit>,
+    ) -> crate::Result<Self::Fruit>;
 
     /// Created a segment collector and
     fn collect_segment(
@@ -224,11 +230,11 @@ where
 
     fn merge_fruits(
         &self,
-        children: Vec<(Left::Fruit, Right::Fruit)>,
+        segment_fruits: Vec<<Self::Child as SegmentCollector>::Fruit>,
     ) -> crate::Result<(Left::Fruit, Right::Fruit)> {
         let mut left_fruits = vec![];
         let mut right_fruits = vec![];
-        for (left_fruit, right_fruit) in children {
+        for (left_fruit, right_fruit) in segment_fruits {
             left_fruits.push(left_fruit);
             right_fruits.push(right_fruit);
         }
@@ -282,7 +288,10 @@ where
         self.0.requires_scoring() || self.1.requires_scoring() || self.2.requires_scoring()
     }
 
-    fn merge_fruits(&self, children: Vec<Self::Fruit>) -> crate::Result<Self::Fruit> {
+    fn merge_fruits(
+        &self,
+        children: Vec<<Self::Child as SegmentCollector>::Fruit>,
+    ) -> crate::Result<Self::Fruit> {
         let mut one_fruits = vec![];
         let mut two_fruits = vec![];
         let mut three_fruits = vec![];
@@ -349,7 +358,10 @@ where
             || self.3.requires_scoring()
     }
 
-    fn merge_fruits(&self, children: Vec<Self::Fruit>) -> crate::Result<Self::Fruit> {
+    fn merge_fruits(
+        &self,
+        children: Vec<<Self::Child as SegmentCollector>::Fruit>,
+    ) -> crate::Result<Self::Fruit> {
         let mut one_fruits = vec![];
         let mut two_fruits = vec![];
         let mut three_fruits = vec![];

src/collector/multi_collector.rs

@@ -34,13 +34,13 @@ impl<TCollector: Collector> Collector for CollectorWrapper<TCollector> {
 
     fn merge_fruits(
         &self,
-        children: Vec<<Self as Collector>::Fruit>,
+        children: Vec<<Self::Child as SegmentCollector>::Fruit>,
     ) -> crate::Result<Box<dyn Fruit>> {
-        let typed_fruit: Vec<TCollector::Fruit> = children
+        let typed_fruit: Vec<<TCollector::Child as SegmentCollector>::Fruit> = children
             .into_iter()
             .map(|untyped_fruit| {
                 untyped_fruit
-                    .downcast::<TCollector::Fruit>()
+                    .downcast::<<TCollector::Child as SegmentCollector>::Fruit>()
                     .map(|boxed_but_typed| *boxed_but_typed)
                     .map_err(|_| {
                         TantivyError::InvalidArgument("Failed to cast child fruit.".to_string())
@@ -55,7 +55,7 @@ impl<TCollector: Collector> Collector for CollectorWrapper<TCollector> {
 impl SegmentCollector for Box<dyn BoxableSegmentCollector> {
     type Fruit = Box<dyn Fruit>;
 
-    fn collect(&mut self, doc: u32, score: f32) {
+    fn collect(&mut self, doc: u32, score: Score) {
         self.as_mut().collect(doc, score);
     }
 
@@ -65,7 +65,7 @@ impl SegmentCollector for Box<dyn BoxableSegmentCollector> {
 }
 
 pub trait BoxableSegmentCollector {
-    fn collect(&mut self, doc: u32, score: f32);
+    fn collect(&mut self, doc: u32, score: Score);
     fn harvest_from_box(self: Box<Self>) -> Box<dyn Fruit>;
 }
 
@@ -74,7 +74,7 @@ pub struct SegmentCollectorWrapper<TSegmentCollector: SegmentCollector>(TSegment
 impl<TSegmentCollector: SegmentCollector> BoxableSegmentCollector
     for SegmentCollectorWrapper<TSegmentCollector>
 {
-    fn collect(&mut self, doc: u32, score: f32) {
+    fn collect(&mut self, doc: u32, score: Score) {
         self.0.collect(doc, score);
     }
 
@@ -259,7 +259,7 @@ mod tests {
 
         let index = Index::create_in_ram(schema);
         {
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+            let mut index_writer = index.writer_for_tests().unwrap();
             index_writer.add_document(doc!(text=>"abc"));
             index_writer.add_document(doc!(text=>"abc abc abc"));
             index_writer.add_document(doc!(text=>"abc abc"));

src/collector/tests.rs

@@ -185,12 +185,15 @@ impl Collector for BytesFastFieldTestCollector {
         _segment_local_id: u32,
         segment_reader: &SegmentReader,
     ) -> crate::Result<BytesFastFieldSegmentCollector> {
+        let reader = segment_reader
+            .fast_fields()
+            .bytes(self.field)
+            .ok_or_else(|| {
+                crate::TantivyError::InvalidArgument("Field is not a bytes fast field.".to_string())
+            })?;
         Ok(BytesFastFieldSegmentCollector {
             vals: Vec::new(),
-            reader: segment_reader
+            reader,
-                .fast_fields()
-                .bytes(self.field)
-                .expect("Field is not a bytes fast field."),
         })
     }
 
@@ -206,7 +209,7 @@ impl Collector for BytesFastFieldTestCollector {
 impl SegmentCollector for BytesFastFieldSegmentCollector {
     type Fruit = Vec<u8>;
 
-    fn collect(&mut self, doc: u32, _score: f32) {
+    fn collect(&mut self, doc: u32, _score: Score) {
         let data = self.reader.get_bytes(doc);
         self.vals.extend(data);
     }

src/collector/top_score_collector.rs

@@ -1,6 +1,4 @@
 use super::Collector;
-use crate::collector::custom_score_top_collector::CustomScoreTopCollector;
-use crate::collector::top_collector::TopSegmentCollector;
 use crate::collector::top_collector::{ComparableDoc, TopCollector};
 use crate::collector::tweak_score_top_collector::TweakedScoreTopCollector;
 use crate::collector::{
@@ -14,8 +12,71 @@ use crate::DocId;
 use crate::Score;
 use crate::SegmentLocalId;
 use crate::SegmentReader;
-use std::collections::BinaryHeap;
+use crate::{collector::custom_score_top_collector::CustomScoreTopCollector, fastfield::FastValue};
+use crate::{collector::top_collector::TopSegmentCollector, TantivyError};
 use std::fmt;
+use std::{collections::BinaryHeap, marker::PhantomData};
+
+struct FastFieldConvertCollector<
+    TCollector: Collector<Fruit = Vec<(u64, DocAddress)>>,
+    TFastValue: FastValue,
+> {
+    pub collector: TCollector,
+    pub field: Field,
+    pub fast_value: std::marker::PhantomData<TFastValue>,
+}
+
+impl<TCollector, TFastValue> Collector for FastFieldConvertCollector<TCollector, TFastValue>
+where
+    TCollector: Collector<Fruit = Vec<(u64, DocAddress)>>,
+    TFastValue: FastValue + 'static,
+{
+    type Fruit = Vec<(TFastValue, DocAddress)>;
+
+    type Child = TCollector::Child;
+
+    fn for_segment(
+        &self,
+        segment_local_id: crate::SegmentLocalId,
+        segment: &SegmentReader,
+    ) -> crate::Result<Self::Child> {
+        let schema = segment.schema();
+        let field_entry = schema.get_field_entry(self.field);
+        if !field_entry.is_fast() {
+            return Err(TantivyError::SchemaError(format!(
+                "Field {:?} is not a fast field.",
+                field_entry.name()
+            )));
+        }
+        let schema_type = TFastValue::to_type();
+        let requested_type = field_entry.field_type().value_type();
+        if schema_type != requested_type {
+            return Err(TantivyError::SchemaError(format!(
+                "Field {:?} is of type {:?}!={:?}",
+                field_entry.name(),
+                schema_type,
+                requested_type
+            )));
+        }
+        self.collector.for_segment(segment_local_id, segment)
+    }
+
+    fn requires_scoring(&self) -> bool {
+        self.collector.requires_scoring()
+    }
+
+    fn merge_fruits(
+        &self,
+        segment_fruits: Vec<<Self::Child as SegmentCollector>::Fruit>,
+    ) -> crate::Result<Self::Fruit> {
+        let raw_result = self.collector.merge_fruits(segment_fruits)?;
+        let transformed_result = raw_result
+            .into_iter()
+            .map(|(score, doc_address)| (TFastValue::from_u64(score), doc_address))
+            .collect::<Vec<_>>();
+        Ok(transformed_result)
+    }
+}
 
 /// The `TopDocs` collector keeps track of the top `K` documents
 /// sorted by their score.
@@ -38,7 +99,7 @@ use std::fmt;
 /// let schema = schema_builder.build();
 /// let index = Index::create_in_ram(schema);
 ///
-/// let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+/// let mut index_writer = index.writer_with_num_threads(1, 10_000_000).unwrap();
 /// index_writer.add_document(doc!(title => "The Name of the Wind"));
 /// index_writer.add_document(doc!(title => "The Diary of Muadib"));
 /// index_writer.add_document(doc!(title => "A Dairy Cow"));
@@ -52,8 +113,8 @@ use std::fmt;
 /// let query = query_parser.parse_query("diary").unwrap();
 /// let top_docs = searcher.search(&query, &TopDocs::with_limit(2)).unwrap();
 ///
-/// assert_eq!(&top_docs[0], &(0.7261542, DocAddress(0, 1)));
+/// assert_eq!(top_docs[0].1, DocAddress(0, 1));
-/// assert_eq!(&top_docs[1], &(0.6099695, DocAddress(0, 3)));
+/// assert_eq!(top_docs[1].1, DocAddress(0, 3));
 /// ```
 pub struct TopDocs(TopCollector<Score>);
 
@@ -73,7 +134,7 @@ struct ScorerByFastFieldReader {
 
 impl CustomSegmentScorer<u64> for ScorerByFastFieldReader {
     fn score(&mut self, doc: DocId) -> u64 {
-        self.ff_reader.get_u64(u64::from(doc))
+        self.ff_reader.get(doc)
     }
 }
 
@@ -87,10 +148,10 @@ impl CustomScorer<u64> for ScorerByField {
     fn segment_scorer(&self, segment_reader: &SegmentReader) -> crate::Result<Self::Child> {
         let ff_reader = segment_reader
             .fast_fields()
-            .u64(self.field)
+            .u64_lenient(self.field)
             .ok_or_else(|| {
                 crate::TantivyError::SchemaError(format!(
-                    "Field requested ({:?}) is not a i64/u64 fast field.",
+                    "Field requested ({:?}) is not a fast field.",
                     self.field
                 ))
             })?;
@@ -112,6 +173,8 @@ impl TopDocs {
     /// This is equivalent to `OFFSET` in MySQL or PostgreSQL and `start` in
     /// Lucene's TopDocsCollector.
     ///
+    /// # Example
+    ///
     /// ```rust
     /// use tantivy::collector::TopDocs;
     /// use tantivy::query::QueryParser;
@@ -123,7 +186,7 @@ impl TopDocs {
     /// let schema = schema_builder.build();
     /// let index = Index::create_in_ram(schema);
     ///
-    /// let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+    /// let mut index_writer = index.writer_with_num_threads(1, 10_000_000).unwrap();
     /// index_writer.add_document(doc!(title => "The Name of the Wind"));
     /// index_writer.add_document(doc!(title => "The Diary of Muadib"));
     /// index_writer.add_document(doc!(title => "A Dairy Cow"));
@@ -139,8 +202,8 @@ impl TopDocs {
     /// let top_docs = searcher.search(&query, &TopDocs::with_limit(2).and_offset(1)).unwrap();
     ///
     /// assert_eq!(top_docs.len(), 2);
-    /// assert_eq!(&top_docs[0], &(0.5204813, DocAddress(0, 4)));
+    /// assert_eq!(top_docs[0].1, DocAddress(0, 4));
-    /// assert_eq!(&top_docs[1], &(0.4793185, DocAddress(0, 3)));
+    /// assert_eq!(top_docs[1].1, DocAddress(0, 3));
     /// ```
     pub fn and_offset(self, offset: usize) -> TopDocs {
         TopDocs(self.0.and_offset(offset))
@@ -148,6 +211,14 @@ impl TopDocs {
 
     /// Set top-K to rank documents by a given fast field.
     ///
+    /// If the field is not a fast or does not exist, this method returns successfully (it is not aware of any schema).
+    /// An error will be returned at the moment of search.
+    ///
+    /// If the field is a FAST field but not a u64 field, search will return successfully but it will return
+    /// returns a monotonic u64-representation (ie. the order is still correct) of the requested field type.
+    ///
+    /// # Example
+    ///
     /// ```rust
     /// # use tantivy::schema::{Schema, FAST, TEXT};
     /// # use tantivy::{doc, Index, DocAddress};
@@ -163,13 +234,13 @@ impl TopDocs {
     /// #   let schema = schema_builder.build();
     /// #  
     /// #   let index = Index::create_in_ram(schema);
-    /// #   let mut index_writer = index.writer_with_num_threads(1, 3_000_000)?;
+    /// #   let mut index_writer = index.writer_with_num_threads(1, 10_000_000)?;
     /// #   index_writer.add_document(doc!(title => "The Name of the Wind", rating => 92u64));
     /// #   index_writer.add_document(doc!(title => "The Diary of Muadib", rating => 97u64));
     /// #   index_writer.add_document(doc!(title => "A Dairy Cow", rating => 63u64));
     /// #   index_writer.add_document(doc!(title => "The Diary of a Young Girl", rating => 80u64));
     /// #   assert!(index_writer.commit().is_ok());
-    /// #   let reader = index.reader().unwrap();
+    /// #   let reader = index.reader()?;
     /// #   let query = QueryParser::for_index(&index, vec![title]).parse_query("diary")?;
     /// #   let top_docs = docs_sorted_by_rating(&reader.searcher(), &query, rating)?;
     /// #   assert_eq!(top_docs,
@@ -177,25 +248,20 @@ impl TopDocs {
     /// #                 (80u64, DocAddress(0u32, 3))]);
     /// #   Ok(())
     /// # }
-    ///
-    ///
     /// /// Searches the document matching the given query, and
     /// /// collects the top 10 documents, order by the u64-`field`
     /// /// given in argument.
-    /// ///
-    /// /// `field` is required to be a FAST field.
     /// fn docs_sorted_by_rating(searcher: &Searcher,
     ///                          query: &dyn Query,
-    ///                          sort_by_field: Field)
+    ///                          rating_field: Field)
     ///     -> tantivy::Result<Vec<(u64, DocAddress)>> {
     ///
     ///     // This is where we build our topdocs collector
     ///     //
-    ///     // Note the generics parameter that needs to match the
+    ///     // Note the `rating_field` needs to be a FAST field here.
-    ///     // type `sort_by_field`.
+    ///     let top_books_by_rating = TopDocs
-    ///     let top_docs_by_rating = TopDocs
     ///                 ::with_limit(10)
-    ///                  .order_by_u64_field(sort_by_field);
+    ///                  .order_by_u64_field(rating_field);
     ///     
     ///     // ... and here are our documents. Note this is a simple vec.
     ///     // The `u64` in the pair is the value of our fast field for
@@ -205,21 +271,105 @@ impl TopDocs {
     ///     // length of 10, or less if not enough documents matched the
     ///     // query.
     ///     let resulting_docs: Vec<(u64, DocAddress)> =
-    ///          searcher.search(query, &top_docs_by_rating)?;
+    ///          searcher.search(query, &top_books_by_rating)?;
     ///     
     ///     Ok(resulting_docs)
     /// }
     /// ```
     ///
-    /// # Panics
+    /// # See also
-    ///
+    ///  
-    /// May panic if the field requested is not a fast field.
+    /// To confortably work with `u64`s, `i64`s, `f64`s, or `date`s, please refer to
-    ///
+    /// [.order_by_fast_field(...)](#method.order_by_fast_field) method.
     pub fn order_by_u64_field(
         self,
         field: Field,
     ) -> impl Collector<Fruit = Vec<(u64, DocAddress)>> {
-        self.custom_score(ScorerByField { field })
+        CustomScoreTopCollector::new(ScorerByField { field }, self.0.into_tscore())
+    }
+
+    /// Set top-K to rank documents by a given fast field.
+    ///
+    /// If the field is not a fast field, or its field type does not match the generic type, this method does not panic,  
+    /// but an explicit error will be returned at the moment of collection.
+    ///
+    /// Note that this method is a generic. The requested fast field type will be often
+    /// inferred in your code by the rust compiler.
+    ///
+    /// Implementation-wise, for performance reason, tantivy will manipulate the u64 representation of your fast
+    /// field until the last moment.
+    ///
+    /// # Example
+    ///
+    /// ```rust
+    /// # use tantivy::schema::{Schema, FAST, TEXT};
+    /// # use tantivy::{doc, Index, DocAddress};
+    /// # use tantivy::query::{Query, AllQuery};
+    /// use tantivy::Searcher;
+    /// use tantivy::collector::TopDocs;
+    /// use tantivy::schema::Field;
+    ///
+    /// # fn main() -> tantivy::Result<()> {
+    /// #   let mut schema_builder = Schema::builder();
+    /// #   let title = schema_builder.add_text_field("company", TEXT);
+    /// #   let rating = schema_builder.add_i64_field("revenue", FAST);
+    /// #   let schema = schema_builder.build();
+    /// #  
+    /// #   let index = Index::create_in_ram(schema);
+    /// #   let mut index_writer = index.writer_with_num_threads(1, 10_000_000)?;
+    /// #   index_writer.add_document(doc!(title => "MadCow Inc.", rating => 92_000_000i64));
+    /// #   index_writer.add_document(doc!(title => "Zozo Cow KKK", rating => 119_000_000i64));
+    /// #   index_writer.add_document(doc!(title => "Declining Cow", rating => -63_000_000i64));
+    /// #   assert!(index_writer.commit().is_ok());
+    /// #   let reader = index.reader()?;
+    /// #   let top_docs = docs_sorted_by_revenue(&reader.searcher(), &AllQuery, rating)?;
+    /// #   assert_eq!(top_docs,
+    /// #            vec![(119_000_000i64, DocAddress(0, 1)),
+    /// #                 (92_000_000i64, DocAddress(0, 0))]);
+    /// #   Ok(())
+    /// # }
+    /// /// Searches the document matching the given query, and
+    /// /// collects the top 10 documents, order by the u64-`field`
+    /// /// given in argument.
+    /// fn docs_sorted_by_revenue(searcher: &Searcher,
+    ///                          query: &dyn Query,
+    ///                          revenue_field: Field)
+    ///     -> tantivy::Result<Vec<(i64, DocAddress)>> {
+    ///
+    ///     // This is where we build our topdocs collector
+    ///     //
+    ///     // Note the generics parameter that needs to match the
+    ///     // type `sort_by_field`. revenue_field here is a FAST i64 field.
+    ///     let top_company_by_revenue = TopDocs
+    ///                 ::with_limit(2)
+    ///                  .order_by_fast_field(revenue_field);
+    ///     
+    ///     // ... and here are our documents. Note this is a simple vec.
+    ///     // The `i64` in the pair is the value of our fast field for
+    ///     // each documents.
+    ///     //
+    ///     // The vec is sorted decreasingly by `sort_by_field`, and has a
+    ///     // length of 10, or less if not enough documents matched the
+    ///     // query.
+    ///     let resulting_docs: Vec<(i64, DocAddress)> =
+    ///          searcher.search(query, &top_company_by_revenue)?;
+    ///     
+    ///     Ok(resulting_docs)
+    /// }
+    /// ```
+    pub fn order_by_fast_field<TFastValue>(
+        self,
+        fast_field: Field,
+    ) -> impl Collector<Fruit = Vec<(TFastValue, DocAddress)>>
+    where
+        TFastValue: FastValue + 'static,
+    {
+        let u64_collector = self.order_by_u64_field(fast_field);
+        FastFieldConvertCollector {
+            collector: u64_collector,
+            field: fast_field,
+            fast_value: PhantomData,
+        }
     }
 
     /// Ranks the documents using a custom score.
@@ -264,7 +414,7 @@ impl TopDocs {
     /// fn create_index() -> tantivy::Result<Index> {
     ///   let schema = create_schema();
     ///   let index = Index::create_in_ram(schema);
-    ///   let mut index_writer = index.writer_with_num_threads(1, 3_000_000)?;
+    ///   let mut index_writer = index.writer_with_num_threads(1, 10_000_000)?;
     ///   let product_name = index.schema().get_field("product_name").unwrap();
     ///   let popularity: Field = index.schema().get_field("popularity").unwrap();
     ///   index_writer.add_document(doc!(product_name => "The Diary of Muadib", popularity => 1u64));
@@ -303,7 +453,7 @@ impl TopDocs {
     ///                 let popularity: u64 = popularity_reader.get(doc);
     ///                 // Well.. For the sake of the example we use a simple logarithm
     ///                 // function.
-    ///                 let popularity_boost_score = ((2u64 + popularity) as f32).log2();
+    ///                 let popularity_boost_score = ((2u64 + popularity) as Score).log2();
     ///                 popularity_boost_score * original_score
     ///             }
     ///           });
@@ -324,7 +474,7 @@ impl TopDocs {
     where
         TScore: 'static + Send + Sync + Clone + PartialOrd,
         TScoreSegmentTweaker: ScoreSegmentTweaker<TScore> + 'static,
-        TScoreTweaker: ScoreTweaker<TScore, Child = TScoreSegmentTweaker>,
+        TScoreTweaker: ScoreTweaker<TScore, Child = TScoreSegmentTweaker> + Send + Sync,
     {
         TweakedScoreTopCollector::new(score_tweaker, self.0.into_tscore())
     }
@@ -371,7 +521,7 @@ impl TopDocs {
     /// # fn main() -> tantivy::Result<()> {
     /// #   let schema = create_schema();
     /// #   let index = Index::create_in_ram(schema);
-    /// #   let mut index_writer = index.writer_with_num_threads(1, 3_000_000)?;
+    /// #   let mut index_writer = index.writer_with_num_threads(1, 10_000_000)?;
     /// #   let product_name = index.schema().get_field("product_name").unwrap();
     /// #   
     /// let popularity: Field = index.schema().get_field("popularity").unwrap();
@@ -438,7 +588,7 @@ impl TopDocs {
     where
         TScore: 'static + Send + Sync + Clone + PartialOrd,
         TCustomSegmentScorer: CustomSegmentScorer<TScore> + 'static,
-        TCustomScorer: CustomScorer<TScore, Child = TCustomSegmentScorer>,
+        TCustomScorer: CustomScorer<TScore, Child = TCustomSegmentScorer> + Send + Sync,
     {
         CustomScoreTopCollector::new(custom_score, self.0.into_tscore())
     }
@@ -479,7 +629,7 @@ impl Collector for TopDocs {
         let mut heap: BinaryHeap<ComparableDoc<Score, DocId>> = BinaryHeap::with_capacity(heap_len);
 
         if let Some(delete_bitset) = reader.delete_bitset() {
-            let mut threshold = f32::MIN;
+            let mut threshold = Score::MIN;
             weight.for_each_pruning(threshold, reader, &mut |doc, score| {
                 if delete_bitset.is_deleted(doc) {
                     return threshold;
@@ -491,16 +641,16 @@ impl Collector for TopDocs {
                 if heap.len() < heap_len {
                     heap.push(heap_item);
                     if heap.len() == heap_len {
-                        threshold = heap.peek().map(|el| el.feature).unwrap_or(f32::MIN);
+                        threshold = heap.peek().map(|el| el.feature).unwrap_or(Score::MIN);
                     }
                     return threshold;
                 }
                 *heap.peek_mut().unwrap() = heap_item;
-                threshold = heap.peek().map(|el| el.feature).unwrap_or(std::f32::MIN);
+                threshold = heap.peek().map(|el| el.feature).unwrap_or(Score::MIN);
                 threshold
             })?;
         } else {
-            weight.for_each_pruning(f32::MIN, reader, &mut |doc, score| {
+            weight.for_each_pruning(Score::MIN, reader, &mut |doc, score| {
                 let heap_item = ComparableDoc {
                     feature: score,
                     doc,
@@ -509,13 +659,13 @@ impl Collector for TopDocs {
                     heap.push(heap_item);
                     // TODO the threshold is suboptimal for heap.len == heap_len
                     if heap.len() == heap_len {
-                        return heap.peek().map(|el| el.feature).unwrap_or(f32::MIN);
+                        return heap.peek().map(|el| el.feature).unwrap_or(Score::MIN);
                     } else {
-                        return f32::MIN;
+                        return Score::MIN;
                     }
                 }
                 *heap.peek_mut().unwrap() = heap_item;
-                heap.peek().map(|el| el.feature).unwrap_or(std::f32::MIN)
+                heap.peek().map(|el| el.feature).unwrap_or(Score::MIN)
             })?;
         }
 
@@ -561,7 +711,7 @@ mod tests {
         let index = Index::create_in_ram(schema);
         {
             // writing the segment
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+            let mut index_writer = index.writer_with_num_threads(1, 10_000_000).unwrap();
             index_writer.add_document(doc!(text_field=>"Hello happy tax payer."));
             index_writer.add_document(doc!(text_field=>"Droopy says hello happy tax payer"));
             index_writer.add_document(doc!(text_field=>"I like Droopy"));
@@ -570,6 +720,13 @@ mod tests {
         index
     }
 
+    fn assert_results_equals(results: &[(Score, DocAddress)], expected: &[(Score, DocAddress)]) {
+        for (result, expected) in results.iter().zip(expected.iter()) {
+            assert_eq!(result.1, expected.1);
+            crate::assert_nearly_equals!(result.0, expected.0);
+        }
+    }
+
     #[test]
     fn test_top_collector_not_at_capacity() {
         let index = make_index();
@@ -582,13 +739,13 @@ mod tests {
             .searcher()
             .search(&text_query, &TopDocs::with_limit(4))
             .unwrap();
-        assert_eq!(
+        assert_results_equals(
-            score_docs,
+            &score_docs,
-            vec![
+            &[
                 (0.81221175, DocAddress(0u32, 1)),
                 (0.5376842, DocAddress(0u32, 2)),
-                (0.48527452, DocAddress(0, 0))
+                (0.48527452, DocAddress(0, 0)),
-            ]
+            ],
         );
     }
 
@@ -604,7 +761,7 @@ mod tests {
             .searcher()
             .search(&text_query, &TopDocs::with_limit(4).and_offset(2))
             .unwrap();
-        assert_eq!(score_docs, vec![(0.48527452, DocAddress(0, 0))]);
+        assert_results_equals(&score_docs[..], &[(0.48527452, DocAddress(0, 0))]);
     }
 
     #[test]
@@ -619,12 +776,12 @@ mod tests {
             .searcher()
             .search(&text_query, &TopDocs::with_limit(2))
             .unwrap();
-        assert_eq!(
+        assert_results_equals(
-            score_docs,
+            &score_docs,
-            vec![
+            &[
                 (0.81221175, DocAddress(0u32, 1)),
                 (0.5376842, DocAddress(0u32, 2)),
-            ]
+            ],
         );
     }
 
@@ -640,12 +797,12 @@ mod tests {
             .searcher()
             .search(&text_query, &TopDocs::with_limit(2).and_offset(1))
             .unwrap();
-        assert_eq!(
+        assert_results_equals(
-            score_docs,
+            &score_docs[..],
-            vec![
+            &[
                 (0.5376842, DocAddress(0u32, 2)),
-                (0.48527452, DocAddress(0, 0))
+                (0.48527452, DocAddress(0, 0)),
-            ]
+            ],
         );
     }
 
@@ -706,8 +863,8 @@ mod tests {
         let top_collector = TopDocs::with_limit(4).order_by_u64_field(size);
         let top_docs: Vec<(u64, DocAddress)> = searcher.search(&query, &top_collector).unwrap();
         assert_eq!(
-            top_docs,
+            &top_docs[..],
-            vec![
+            &[
                 (64, DocAddress(0, 1)),
                 (16, DocAddress(0, 2)),
                 (12, DocAddress(0, 0))
@@ -715,6 +872,94 @@ mod tests {
         );
     }
 
+    #[test]
+    fn test_top_field_collector_datetime() -> crate::Result<()> {
+        use std::str::FromStr;
+        let mut schema_builder = Schema::builder();
+        let name = schema_builder.add_text_field("name", TEXT);
+        let birthday = schema_builder.add_date_field("birthday", FAST);
+        let schema = schema_builder.build();
+        let index = Index::create_in_ram(schema);
+        let mut index_writer = index.writer_for_tests()?;
+        let pr_birthday = crate::DateTime::from_str("1898-04-09T00:00:00+00:00")?;
+        index_writer.add_document(doc!(
+            name => "Paul Robeson",
+            birthday => pr_birthday
+        ));
+        let mr_birthday = crate::DateTime::from_str("1947-11-08T00:00:00+00:00")?;
+        index_writer.add_document(doc!(
+            name => "Minnie Riperton",
+            birthday => mr_birthday
+        ));
+        index_writer.commit()?;
+        let searcher = index.reader()?.searcher();
+        let top_collector = TopDocs::with_limit(3).order_by_fast_field(birthday);
+        let top_docs: Vec<(crate::DateTime, DocAddress)> =
+            searcher.search(&AllQuery, &top_collector)?;
+        assert_eq!(
+            &top_docs[..],
+            &[
+                (mr_birthday, DocAddress(0, 1)),
+                (pr_birthday, DocAddress(0, 0)),
+            ]
+        );
+        Ok(())
+    }
+
+    #[test]
+    fn test_top_field_collector_i64() -> crate::Result<()> {
+        let mut schema_builder = Schema::builder();
+        let city = schema_builder.add_text_field("city", TEXT);
+        let altitude = schema_builder.add_i64_field("altitude", FAST);
+        let schema = schema_builder.build();
+        let index = Index::create_in_ram(schema);
+        let mut index_writer = index.writer_for_tests()?;
+        index_writer.add_document(doc!(
+                city => "georgetown",
+                altitude =>  -1i64,
+        ));
+        index_writer.add_document(doc!(
+            city => "tokyo",
+            altitude =>  40i64,
+        ));
+        index_writer.commit()?;
+        let searcher = index.reader()?.searcher();
+        let top_collector = TopDocs::with_limit(3).order_by_fast_field(altitude);
+        let top_docs: Vec<(i64, DocAddress)> = searcher.search(&AllQuery, &top_collector)?;
+        assert_eq!(
+            &top_docs[..],
+            &[(40i64, DocAddress(0, 1)), (-1i64, DocAddress(0, 0)),]
+        );
+        Ok(())
+    }
+
+    #[test]
+    fn test_top_field_collector_f64() -> crate::Result<()> {
+        let mut schema_builder = Schema::builder();
+        let city = schema_builder.add_text_field("city", TEXT);
+        let altitude = schema_builder.add_f64_field("altitude", FAST);
+        let schema = schema_builder.build();
+        let index = Index::create_in_ram(schema);
+        let mut index_writer = index.writer_for_tests()?;
+        index_writer.add_document(doc!(
+                city => "georgetown",
+                altitude =>  -1.0f64,
+        ));
+        index_writer.add_document(doc!(
+            city => "tokyo",
+            altitude =>  40f64,
+        ));
+        index_writer.commit()?;
+        let searcher = index.reader()?.searcher();
+        let top_collector = TopDocs::with_limit(3).order_by_fast_field(altitude);
+        let top_docs: Vec<(f64, DocAddress)> = searcher.search(&AllQuery, &top_collector)?;
+        assert_eq!(
+            &top_docs[..],
+            &[(40f64, DocAddress(0, 1)), (-1.0f64, DocAddress(0, 0)),]
+        );
+        Ok(())
+    }
+
     #[test]
     #[should_panic]
     fn test_field_does_not_exist() {
@@ -737,29 +982,41 @@ mod tests {
     }
 
     #[test]
-    fn test_field_not_fast_field() {
+    fn test_field_not_fast_field() -> crate::Result<()> {
         let mut schema_builder = Schema::builder();
-        let title = schema_builder.add_text_field(TITLE, TEXT);
         let size = schema_builder.add_u64_field(SIZE, STORED);
         let schema = schema_builder.build();
-        let (index, _) = index("beer", title, schema, |index_writer| {
+        let index = Index::create_in_ram(schema);
-            index_writer.add_document(doc!(
+        let mut index_writer = index.writer_for_tests()?;
-                title => "bottle of beer",
+        index_writer.add_document(doc!(size=>1u64));
-                size => 12u64,
+        index_writer.commit()?;
-            ));
+        let searcher = index.reader()?.searcher();
-        });
-        let searcher = index.reader().unwrap().searcher();
         let segment = searcher.segment_reader(0);
         let top_collector = TopDocs::with_limit(4).order_by_u64_field(size);
-        let err = top_collector.for_segment(0, segment);
+        let err = top_collector.for_segment(0, segment).err().unwrap();
-        if let Err(crate::TantivyError::SchemaError(msg)) = err {
+        assert!(
-            assert_eq!(
+            matches!(err, crate::TantivyError::SchemaError(msg) if msg == "Field requested (Field(0)) is not a fast field.")
-                msg,
+        );
-                "Field requested (Field(1)) is not a i64/u64 fast field."
+        Ok(())
-            );
+    }
-        } else {
+
-            assert!(false);
+    #[test]
-        }
+    fn test_field_wrong_type() -> crate::Result<()> {
+        let mut schema_builder = Schema::builder();
+        let size = schema_builder.add_u64_field(SIZE, STORED);
+        let schema = schema_builder.build();
+        let index = Index::create_in_ram(schema);
+        let mut index_writer = index.writer_for_tests()?;
+        index_writer.add_document(doc!(size=>1u64));
+        index_writer.commit()?;
+        let searcher = index.reader()?.searcher();
+        let segment = searcher.segment_reader(0);
+        let top_collector = TopDocs::with_limit(4).order_by_fast_field::<i64>(size);
+        let err = top_collector.for_segment(0, segment).err().unwrap();
+        assert!(
+            matches!(err, crate::TantivyError::SchemaError(msg) if msg == "Field \"size\" is not a fast field.")
+        );
+        Ok(())
     }
 
     #[test]
@@ -813,8 +1070,7 @@ mod tests {
         mut doc_adder: impl FnMut(&mut IndexWriter) -> (),
     ) -> (Index, Box<dyn Query>) {
         let index = Index::create_in_ram(schema);
-
+        let mut index_writer = index.writer_with_num_threads(1, 10_000_000).unwrap();
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
         doc_adder(&mut index_writer);
         index_writer.commit().unwrap();
         let query_parser = QueryParser::for_index(&index, vec![query_field]);

src/collector/tweak_score_top_collector.rs

@@ -49,7 +49,7 @@ pub trait ScoreTweaker<TScore>: Sync {
 
 impl<TScoreTweaker, TScore> Collector for TweakedScoreTopCollector<TScoreTweaker, TScore>
 where
-    TScoreTweaker: ScoreTweaker<TScore>,
+    TScoreTweaker: ScoreTweaker<TScore> + Send + Sync,
     TScore: 'static + PartialOrd + Clone + Send + Sync,
 {
     type Fruit = Vec<(TScore, DocAddress)>;

src/common/bitpacker.rs

@@ -1,6 +1,7 @@
 use byteorder::{ByteOrder, LittleEndian, WriteBytesExt};
 use std::io;
-use std::ops::Deref;
+
+use crate::directory::OwnedBytes;
 
 pub(crate) struct BitPacker {
     mini_buffer: u64,
@@ -60,20 +61,14 @@ impl BitPacker {
 }
 
 #[derive(Clone)]
-pub struct BitUnpacker<Data>
+pub struct BitUnpacker {
-where
-    Data: Deref<Target = [u8]>,
-{
     num_bits: u64,
     mask: u64,
-    data: Data,
+    data: OwnedBytes,
 }
 
-impl<Data> BitUnpacker<Data>
+impl BitUnpacker {
-where
+    pub fn new(data: OwnedBytes, num_bits: u8) -> BitUnpacker {
-    Data: Deref<Target = [u8]>,
-{
-    pub fn new(data: Data, num_bits: u8) -> BitUnpacker<Data> {
         let mask: u64 = if num_bits == 64 {
             !0u64
         } else {
@@ -90,7 +85,7 @@ where
         if self.num_bits == 0 {
             return 0u64;
         }
-        let data: &[u8] = &*self.data;
+        let data: &[u8] = self.data.as_slice();
         let num_bits = self.num_bits;
         let mask = self.mask;
         let addr_in_bits = idx * num_bits;
@@ -109,8 +104,9 @@ where
 #[cfg(test)]
 mod test {
     use super::{BitPacker, BitUnpacker};
+    use crate::directory::OwnedBytes;
 
-    fn create_fastfield_bitpacker(len: usize, num_bits: u8) -> (BitUnpacker<Vec<u8>>, Vec<u64>) {
+    fn create_fastfield_bitpacker(len: usize, num_bits: u8) -> (BitUnpacker, Vec<u64>) {
         let mut data = Vec::new();
         let mut bitpacker = BitPacker::new();
         let max_val: u64 = (1u64 << num_bits as u64) - 1u64;
@@ -122,7 +118,7 @@ mod test {
         }
         bitpacker.close(&mut data).unwrap();
         assert_eq!(data.len(), ((num_bits as usize) * len + 7) / 8 + 7);
-        let bitunpacker = BitUnpacker::new(data, num_bits);
+        let bitunpacker = BitUnpacker::new(OwnedBytes::new(data), num_bits);
         (bitunpacker, vals)
     }
 

src/common/composite_file.rs

@@ -1,14 +1,15 @@
 use crate::common::BinarySerializable;
 use crate::common::CountingWriter;
 use crate::common::VInt;
-use crate::directory::ReadOnlySource;
+use crate::directory::FileSlice;
 use crate::directory::{TerminatingWrite, WritePtr};
 use crate::schema::Field;
 use crate::space_usage::FieldUsage;
 use crate::space_usage::PerFieldSpaceUsage;
 use std::collections::HashMap;
-use std::io::Write;
+use std::io::{self, Read, Write};
-use std::io::{self, Read};
+
+use super::HasLen;
 
 #[derive(Eq, PartialEq, Hash, Copy, Ord, PartialOrd, Clone, Debug)]
 pub struct FileAddr {
@@ -103,25 +104,26 @@ impl<W: TerminatingWrite + Write> CompositeWrite<W> {
 /// for each field.
 #[derive(Clone)]
 pub struct CompositeFile {
-    data: ReadOnlySource,
+    data: FileSlice,
     offsets_index: HashMap<FileAddr, (usize, usize)>,
 }
 
 impl CompositeFile {
     /// Opens a composite file stored in a given
-    /// `ReadOnlySource`.
+    /// `FileSlice`.
-    pub fn open(data: &ReadOnlySource) -> io::Result<CompositeFile> {
+    pub fn open(data: &FileSlice) -> io::Result<CompositeFile> {
         let end = data.len();
-        let footer_len_data = data.slice_from(end - 4);
+        let footer_len_data = data.slice_from(end - 4).read_bytes()?;
         let footer_len = u32::deserialize(&mut footer_len_data.as_slice())? as usize;
         let footer_start = end - 4 - footer_len;
-        let footer_data = data.slice(footer_start, footer_start + footer_len);
+        let footer_data = data
+            .slice(footer_start, footer_start + footer_len)
+            .read_bytes()?;
         let mut footer_buffer = footer_data.as_slice();
         let num_fields = VInt::deserialize(&mut footer_buffer)?.0 as usize;
 
         let mut file_addrs = vec![];
         let mut offsets = vec![];
-
         let mut field_index = HashMap::new();
 
         let mut offset = 0;
@@ -150,19 +152,19 @@ impl CompositeFile {
     pub fn empty() -> CompositeFile {
         CompositeFile {
             offsets_index: HashMap::new(),
-            data: ReadOnlySource::empty(),
+            data: FileSlice::empty(),
         }
     }
 
-    /// Returns the `ReadOnlySource` associated
+    /// Returns the `FileSlice` associated
     /// to a given `Field` and stored in a `CompositeFile`.
-    pub fn open_read(&self, field: Field) -> Option<ReadOnlySource> {
+    pub fn open_read(&self, field: Field) -> Option<FileSlice> {
         self.open_read_with_idx(field, 0)
     }
 
-    /// Returns the `ReadOnlySource` associated
+    /// Returns the `FileSlice` associated
     /// to a given `Field` and stored in a `CompositeFile`.
-    pub fn open_read_with_idx(&self, field: Field, idx: usize) -> Option<ReadOnlySource> {
+    pub fn open_read_with_idx(&self, field: Field, idx: usize) -> Option<FileSlice> {
         self.offsets_index
             .get(&FileAddr { field, idx })
             .map(|&(from, to)| self.data.slice(from, to))
@@ -192,46 +194,44 @@ mod test {
     use std::path::Path;
 
     #[test]
-    fn test_composite_file() {
+    fn test_composite_file() -> crate::Result<()> {
         let path = Path::new("test_path");
-        let mut directory = RAMDirectory::create();
+        let directory = RAMDirectory::create();
         {
             let w = directory.open_write(path).unwrap();
             let mut composite_write = CompositeWrite::wrap(w);
-            {
+            let mut write_0 = composite_write.for_field(Field::from_field_id(0u32));
-                let mut write_0 = composite_write.for_field(Field::from_field_id(0u32));
+            VInt(32431123u64).serialize(&mut write_0)?;
-                VInt(32431123u64).serialize(&mut write_0).unwrap();
+            write_0.flush()?;
-                write_0.flush().unwrap();
+            let mut write_4 = composite_write.for_field(Field::from_field_id(4u32));
-            }
+            VInt(2).serialize(&mut write_4)?;
-
+            write_4.flush()?;
-            {
+            composite_write.close()?;
-                let mut write_4 = composite_write.for_field(Field::from_field_id(4u32));
-                VInt(2).serialize(&mut write_4).unwrap();
-                write_4.flush().unwrap();
-            }
-            composite_write.close().unwrap();
         }
         {
-            let r = directory.open_read(path).unwrap();
+            let r = directory.open_read(path)?;
-            let composite_file = CompositeFile::open(&r).unwrap();
+            let composite_file = CompositeFile::open(&r)?;
             {
                 let file0 = composite_file
                     .open_read(Field::from_field_id(0u32))
-                    .unwrap();
+                    .unwrap()
+                    .read_bytes()?;
                 let mut file0_buf = file0.as_slice();
-                let payload_0 = VInt::deserialize(&mut file0_buf).unwrap().0;
+                let payload_0 = VInt::deserialize(&mut file0_buf)?.0;
                 assert_eq!(file0_buf.len(), 0);
                 assert_eq!(payload_0, 32431123u64);
             }
             {
                 let file4 = composite_file
                     .open_read(Field::from_field_id(4u32))
-                    .unwrap();
+                    .unwrap()
+                    .read_bytes()?;
                 let mut file4_buf = file4.as_slice();
-                let payload_4 = VInt::deserialize(&mut file4_buf).unwrap().0;
+                let payload_4 = VInt::deserialize(&mut file4_buf)?.0;
                 assert_eq!(file4_buf.len(), 0);
                 assert_eq!(payload_4, 2u64);
             }
         }
+        Ok(())
     }
 }

src/common/mod.rs

@@ -10,7 +10,9 @@ pub(crate) use self::bitset::TinySet;
 pub(crate) use self::composite_file::{CompositeFile, CompositeWrite};
 pub use self::counting_writer::CountingWriter;
 pub use self::serialize::{BinarySerializable, FixedSize};
-pub use self::vint::{read_u32_vint, serialize_vint_u32, write_u32_vint, VInt};
+pub use self::vint::{
+    read_u32_vint, read_u32_vint_no_advance, serialize_vint_u32, write_u32_vint, VInt,
+};
 pub use byteorder::LittleEndian as Endianness;
 
 /// Segment's max doc must be `< MAX_DOC_LIMIT`.

src/common/serialize.rs

@@ -89,6 +89,19 @@ impl FixedSize for u64 {
     const SIZE_IN_BYTES: usize = 8;
 }
 
+impl BinarySerializable for f32 {
+    fn serialize<W: Write>(&self, writer: &mut W) -> io::Result<()> {
+        writer.write_f32::<Endianness>(*self)
+    }
+    fn deserialize<R: Read>(reader: &mut R) -> io::Result<Self> {
+        reader.read_f32::<Endianness>()
+    }
+}
+
+impl FixedSize for f32 {
+    const SIZE_IN_BYTES: usize = 4;
+}
+
 impl BinarySerializable for i64 {
     fn serialize<W: Write>(&self, writer: &mut W) -> io::Result<()> {
         writer.write_i64::<Endianness>(*self)

src/common/vint.rs

@@ -5,12 +5,12 @@ use std::io::Read;
 use std::io::Write;
 
 ///   Wrapper over a `u64` that serializes as a variable int.
-#[derive(Debug, Eq, PartialEq)]
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
 pub struct VInt(pub u64);
 
 const STOP_BIT: u8 = 128;
 
-pub fn serialize_vint_u32(val: u32) -> (u64, usize) {
+pub fn serialize_vint_u32(val: u32, buf: &mut [u8; 8]) -> &[u8] {
     const START_2: u64 = 1 << 7;
     const START_3: u64 = 1 << 14;
     const START_4: u64 = 1 << 21;
@@ -29,7 +29,7 @@ pub fn serialize_vint_u32(val: u32) -> (u64, usize) {
 
     let val = u64::from(val);
     const STOP_BIT: u64 = 128u64;
-    match val {
+    let (res, num_bytes) = match val {
         0..=STOP_1 => (val | STOP_BIT, 1),
         START_2..=STOP_2 => (
             (val & MASK_1) | ((val & MASK_2) << 1) | (STOP_BIT << (8)),
@@ -56,7 +56,9 @@ pub fn serialize_vint_u32(val: u32) -> (u64, usize) {
                 | (STOP_BIT << (8 * 4)),
             5,
         ),
-    }
+    };
+    LittleEndian::write_u64(&mut buf[..], res);
+    &buf[0..num_bytes]
 }
 
 /// Returns the number of bytes covered by a
@@ -85,23 +87,26 @@ fn vint_len(data: &[u8]) -> usize {
 /// If the buffer does not start by a valid
 /// vint payload
 pub fn read_u32_vint(data: &mut &[u8]) -> u32 {
-    let vlen = vint_len(*data);
+    let (result, vlen) = read_u32_vint_no_advance(*data);
+    *data = &data[vlen..];
+    result
+}
+
+pub fn read_u32_vint_no_advance(data: &[u8]) -> (u32, usize) {
+    let vlen = vint_len(data);
     let mut result = 0u32;
     let mut shift = 0u64;
     for &b in &data[..vlen] {
         result |= u32::from(b & 127u8) << shift;
         shift += 7;
     }
-    *data = &data[vlen..];
+    (result, vlen)
-    result
 }
-
 /// Write a `u32` as a vint payload.
 pub fn write_u32_vint<W: io::Write>(val: u32, writer: &mut W) -> io::Result<()> {
-    let (val, num_bytes) = serialize_vint_u32(val);
+    let mut buf = [0u8; 8];
-    let mut buffer = [0u8; 8];
+    let data = serialize_vint_u32(val, &mut buf);
-    LittleEndian::write_u64(&mut buffer, val);
+    writer.write_all(&data)
-    writer.write_all(&buffer[..num_bytes])
 }
 
 impl VInt {
@@ -172,7 +177,6 @@ mod tests {
     use super::serialize_vint_u32;
     use super::VInt;
     use crate::common::BinarySerializable;
-    use byteorder::{ByteOrder, LittleEndian};
 
     fn aux_test_vint(val: u64) {
         let mut v = [14u8; 10];
@@ -208,12 +212,10 @@ mod tests {
 
     fn aux_test_serialize_vint_u32(val: u32) {
         let mut buffer = [0u8; 10];
-        let mut buffer2 = [0u8; 10];
+        let mut buffer2 = [0u8; 8];
         let len_vint = VInt(val as u64).serialize_into(&mut buffer);
-        let (vint, len) = serialize_vint_u32(val);
+        let res2 = serialize_vint_u32(val, &mut buffer2);
-        assert_eq!(len, len_vint, "len wrong for val {}", val);
+        assert_eq!(&buffer[..len_vint], res2, "array wrong for {}", val);
-        LittleEndian::write_u64(&mut buffer2, vint);
-        assert_eq!(&buffer[..len], &buffer2[..len], "array wrong for {}", val);
     }
 
     #[test]

src/core/index.rs

@@ -21,11 +21,12 @@ use crate::schema::FieldType;
 use crate::schema::Schema;
 use crate::tokenizer::{TextAnalyzer, TokenizerManager};
 use crate::IndexWriter;
-use std::borrow::BorrowMut;
 use std::collections::HashSet;
 use std::fmt;
+
 #[cfg(feature = "mmap")]
-use std::path::{Path, PathBuf};
+use std::path::Path;
+use std::path::PathBuf;
 use std::sync::Arc;
 
 fn load_metas(
@@ -55,7 +56,9 @@ pub struct Index {
 }
 
 impl Index {
-    /// Examines the director to see if it contains an index
+    /// Examines the directory to see if it contains an index.
+    ///
+    /// Effectively, it only checks for the presence of the `meta.json` file.
     pub fn exists<Dir: Directory>(dir: &Dir) -> bool {
         dir.exists(&META_FILEPATH)
     }
@@ -138,7 +141,9 @@ impl Index {
         Index::create(mmap_directory, schema)
     }
 
-    /// Creates a new index given an implementation of the trait `Directory`
+    /// Creates a new index given an implementation of the trait `Directory`.
+    ///
+    /// If a directory previously existed, it will be erased.
     pub fn create<Dir: Directory>(dir: Dir, schema: Schema) -> crate::Result<Index> {
         let directory = ManagedDirectory::wrap(dir)?;
         Index::from_directory(directory, schema)
@@ -147,8 +152,8 @@ impl Index {
     /// Create a new index from a directory.
     ///
     /// This will overwrite existing meta.json
-    fn from_directory(mut directory: ManagedDirectory, schema: Schema) -> crate::Result<Index> {
+    fn from_directory(directory: ManagedDirectory, schema: Schema) -> crate::Result<Index> {
-        save_new_metas(schema.clone(), directory.borrow_mut())?;
+        save_new_metas(schema.clone(), &directory)?;
         let metas = IndexMeta::with_schema(schema);
         Index::create_from_metas(directory, &metas, SegmentMetaInventory::default())
     }
@@ -281,7 +286,7 @@ impl Index {
                 TantivyError::LockFailure(
                     err,
                     Some(
-                        "Failed to acquire index lock. If you are using\
+                        "Failed to acquire index lock. If you are using \
                          a regular directory, this means there is already an \
                          `IndexWriter` working on this `Directory`, in this process \
                          or in a different process."
@@ -298,6 +303,15 @@ impl Index {
         )
     }
 
+    /// Helper to create an index writer for tests.
+    ///
+    /// That index writer only simply has a single thread and a heap of 5 MB.
+    /// Using a single thread gives us a deterministic allocation of DocId.
+    #[cfg(test)]
+    pub fn writer_for_tests(&self) -> crate::Result<IndexWriter> {
+        self.writer_with_num_threads(1, 10_000_000)
+    }
+
     /// Creates a multithreaded writer
     ///
     /// Tantivy will automatically define the number of threads to use.
@@ -500,7 +514,7 @@ mod tests {
             let schema = throw_away_schema();
             let field = schema.get_field("num_likes").unwrap();
             let mut index = Index::create_from_tempdir(schema).unwrap();
-            let mut writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+            let mut writer = index.writer_for_tests().unwrap();
             writer.commit().unwrap();
             let reader = index
                 .reader_builder()
@@ -537,23 +551,33 @@ mod tests {
             test_index_on_commit_reload_policy_aux(field, &write_index, &reader);
         }
     }
-
     fn test_index_on_commit_reload_policy_aux(field: Field, index: &Index, reader: &IndexReader) {
         let mut reader_index = reader.index();
         let (sender, receiver) = crossbeam::channel::unbounded();
         let _watch_handle = reader_index.directory_mut().watch(Box::new(move || {
             let _ = sender.send(());
         }));
-        let mut writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut writer = index.writer_for_tests().unwrap();
         assert_eq!(reader.searcher().num_docs(), 0);
         writer.add_document(doc!(field=>1u64));
         writer.commit().unwrap();
-        assert!(receiver.recv().is_ok());
+        // We need a loop here because it is possible for notify to send more than
-        assert_eq!(reader.searcher().num_docs(), 1);
+        // one modify event. It was observed on CI on MacOS.
+        loop {
+            assert!(receiver.recv().is_ok());
+            if reader.searcher().num_docs() == 1 {
+                break;
+            }
+        }
         writer.add_document(doc!(field=>2u64));
         writer.commit().unwrap();
-        assert!(receiver.recv().is_ok());
+        // ... Same as above
-        assert_eq!(reader.searcher().num_docs(), 2);
+        loop {
+            assert!(receiver.recv().is_ok());
+            if reader.searcher().num_docs() == 2 {
+                break;
+            }
+        }
     }
 
     // This test will not pass on windows, because windows

src/core/index_meta.rs

@@ -213,7 +213,7 @@ pub struct IndexMeta {
     #[serde(skip_serializing_if = "Option::is_none")]
     /// Payload associated to the last commit.
     ///
-    /// Upon commit, clients can optionally add a small `Striing` payload to their commit
+    /// Upon commit, clients can optionally add a small `String` payload to their commit
     /// to help identify this commit.
     /// This payload is entirely unused by tantivy.
     pub payload: Option<String>,
@@ -301,7 +301,7 @@ mod tests {
         let json = serde_json::ser::to_string(&index_metas).expect("serialization failed");
         assert_eq!(
             json,
-            r#"{"segments":[],"schema":[{"name":"text","type":"text","options":{"indexing":{"record":"position","tokenizer":"default"},"stored":false}}],"opstamp":0}"#
+            r#"{"segments":[],"schema":[{"name":"text","type":"text","options":{"indexing":{"record":"position","tokenizer":"default","fieldnorms":true},"stored":false}}],"opstamp":0}"#
         );
     }
 }

src/core/inverted_index_reader.rs

@@ -1,9 +1,10 @@
+use std::io;
+
 use crate::common::BinarySerializable;
-use crate::directory::ReadOnlySource;
+use crate::directory::FileSlice;
 use crate::positions::PositionReader;
 use crate::postings::TermInfo;
 use crate::postings::{BlockSegmentPostings, SegmentPostings};
-use crate::schema::FieldType;
 use crate::schema::IndexRecordOption;
 use crate::schema::Term;
 use crate::termdict::TermDictionary;
@@ -15,7 +16,7 @@ use crate::termdict::TermDictionary;
 ///
 /// It is safe to delete the segment associated to
 /// an `InvertedIndexReader`. As long as it is open,
-/// the `ReadOnlySource` it is relying on should
+/// the `FileSlice` it is relying on should
 /// stay available.
 ///
 ///
@@ -23,9 +24,9 @@ use crate::termdict::TermDictionary;
 /// the `SegmentReader`'s [`.inverted_index(...)`] method
 pub struct InvertedIndexReader {
     termdict: TermDictionary,
-    postings_source: ReadOnlySource,
+    postings_file_slice: FileSlice,
-    positions_source: ReadOnlySource,
+    positions_file_slice: FileSlice,
-    positions_idx_source: ReadOnlySource,
+    positions_idx_file_slice: FileSlice,
     record_option: IndexRecordOption,
     total_num_tokens: u64,
 }
@@ -34,35 +35,31 @@ impl InvertedIndexReader {
     #[cfg_attr(feature = "cargo-clippy", allow(clippy::needless_pass_by_value))] // for symmetry
     pub(crate) fn new(
         termdict: TermDictionary,
-        postings_source: ReadOnlySource,
+        postings_file_slice: FileSlice,
-        positions_source: ReadOnlySource,
+        positions_file_slice: FileSlice,
-        positions_idx_source: ReadOnlySource,
+        positions_idx_file_slice: FileSlice,
         record_option: IndexRecordOption,
-    ) -> InvertedIndexReader {
+    ) -> io::Result<InvertedIndexReader> {
-        let total_num_tokens_data = postings_source.slice(0, 8);
+        let (total_num_tokens_slice, postings_body) = postings_file_slice.split(8);
-        let mut total_num_tokens_cursor = total_num_tokens_data.as_slice();
+        let total_num_tokens = u64::deserialize(&mut total_num_tokens_slice.read_bytes()?)?;
-        let total_num_tokens = u64::deserialize(&mut total_num_tokens_cursor).unwrap_or(0u64);
+        Ok(InvertedIndexReader {
-        InvertedIndexReader {
             termdict,
-            postings_source: postings_source.slice_from(8),
+            postings_file_slice: postings_body,
-            positions_source,
+            positions_file_slice,
-            positions_idx_source,
+            positions_idx_file_slice,
             record_option,
             total_num_tokens,
-        }
+        })
     }
 
     /// Creates an empty `InvertedIndexReader` object, which
     /// contains no terms at all.
-    pub fn empty(field_type: &FieldType) -> InvertedIndexReader {
+    pub fn empty(record_option: IndexRecordOption) -> InvertedIndexReader {
-        let record_option = field_type
-            .get_index_record_option()
-            .unwrap_or(IndexRecordOption::Basic);
         InvertedIndexReader {
             termdict: TermDictionary::empty(),
-            postings_source: ReadOnlySource::empty(),
+            postings_file_slice: FileSlice::empty(),
-            positions_source: ReadOnlySource::empty(),
+            positions_file_slice: FileSlice::empty(),
-            positions_idx_source: ReadOnlySource::empty(),
+            positions_idx_file_slice: FileSlice::empty(),
             record_option,
             total_num_tokens: 0u64,
         }
@@ -92,11 +89,12 @@ impl InvertedIndexReader {
         &self,
         term_info: &TermInfo,
         block_postings: &mut BlockSegmentPostings,
-    ) {
+    ) -> io::Result<()> {
-        let offset = term_info.postings_offset as usize;
+        let postings_slice = self
-        let end_source = self.postings_source.len();
+            .postings_file_slice
-        let postings_slice = self.postings_source.slice(offset, end_source);
+            .slice_from(term_info.postings_offset as usize);
-        block_postings.reset(term_info.doc_freq, postings_slice);
+        block_postings.reset(term_info.doc_freq, postings_slice.read_bytes()?);
+        Ok(())
     }
 
     /// Returns a block postings given a `Term`.
@@ -107,9 +105,11 @@ impl InvertedIndexReader {
         &self,
         term: &Term,
         option: IndexRecordOption,
-    ) -> Option<BlockSegmentPostings> {
+    ) -> io::Result<Option<BlockSegmentPostings>> {
-        self.get_term_info(term)
+        Ok(self
+            .get_term_info(term)
             .map(move |term_info| self.read_block_postings_from_terminfo(&term_info, option))
+            .transpose()?)
     }
 
     /// Returns a block postings given a `term_info`.
@@ -120,10 +120,10 @@ impl InvertedIndexReader {
         &self,
         term_info: &TermInfo,
         requested_option: IndexRecordOption,
-    ) -> BlockSegmentPostings {
+    ) -> io::Result<BlockSegmentPostings> {
         let offset = term_info.postings_offset as usize;
-        let postings_data = self.postings_source.slice_from(offset);
+        let postings_data = self.postings_file_slice.slice_from(offset);
-        BlockSegmentPostings::from_data(
+        BlockSegmentPostings::open(
             term_info.doc_freq,
             postings_data,
             self.record_option,
@@ -139,20 +139,23 @@ impl InvertedIndexReader {
         &self,
         term_info: &TermInfo,
         option: IndexRecordOption,
-    ) -> SegmentPostings {
+    ) -> io::Result<SegmentPostings> {
-        let block_postings = self.read_block_postings_from_terminfo(term_info, option);
+        let block_postings = self.read_block_postings_from_terminfo(term_info, option)?;
         let position_stream = {
             if option.has_positions() {
-                let position_reader = self.positions_source.clone();
+                let position_reader = self.positions_file_slice.clone();
-                let skip_reader = self.positions_idx_source.clone();
+                let skip_reader = self.positions_idx_file_slice.clone();
                 let position_reader =
-                    PositionReader::new(position_reader, skip_reader, term_info.positions_idx);
+                    PositionReader::new(position_reader, skip_reader, term_info.positions_idx)?;
                 Some(position_reader)
             } else {
                 None
             }
         };
-        SegmentPostings::from_block_postings(block_postings, position_stream)
+        Ok(SegmentPostings::from_block_postings(
+            block_postings,
+            position_stream,
+        ))
     }
 
     /// Returns the total number of tokens recorded for all documents
@@ -171,24 +174,31 @@ impl InvertedIndexReader {
     /// For instance, requesting `IndexRecordOption::Freq` for a
     /// `TextIndexingOptions` that does not index position will return a `SegmentPostings`
     /// with `DocId`s and frequencies.
-    pub fn read_postings(&self, term: &Term, option: IndexRecordOption) -> Option<SegmentPostings> {
+    pub fn read_postings(
+        &self,
+        term: &Term,
+        option: IndexRecordOption,
+    ) -> io::Result<Option<SegmentPostings>> {
         self.get_term_info(term)
             .map(move |term_info| self.read_postings_from_terminfo(&term_info, option))
+            .transpose()
     }
 
     pub(crate) fn read_postings_no_deletes(
         &self,
         term: &Term,
         option: IndexRecordOption,
-    ) -> Option<SegmentPostings> {
+    ) -> io::Result<Option<SegmentPostings>> {
         self.get_term_info(term)
             .map(|term_info| self.read_postings_from_terminfo(&term_info, option))
+            .transpose()
     }
 
     /// Returns the number of documents containing the term.
-    pub fn doc_freq(&self, term: &Term) -> u32 {
+    pub fn doc_freq(&self, term: &Term) -> io::Result<u32> {
-        self.get_term_info(term)
+        Ok(self
+            .get_term_info(term)
             .map(|term_info| term_info.doc_freq)
-            .unwrap_or(0u32)
+            .unwrap_or(0u32))
     }
 }

src/core/searcher.rs

@@ -11,8 +11,8 @@ use crate::store::StoreReader;
 use crate::termdict::TermMerger;
 use crate::DocAddress;
 use crate::Index;
-use std::fmt;
 use std::sync::Arc;
+use std::{fmt, io};
 
 /// Holds a list of `SegmentReader`s ready for search.
 ///
@@ -32,17 +32,17 @@ impl Searcher {
         schema: Schema,
         index: Index,
         segment_readers: Vec<SegmentReader>,
-    ) -> Searcher {
+    ) -> io::Result<Searcher> {
-        let store_readers = segment_readers
+        let store_readers: Vec<StoreReader> = segment_readers
             .iter()
             .map(SegmentReader::get_store_reader)
-            .collect();
+            .collect::<io::Result<Vec<_>>>()?;
-        Searcher {
+        Ok(Searcher {
             schema,
             index,
             segment_readers,
             store_readers,
-        }
+        })
     }
 
     /// Returns the `Index` associated to the `Searcher`
@@ -75,13 +75,14 @@ impl Searcher {
 
     /// Return the overall number of documents containing
     /// the given term.
-    pub fn doc_freq(&self, term: &Term) -> u64 {
+    pub fn doc_freq(&self, term: &Term) -> crate::Result<u64> {
-        self.segment_readers
+        let mut total_doc_freq = 0;
-            .iter()
+        for segment_reader in &self.segment_readers {
-            .map(|segment_reader| {
+            let inverted_index = segment_reader.inverted_index(term.field())?;
-                u64::from(segment_reader.inverted_index(term.field()).doc_freq(term))
+            let doc_freq = inverted_index.doc_freq(term)?;
-            })
+            total_doc_freq += u64::from(doc_freq);
-            .sum::<u64>()
+        }
+        Ok(total_doc_freq)
     }
 
     /// Return the list of segment readers
@@ -148,22 +149,22 @@ impl Searcher {
     }
 
     /// Return the field searcher associated to a `Field`.
-    pub fn field(&self, field: Field) -> FieldSearcher {
+    pub fn field(&self, field: Field) -> crate::Result<FieldSearcher> {
-        let inv_index_readers = self
+        let inv_index_readers: Vec<Arc<InvertedIndexReader>> = self
             .segment_readers
             .iter()
             .map(|segment_reader| segment_reader.inverted_index(field))
-            .collect::<Vec<_>>();
+            .collect::<crate::Result<Vec<_>>>()?;
-        FieldSearcher::new(inv_index_readers)
+        Ok(FieldSearcher::new(inv_index_readers))
     }
 
     /// Summarize total space usage of this searcher.
-    pub fn space_usage(&self) -> SearcherSpaceUsage {
+    pub fn space_usage(&self) -> io::Result<SearcherSpaceUsage> {
         let mut space_usage = SearcherSpaceUsage::new();
-        for segment_reader in self.segment_readers.iter() {
+        for segment_reader in &self.segment_readers {
-            space_usage.add_segment(segment_reader.space_usage());
+            space_usage.add_segment(segment_reader.space_usage()?);
         }
-        space_usage
+        Ok(space_usage)
     }
 }
 

src/core/segment.rs

@@ -4,7 +4,7 @@ use crate::core::SegmentId;
 use crate::core::SegmentMeta;
 use crate::directory::error::{OpenReadError, OpenWriteError};
 use crate::directory::Directory;
-use crate::directory::{ReadOnlySource, WritePtr};
+use crate::directory::{FileSlice, WritePtr};
 use crate::indexer::segment_serializer::SegmentSerializer;
 use crate::schema::Schema;
 use crate::Opstamp;
@@ -78,10 +78,9 @@ impl Segment {
     }
 
     /// Open one of the component file for a *regular* read.
-    pub fn open_read(&self, component: SegmentComponent) -> Result<ReadOnlySource, OpenReadError> {
+    pub fn open_read(&self, component: SegmentComponent) -> Result<FileSlice, OpenReadError> {
         let path = self.relative_path(component);
-        let source = self.index.directory().open_read(&path)?;
+        self.index.directory().open_read(&path)
-        Ok(source)
     }
 
     /// Open one of the component file for *regular* write.

src/core/segment_component.rs

@@ -20,7 +20,7 @@ pub enum SegmentComponent {
     /// Dictionary associating `Term`s to `TermInfo`s which is
     /// simply an address into the `postings` file and the `positions` file.
     TERMS,
-    /// Row-oriented, LZ4-compressed storage of the documents.
+    /// Row-oriented, compressed storage of the documents.
     /// Accessing a document from the store is relatively slow, as it
     /// requires to decompress the entire block it belongs to.
     STORE,

src/core/segment_reader.rs

@@ -1,26 +1,26 @@
-use crate::common::CompositeFile;
 use crate::common::HasLen;
 use crate::core::InvertedIndexReader;
 use crate::core::Segment;
 use crate::core::SegmentComponent;
 use crate::core::SegmentId;
-use crate::directory::ReadOnlySource;
+use crate::directory::FileSlice;
 use crate::fastfield::DeleteBitSet;
 use crate::fastfield::FacetReader;
 use crate::fastfield::FastFieldReaders;
-use crate::fieldnorm::FieldNormReader;
+use crate::fieldnorm::{FieldNormReader, FieldNormReaders};
-use crate::schema::Field;
 use crate::schema::FieldType;
 use crate::schema::Schema;
+use crate::schema::{Field, IndexRecordOption};
 use crate::space_usage::SegmentSpaceUsage;
 use crate::store::StoreReader;
 use crate::termdict::TermDictionary;
 use crate::DocId;
+use crate::{common::CompositeFile, error::DataCorruption};
 use fail::fail_point;
-use std::collections::HashMap;
 use std::fmt;
 use std::sync::Arc;
 use std::sync::RwLock;
+use std::{collections::HashMap, io};
 
 /// Entry point to access all of the datastructures of the `Segment`
 ///
@@ -48,9 +48,9 @@ pub struct SegmentReader {
     positions_composite: CompositeFile,
     positions_idx_composite: CompositeFile,
     fast_fields_readers: Arc<FastFieldReaders>,
-    fieldnorms_composite: CompositeFile,
+    fieldnorm_readers: FieldNormReaders,
 
-    store_source: ReadOnlySource,
+    store_file: FileSlice,
     delete_bitset_opt: Option<DeleteBitSet>,
     schema: Schema,
 }
@@ -106,16 +106,26 @@ impl SegmentReader {
     }
 
     /// Accessor to the `FacetReader` associated to a given `Field`.
-    pub fn facet_reader(&self, field: Field) -> Option<FacetReader> {
+    pub fn facet_reader(&self, field: Field) -> crate::Result<FacetReader> {
         let field_entry = self.schema.get_field_entry(field);
         if field_entry.field_type() != &FieldType::HierarchicalFacet {
-            return None;
+            return Err(crate::TantivyError::InvalidArgument(format!(
+                "Field {:?} is not a facet field.",
+                field_entry.name()
+            )));
         }
-        let term_ords_reader = self.fast_fields().u64s(field)?;
+        let term_ords_reader = self.fast_fields().u64s(field).ok_or_else(|| {
-        let termdict_source = self.termdict_composite.open_read(field)?;
+            DataCorruption::comment_only(format!(
-        let termdict = TermDictionary::from_source(&termdict_source);
+                "Cannot find data for hierarchical facet {:?}",
-        let facet_reader = FacetReader::new(term_ords_reader, termdict);
+                field_entry.name()
-        Some(facet_reader)
+            ))
+        })?;
+        let termdict = self
+            .termdict_composite
+            .open_read(field)
+            .map(TermDictionary::open)
+            .unwrap_or_else(|| Ok(TermDictionary::empty()))?;
+        Ok(FacetReader::new(term_ords_reader, termdict))
     }
 
     /// Accessor to the segment's `Field norms`'s reader.
@@ -125,47 +135,45 @@ impl SegmentReader {
     ///
     /// They are simply stored as a fast field, serialized in
     /// the `.fieldnorm` file of the segment.
-    pub fn get_fieldnorms_reader(&self, field: Field) -> FieldNormReader {
+    pub fn get_fieldnorms_reader(&self, field: Field) -> crate::Result<FieldNormReader> {
-        if let Some(fieldnorm_source) = self.fieldnorms_composite.open_read(field) {
+        self.fieldnorm_readers.get_field(field)?.ok_or_else(|| {
-            FieldNormReader::open(fieldnorm_source)
-        } else {
             let field_name = self.schema.get_field_name(field);
             let err_msg = format!(
-                "Field norm not found for field {:?}. Was it market as indexed during indexing.",
+                "Field norm not found for field {:?}. Was it marked as indexed during indexing?",
                 field_name
             );
-            panic!(err_msg);
+            crate::TantivyError::SchemaError(err_msg)
-        }
+        })
     }
 
     /// Accessor to the segment's `StoreReader`.
-    pub fn get_store_reader(&self) -> StoreReader {
+    pub fn get_store_reader(&self) -> io::Result<StoreReader> {
-        StoreReader::from_source(self.store_source.clone())
+        StoreReader::open(self.store_file.clone())
     }
 
     /// Open a new segment for reading.
     pub fn open(segment: &Segment) -> crate::Result<SegmentReader> {
-        let termdict_source = segment.open_read(SegmentComponent::TERMS)?;
+        let termdict_file = segment.open_read(SegmentComponent::TERMS)?;
-        let termdict_composite = CompositeFile::open(&termdict_source)?;
+        let termdict_composite = CompositeFile::open(&termdict_file)?;
 
-        let store_source = segment.open_read(SegmentComponent::STORE)?;
+        let store_file = segment.open_read(SegmentComponent::STORE)?;
 
         fail_point!("SegmentReader::open#middle");
 
-        let postings_source = segment.open_read(SegmentComponent::POSTINGS)?;
+        let postings_file = segment.open_read(SegmentComponent::POSTINGS)?;
-        let postings_composite = CompositeFile::open(&postings_source)?;
+        let postings_composite = CompositeFile::open(&postings_file)?;
 
         let positions_composite = {
-            if let Ok(source) = segment.open_read(SegmentComponent::POSITIONS) {
+            if let Ok(positions_file) = segment.open_read(SegmentComponent::POSITIONS) {
-                CompositeFile::open(&source)?
+                CompositeFile::open(&positions_file)?
             } else {
                 CompositeFile::empty()
             }
         };
 
         let positions_idx_composite = {
-            if let Ok(source) = segment.open_read(SegmentComponent::POSITIONSSKIP) {
+            if let Ok(positions_skip_file) = segment.open_read(SegmentComponent::POSITIONSSKIP) {
-                CompositeFile::open(&source)?
+                CompositeFile::open(&positions_skip_file)?
             } else {
                 CompositeFile::empty()
             }
@@ -178,26 +186,27 @@ impl SegmentReader {
         let fast_field_readers =
             Arc::new(FastFieldReaders::load_all(&schema, &fast_fields_composite)?);
 
-        let fieldnorms_data = segment.open_read(SegmentComponent::FIELDNORMS)?;
+        let fieldnorm_data = segment.open_read(SegmentComponent::FIELDNORMS)?;
-        let fieldnorms_composite = CompositeFile::open(&fieldnorms_data)?;
+        let fieldnorm_readers = FieldNormReaders::open(fieldnorm_data)?;
 
         let delete_bitset_opt = if segment.meta().has_deletes() {
             let delete_data = segment.open_read(SegmentComponent::DELETE)?;
-            Some(DeleteBitSet::open(delete_data))
+            let delete_bitset = DeleteBitSet::open(delete_data)?;
+            Some(delete_bitset)
         } else {
             None
         };
 
         Ok(SegmentReader {
-            inv_idx_reader_cache: Arc::new(RwLock::new(HashMap::new())),
+            inv_idx_reader_cache: Default::default(),
             max_doc: segment.meta().max_doc(),
             num_docs: segment.meta().num_docs(),
             termdict_composite,
             postings_composite,
             fast_fields_readers: fast_field_readers,
-            fieldnorms_composite,
+            fieldnorm_readers,
             segment_id: segment.id(),
-            store_source,
+            store_file,
             delete_bitset_opt,
             positions_composite,
             positions_idx_composite,
@@ -212,58 +221,64 @@ impl SegmentReader {
     /// The field reader is in charge of iterating through the
     /// term dictionary associated to a specific field,
     /// and opening the posting list associated to any term.
-    pub fn inverted_index(&self, field: Field) -> Arc<InvertedIndexReader> {
+    ///
+    /// If the field is marked as index, a warn is logged and an empty `InvertedIndexReader`
+    /// is returned.
+    /// Similarly if the field is marked as indexed but no term has been indexed for the given
+    /// index. an empty `InvertedIndexReader` is returned (but no warning is logged).
+    pub fn inverted_index(&self, field: Field) -> crate::Result<Arc<InvertedIndexReader>> {
         if let Some(inv_idx_reader) = self
             .inv_idx_reader_cache
             .read()
             .expect("Lock poisoned. This should never happen")
             .get(&field)
         {
-            return Arc::clone(inv_idx_reader);
+            return Ok(Arc::clone(inv_idx_reader));
         }
         let field_entry = self.schema.get_field_entry(field);
         let field_type = field_entry.field_type();
         let record_option_opt = field_type.get_index_record_option();
 
         if record_option_opt.is_none() {
-            panic!("Field {:?} does not seem indexed.", field_entry.name());
+            warn!("Field {:?} does not seem indexed.", field_entry.name());
         }
 
-        let record_option = record_option_opt.unwrap();
+        let postings_file_opt = self.postings_composite.open_read(field);
 
-        let postings_source_opt = self.postings_composite.open_read(field);
+        if postings_file_opt.is_none() || record_option_opt.is_none() {
-
-        if postings_source_opt.is_none() {
             // no documents in the segment contained this field.
             // As a result, no data is associated to the inverted index.
             //
             // Returns an empty inverted index.
-            return Arc::new(InvertedIndexReader::empty(field_type));
+            let record_option = record_option_opt.unwrap_or(IndexRecordOption::Basic);
+            return Ok(Arc::new(InvertedIndexReader::empty(record_option)));
         }
 
-        let postings_source = postings_source_opt.unwrap();
+        let record_option = record_option_opt.unwrap();
+        let postings_file = postings_file_opt.unwrap();
 
-        let termdict_source = self.termdict_composite.open_read(field).expect(
+        let termdict_file: FileSlice = self.termdict_composite.open_read(field)
-            "Failed to open field term dictionary in composite file. Is the field indexed?",
+            .ok_or_else(||
-        );
+               DataCorruption::comment_only(format!("Failed to open field {:?}'s term dictionary in the composite file. Has the schema been modified?", field_entry.name()))
+            )?;
 
-        let positions_source = self
+        let positions_file = self
             .positions_composite
             .open_read(field)
             .expect("Index corrupted. Failed to open field positions in composite file.");
 
-        let positions_idx_source = self
+        let positions_idx_file = self
             .positions_idx_composite
             .open_read(field)
             .expect("Index corrupted. Failed to open field positions in composite file.");
 
         let inv_idx_reader = Arc::new(InvertedIndexReader::new(
-            TermDictionary::from_source(&termdict_source),
+            TermDictionary::open(termdict_file)?,
-            postings_source,
+            postings_file,
-            positions_source,
+            positions_file,
-            positions_idx_source,
+            positions_idx_file,
             record_option,
-        ));
+        )?);
 
         // by releasing the lock in between, we may end up opening the inverting index
         // twice, but this is fine.
@@ -272,7 +287,7 @@ impl SegmentReader {
             .expect("Field reader cache lock poisoned. This should never happen.")
             .insert(field, Arc::clone(&inv_idx_reader));
 
-        inv_idx_reader
+        Ok(inv_idx_reader)
     }
 
     /// Returns the segment id
@@ -300,21 +315,21 @@ impl SegmentReader {
     }
 
     /// Summarize total space usage of this segment.
-    pub fn space_usage(&self) -> SegmentSpaceUsage {
+    pub fn space_usage(&self) -> io::Result<SegmentSpaceUsage> {
-        SegmentSpaceUsage::new(
+        Ok(SegmentSpaceUsage::new(
             self.num_docs(),
             self.termdict_composite.space_usage(),
             self.postings_composite.space_usage(),
             self.positions_composite.space_usage(),
             self.positions_idx_composite.space_usage(),
             self.fast_fields_readers.space_usage(),
-            self.fieldnorms_composite.space_usage(),
+            self.fieldnorm_readers.space_usage(),
-            self.get_store_reader().space_usage(),
+            self.get_store_reader()?.space_usage(),
             self.delete_bitset_opt
                 .as_ref()
                 .map(DeleteBitSet::space_usage)
                 .unwrap_or(0),
-        )
+        ))
     }
 }
 
@@ -331,7 +346,7 @@ mod test {
     use crate::DocId;
 
     #[test]
-    fn test_alive_docs_iterator() {
+    fn test_alive_docs_iterator() -> crate::Result<()> {
         let mut schema_builder = Schema::builder();
         schema_builder.add_text_field("name", TEXT | STORED);
         let schema = schema_builder.build();
@@ -339,26 +354,26 @@ mod test {
         let name = schema.get_field("name").unwrap();
 
         {
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+            let mut index_writer = index.writer_for_tests()?;
             index_writer.add_document(doc!(name => "tantivy"));
             index_writer.add_document(doc!(name => "horse"));
             index_writer.add_document(doc!(name => "jockey"));
             index_writer.add_document(doc!(name => "cap"));
-
             // we should now have one segment with two docs
-            index_writer.commit().unwrap();
+            index_writer.commit()?;
         }
 
         {
-            let mut index_writer2 = index.writer(50_000_000).unwrap();
+            let mut index_writer2 = index.writer(50_000_000)?;
             index_writer2.delete_term(Term::from_field_text(name, "horse"));
             index_writer2.delete_term(Term::from_field_text(name, "cap"));
 
             // ok, now we should have a deleted doc
-            index_writer2.commit().unwrap();
+            index_writer2.commit()?;
         }
-        let searcher = index.reader().unwrap().searcher();
+        let searcher = index.reader()?.searcher();
         let docs: Vec<DocId> = searcher.segment_reader(0).doc_ids_alive().collect();
         assert_eq!(vec![0u32, 2u32], docs);
+        Ok(())
     }
 }

src/directory/directory.rs

@@ -3,7 +3,7 @@ use crate::directory::error::LockError;
 use crate::directory::error::{DeleteError, OpenReadError, OpenWriteError};
 use crate::directory::WatchCallback;
 use crate::directory::WatchHandle;
-use crate::directory::{ReadOnlySource, WritePtr};
+use crate::directory::{FileSlice, WritePtr};
 use std::fmt;
 use std::io;
 use std::io::Write;
@@ -11,7 +11,6 @@ use std::marker::Send;
 use std::marker::Sync;
 use std::path::Path;
 use std::path::PathBuf;
-use std::result;
 use std::thread;
 use std::time::Duration;
 
@@ -80,7 +79,7 @@ fn try_acquire_lock(
 ) -> Result<DirectoryLock, TryAcquireLockError> {
     let mut write = directory.open_write(filepath).map_err(|e| match e {
         OpenWriteError::FileAlreadyExists(_) => TryAcquireLockError::FileExists,
-        OpenWriteError::IOError(io_error) => TryAcquireLockError::IOError(io_error.into()),
+        OpenWriteError::IOError { io_error, .. } => TryAcquireLockError::IOError(io_error),
     })?;
     write.flush().map_err(TryAcquireLockError::IOError)?;
     Ok(DirectoryLock::from(Box::new(DirectoryLockGuard {
@@ -117,19 +116,19 @@ pub trait Directory: DirectoryClone + fmt::Debug + Send + Sync + 'static {
     /// change.
     ///
     /// Specifically, subsequent writes or flushes should
-    /// have no effect on the returned `ReadOnlySource` object.
+    /// have no effect on the returned `FileSlice` object.
     ///
     /// You should only use this to read files create with [Directory::open_write].
-    fn open_read(&self, path: &Path) -> result::Result<ReadOnlySource, OpenReadError>;
+    fn open_read(&self, path: &Path) -> Result<FileSlice, OpenReadError>;
 
     /// Removes a file
     ///
     /// Removing a file will not affect an eventual
-    /// existing ReadOnlySource pointing to it.
+    /// existing FileSlice pointing to it.
     ///
     /// Removing a nonexistent file, yields a
     /// `DeleteError::DoesNotExist`.
-    fn delete(&self, path: &Path) -> result::Result<(), DeleteError>;
+    fn delete(&self, path: &Path) -> Result<(), DeleteError>;
 
     /// Returns true iff the file exists
     fn exists(&self, path: &Path) -> bool;
@@ -139,7 +138,7 @@ pub trait Directory: DirectoryClone + fmt::Debug + Send + Sync + 'static {
     ///
     /// Right after this call, the file should be created
     /// and any subsequent call to `open_read` for the
-    /// same path should return a `ReadOnlySource`.
+    /// same path should return a `FileSlice`.
     ///
     /// Write operations may be aggressively buffered.
     /// The client of this trait is responsible for calling flush
@@ -153,7 +152,7 @@ pub trait Directory: DirectoryClone + fmt::Debug + Send + Sync + 'static {
     /// was not called.
     ///
     /// The file may not previously exist.
-    fn open_write(&mut self, path: &Path) -> Result<WritePtr, OpenWriteError>;
+    fn open_write(&self, path: &Path) -> Result<WritePtr, OpenWriteError>;
 
     /// Reads the full content file that has been written using
     /// atomic_write.
@@ -169,7 +168,7 @@ pub trait Directory: DirectoryClone + fmt::Debug + Send + Sync + 'static {
     /// a partially written file.
     ///
     /// The file may or may not previously exist.
-    fn atomic_write(&mut self, path: &Path, data: &[u8]) -> io::Result<()>;
+    fn atomic_write(&self, path: &Path, data: &[u8]) -> io::Result<()>;
 
     /// Acquire a lock in the given directory.
     ///

src/directory/error.rs

@@ -1,162 +1,67 @@
 use crate::Version;
-use std::error::Error as StdError;
 use std::fmt;
 use std::io;
 use std::path::PathBuf;
 
 /// Error while trying to acquire a directory lock.
-#[derive(Debug, Fail)]
+#[derive(Debug, Error)]
 pub enum LockError {
     /// Failed to acquired a lock as it is already held by another
     /// client.
     /// - In the context of a blocking lock, this means the lock was not released within some `timeout` period.
     /// - In the context of a non-blocking lock, this means the lock was busy at the moment of the call.
-    #[fail(
+    #[error("Could not acquire lock as it is already held, possibly by a different process.")]
-        display = "Could not acquire lock as it is already held, possibly by a different process."
-    )]
     LockBusy,
     /// Trying to acquire a lock failed with an `IOError`
-    #[fail(display = "Failed to acquire the lock due to an io:Error.")]
+    #[error("Failed to acquire the lock due to an io:Error.")]
     IOError(io::Error),
 }
 
-/// General IO error with an optional path to the offending file.
-#[derive(Debug)]
-pub struct IOError {
-    path: Option<PathBuf>,
-    err: io::Error,
-}
-
-impl Into<io::Error> for IOError {
-    fn into(self) -> io::Error {
-        self.err
-    }
-}
-
-impl fmt::Display for IOError {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match self.path {
-            Some(ref path) => write!(f, "io error occurred on path '{:?}': '{}'", path, self.err),
-            None => write!(f, "io error occurred: '{}'", self.err),
-        }
-    }
-}
-
-impl StdError for IOError {
-    fn description(&self) -> &str {
-        "io error occurred"
-    }
-
-    fn cause(&self) -> Option<&dyn StdError> {
-        Some(&self.err)
-    }
-}
-
-impl IOError {
-    pub(crate) fn with_path(path: PathBuf, err: io::Error) -> Self {
-        IOError {
-            path: Some(path),
-            err,
-        }
-    }
-}
-
-impl From<io::Error> for IOError {
-    fn from(err: io::Error) -> IOError {
-        IOError { path: None, err }
-    }
-}
-
 /// Error that may occur when opening a directory
-#[derive(Debug)]
+#[derive(Debug, Error)]
 pub enum OpenDirectoryError {
     /// The underlying directory does not exists.
+    #[error("Directory does not exist: '{0}'.")]
     DoesNotExist(PathBuf),
     /// The path exists but is not a directory.
+    #[error("Path exists but is not a directory: '{0}'.")]
     NotADirectory(PathBuf),
+    /// Failed to create a temp directory.
+    #[error("Failed to create a temporary directory: '{0}'.")]
+    FailedToCreateTempDir(io::Error),
     /// IoError
-    IoError(io::Error),
+    #[error("IOError '{io_error:?}' while create directory in: '{directory_path:?}'.")]
-}
+    IoError {
-
+        /// underlying io Error.
-impl From<io::Error> for OpenDirectoryError {
+        io_error: io::Error,
-    fn from(io_err: io::Error) -> Self {
+        /// directory we tried to open.
-        OpenDirectoryError::IoError(io_err)
+        directory_path: PathBuf,
-    }
+    },
-}
-
-impl fmt::Display for OpenDirectoryError {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match *self {
-            OpenDirectoryError::DoesNotExist(ref path) => {
-                write!(f, "the underlying directory '{:?}' does not exist", path)
-            }
-            OpenDirectoryError::NotADirectory(ref path) => {
-                write!(f, "the path '{:?}' exists but is not a directory", path)
-            }
-            OpenDirectoryError::IoError(ref err) => write!(
-                f,
-                "IOError while trying to open/create the directory. {:?}",
-                err
-            ),
-        }
-    }
-}
-
-impl StdError for OpenDirectoryError {
-    fn description(&self) -> &str {
-        "error occurred while opening a directory"
-    }
-
-    fn cause(&self) -> Option<&dyn StdError> {
-        None
-    }
 }
 
 /// Error that may occur when starting to write in a file
-#[derive(Debug)]
+#[derive(Debug, Error)]
 pub enum OpenWriteError {
     /// Our directory is WORM, writing an existing file is forbidden.
     /// Checkout the `Directory` documentation.
+    #[error("File already exists: '{0}'")]
     FileAlreadyExists(PathBuf),
     /// Any kind of IO error that happens when
     /// writing in the underlying IO device.
-    IOError(IOError),
+    #[error("IOError '{io_error:?}' while opening file for write: '{filepath}'.")]
+    IOError {
+        /// The underlying `io::Error`.
+        io_error: io::Error,
+        /// File path of the file that tantivy failed to open for write.
+        filepath: PathBuf,
+    },
 }
 
-impl From<IOError> for OpenWriteError {
+impl OpenWriteError {
-    fn from(err: IOError) -> OpenWriteError {
+    pub(crate) fn wrap_io_error(io_error: io::Error, filepath: PathBuf) -> Self {
-        OpenWriteError::IOError(err)
+        Self::IOError { io_error, filepath }
     }
 }
-
-impl fmt::Display for OpenWriteError {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match *self {
-            OpenWriteError::FileAlreadyExists(ref path) => {
-                write!(f, "the file '{:?}' already exists", path)
-            }
-            OpenWriteError::IOError(ref err) => write!(
-                f,
-                "an io error occurred while opening a file for writing: '{}'",
-                err
-            ),
-        }
-    }
-}
-
-impl StdError for OpenWriteError {
-    fn description(&self) -> &str {
-        "error occurred while opening a file for writing"
-    }
-
-    fn cause(&self) -> Option<&dyn StdError> {
-        match *self {
-            OpenWriteError::FileAlreadyExists(_) => None,
-            OpenWriteError::IOError(ref err) => Some(err),
-        }
-    }
-}
-
 /// Type of index incompatibility between the library and the index found on disk
 /// Used to catch and provide a hint to solve this incompatibility issue
 pub enum Incompatibility {
@@ -217,55 +122,46 @@ impl fmt::Debug for Incompatibility {
 }
 
 /// Error that may occur when accessing a file read
-#[derive(Debug)]
+#[derive(Debug, Error)]
 pub enum OpenReadError {
     /// The file does not exists.
+    #[error("Files does not exists: {0:?}")]
     FileDoesNotExist(PathBuf),
-    /// Any kind of IO error that happens when
+    /// Any kind of io::Error.
-    /// interacting with the underlying IO device.
+    #[error(
-    IOError(IOError),
+        "IOError: '{io_error:?}' happened while opening the following file for Read: {filepath}."
-    /// This library doesn't support the index version found on disk
+    )]
+    IOError {
+        /// The underlying `io::Error`.
+        io_error: io::Error,
+        /// File path of the file that tantivy failed to open for read.
+        filepath: PathBuf,
+    },
+    /// This library does not support the index version found in file footer.
+    #[error("Index version unsupported: {0:?}")]
     IncompatibleIndex(Incompatibility),
 }
 
-impl From<IOError> for OpenReadError {
+impl OpenReadError {
-    fn from(err: IOError) -> OpenReadError {
+    pub(crate) fn wrap_io_error(io_error: io::Error, filepath: PathBuf) -> Self {
-        OpenReadError::IOError(err)
+        Self::IOError { io_error, filepath }
     }
 }
-
-impl fmt::Display for OpenReadError {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match *self {
-            OpenReadError::FileDoesNotExist(ref path) => {
-                write!(f, "the file '{:?}' does not exist", path)
-            }
-            OpenReadError::IOError(ref err) => write!(
-                f,
-                "an io error occurred while opening a file for reading: '{}'",
-                err
-            ),
-            OpenReadError::IncompatibleIndex(ref footer) => {
-                write!(f, "Incompatible index format: {:?}", footer)
-            }
-        }
-    }
-}
-
 /// Error that may occur when trying to delete a file
-#[derive(Debug)]
+#[derive(Debug, Error)]
 pub enum DeleteError {
     /// The file does not exists.
+    #[error("File does not exists: '{0}'.")]
     FileDoesNotExist(PathBuf),
     /// Any kind of IO error that happens when
     /// interacting with the underlying IO device.
-    IOError(IOError),
+    #[error("The following IO error happened while deleting file '{filepath}': '{io_error:?}'.")]
-}
+    IOError {
-
+        /// The underlying `io::Error`.
-impl From<IOError> for DeleteError {
+        io_error: io::Error,
-    fn from(err: IOError) -> DeleteError {
+        /// File path of the file that tantivy failed to delete.
-        DeleteError::IOError(err)
+        filepath: PathBuf,
-    }
+    },
 }
 
 impl From<Incompatibility> for OpenReadError {
@@ -273,29 +169,3 @@ impl From<Incompatibility> for OpenReadError {
         OpenReadError::IncompatibleIndex(incompatibility)
     }
 }
-
-impl fmt::Display for DeleteError {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match *self {
-            DeleteError::FileDoesNotExist(ref path) => {
-                write!(f, "the file '{:?}' does not exist", path)
-            }
-            DeleteError::IOError(ref err) => {
-                write!(f, "an io error occurred while deleting a file: '{}'", err)
-            }
-        }
-    }
-}
-
-impl StdError for DeleteError {
-    fn description(&self) -> &str {
-        "error occurred while deleting a file"
-    }
-
-    fn cause(&self) -> Option<&dyn StdError> {
-        match *self {
-            DeleteError::FileDoesNotExist(_) => None,
-            DeleteError::IOError(ref err) => Some(err),
-        }
-    }
-}

src/directory/file_slice.rs

@@ -0,0 +1,237 @@
+use stable_deref_trait::StableDeref;
+
+use crate::common::HasLen;
+use crate::directory::OwnedBytes;
+use std::sync::Arc;
+use std::{io, ops::Deref};
+
+pub type BoxedData = Box<dyn Deref<Target = [u8]> + Send + Sync + 'static>;
+
+/// Objects that represents files sections in tantivy.
+///
+/// By contract, whatever happens to the directory file, as long as a FileHandle
+/// is alive, the data associated with it cannot be altered or destroyed.
+///
+/// The underlying behavior is therefore specific to the `Directory` that created it.
+/// Despite its name, a `FileSlice` may or may not directly map to an actual file
+/// on the filesystem.
+pub trait FileHandle: 'static + Send + Sync + HasLen {
+    /// Reads a slice of bytes.
+    ///
+    /// This method may panic if the range requested is invalid.
+    fn read_bytes(&self, from: usize, to: usize) -> io::Result<OwnedBytes>;
+}
+
+impl FileHandle for &'static [u8] {
+    fn read_bytes(&self, from: usize, to: usize) -> io::Result<OwnedBytes> {
+        let bytes = &self[from..to];
+        Ok(OwnedBytes::new(bytes))
+    }
+}
+
+impl<T: Deref<Target = [u8]>> HasLen for T {
+    fn len(&self) -> usize {
+        self.as_ref().len()
+    }
+}
+
+impl<B> From<B> for FileSlice
+where
+    B: StableDeref + Deref<Target = [u8]> + 'static + Send + Sync,
+{
+    fn from(bytes: B) -> FileSlice {
+        FileSlice::new(OwnedBytes::new(bytes))
+    }
+}
+
+/// Logical slice of read only file in tantivy.
+//
+/// It can be cloned and sliced cheaply.
+///
+#[derive(Clone)]
+pub struct FileSlice {
+    data: Arc<Box<dyn FileHandle>>,
+    start: usize,
+    stop: usize,
+}
+
+impl FileSlice {
+    /// Wraps a FileHandle.
+    pub fn new<D>(data: D) -> Self
+    where
+        D: FileHandle,
+    {
+        let len = data.len();
+        FileSlice {
+            data: Arc::new(Box::new(data)),
+            start: 0,
+            stop: len,
+        }
+    }
+
+    /// Creates a fileslice that is just a view over a slice of the data.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `to < from` or if `to` exceeds the filesize.
+    pub fn slice(&self, from: usize, to: usize) -> FileSlice {
+        assert!(to <= self.len());
+        assert!(to >= from);
+        FileSlice {
+            data: self.data.clone(),
+            start: self.start + from,
+            stop: self.start + to,
+        }
+    }
+
+    /// Creates an empty FileSlice
+    pub fn empty() -> FileSlice {
+        const EMPTY_SLICE: &[u8] = &[];
+        FileSlice::from(EMPTY_SLICE)
+    }
+
+    /// Returns a `OwnedBytes` with all of the data in the `FileSlice`.
+    ///
+    /// The behavior is strongly dependant on the implementation of the underlying
+    /// `Directory` and the `FileSliceTrait` it creates.
+    /// In particular, it is  up to the `Directory` implementation
+    /// to handle caching if needed.
+    pub fn read_bytes(&self) -> io::Result<OwnedBytes> {
+        self.data.read_bytes(self.start, self.stop)
+    }
+
+    /// Reads a specific slice of data.
+    ///
+    /// This is equivalent to running `file_slice.slice(from, to).read_bytes()`.
+    pub fn read_bytes_slice(&self, from: usize, to: usize) -> io::Result<OwnedBytes> {
+        assert!(from <= to);
+        assert!(
+            self.start + to <= self.stop,
+            "`to` exceeds the fileslice length"
+        );
+        self.data.read_bytes(self.start + from, self.start + to)
+    }
+
+    /// Splits the FileSlice at the given offset and return two file slices.
+    /// `file_slice[..split_offset]` and `file_slice[split_offset..]`.
+    ///
+    /// This operation is cheap and must not copy any underlying data.
+    pub fn split(self, left_len: usize) -> (FileSlice, FileSlice) {
+        let left = self.slice_to(left_len);
+        let right = self.slice_from(left_len);
+        (left, right)
+    }
+
+    /// Splits the file slice at the given offset and return two file slices.
+    /// `file_slice[..split_offset]` and `file_slice[split_offset..]`.
+    pub fn split_from_end(self, right_len: usize) -> (FileSlice, FileSlice) {
+        let left_len = self.len() - right_len;
+        self.split(left_len)
+    }
+
+    /// Like `.slice(...)` but enforcing only the `from`
+    /// boundary.
+    ///
+    /// Equivalent to `.slice(from_offset, self.len())`
+    pub fn slice_from(&self, from_offset: usize) -> FileSlice {
+        self.slice(from_offset, self.len())
+    }
+
+    /// Like `.slice(...)` but enforcing only the `to`
+    /// boundary.
+    ///
+    /// Equivalent to `.slice(0, to_offset)`
+    pub fn slice_to(&self, to_offset: usize) -> FileSlice {
+        self.slice(0, to_offset)
+    }
+}
+
+impl HasLen for FileSlice {
+    fn len(&self) -> usize {
+        self.stop - self.start
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::{FileHandle, FileSlice};
+    use crate::common::HasLen;
+    use std::io;
+
+    #[test]
+    fn test_file_slice() -> io::Result<()> {
+        let file_slice = FileSlice::new(b"abcdef".as_ref());
+        assert_eq!(file_slice.len(), 6);
+        assert_eq!(file_slice.slice_from(2).read_bytes()?.as_slice(), b"cdef");
+        assert_eq!(file_slice.slice_to(2).read_bytes()?.as_slice(), b"ab");
+        assert_eq!(
+            file_slice
+                .slice_from(1)
+                .slice_to(2)
+                .read_bytes()?
+                .as_slice(),
+            b"bc"
+        );
+        {
+            let (left, right) = file_slice.clone().split(0);
+            assert_eq!(left.read_bytes()?.as_slice(), b"");
+            assert_eq!(right.read_bytes()?.as_slice(), b"abcdef");
+        }
+        {
+            let (left, right) = file_slice.clone().split(2);
+            assert_eq!(left.read_bytes()?.as_slice(), b"ab");
+            assert_eq!(right.read_bytes()?.as_slice(), b"cdef");
+        }
+        {
+            let (left, right) = file_slice.clone().split_from_end(0);
+            assert_eq!(left.read_bytes()?.as_slice(), b"abcdef");
+            assert_eq!(right.read_bytes()?.as_slice(), b"");
+        }
+        {
+            let (left, right) = file_slice.clone().split_from_end(2);
+            assert_eq!(left.read_bytes()?.as_slice(), b"abcd");
+            assert_eq!(right.read_bytes()?.as_slice(), b"ef");
+        }
+        Ok(())
+    }
+
+    #[test]
+    fn test_file_slice_trait_slice_len() {
+        let blop: &'static [u8] = b"abc";
+        let owned_bytes: Box<dyn FileHandle> = Box::new(blop);
+        assert_eq!(owned_bytes.len(), 3);
+    }
+
+    #[test]
+    fn test_slice_simple_read() -> io::Result<()> {
+        let slice = FileSlice::new(&b"abcdef"[..]);
+        assert_eq!(slice.len(), 6);
+        assert_eq!(slice.read_bytes()?.as_ref(), b"abcdef");
+        assert_eq!(slice.slice(1, 4).read_bytes()?.as_ref(), b"bcd");
+        Ok(())
+    }
+
+    #[test]
+    fn test_slice_read_slice() -> io::Result<()> {
+        let slice_deref = FileSlice::new(&b"abcdef"[..]);
+        assert_eq!(slice_deref.read_bytes_slice(1, 4)?.as_ref(), b"bcd");
+        Ok(())
+    }
+
+    #[test]
+    #[should_panic(expected = "assertion failed: from <= to")]
+    fn test_slice_read_slice_invalid_range() {
+        let slice_deref = FileSlice::new(&b"abcdef"[..]);
+        assert_eq!(slice_deref.read_bytes_slice(1, 0).unwrap().as_ref(), b"bcd");
+    }
+
+    #[test]
+    #[should_panic(expected = "`to` exceeds the fileslice length")]
+    fn test_slice_read_slice_invalid_range_exceeds() {
+        let slice_deref = FileSlice::new(&b"abcdef"[..]);
+        assert_eq!(
+            slice_deref.read_bytes_slice(0, 10).unwrap().as_ref(),
+            b"bcd"
+        );
+    }
+}

src/directory/footer.rs

@@ -1,9 +1,8 @@
-use crate::common::{BinarySerializable, CountingWriter, FixedSize, VInt};
+use crate::common::{BinarySerializable, CountingWriter, FixedSize, HasLen, VInt};
 use crate::directory::error::Incompatibility;
-use crate::directory::read_only_source::ReadOnlySource;
+use crate::directory::FileSlice;
 use crate::directory::{AntiCallToken, TerminatingWrite};
 use crate::Version;
-use byteorder::{ByteOrder, LittleEndian, WriteBytesExt};
 use crc32fast::Hasher;
 use std::io;
 use std::io::Write;
@@ -64,26 +63,26 @@ impl Footer {
         let mut counting_write = CountingWriter::wrap(&mut write);
         self.serialize(&mut counting_write)?;
         let written_len = counting_write.written_bytes();
-        write.write_u32::<LittleEndian>(written_len as u32)?;
+        (written_len as u32).serialize(write)?;
         Ok(())
     }
 
-    pub fn extract_footer(source: ReadOnlySource) -> Result<(Footer, ReadOnlySource), io::Error> {
+    pub fn extract_footer(file: FileSlice) -> io::Result<(Footer, FileSlice)> {
-        if source.len() < 4 {
+        if file.len() < 4 {
             return Err(io::Error::new(
                 io::ErrorKind::UnexpectedEof,
                 format!(
                     "File corrupted. The file is smaller than 4 bytes (len={}).",
-                    source.len()
+                    file.len()
                 ),
             ));
         }
-        let (body_footer, footer_len_bytes) = source.split_from_end(u32::SIZE_IN_BYTES);
+        let (body_footer, footer_len_file) = file.split_from_end(u32::SIZE_IN_BYTES);
-        let footer_len = LittleEndian::read_u32(footer_len_bytes.as_slice()) as usize;
+        let mut footer_len_bytes = footer_len_file.read_bytes()?;
-        let body_len = body_footer.len() - footer_len;
+        let footer_len = u32::deserialize(&mut footer_len_bytes)? as usize;
-        let (body, footer_data) = body_footer.split(body_len);
+        let (body, footer) = body_footer.split_from_end(footer_len);
-        let mut cursor = footer_data.as_slice();
+        let mut footer_bytes = footer.read_bytes()?;
-        let footer = Footer::deserialize(&mut cursor)?;
+        let footer = Footer::deserialize(&mut footer_bytes)?;
         Ok((footer, body))
     }
 
@@ -94,12 +93,24 @@ impl Footer {
         match &self.versioned_footer {
             VersionedFooter::V1 {
                 crc32: _crc,
-                store_compression: compression,
+                store_compression,
             } => {
-                if &library_version.store_compression != compression {
+                if &library_version.store_compression != store_compression {
                     return Err(Incompatibility::CompressionMismatch {
                         library_compression_format: library_version.store_compression.to_string(),
-                        index_compression_format: compression.to_string(),
+                        index_compression_format: store_compression.to_string(),
+                    });
+                }
+                Ok(())
+            }
+            VersionedFooter::V2 {
+                crc32: _crc,
+                store_compression,
+            } => {
+                if &library_version.store_compression != store_compression {
+                    return Err(Incompatibility::CompressionMismatch {
+                        library_compression_format: library_version.store_compression.to_string(),
+                        index_compression_format: store_compression.to_string(),
                     });
                 }
                 Ok(())
@@ -120,24 +131,29 @@ pub enum VersionedFooter {
         crc32: CrcHashU32,
         store_compression: String,
     },
+    // Introduction of the Block WAND information.
+    V2 {
+        crc32: CrcHashU32,
+        store_compression: String,
+    },
 }
 
 impl BinarySerializable for VersionedFooter {
     fn serialize<W: io::Write>(&self, writer: &mut W) -> io::Result<()> {
         let mut buf = Vec::new();
         match self {
-            VersionedFooter::V1 {
+            VersionedFooter::V2 {
                 crc32,
                 store_compression: compression,
             } => {
                 // Serializes a valid `VersionedFooter` or panics if the version is unknown
                 // [   version    |   crc_hash  | compression_mode ]
                 // [    0..4      |     4..8    |     variable     ]
-                BinarySerializable::serialize(&1u32, &mut buf)?;
+                BinarySerializable::serialize(&2u32, &mut buf)?;
                 BinarySerializable::serialize(crc32, &mut buf)?;
                 BinarySerializable::serialize(compression, &mut buf)?;
             }
-            VersionedFooter::UnknownVersion => {
+            VersionedFooter::V1 { .. } | VersionedFooter::UnknownVersion => {
                 return Err(io::Error::new(
                     io::ErrorKind::InvalidInput,
                     "Cannot serialize an unknown versioned footer ",
@@ -166,22 +182,30 @@ impl BinarySerializable for VersionedFooter {
         reader.read_exact(&mut buf[..])?;
         let mut cursor = &buf[..];
         let version = u32::deserialize(&mut cursor)?;
-        if version == 1 {
+        if version != 1 && version != 2 {
-            let crc32 = u32::deserialize(&mut cursor)?;
+            return Ok(VersionedFooter::UnknownVersion);
-            let compression = String::deserialize(&mut cursor)?;
-            Ok(VersionedFooter::V1 {
-                crc32,
-                store_compression: compression,
-            })
-        } else {
-            Ok(VersionedFooter::UnknownVersion)
         }
+        let crc32 = u32::deserialize(&mut cursor)?;
+        let store_compression = String::deserialize(&mut cursor)?;
+        Ok(if version == 1 {
+            VersionedFooter::V1 {
+                crc32,
+                store_compression,
+            }
+        } else {
+            assert_eq!(version, 2);
+            VersionedFooter::V2 {
+                crc32,
+                store_compression,
+            }
+        })
     }
 }
 
 impl VersionedFooter {
     pub fn crc(&self) -> Option<CrcHashU32> {
         match self {
+            VersionedFooter::V2 { crc32, .. } => Some(*crc32),
             VersionedFooter::V1 { crc32, .. } => Some(*crc32),
             VersionedFooter::UnknownVersion { .. } => None,
         }
@@ -219,7 +243,7 @@ impl<W: TerminatingWrite> Write for FooterProxy<W> {
 impl<W: TerminatingWrite> TerminatingWrite for FooterProxy<W> {
     fn terminate_ref(&mut self, _: AntiCallToken) -> io::Result<()> {
         let crc32 = self.hasher.take().unwrap().finalize();
-        let footer = Footer::new(VersionedFooter::V1 {
+        let footer = Footer::new(VersionedFooter::V2 {
             crc32,
             store_compression: crate::store::COMPRESSION.to_string(),
         });
@@ -246,17 +270,17 @@ mod tests {
         let mut vec = Vec::new();
         let footer_proxy = FooterProxy::new(&mut vec);
         assert!(footer_proxy.terminate().is_ok());
-        assert_eq!(vec.len(), 167);
+        if crate::store::COMPRESSION == "lz4" {
-        let footer = Footer::deserialize(&mut &vec[..]).unwrap();
+            assert_eq!(vec.len(), 158);
-        if let VersionedFooter::V1 {
-            crc32: _,
-            store_compression,
-        } = footer.versioned_footer
-        {
-            assert_eq!(store_compression, crate::store::COMPRESSION);
         } else {
-            panic!("Versioned footer should be V1.");
+            assert_eq!(vec.len(), 167);
         }
+        let footer = Footer::deserialize(&mut &vec[..]).unwrap();
+        assert!(matches!(
+           footer.versioned_footer,
+           VersionedFooter::V2 { store_compression, .. }
+           if store_compression == crate::store::COMPRESSION
+        ));
         assert_eq!(&footer.version, crate::version());
     }
 
@@ -264,7 +288,7 @@ mod tests {
     fn test_serialize_deserialize_footer() {
         let mut buffer = Vec::new();
         let crc32 = 123456u32;
-        let footer: Footer = Footer::new(VersionedFooter::V1 {
+        let footer: Footer = Footer::new(VersionedFooter::V2 {
             crc32,
             store_compression: "lz4".to_string(),
         });
@@ -276,7 +300,7 @@ mod tests {
     #[test]
     fn footer_length() {
         let crc32 = 1111111u32;
-        let versioned_footer = VersionedFooter::V1 {
+        let versioned_footer = VersionedFooter::V2 {
             crc32,
             store_compression: "lz4".to_string(),
         };
@@ -297,7 +321,7 @@ mod tests {
             // versionned footer length
             12 | 128,
             // index format version
-            1,
+            2,
             0,
             0,
             0,
@@ -316,7 +340,7 @@ mod tests {
         let versioned_footer = VersionedFooter::deserialize(&mut cursor).unwrap();
         assert!(cursor.is_empty());
         let expected_crc: u32 = LittleEndian::read_u32(&v_footer_bytes[5..9]) as CrcHashU32;
-        let expected_versioned_footer: VersionedFooter = VersionedFooter::V1 {
+        let expected_versioned_footer: VersionedFooter = VersionedFooter::V2 {
             crc32: expected_crc,
             store_compression: "lz4".to_string(),
         };

src/directory/managed_directory.rs

@@ -1,11 +1,11 @@
-use crate::core::MANAGED_FILEPATH;
+use crate::core::{MANAGED_FILEPATH, META_FILEPATH};
-use crate::directory::error::{DeleteError, IOError, LockError, OpenReadError, OpenWriteError};
+use crate::directory::error::{DeleteError, LockError, OpenReadError, OpenWriteError};
 use crate::directory::footer::{Footer, FooterProxy};
 use crate::directory::DirectoryLock;
 use crate::directory::GarbageCollectionResult;
 use crate::directory::Lock;
 use crate::directory::META_LOCK;
-use crate::directory::{ReadOnlySource, WritePtr};
+use crate::directory::{FileSlice, WritePtr};
 use crate::directory::{WatchCallback, WatchHandle};
 use crate::error::DataCorruption;
 use crate::Directory;
@@ -53,7 +53,7 @@ struct MetaInformation {
 /// Saves the file containing the list of existing files
 /// that were created by tantivy.
 fn save_managed_paths(
-    directory: &mut dyn Directory,
+    directory: &dyn Directory,
     wlock: &RwLockWriteGuard<'_, MetaInformation>,
 ) -> io::Result<()> {
     let mut w = serde_json::to_vec(&wlock.managed_paths)?;
@@ -86,7 +86,7 @@ impl ManagedDirectory {
                 directory: Box::new(directory),
                 meta_informations: Arc::default(),
             }),
-            Err(OpenReadError::IOError(e)) => Err(From::from(e)),
+            io_err @ Err(OpenReadError::IOError { .. }) => Err(io_err.err().unwrap().into()),
             Err(OpenReadError::IncompatibleIndex(incompatibility)) => {
                 // For the moment, this should never happen  `meta.json`
                 // do not have any footer and cannot detect incompatibility.
@@ -168,7 +168,7 @@ impl ManagedDirectory {
                         DeleteError::FileDoesNotExist(_) => {
                             deleted_files.push(file_to_delete.clone());
                         }
-                        DeleteError::IOError(_) => {
+                        DeleteError::IOError { .. } => {
                             failed_to_delete_files.push(file_to_delete.clone());
                             if !cfg!(target_os = "windows") {
                                 // On windows, delete is expected to fail if the file
@@ -212,7 +212,7 @@ impl ManagedDirectory {
     /// File starting by "." are reserved to locks.
     /// They are not managed and cannot be subjected
     /// to garbage collection.
-    fn register_file_as_managed(&mut self, filepath: &Path) -> io::Result<()> {
+    fn register_file_as_managed(&self, filepath: &Path) -> io::Result<()> {
         // Files starting by "." (e.g. lock files) are not managed.
         if !is_managed(filepath) {
             return Ok(());
@@ -223,7 +223,7 @@ impl ManagedDirectory {
             .expect("Managed file lock poisoned");
         let has_changed = meta_wlock.managed_paths.insert(filepath.to_owned());
         if has_changed {
-            save_managed_paths(self.directory.as_mut(), &meta_wlock)?;
+            save_managed_paths(self.directory.as_ref(), &meta_wlock)?;
         }
         Ok(())
     }
@@ -231,10 +231,19 @@ impl ManagedDirectory {
     /// Verify checksum of a managed file
     pub fn validate_checksum(&self, path: &Path) -> result::Result<bool, OpenReadError> {
         let reader = self.directory.open_read(path)?;
-        let (footer, data) = Footer::extract_footer(reader)
+        let (footer, data) =
-            .map_err(|err| IOError::with_path(path.to_path_buf(), err))?;
+            Footer::extract_footer(reader).map_err(|io_error| OpenReadError::IOError {
+                io_error,
+                filepath: path.to_path_buf(),
+            })?;
+        let bytes = data
+            .read_bytes()
+            .map_err(|io_error| OpenReadError::IOError {
+                filepath: path.to_path_buf(),
+                io_error,
+            })?;
         let mut hasher = Hasher::new();
-        hasher.update(data.as_slice());
+        hasher.update(bytes.as_slice());
         let crc = hasher.finalize();
         Ok(footer
             .versioned_footer
@@ -245,35 +254,37 @@ impl ManagedDirectory {
 
     /// List files for which checksum does not match content
     pub fn list_damaged(&self) -> result::Result<HashSet<PathBuf>, OpenReadError> {
-        let mut hashset = HashSet::new();
+        let mut managed_paths = self
-        let managed_paths = self
             .meta_informations
             .read()
             .expect("Managed directory rlock poisoned in list damaged.")
             .managed_paths
             .clone();
 
-        for path in managed_paths.into_iter() {
+        managed_paths.remove(*META_FILEPATH);
+
+        let mut damaged_files = HashSet::new();
+        for path in managed_paths {
             if !self.validate_checksum(&path)? {
-                hashset.insert(path);
+                damaged_files.insert(path);
             }
         }
-        Ok(hashset)
+        Ok(damaged_files)
     }
 }
 
 impl Directory for ManagedDirectory {
-    fn open_read(&self, path: &Path) -> result::Result<ReadOnlySource, OpenReadError> {
+    fn open_read(&self, path: &Path) -> result::Result<FileSlice, OpenReadError> {
-        let read_only_source = self.directory.open_read(path)?;
+        let file_slice = self.directory.open_read(path)?;
-        let (footer, reader) = Footer::extract_footer(read_only_source)
+        let (footer, reader) = Footer::extract_footer(file_slice)
-            .map_err(|err| IOError::with_path(path.to_path_buf(), err))?;
+            .map_err(|io_error| OpenReadError::wrap_io_error(io_error, path.to_path_buf()))?;
         footer.is_compatible()?;
         Ok(reader)
     }
 
-    fn open_write(&mut self, path: &Path) -> result::Result<WritePtr, OpenWriteError> {
+    fn open_write(&self, path: &Path) -> result::Result<WritePtr, OpenWriteError> {
         self.register_file_as_managed(path)
-            .map_err(|e| IOError::with_path(path.to_owned(), e))?;
+            .map_err(|io_error| OpenWriteError::wrap_io_error(io_error, path.to_path_buf()))?;
         Ok(io::BufWriter::new(Box::new(FooterProxy::new(
             self.directory
                 .open_write(path)?
@@ -283,7 +294,7 @@ impl Directory for ManagedDirectory {
         ))))
     }
 
-    fn atomic_write(&mut self, path: &Path, data: &[u8]) -> io::Result<()> {
+    fn atomic_write(&self, path: &Path, data: &[u8]) -> io::Result<()> {
         self.register_file_as_managed(path)?;
         self.directory.atomic_write(path, data)
     }
@@ -397,39 +408,37 @@ mod tests_mmap_specific {
     }
 
     #[test]
-    fn test_checksum() {
+    fn test_checksum() -> crate::Result<()> {
         let test_path1: &'static Path = Path::new("some_path_for_test");
         let test_path2: &'static Path = Path::new("other_test_path");
 
         let tempdir = TempDir::new().unwrap();
         let tempdir_path = PathBuf::from(tempdir.path());
 
-        let mmap_directory = MmapDirectory::open(&tempdir_path).unwrap();
+        let mmap_directory = MmapDirectory::open(&tempdir_path)?;
-        let mut managed_directory = ManagedDirectory::wrap(mmap_directory).unwrap();
+        let managed_directory = ManagedDirectory::wrap(mmap_directory)?;
-        let mut write = managed_directory.open_write(test_path1).unwrap();
+        let mut write = managed_directory.open_write(test_path1)?;
-        write.write_all(&[0u8, 1u8]).unwrap();
+        write.write_all(&[0u8, 1u8])?;
-        write.terminate().unwrap();
+        write.terminate()?;
 
-        let mut write = managed_directory.open_write(test_path2).unwrap();
+        let mut write = managed_directory.open_write(test_path2)?;
-        write.write_all(&[3u8, 4u8, 5u8]).unwrap();
+        write.write_all(&[3u8, 4u8, 5u8])?;
-        write.terminate().unwrap();
+        write.terminate()?;
 
-        let read_source = managed_directory.open_read(test_path2).unwrap();
+        let read_file = managed_directory.open_read(test_path2)?.read_bytes()?;
-        assert_eq!(read_source.as_slice(), &[3u8, 4u8, 5u8]);
+        assert_eq!(read_file.as_slice(), &[3u8, 4u8, 5u8]);
         assert!(managed_directory.list_damaged().unwrap().is_empty());
 
         let mut corrupted_path = tempdir_path.clone();
         corrupted_path.push(test_path2);
-        let mut file = OpenOptions::new()
+        let mut file = OpenOptions::new().write(true).open(&corrupted_path)?;
-            .write(true)
+        file.write_all(&[255u8])?;
-            .open(&corrupted_path)
+        file.flush()?;
-            .unwrap();
-        file.write_all(&[255u8]).unwrap();
-        file.flush().unwrap();
         drop(file);
 
-        let damaged = managed_directory.list_damaged().unwrap();
+        let damaged = managed_directory.list_damaged()?;
         assert_eq!(damaged.len(), 1);
         assert!(damaged.contains(test_path2));
+        Ok(())
     }
 }

src/directory/mmap_directory.rs

@@ -1,14 +1,12 @@
 use crate::core::META_FILEPATH;
 use crate::directory::error::LockError;
-use crate::directory::error::{
+use crate::directory::error::{DeleteError, OpenDirectoryError, OpenReadError, OpenWriteError};
-    DeleteError, IOError, OpenDirectoryError, OpenReadError, OpenWriteError,
-};
-use crate::directory::read_only_source::BoxedData;
 use crate::directory::AntiCallToken;
+use crate::directory::BoxedData;
 use crate::directory::Directory;
 use crate::directory::DirectoryLock;
+use crate::directory::FileSlice;
 use crate::directory::Lock;
-use crate::directory::ReadOnlySource;
 use crate::directory::WatchCallback;
 use crate::directory::WatchCallbackList;
 use crate::directory::WatchHandle;
@@ -19,7 +17,7 @@ use notify::RawEvent;
 use notify::RecursiveMode;
 use notify::Watcher;
 use serde::{Deserialize, Serialize};
-use std::collections::HashMap;
+use stable_deref_trait::StableDeref;
 use std::convert::From;
 use std::fmt;
 use std::fs::OpenOptions;
@@ -34,6 +32,7 @@ use std::sync::Mutex;
 use std::sync::RwLock;
 use std::sync::Weak;
 use std::thread;
+use std::{collections::HashMap, ops::Deref};
 use tempfile::TempDir;
 
 /// Create a default io error given a string.
@@ -44,17 +43,17 @@ pub(crate) fn make_io_err(msg: String) -> io::Error {
 /// Returns None iff the file exists, can be read, but is empty (and hence
 /// cannot be mmapped)
 fn open_mmap(full_path: &Path) -> result::Result<Option<Mmap>, OpenReadError> {
-    let file = File::open(full_path).map_err(|e| {
+    let file = File::open(full_path).map_err(|io_err| {
-        if e.kind() == io::ErrorKind::NotFound {
+        if io_err.kind() == io::ErrorKind::NotFound {
-            OpenReadError::FileDoesNotExist(full_path.to_owned())
+            OpenReadError::FileDoesNotExist(full_path.to_path_buf())
         } else {
-            OpenReadError::IOError(IOError::with_path(full_path.to_owned(), e))
+            OpenReadError::wrap_io_error(io_err, full_path.to_path_buf())
         }
     })?;
 
     let meta_data = file
         .metadata()
-        .map_err(|e| IOError::with_path(full_path.to_owned(), e))?;
+        .map_err(|io_err| OpenReadError::wrap_io_error(io_err, full_path.to_owned()))?;
     if meta_data.len() == 0 {
         // if the file size is 0, it will not be possible
         // to mmap the file, so we return None
@@ -64,7 +63,7 @@ fn open_mmap(full_path: &Path) -> result::Result<Option<Mmap>, OpenReadError> {
     unsafe {
         memmap::Mmap::map(&file)
             .map(Some)
-            .map_err(|e| From::from(IOError::with_path(full_path.to_owned(), e)))
+            .map_err(|io_err| OpenReadError::wrap_io_error(io_err, full_path.to_path_buf()))
     }
 }
 
@@ -183,6 +182,10 @@ impl WatcherWrapper {
                         }
                     }
                 }
+            })
+            .map_err(|io_error| OpenDirectoryError::IoError {
+                io_error,
+                directory_path: path.to_path_buf(),
             })?;
         Ok(WatcherWrapper {
             _watcher: Mutex::new(watcher),
@@ -272,9 +275,11 @@ impl MmapDirectory {
     /// This is mostly useful to test the MmapDirectory itself.
     /// For your unit tests, prefer the RAMDirectory.
     pub fn create_from_tempdir() -> Result<MmapDirectory, OpenDirectoryError> {
-        let tempdir = TempDir::new().map_err(OpenDirectoryError::IoError)?;
+        let tempdir = TempDir::new().map_err(OpenDirectoryError::FailedToCreateTempDir)?;
-        let tempdir_path = PathBuf::from(tempdir.path());
+        Ok(MmapDirectory::new(
-        Ok(MmapDirectory::new(tempdir_path, Some(tempdir)))
+            tempdir.path().to_path_buf(),
+            Some(tempdir),
+        ))
     }
 
     /// Opens a MmapDirectory in a directory.
@@ -396,8 +401,20 @@ impl TerminatingWrite for SafeFileWriter {
     }
 }
 
+#[derive(Clone)]
+struct MmapArc(Arc<Box<dyn Deref<Target = [u8]> + Send + Sync>>);
+
+impl Deref for MmapArc {
+    type Target = [u8];
+
+    fn deref(&self) -> &[u8] {
+        self.0.deref()
+    }
+}
+unsafe impl StableDeref for MmapArc {}
+
 impl Directory for MmapDirectory {
-    fn open_read(&self, path: &Path) -> result::Result<ReadOnlySource, OpenReadError> {
+    fn open_read(&self, path: &Path) -> result::Result<FileSlice, OpenReadError> {
         debug!("Open Read {:?}", path);
         let full_path = self.resolve_path(path);
 
@@ -407,12 +424,14 @@ impl Directory for MmapDirectory {
                  on mmap cache while reading {:?}",
                 path
             );
-            IOError::with_path(path.to_owned(), make_io_err(msg))
+            let io_err = make_io_err(msg);
+            OpenReadError::wrap_io_error(io_err, path.to_path_buf())
         })?;
-        Ok(mmap_cache
+        if let Some(mmap_arc) = mmap_cache.get_mmap(&full_path)? {
-            .get_mmap(&full_path)?
+            Ok(FileSlice::from(MmapArc(mmap_arc)))
-            .map(ReadOnlySource::from)
+        } else {
-            .unwrap_or_else(ReadOnlySource::empty))
+            Ok(FileSlice::empty())
+        }
     }
 
     /// Any entry associated to the path in the mmap will be
@@ -420,14 +439,18 @@ impl Directory for MmapDirectory {
     fn delete(&self, path: &Path) -> result::Result<(), DeleteError> {
         let full_path = self.resolve_path(path);
         match fs::remove_file(&full_path) {
-            Ok(_) => self
+            Ok(_) => self.sync_directory().map_err(|e| DeleteError::IOError {
-                .sync_directory()
+                io_error: e,
-                .map_err(|e| IOError::with_path(path.to_owned(), e).into()),
+                filepath: path.to_path_buf(),
+            }),
             Err(e) => {
                 if e.kind() == io::ErrorKind::NotFound {
                     Err(DeleteError::FileDoesNotExist(path.to_owned()))
                 } else {
-                    Err(IOError::with_path(path.to_owned(), e).into())
+                    Err(DeleteError::IOError {
+                        io_error: e,
+                        filepath: path.to_path_buf(),
+                    })
                 }
             }
         }
@@ -438,7 +461,7 @@ impl Directory for MmapDirectory {
         full_path.exists()
     }
 
-    fn open_write(&mut self, path: &Path) -> Result<WritePtr, OpenWriteError> {
+    fn open_write(&self, path: &Path) -> Result<WritePtr, OpenWriteError> {
         debug!("Open Write {:?}", path);
         let full_path = self.resolve_path(path);
 
@@ -447,22 +470,22 @@ impl Directory for MmapDirectory {
             .create_new(true)
             .open(full_path);
 
-        let mut file = open_res.map_err(|err| {
+        let mut file = open_res.map_err(|io_err| {
-            if err.kind() == io::ErrorKind::AlreadyExists {
+            if io_err.kind() == io::ErrorKind::AlreadyExists {
-                OpenWriteError::FileAlreadyExists(path.to_owned())
+                OpenWriteError::FileAlreadyExists(path.to_path_buf())
             } else {
-                IOError::with_path(path.to_owned(), err).into()
+                OpenWriteError::wrap_io_error(io_err, path.to_path_buf())
             }
         })?;
 
         // making sure the file is created.
         file.flush()
-            .map_err(|e| IOError::with_path(path.to_owned(), e))?;
+            .map_err(|io_error| OpenWriteError::wrap_io_error(io_error, path.to_path_buf()))?;
 
         // Apparetntly, on some filesystem syncing the parent
         // directory is required.
         self.sync_directory()
-            .map_err(|e| IOError::with_path(path.to_owned(), e))?;
+            .map_err(|io_err| OpenWriteError::wrap_io_error(io_err, path.to_path_buf()))?;
 
         let writer = SafeFileWriter::new(file);
         Ok(BufWriter::new(Box::new(writer)))
@@ -473,25 +496,28 @@ impl Directory for MmapDirectory {
         let mut buffer = Vec::new();
         match File::open(&full_path) {
             Ok(mut file) => {
-                file.read_to_end(&mut buffer)
+                file.read_to_end(&mut buffer).map_err(|io_error| {
-                    .map_err(|e| IOError::with_path(path.to_owned(), e))?;
+                    OpenReadError::wrap_io_error(io_error, path.to_path_buf())
+                })?;
                 Ok(buffer)
             }
-            Err(e) => {
+            Err(io_error) => {
-                if e.kind() == io::ErrorKind::NotFound {
+                if io_error.kind() == io::ErrorKind::NotFound {
                     Err(OpenReadError::FileDoesNotExist(path.to_owned()))
                 } else {
-                    Err(IOError::with_path(path.to_owned(), e).into())
+                    Err(OpenReadError::wrap_io_error(io_error, path.to_path_buf()))
                 }
             }
         }
     }
 
-    fn atomic_write(&mut self, path: &Path, data: &[u8]) -> io::Result<()> {
+    fn atomic_write(&self, path: &Path, content: &[u8]) -> io::Result<()> {
         debug!("Atomic Write {:?}", path);
+        let mut tempfile = tempfile::Builder::new().tempfile_in(&self.inner.root_path)?;
+        tempfile.write_all(content)?;
+        tempfile.flush()?;
         let full_path = self.resolve_path(path);
-        let meta_file = atomicwrites::AtomicFile::new(full_path, atomicwrites::AllowOverwrite);
+        tempfile.into_temp_path().persist(full_path)?;
-        meta_file.write(|f| f.write_all(data))?;
         Ok(())
     }
 
@@ -527,10 +553,10 @@ mod tests {
     // The following tests are specific to the MmapDirectory
 
     use super::*;
-    use crate::indexer::LogMergePolicy;
     use crate::schema::{Schema, SchemaBuilder, TEXT};
     use crate::Index;
     use crate::ReloadPolicy;
+    use crate::{common::HasLen, indexer::LogMergePolicy};
     use std::fs;
     use std::sync::atomic::{AtomicUsize, Ordering};
 
@@ -545,7 +571,7 @@ mod tests {
         // cannot be mmapped.
         //
         // In that case the directory returns a SharedVecSlice.
-        let mut mmap_directory = MmapDirectory::create_from_tempdir().unwrap();
+        let mmap_directory = MmapDirectory::create_from_tempdir().unwrap();
         let path = PathBuf::from("test");
         {
             let mut w = mmap_directory.open_write(&path).unwrap();
@@ -561,7 +587,7 @@ mod tests {
 
         // here we test if the cache releases
         // mmaps correctly.
-        let mut mmap_directory = MmapDirectory::create_from_tempdir().unwrap();
+        let mmap_directory = MmapDirectory::create_from_tempdir().unwrap();
         let num_paths = 10;
         let paths: Vec<PathBuf> = (0..num_paths)
             .map(|i| PathBuf::from(&*format!("file_{}", i)))
@@ -652,7 +678,7 @@ mod tests {
         {
             let index = Index::create(mmap_directory.clone(), schema).unwrap();
 
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+            let mut index_writer = index.writer_for_tests().unwrap();
             let mut log_merge_policy = LogMergePolicy::default();
             log_merge_policy.set_min_merge_size(3);
             index_writer.set_merge_policy(Box::new(log_merge_policy));

src/directory/mod.rs

@@ -9,10 +9,11 @@ mod mmap_directory;
 
 mod directory;
 mod directory_lock;
+mod file_slice;
 mod footer;
 mod managed_directory;
+mod owned_bytes;
 mod ram_directory;
-mod read_only_source;
 mod watch_event_router;
 
 /// Errors specific to the directory module.
@@ -21,11 +22,14 @@ pub mod error;
 pub use self::directory::DirectoryLock;
 pub use self::directory::{Directory, DirectoryClone};
 pub use self::directory_lock::{Lock, INDEX_WRITER_LOCK, META_LOCK};
+pub(crate) use self::file_slice::BoxedData;
+pub use self::file_slice::{FileHandle, FileSlice};
+pub use self::owned_bytes::OwnedBytes;
 pub use self::ram_directory::RAMDirectory;
-pub use self::read_only_source::ReadOnlySource;
 pub use self::watch_event_router::{WatchCallback, WatchCallbackList, WatchHandle};
 use std::io::{self, BufWriter, Write};
 use std::path::PathBuf;
+
 /// Outcome of the Garbage collection
 pub struct GarbageCollectionResult {
     /// List of files that were deleted in this cycle

src/directory/owned_bytes.rs

@@ -0,0 +1,255 @@
+use crate::directory::FileHandle;
+use stable_deref_trait::StableDeref;
+use std::mem;
+use std::ops::Deref;
+use std::sync::Arc;
+use std::{fmt, io};
+
+/// An OwnedBytes simply wraps an object that owns a slice of data and exposes
+/// this data as a static slice.
+///
+/// The backing object is required to be `StableDeref`.
+#[derive(Clone)]
+pub struct OwnedBytes {
+    data: &'static [u8],
+    box_stable_deref: Arc<dyn Deref<Target = [u8]> + Sync + Send>,
+}
+
+impl FileHandle for OwnedBytes {
+    fn read_bytes(&self, from: usize, to: usize) -> io::Result<OwnedBytes> {
+        Ok(self.slice(from, to))
+    }
+}
+
+impl OwnedBytes {
+    /// Creates an empty `OwnedBytes`.
+    pub fn empty() -> OwnedBytes {
+        OwnedBytes::new(&[][..])
+    }
+
+    /// Creates an `OwnedBytes` intance given a `StableDeref` object.
+    pub fn new<T: StableDeref + Deref<Target = [u8]> + 'static + Send + Sync>(
+        data_holder: T,
+    ) -> OwnedBytes {
+        let box_stable_deref = Arc::new(data_holder);
+        let bytes: &[u8] = box_stable_deref.as_ref();
+        let data = unsafe { mem::transmute::<_, &'static [u8]>(bytes.deref()) };
+        OwnedBytes {
+            box_stable_deref,
+            data,
+        }
+    }
+
+    /// creates a fileslice that is just a view over a slice of the data.
+    pub fn slice(&self, from: usize, to: usize) -> Self {
+        OwnedBytes {
+            data: &self.data[from..to],
+            box_stable_deref: self.box_stable_deref.clone(),
+        }
+    }
+
+    /// Returns the underlying slice of data.
+    /// `Deref` and `AsRef` are also available.
+    #[inline(always)]
+    pub fn as_slice(&self) -> &[u8] {
+        self.data
+    }
+
+    /// Returns the len of the slice.
+    #[inline(always)]
+    pub fn len(&self) -> usize {
+        self.data.len()
+    }
+
+    /// Splits the OwnedBytes into two OwnedBytes `(left, right)`.
+    ///
+    /// Left will hold `split_len` bytes.
+    ///
+    /// This operation is cheap and does not require to copy any memory.
+    /// On the other hand, both `left` and `right` retain a handle over
+    /// the entire slice of memory. In other words, the memory will only
+    /// be released when both left and right are dropped.
+    pub fn split(self, split_len: usize) -> (OwnedBytes, OwnedBytes) {
+        let right_box_stable_deref = self.box_stable_deref.clone();
+        let left = OwnedBytes {
+            data: &self.data[..split_len],
+            box_stable_deref: self.box_stable_deref,
+        };
+        let right = OwnedBytes {
+            data: &self.data[split_len..],
+            box_stable_deref: right_box_stable_deref,
+        };
+        (left, right)
+    }
+
+    /// Returns true iff this `OwnedBytes` is empty.
+    #[inline(always)]
+    pub fn is_empty(&self) -> bool {
+        self.as_slice().is_empty()
+    }
+
+    /// Drops the left most `advance_len` bytes.
+    ///
+    /// See also [.clip(clip_len: usize))](#method.clip).
+    #[inline(always)]
+    pub fn advance(&mut self, advance_len: usize) {
+        self.data = &self.data[advance_len..]
+    }
+}
+
+impl fmt::Debug for OwnedBytes {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        // We truncate the bytes in order to make sure the debug string
+        // is not too long.
+        let bytes_truncated: &[u8] = if self.len() > 8 {
+            &self.as_slice()[..10]
+        } else {
+            self.as_slice()
+        };
+        write!(f, "OwnedBytes({:?}, len={})", bytes_truncated, self.len())
+    }
+}
+
+impl Deref for OwnedBytes {
+    type Target = [u8];
+
+    fn deref(&self) -> &Self::Target {
+        self.as_slice()
+    }
+}
+
+impl io::Read for OwnedBytes {
+    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
+        let read_len = {
+            let data = self.as_slice();
+            if data.len() >= buf.len() {
+                let buf_len = buf.len();
+                buf.copy_from_slice(&data[..buf_len]);
+                buf.len()
+            } else {
+                let data_len = data.len();
+                buf[..data_len].copy_from_slice(data);
+                data_len
+            }
+        };
+        self.advance(read_len);
+        Ok(read_len)
+    }
+    fn read_to_end(&mut self, buf: &mut Vec<u8>) -> io::Result<usize> {
+        let read_len = {
+            let data = self.as_slice();
+            buf.extend(data);
+            data.len()
+        };
+        self.advance(read_len);
+        Ok(read_len)
+    }
+    fn read_exact(&mut self, buf: &mut [u8]) -> io::Result<()> {
+        let read_len = self.read(buf)?;
+        if read_len != buf.len() {
+            return Err(io::Error::new(
+                io::ErrorKind::UnexpectedEof,
+                "failed to fill whole buffer",
+            ));
+        }
+        Ok(())
+    }
+}
+
+impl AsRef<[u8]> for OwnedBytes {
+    fn as_ref(&self) -> &[u8] {
+        self.as_slice()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::io::{self, Read};
+
+    use super::OwnedBytes;
+
+    #[test]
+    fn test_owned_bytes_debug() {
+        let short_bytes = OwnedBytes::new(b"abcd".as_ref());
+        assert_eq!(
+            format!("{:?}", short_bytes),
+            "OwnedBytes([97, 98, 99, 100], len=4)"
+        );
+        let long_bytes = OwnedBytes::new(b"abcdefghijklmnopq".as_ref());
+        assert_eq!(
+            format!("{:?}", long_bytes),
+            "OwnedBytes([97, 98, 99, 100, 101, 102, 103, 104, 105, 106], len=17)"
+        );
+    }
+
+    #[test]
+    fn test_owned_bytes_read() -> io::Result<()> {
+        let mut bytes = OwnedBytes::new(b"abcdefghiklmnopqrstuvwxyz".as_ref());
+        {
+            let mut buf = [0u8; 5];
+            bytes.read_exact(&mut buf[..]).unwrap();
+            assert_eq!(&buf, b"abcde");
+            assert_eq!(bytes.as_slice(), b"fghiklmnopqrstuvwxyz")
+        }
+        {
+            let mut buf = [0u8; 2];
+            bytes.read_exact(&mut buf[..]).unwrap();
+            assert_eq!(&buf, b"fg");
+            assert_eq!(bytes.as_slice(), b"hiklmnopqrstuvwxyz")
+        }
+        Ok(())
+    }
+
+    #[test]
+    fn test_owned_bytes_read_right_at_the_end() -> io::Result<()> {
+        let mut bytes = OwnedBytes::new(b"abcde".as_ref());
+        let mut buf = [0u8; 5];
+        assert_eq!(bytes.read(&mut buf[..]).unwrap(), 5);
+        assert_eq!(&buf, b"abcde");
+        assert_eq!(bytes.as_slice(), b"");
+        assert_eq!(bytes.read(&mut buf[..]).unwrap(), 0);
+        assert_eq!(&buf, b"abcde");
+        Ok(())
+    }
+    #[test]
+    fn test_owned_bytes_read_incomplete() -> io::Result<()> {
+        let mut bytes = OwnedBytes::new(b"abcde".as_ref());
+        let mut buf = [0u8; 7];
+        assert_eq!(bytes.read(&mut buf[..]).unwrap(), 5);
+        assert_eq!(&buf[..5], b"abcde");
+        assert_eq!(bytes.read(&mut buf[..]).unwrap(), 0);
+        Ok(())
+    }
+
+    #[test]
+    fn test_owned_bytes_read_to_end() -> io::Result<()> {
+        let mut bytes = OwnedBytes::new(b"abcde".as_ref());
+        let mut buf = Vec::new();
+        bytes.read_to_end(&mut buf)?;
+        assert_eq!(buf.as_slice(), b"abcde".as_ref());
+        Ok(())
+    }
+
+    #[test]
+    fn test_owned_bytes_split() {
+        let bytes = OwnedBytes::new(b"abcdefghi".as_ref());
+        let (left, right) = bytes.split(3);
+        assert_eq!(left.as_slice(), b"abc");
+        assert_eq!(right.as_slice(), b"defghi");
+    }
+
+    #[test]
+    fn test_owned_bytes_split_boundary() {
+        let bytes = OwnedBytes::new(b"abcdefghi".as_ref());
+        {
+            let (left, right) = bytes.clone().split(0);
+            assert_eq!(left.as_slice(), b"");
+            assert_eq!(right.as_slice(), b"abcdefghi");
+        }
+        {
+            let (left, right) = bytes.split(9);
+            assert_eq!(left.as_slice(), b"abcdefghi");
+            assert_eq!(right.as_slice(), b"");
+        }
+    }
+}

src/directory/ram_directory.rs

@@ -1,9 +1,9 @@
-use crate::core::META_FILEPATH;
 use crate::directory::error::{DeleteError, OpenReadError, OpenWriteError};
 use crate::directory::AntiCallToken;
 use crate::directory::WatchCallbackList;
-use crate::directory::{Directory, ReadOnlySource, WatchCallback, WatchHandle};
+use crate::directory::{Directory, FileSlice, WatchCallback, WatchHandle};
 use crate::directory::{TerminatingWrite, WritePtr};
+use crate::{common::HasLen, core::META_FILEPATH};
 use fail::fail_point;
 use std::collections::HashMap;
 use std::fmt;
@@ -80,17 +80,17 @@ impl TerminatingWrite for VecWriter {
 
 #[derive(Default)]
 struct InnerDirectory {
-    fs: HashMap<PathBuf, ReadOnlySource>,
+    fs: HashMap<PathBuf, FileSlice>,
     watch_router: WatchCallbackList,
 }
 
 impl InnerDirectory {
     fn write(&mut self, path: PathBuf, data: &[u8]) -> bool {
-        let data = ReadOnlySource::new(Vec::from(data));
+        let data = FileSlice::from(data.to_vec());
         self.fs.insert(path, data).is_some()
     }
 
-    fn open_read(&self, path: &Path) -> Result<ReadOnlySource, OpenReadError> {
+    fn open_read(&self, path: &Path) -> Result<FileSlice, OpenReadError> {
         self.fs
             .get(path)
             .ok_or_else(|| OpenReadError::FileDoesNotExist(PathBuf::from(path)))
@@ -151,11 +151,11 @@ impl RAMDirectory {
     /// written using the `atomic_write` api.
     ///
     /// If an error is encounterred, files may be persisted partially.
-    pub fn persist(&self, dest: &mut dyn Directory) -> crate::Result<()> {
+    pub fn persist(&self, dest: &dyn Directory) -> crate::Result<()> {
         let wlock = self.fs.write().unwrap();
-        for (path, source) in wlock.fs.iter() {
+        for (path, file) in wlock.fs.iter() {
             let mut dest_wrt = dest.open_write(path)?;
-            dest_wrt.write_all(source.as_slice())?;
+            dest_wrt.write_all(file.read_bytes()?.as_slice())?;
             dest_wrt.terminate()?;
         }
         Ok(())
@@ -163,15 +163,16 @@ impl RAMDirectory {
 }
 
 impl Directory for RAMDirectory {
-    fn open_read(&self, path: &Path) -> result::Result<ReadOnlySource, OpenReadError> {
+    fn open_read(&self, path: &Path) -> result::Result<FileSlice, OpenReadError> {
         self.fs.read().unwrap().open_read(path)
     }
 
     fn delete(&self, path: &Path) -> result::Result<(), DeleteError> {
         fail_point!("RAMDirectory::delete", |_| {
-            use crate::directory::error::IOError;
+            Err(DeleteError::IOError {
-            let io_error = IOError::from(io::Error::from(io::ErrorKind::Other));
+                io_error: io::Error::from(io::ErrorKind::Other),
-            Err(DeleteError::from(io_error))
+                filepath: path.to_path_buf(),
+            })
         });
         self.fs.write().unwrap().delete(path)
     }
@@ -180,7 +181,7 @@ impl Directory for RAMDirectory {
         self.fs.read().unwrap().exists(path)
     }
 
-    fn open_write(&mut self, path: &Path) -> Result<WritePtr, OpenWriteError> {
+    fn open_write(&self, path: &Path) -> Result<WritePtr, OpenWriteError> {
         let mut fs = self.fs.write().unwrap();
         let path_buf = PathBuf::from(path);
         let vec_writer = VecWriter::new(path_buf.clone(), self.clone());
@@ -194,10 +195,17 @@ impl Directory for RAMDirectory {
     }
 
     fn atomic_read(&self, path: &Path) -> Result<Vec<u8>, OpenReadError> {
-        Ok(self.open_read(path)?.as_slice().to_owned())
+        let bytes =
+            self.open_read(path)?
+                .read_bytes()
+                .map_err(|io_error| OpenReadError::IOError {
+                    io_error,
+                    filepath: path.to_path_buf(),
+                })?;
+        Ok(bytes.as_slice().to_owned())
     }
 
-    fn atomic_write(&mut self, path: &Path, data: &[u8]) -> io::Result<()> {
+    fn atomic_write(&self, path: &Path, data: &[u8]) -> io::Result<()> {
         fail_point!("RAMDirectory::atomic_write", |msg| Err(io::Error::new(
             io::ErrorKind::Other,
             msg.unwrap_or_else(|| "Undefined".to_string())
@@ -234,13 +242,13 @@ mod tests {
         let msg_seq: &'static [u8] = b"sequential is the way";
         let path_atomic: &'static Path = Path::new("atomic");
         let path_seq: &'static Path = Path::new("seq");
-        let mut directory = RAMDirectory::create();
+        let directory = RAMDirectory::create();
         assert!(directory.atomic_write(path_atomic, msg_atomic).is_ok());
         let mut wrt = directory.open_write(path_seq).unwrap();
         assert!(wrt.write_all(msg_seq).is_ok());
         assert!(wrt.flush().is_ok());
-        let mut directory_copy = RAMDirectory::create();
+        let directory_copy = RAMDirectory::create();
-        assert!(directory.persist(&mut directory_copy).is_ok());
+        assert!(directory.persist(&directory_copy).is_ok());
         assert_eq!(directory_copy.atomic_read(path_atomic).unwrap(), msg_atomic);
         assert_eq!(directory_copy.atomic_read(path_seq).unwrap(), msg_seq);
     }

src/directory/read_only_source.rs

@@ -1,137 +0,0 @@
-use crate::common::HasLen;
-use stable_deref_trait::{CloneStableDeref, StableDeref};
-use std::ops::Deref;
-use std::sync::Arc;
-
-pub type BoxedData = Box<dyn Deref<Target = [u8]> + Send + Sync + 'static>;
-
-/// Read object that represents files in tantivy.
-///
-/// These read objects are only in charge to deliver
-/// the data in the form of a constant read-only `&[u8]`.
-/// Whatever happens to the directory file, the data
-/// hold by this object should never be altered or destroyed.
-pub struct ReadOnlySource {
-    data: Arc<BoxedData>,
-    start: usize,
-    stop: usize,
-}
-
-unsafe impl StableDeref for ReadOnlySource {}
-unsafe impl CloneStableDeref for ReadOnlySource {}
-
-impl Deref for ReadOnlySource {
-    type Target = [u8];
-
-    fn deref(&self) -> &[u8] {
-        self.as_slice()
-    }
-}
-
-impl From<Arc<BoxedData>> for ReadOnlySource {
-    fn from(data: Arc<BoxedData>) -> Self {
-        let len = data.len();
-        ReadOnlySource {
-            data,
-            start: 0,
-            stop: len,
-        }
-    }
-}
-
-impl ReadOnlySource {
-    pub(crate) fn new<D>(data: D) -> ReadOnlySource
-    where
-        D: Deref<Target = [u8]> + Send + Sync + 'static,
-    {
-        let len = data.len();
-        ReadOnlySource {
-            data: Arc::new(Box::new(data)),
-            start: 0,
-            stop: len,
-        }
-    }
-
-    /// Creates an empty ReadOnlySource
-    pub fn empty() -> ReadOnlySource {
-        ReadOnlySource::new(&[][..])
-    }
-
-    /// Returns the data underlying the ReadOnlySource object.
-    pub fn as_slice(&self) -> &[u8] {
-        &self.data[self.start..self.stop]
-    }
-
-    /// Splits into 2 `ReadOnlySource`, at the offset given
-    /// as an argument.
-    pub fn split(self, addr: usize) -> (ReadOnlySource, ReadOnlySource) {
-        let left = self.slice(0, addr);
-        let right = self.slice_from(addr);
-        (left, right)
-    }
-
-    /// Splits into 2 `ReadOnlySource`, at the offset `end - right_len`.
-    pub fn split_from_end(self, right_len: usize) -> (ReadOnlySource, ReadOnlySource) {
-        let left_len = self.len() - right_len;
-        self.split(left_len)
-    }
-
-    /// Creates a ReadOnlySource that is just a
-    /// view over a slice of the data.
-    ///
-    /// Keep in mind that any living slice extends
-    /// the lifetime of the original ReadOnlySource,
-    ///
-    /// For instance, if `ReadOnlySource` wraps 500MB
-    /// worth of data in anonymous memory, and only a
-    /// 1KB slice is remaining, the whole `500MBs`
-    /// are retained in memory.
-    pub fn slice(&self, start: usize, stop: usize) -> ReadOnlySource {
-        assert!(
-            start <= stop,
-            "Requested negative slice [{}..{}]",
-            start,
-            stop
-        );
-        assert!(stop <= self.len());
-        ReadOnlySource {
-            data: self.data.clone(),
-            start: self.start + start,
-            stop: self.start + stop,
-        }
-    }
-
-    /// Like `.slice(...)` but enforcing only the `from`
-    /// boundary.
-    ///
-    /// Equivalent to `.slice(from_offset, self.len())`
-    pub fn slice_from(&self, from_offset: usize) -> ReadOnlySource {
-        self.slice(from_offset, self.len())
-    }
-
-    /// Like `.slice(...)` but enforcing only the `to`
-    /// boundary.
-    ///
-    /// Equivalent to `.slice(0, to_offset)`
-    pub fn slice_to(&self, to_offset: usize) -> ReadOnlySource {
-        self.slice(0, to_offset)
-    }
-}
-
-impl HasLen for ReadOnlySource {
-    fn len(&self) -> usize {
-        self.stop - self.start
-    }
-}
-
-impl Clone for ReadOnlySource {
-    fn clone(&self) -> Self {
-        self.slice_from(0)
-    }
-}
-
-impl From<Vec<u8>> for ReadOnlySource {
-    fn from(data: Vec<u8>) -> ReadOnlySource {
-        ReadOnlySource::new(data)
-    }
-}

src/directory/tests.rs

@@ -20,45 +20,47 @@ mod mmap_directory_tests {
     }
 
     #[test]
-    fn test_simple() {
+    fn test_simple() -> crate::Result<()> {
-        let mut directory = make_directory();
+        let directory = make_directory();
-        super::test_simple(&mut directory);
+        super::test_simple(&directory)
     }
 
     #[test]
     fn test_write_create_the_file() {
-        let mut directory = make_directory();
+        let directory = make_directory();
-        super::test_write_create_the_file(&mut directory);
+        super::test_write_create_the_file(&directory);
     }
 
     #[test]
-    fn test_rewrite_forbidden() {
+    fn test_rewrite_forbidden() -> crate::Result<()> {
-        let mut directory = make_directory();
+        let directory = make_directory();
-        super::test_rewrite_forbidden(&mut directory);
+        super::test_rewrite_forbidden(&directory)?;
+        Ok(())
     }
 
     #[test]
-    fn test_directory_delete() {
+    fn test_directory_delete() -> crate::Result<()> {
-        let mut directory = make_directory();
+        let directory = make_directory();
-        super::test_directory_delete(&mut directory);
+        super::test_directory_delete(&directory)?;
+        Ok(())
     }
 
     #[test]
     fn test_lock_non_blocking() {
-        let mut directory = make_directory();
+        let directory = make_directory();
-        super::test_lock_non_blocking(&mut directory);
+        super::test_lock_non_blocking(&directory);
     }
 
     #[test]
     fn test_lock_blocking() {
-        let mut directory = make_directory();
+        let directory = make_directory();
-        super::test_lock_blocking(&mut directory);
+        super::test_lock_blocking(&directory);
     }
 
     #[test]
     fn test_watch() {
-        let mut directory = make_directory();
+        let directory = make_directory();
-        super::test_watch(&mut directory);
+        super::test_watch(&directory);
     }
 }
 
@@ -72,45 +74,47 @@ mod ram_directory_tests {
     }
 
     #[test]
-    fn test_simple() {
+    fn test_simple() -> crate::Result<()> {
-        let mut directory = make_directory();
+        let directory = make_directory();
-        super::test_simple(&mut directory);
+        super::test_simple(&directory)
     }
 
     #[test]
     fn test_write_create_the_file() {
-        let mut directory = make_directory();
+        let directory = make_directory();
-        super::test_write_create_the_file(&mut directory);
+        super::test_write_create_the_file(&directory);
     }
 
     #[test]
-    fn test_rewrite_forbidden() {
+    fn test_rewrite_forbidden() -> crate::Result<()> {
-        let mut directory = make_directory();
+        let directory = make_directory();
-        super::test_rewrite_forbidden(&mut directory);
+        super::test_rewrite_forbidden(&directory)?;
+        Ok(())
     }
 
     #[test]
-    fn test_directory_delete() {
+    fn test_directory_delete() -> crate::Result<()> {
-        let mut directory = make_directory();
+        let directory = make_directory();
-        super::test_directory_delete(&mut directory);
+        super::test_directory_delete(&directory)?;
+        Ok(())
     }
 
     #[test]
     fn test_lock_non_blocking() {
-        let mut directory = make_directory();
+        let directory = make_directory();
-        super::test_lock_non_blocking(&mut directory);
+        super::test_lock_non_blocking(&directory);
     }
 
     #[test]
     fn test_lock_blocking() {
-        let mut directory = make_directory();
+        let directory = make_directory();
-        super::test_lock_blocking(&mut directory);
+        super::test_lock_blocking(&directory);
     }
 
     #[test]
     fn test_watch() {
-        let mut directory = make_directory();
+        let directory = make_directory();
-        super::test_watch(&mut directory);
+        super::test_watch(&directory);
     }
 }
 
@@ -118,43 +122,37 @@ mod ram_directory_tests {
 #[should_panic]
 fn ram_directory_panics_if_flush_forgotten() {
     let test_path: &'static Path = Path::new("some_path_for_test");
-    let mut ram_directory = RAMDirectory::create();
+    let ram_directory = RAMDirectory::create();
     let mut write_file = ram_directory.open_write(test_path).unwrap();
     assert!(write_file.write_all(&[4]).is_ok());
 }
 
-fn test_simple(directory: &mut dyn Directory) {
+fn test_simple(directory: &dyn Directory) -> crate::Result<()> {
     let test_path: &'static Path = Path::new("some_path_for_test");
-    {
+    let mut write_file = directory.open_write(test_path)?;
-        let mut write_file = directory.open_write(test_path).unwrap();
+    assert!(directory.exists(test_path));
-        assert!(directory.exists(test_path));
+    write_file.write_all(&[4])?;
-        write_file.write_all(&[4]).unwrap();
+    write_file.write_all(&[3])?;
-        write_file.write_all(&[3]).unwrap();
+    write_file.write_all(&[7, 3, 5])?;
-        write_file.write_all(&[7, 3, 5]).unwrap();
+    write_file.flush()?;
-        write_file.flush().unwrap();
+    let read_file = directory.open_read(test_path)?.read_bytes()?;
-    }
+    assert_eq!(read_file.as_slice(), &[4u8, 3u8, 7u8, 3u8, 5u8]);
-    {
+    mem::drop(read_file);
-        let read_file = directory.open_read(test_path).unwrap();
-        let data: &[u8] = &*read_file;
-        assert_eq!(data, &[4u8, 3u8, 7u8, 3u8, 5u8]);
-    }
     assert!(directory.delete(test_path).is_ok());
     assert!(!directory.exists(test_path));
+    Ok(())
 }
 
-fn test_rewrite_forbidden(directory: &mut dyn Directory) {
+fn test_rewrite_forbidden(directory: &dyn Directory) -> crate::Result<()> {
     let test_path: &'static Path = Path::new("some_path_for_test");
-    {
+    directory.open_write(test_path)?;
-        directory.open_write(test_path).unwrap();
+    assert!(directory.exists(test_path));
-        assert!(directory.exists(test_path));
+    assert!(directory.open_write(test_path).is_err());
-    }
-    {
-        assert!(directory.open_write(test_path).is_err());
-    }
     assert!(directory.delete(test_path).is_ok());
+    Ok(())
 }
 
-fn test_write_create_the_file(directory: &mut dyn Directory) {
+fn test_write_create_the_file(directory: &dyn Directory) {
     let test_path: &'static Path = Path::new("some_path_for_test");
     {
         assert!(directory.open_read(test_path).is_err());
@@ -165,21 +163,20 @@ fn test_write_create_the_file(directory: &mut dyn Directory) {
     }
 }
 
-fn test_directory_delete(directory: &mut dyn Directory) {
+fn test_directory_delete(directory: &dyn Directory) -> crate::Result<()> {
     let test_path: &'static Path = Path::new("some_path_for_test");
     assert!(directory.open_read(test_path).is_err());
-    let mut write_file = directory.open_write(&test_path).unwrap();
+    let mut write_file = directory.open_write(&test_path)?;
-    write_file.write_all(&[1, 2, 3, 4]).unwrap();
+    write_file.write_all(&[1, 2, 3, 4])?;
-    write_file.flush().unwrap();
+    write_file.flush()?;
     {
-        let read_handle = directory.open_read(&test_path).unwrap();
+        let read_handle = directory.open_read(&test_path)?.read_bytes()?;
-        assert_eq!(&*read_handle, &[1u8, 2u8, 3u8, 4u8]);
+        assert_eq!(read_handle.as_slice(), &[1u8, 2u8, 3u8, 4u8]);
         // Mapped files can't be deleted on Windows
         if !cfg!(windows) {
             assert!(directory.delete(&test_path).is_ok());
-            assert_eq!(&*read_handle, &[1u8, 2u8, 3u8, 4u8]);
+            assert_eq!(read_handle.as_slice(), &[1u8, 2u8, 3u8, 4u8]);
         }
-
         assert!(directory.delete(Path::new("SomeOtherPath")).is_err());
     }
 
@@ -189,9 +186,10 @@ fn test_directory_delete(directory: &mut dyn Directory) {
 
     assert!(directory.open_read(&test_path).is_err());
     assert!(directory.delete(&test_path).is_err());
+    Ok(())
 }
 
-fn test_watch(directory: &mut dyn Directory) {
+fn test_watch(directory: &dyn Directory) {
     let num_progress: Arc<AtomicUsize> = Default::default();
     let counter: Arc<AtomicUsize> = Default::default();
     let counter_clone = counter.clone();
@@ -211,22 +209,22 @@ fn test_watch(directory: &mut dyn Directory) {
         .unwrap();
 
     for i in 0..10 {
-        assert_eq!(i, counter.load(SeqCst));
+        assert!(i <= counter.load(SeqCst));
         assert!(directory
             .atomic_write(Path::new("meta.json"), b"random_test_data_2")
             .is_ok());
         assert_eq!(receiver.recv_timeout(Duration::from_millis(500)), Ok(i));
-        assert_eq!(i + 1, counter.load(SeqCst));
+        assert!(i + 1 <= counter.load(SeqCst)); // notify can trigger more than once.
     }
     mem::drop(watch_handle);
     assert!(directory
         .atomic_write(Path::new("meta.json"), b"random_test_data")
         .is_ok());
     assert!(receiver.recv_timeout(Duration::from_millis(500)).is_ok());
-    assert_eq!(10, counter.load(SeqCst));
+    assert!(10 <= counter.load(SeqCst));
 }
 
-fn test_lock_non_blocking(directory: &mut dyn Directory) {
+fn test_lock_non_blocking(directory: &dyn Directory) {
     {
         let lock_a_res = directory.acquire_lock(&Lock {
             filepath: PathBuf::from("a.lock"),
@@ -251,7 +249,7 @@ fn test_lock_non_blocking(directory: &mut dyn Directory) {
     assert!(lock_a_res.is_ok());
 }
 
-fn test_lock_blocking(directory: &mut dyn Directory) {
+fn test_lock_blocking(directory: &dyn Directory) {
     let lock_a_res = directory.acquire_lock(&Lock {
         filepath: PathBuf::from("a.lock"),
         is_blocking: true,

src/directory/watch_event_router.rs

@@ -5,7 +5,7 @@ use std::sync::RwLock;
 use std::sync::Weak;
 
 /// Type alias for callbacks registered when watching files of a `Directory`.
-pub type WatchCallback = Box<dyn Fn() -> () + Sync + Send>;
+pub type WatchCallback = Box<dyn Fn() + Sync + Send>;
 
 /// Helper struct to implement the watch method in `Directory` implementations.
 ///
@@ -29,10 +29,17 @@ impl WatchHandle {
     pub fn new(watch_callback: Arc<WatchCallback>) -> WatchHandle {
         WatchHandle(watch_callback)
     }
+
+    /// Returns an empty watch handle.
+    ///
+    /// This function is only useful when implementing a readonly directory.
+    pub fn empty() -> WatchHandle {
+        WatchHandle::new(Arc::new(Box::new(|| {})))
+    }
 }
 
 impl WatchCallbackList {
-    /// Suscribes a new callback and returns a handle that controls the lifetime of the callback.
+    /// Subscribes a new callback and returns a handle that controls the lifetime of the callback.
     pub fn subscribe(&self, watch_callback: WatchCallback) -> WatchHandle {
         let watch_callback_arc = Arc::new(watch_callback);
         let watch_callback_weak = Arc::downgrade(&watch_callback_arc);

src/docset.rs

@@ -38,6 +38,7 @@ pub trait DocSet {
     /// Calling `seek(TERMINATED)` is also legal and is the normal way to consume a DocSet.
     fn seek(&mut self, target: DocId) -> DocId {
         let mut doc = self.doc();
+        debug_assert!(doc <= target);
         while doc < target {
             doc = self.advance();
         }

src/error.rs

@@ -2,21 +2,27 @@
 
 use std::io;
 
-use crate::directory::error::{IOError, OpenDirectoryError, OpenReadError, OpenWriteError};
 use crate::directory::error::{Incompatibility, LockError};
 use crate::fastfield::FastFieldNotAvailableError;
 use crate::query;
-use crate::schema;
+use crate::{
+    directory::error::{OpenDirectoryError, OpenReadError, OpenWriteError},
+    schema,
+};
 use std::fmt;
 use std::path::PathBuf;
 use std::sync::PoisonError;
 
+/// Represents a `DataCorruption` error.
+///
+/// When facing data corruption, tantivy  actually panic or return this error.
 pub struct DataCorruption {
     filepath: Option<PathBuf>,
     comment: String,
 }
 
 impl DataCorruption {
+    /// Creates a `DataCorruption` Error.
     pub fn new(filepath: PathBuf, comment: String) -> DataCorruption {
         DataCorruption {
             filepath: Some(filepath),
@@ -24,10 +30,11 @@ impl DataCorruption {
         }
     }
 
-    pub fn comment_only(comment: String) -> DataCorruption {
+    /// Creates a `DataCorruption` Error, when the filepath is irrelevant.
+    pub fn comment_only<TStr: ToString>(comment: TStr) -> DataCorruption {
         DataCorruption {
             filepath: None,
-            comment,
+            comment: comment.to_string(),
         }
     }
 }
@@ -43,44 +50,47 @@ impl fmt::Debug for DataCorruption {
     }
 }
 
-/// The library's failure based error enum
+/// The library's error enum
-#[derive(Debug, Fail)]
+#[derive(Debug, Error)]
 pub enum TantivyError {
-    /// Path does not exist.
+    /// Failed to open the directory.
-    #[fail(display = "Path does not exist: '{:?}'", _0)]
+    #[error("Failed to open the directory: '{0:?}'")]
-    PathDoesNotExist(PathBuf),
+    OpenDirectoryError(#[from] OpenDirectoryError),
-    /// File already exists, this is a problem when we try to write into a new file.
+    /// Failed to open a file for read.
-    #[fail(display = "File already exists: '{:?}'", _0)]
+    #[error("Failed to open file for read: '{0:?}'")]
-    FileAlreadyExists(PathBuf),
+    OpenReadError(#[from] OpenReadError),
+    /// Failed to open a file for write.
+    #[error("Failed to open file for write: '{0:?}'")]
+    OpenWriteError(#[from] OpenWriteError),
     /// Index already exists in this directory
-    #[fail(display = "Index already exists")]
+    #[error("Index already exists")]
     IndexAlreadyExists,
     /// Failed to acquire file lock
-    #[fail(display = "Failed to acquire Lockfile: {:?}. {:?}", _0, _1)]
+    #[error("Failed to acquire Lockfile: {0:?}. {1:?}")]
     LockFailure(LockError, Option<String>),
     /// IO Error.
-    #[fail(display = "An IO error occurred: '{}'", _0)]
+    #[error("An IO error occurred: '{0}'")]
-    IOError(#[cause] IOError),
+    IOError(#[from] io::Error),
     /// Data corruption.
-    #[fail(display = "{:?}", _0)]
+    #[error("Data corrupted: '{0:?}'")]
     DataCorruption(DataCorruption),
     /// A thread holding the locked panicked and poisoned the lock.
-    #[fail(display = "A thread holding the locked panicked and poisoned the lock")]
+    #[error("A thread holding the locked panicked and poisoned the lock")]
     Poisoned,
     /// Invalid argument was passed by the user.
-    #[fail(display = "An invalid argument was passed: '{}'", _0)]
+    #[error("An invalid argument was passed: '{0}'")]
     InvalidArgument(String),
     /// An Error happened in one of the thread.
-    #[fail(display = "An error occurred in a thread: '{}'", _0)]
+    #[error("An error occurred in a thread: '{0}'")]
     ErrorInThread(String),
     /// An Error appeared related to the schema.
-    #[fail(display = "Schema error: '{}'", _0)]
+    #[error("Schema error: '{0}'")]
     SchemaError(String),
     /// System error. (e.g.: We failed spawning a new thread)
-    #[fail(display = "System error.'{}'", _0)]
+    #[error("System error.'{0}'")]
     SystemError(String),
     /// Index incompatible with current version of tantivy
-    #[fail(display = "{:?}", _0)]
+    #[error("{0:?}")]
     IncompatibleIndex(Incompatibility),
 }
 
@@ -89,31 +99,17 @@ impl From<DataCorruption> for TantivyError {
         TantivyError::DataCorruption(data_corruption)
     }
 }
-
 impl From<FastFieldNotAvailableError> for TantivyError {
     fn from(fastfield_error: FastFieldNotAvailableError) -> TantivyError {
         TantivyError::SchemaError(format!("{}", fastfield_error))
     }
 }
-
 impl From<LockError> for TantivyError {
     fn from(lock_error: LockError) -> TantivyError {
         TantivyError::LockFailure(lock_error, None)
     }
 }
 
-impl From<IOError> for TantivyError {
-    fn from(io_error: IOError) -> TantivyError {
-        TantivyError::IOError(io_error)
-    }
-}
-
-impl From<io::Error> for TantivyError {
-    fn from(io_error: io::Error) -> TantivyError {
-        TantivyError::IOError(io_error.into())
-    }
-}
-
 impl From<query::QueryParserError> for TantivyError {
     fn from(parsing_error: query::QueryParserError) -> TantivyError {
         TantivyError::InvalidArgument(format!("Query is invalid. {:?}", parsing_error))
@@ -126,15 +122,9 @@ impl<Guard> From<PoisonError<Guard>> for TantivyError {
     }
 }
 
-impl From<OpenReadError> for TantivyError {
+impl From<chrono::ParseError> for TantivyError {
-    fn from(error: OpenReadError) -> TantivyError {
+    fn from(err: chrono::ParseError) -> TantivyError {
-        match error {
+        TantivyError::InvalidArgument(err.to_string())
-            OpenReadError::FileDoesNotExist(filepath) => TantivyError::PathDoesNotExist(filepath),
-            OpenReadError::IOError(io_error) => TantivyError::IOError(io_error),
-            OpenReadError::IncompatibleIndex(incompatibility) => {
-                TantivyError::IncompatibleIndex(incompatibility)
-            }
-        }
     }
 }
 
@@ -144,35 +134,9 @@ impl From<schema::DocParsingError> for TantivyError {
     }
 }
 
-impl From<OpenWriteError> for TantivyError {
-    fn from(error: OpenWriteError) -> TantivyError {
-        match error {
-            OpenWriteError::FileAlreadyExists(filepath) => {
-                TantivyError::FileAlreadyExists(filepath)
-            }
-            OpenWriteError::IOError(io_error) => TantivyError::IOError(io_error),
-        }
-    }
-}
-
-impl From<OpenDirectoryError> for TantivyError {
-    fn from(error: OpenDirectoryError) -> TantivyError {
-        match error {
-            OpenDirectoryError::DoesNotExist(directory_path) => {
-                TantivyError::PathDoesNotExist(directory_path)
-            }
-            OpenDirectoryError::NotADirectory(directory_path) => {
-                TantivyError::InvalidArgument(format!("{:?} is not a directory", directory_path))
-            }
-            OpenDirectoryError::IoError(err) => TantivyError::IOError(IOError::from(err)),
-        }
-    }
-}
-
 impl From<serde_json::Error> for TantivyError {
     fn from(error: serde_json::Error) -> TantivyError {
-        let io_err = io::Error::from(error);
+        TantivyError::IOError(error.into())
-        TantivyError::IOError(io_err.into())
     }
 }
 

src/fastfield/bytes/mod.rs

@@ -6,31 +6,114 @@ pub use self::writer::BytesFastFieldWriter;
 
 #[cfg(test)]
 mod tests {
-    use crate::schema::Schema;
+    use crate::schema::{BytesOptions, IndexRecordOption, Schema, Value};
-    use crate::Index;
+    use crate::{query::TermQuery, schema::FAST, schema::INDEXED, schema::STORED};
+    use crate::{DocAddress, DocSet, Index, Searcher, Term};
+    use std::ops::Deref;
 
     #[test]
-    fn test_bytes() {
+    fn test_bytes() -> crate::Result<()> {
         let mut schema_builder = Schema::builder();
-        let field = schema_builder.add_bytes_field("bytesfield");
+        let bytes_field = schema_builder.add_bytes_field("bytesfield", FAST);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests()?;
-        index_writer.add_document(doc!(field=>vec![0u8, 1, 2, 3]));
+        index_writer.add_document(doc!(bytes_field=>vec![0u8, 1, 2, 3]));
-        index_writer.add_document(doc!(field=>vec![]));
+        index_writer.add_document(doc!(bytes_field=>vec![]));
-        index_writer.add_document(doc!(field=>vec![255u8]));
+        index_writer.add_document(doc!(bytes_field=>vec![255u8]));
-        index_writer.add_document(doc!(field=>vec![1u8, 3, 5, 7, 9]));
+        index_writer.add_document(doc!(bytes_field=>vec![1u8, 3, 5, 7, 9]));
-        index_writer.add_document(doc!(field=>vec![0u8; 1000]));
+        index_writer.add_document(doc!(bytes_field=>vec![0u8; 1000]));
-        assert!(index_writer.commit().is_ok());
+        index_writer.commit()?;
-        let searcher = index.reader().unwrap().searcher();
+        let searcher = index.reader()?.searcher();
         let segment_reader = searcher.segment_reader(0);
-        let bytes_reader = segment_reader.fast_fields().bytes(field).unwrap();
+        let bytes_reader = segment_reader.fast_fields().bytes(bytes_field).unwrap();
-
         assert_eq!(bytes_reader.get_bytes(0), &[0u8, 1, 2, 3]);
         assert!(bytes_reader.get_bytes(1).is_empty());
         assert_eq!(bytes_reader.get_bytes(2), &[255u8]);
         assert_eq!(bytes_reader.get_bytes(3), &[1u8, 3, 5, 7, 9]);
         let long = vec![0u8; 1000];
         assert_eq!(bytes_reader.get_bytes(4), long.as_slice());
+        Ok(())
+    }
+
+    fn create_index_for_test<T: Into<BytesOptions>>(
+        byte_options: T,
+    ) -> crate::Result<impl Deref<Target = Searcher>> {
+        let mut schema_builder = Schema::builder();
+        let field = schema_builder.add_bytes_field("string_bytes", byte_options.into());
+        let schema = schema_builder.build();
+        let index = Index::create_in_ram(schema);
+        let mut index_writer = index.writer_for_tests()?;
+        index_writer.add_document(doc!(
+                field => b"tantivy".as_ref(),
+                field => b"lucene".as_ref()
+        ));
+        index_writer.commit()?;
+        Ok(index.reader()?.searcher())
+    }
+
+    #[test]
+    fn test_stored_bytes() -> crate::Result<()> {
+        let searcher = create_index_for_test(STORED)?;
+        assert_eq!(searcher.num_docs(), 1);
+        let retrieved_doc = searcher.doc(DocAddress(0u32, 0u32))?;
+        let field = searcher.schema().get_field("string_bytes").unwrap();
+        let values: Vec<&Value> = retrieved_doc.get_all(field).collect();
+        assert_eq!(values.len(), 2);
+        let values_bytes: Vec<&[u8]> = values
+            .into_iter()
+            .flat_map(|value| value.bytes_value())
+            .collect();
+        assert_eq!(values_bytes, &[&b"tantivy"[..], &b"lucene"[..]]);
+        Ok(())
+    }
+
+    #[test]
+    fn test_non_stored_bytes() -> crate::Result<()> {
+        let searcher = create_index_for_test(INDEXED)?;
+        assert_eq!(searcher.num_docs(), 1);
+        let retrieved_doc = searcher.doc(DocAddress(0u32, 0u32))?;
+        let field = searcher.schema().get_field("string_bytes").unwrap();
+        assert!(retrieved_doc.get_first(field).is_none());
+        Ok(())
+    }
+
+    #[test]
+    fn test_index_bytes() -> crate::Result<()> {
+        let searcher = create_index_for_test(INDEXED)?;
+        assert_eq!(searcher.num_docs(), 1);
+        let field = searcher.schema().get_field("string_bytes").unwrap();
+        let term = Term::from_field_bytes(field, b"lucene".as_ref());
+        let term_query = TermQuery::new(term, IndexRecordOption::Basic);
+        let term_weight = term_query.specialized_weight(&searcher, true)?;
+        let term_scorer = term_weight.specialized_scorer(searcher.segment_reader(0), 1.0f32)?;
+        assert_eq!(term_scorer.doc(), 0u32);
+        Ok(())
+    }
+
+    #[test]
+    fn test_non_index_bytes() -> crate::Result<()> {
+        let searcher = create_index_for_test(STORED)?;
+        assert_eq!(searcher.num_docs(), 1);
+        let field = searcher.schema().get_field("string_bytes").unwrap();
+        let term = Term::from_field_bytes(field, b"lucene".as_ref());
+        let term_query = TermQuery::new(term, IndexRecordOption::Basic);
+        let term_weight_res = term_query.specialized_weight(&searcher, false);
+        assert!(matches!(
+            term_weight_res,
+            Err(crate::TantivyError::SchemaError(_))
+        ));
+        Ok(())
+    }
+
+    #[test]
+    fn test_fast_bytes_multivalue_value() -> crate::Result<()> {
+        let searcher = create_index_for_test(FAST)?;
+        assert_eq!(searcher.num_docs(), 1);
+        let fast_fields = searcher.segment_reader(0u32).fast_fields();
+        let field = searcher.schema().get_field("string_bytes").unwrap();
+        let fast_field_reader = fast_fields.bytes(field).unwrap();
+        assert_eq!(fast_field_reader.get_bytes(0u32), b"tantivy");
+        Ok(())
     }
 }

src/fastfield/bytes/reader.rs

@@ -1,6 +1,5 @@
-use owning_ref::OwningRef;
+use crate::directory::FileSlice;
-
+use crate::directory::OwnedBytes;
-use crate::directory::ReadOnlySource;
 use crate::fastfield::FastFieldReader;
 use crate::DocId;
 
@@ -17,16 +16,16 @@ use crate::DocId;
 #[derive(Clone)]
 pub struct BytesFastFieldReader {
     idx_reader: FastFieldReader<u64>,
-    values: OwningRef<ReadOnlySource, [u8]>,
+    values: OwnedBytes,
 }
 
 impl BytesFastFieldReader {
     pub(crate) fn open(
         idx_reader: FastFieldReader<u64>,
-        values_source: ReadOnlySource,
+        values_file: FileSlice,
-    ) -> BytesFastFieldReader {
+    ) -> crate::Result<BytesFastFieldReader> {
-        let values = OwningRef::new(values_source).map(|source| &source[..]);
+        let values = values_file.read_bytes()?;
-        BytesFastFieldReader { idx_reader, values }
+        Ok(BytesFastFieldReader { idx_reader, values })
     }
 
     fn range(&self, doc: DocId) -> (usize, usize) {
@@ -38,7 +37,7 @@ impl BytesFastFieldReader {
     /// Returns the bytes associated to the given `doc`
     pub fn get_bytes(&self, doc: DocId) -> &[u8] {
         let (start, stop) = self.range(doc);
-        &self.values[start..stop]
+        &self.values.as_slice()[start..stop]
     }
 
     /// Returns the overall number of bytes in this bytes fast field.

src/fastfield/bytes/writer.rs

@@ -49,16 +49,10 @@ impl BytesFastFieldWriter {
     /// matching field values present in the document.
     pub fn add_document(&mut self, doc: &Document) {
         self.next_doc();
-        for field_value in doc.field_values() {
+        for field_value in doc.get_all(self.field) {
-            if field_value.field() == self.field {
+            if let Value::Bytes(ref bytes) = field_value {
-                if let Value::Bytes(ref bytes) = *field_value.value() {
+                self.vals.extend_from_slice(bytes);
-                    self.vals.extend_from_slice(bytes);
+                return;
-                } else {
-                    panic!(
-                        "Bytes field contained non-Bytes Value!. Field {:?} = {:?}",
-                        self.field, field_value
-                    );
-                }
             }
         }
     }
@@ -76,21 +70,18 @@ impl BytesFastFieldWriter {
 
     /// Serializes the fast field values by pushing them to the `FastFieldSerializer`.
     pub fn serialize(&self, serializer: &mut FastFieldSerializer) -> io::Result<()> {
-        {
+        // writing the offset index
-            // writing the offset index
+        let mut doc_index_serializer =
-            let mut doc_index_serializer =
+            serializer.new_u64_fast_field_with_idx(self.field, 0, self.vals.len() as u64, 0)?;
-                serializer.new_u64_fast_field_with_idx(self.field, 0, self.vals.len() as u64, 0)?;
+        for &offset in &self.doc_index {
-            for &offset in &self.doc_index {
+            doc_index_serializer.add_val(offset)?;
-                doc_index_serializer.add_val(offset)?;
-            }
-            doc_index_serializer.add_val(self.vals.len() as u64)?;
-            doc_index_serializer.close_field()?;
-        }
-        {
-            // writing the values themselves
-            let mut value_serializer = serializer.new_bytes_fast_field_with_idx(self.field, 1)?;
-            value_serializer.write_all(&self.vals)?;
         }
+        doc_index_serializer.add_val(self.vals.len() as u64)?;
+        doc_index_serializer.close_field()?;
+        // writing the values themselves
+        serializer
+            .new_bytes_fast_field_with_idx(self.field, 1)?
+            .write_all(&self.vals)?;
         Ok(())
     }
 }

src/fastfield/delete.rs

@@ -1,5 +1,6 @@
 use crate::common::{BitSet, HasLen};
-use crate::directory::ReadOnlySource;
+use crate::directory::FileSlice;
+use crate::directory::OwnedBytes;
 use crate::directory::WritePtr;
 use crate::space_usage::ByteCount;
 use crate::DocId;
@@ -9,6 +10,8 @@ use std::io::Write;
 /// Write a delete `BitSet`
 ///
 /// where `delete_bitset` is the set of deleted `DocId`.
+/// Warning: this function does not call terminate. The caller is in charge of
+/// closing the writer properly.
 pub fn write_delete_bitset(
     delete_bitset: &BitSet,
     max_doc: u32,
@@ -37,22 +40,41 @@ pub fn write_delete_bitset(
 /// Set of deleted `DocId`s.
 #[derive(Clone)]
 pub struct DeleteBitSet {
-    data: ReadOnlySource,
+    data: OwnedBytes,
     len: usize,
 }
 
 impl DeleteBitSet {
-    /// Opens a delete bitset given its data source.
+    #[cfg(test)]
-    pub fn open(data: ReadOnlySource) -> DeleteBitSet {
+    pub(crate) fn for_test(docs: &[DocId], max_doc: u32) -> DeleteBitSet {
-        let num_deleted: usize = data
+        use crate::directory::{Directory, RAMDirectory, TerminatingWrite};
+        use std::path::Path;
+        assert!(docs.iter().all(|&doc| doc < max_doc));
+        let mut bitset = BitSet::with_max_value(max_doc);
+        for &doc in docs {
+            bitset.insert(doc);
+        }
+        let directory = RAMDirectory::create();
+        let path = Path::new("dummydeletebitset");
+        let mut wrt = directory.open_write(path).unwrap();
+        write_delete_bitset(&bitset, max_doc, &mut wrt).unwrap();
+        wrt.terminate().unwrap();
+        let file = directory.open_read(path).unwrap();
+        Self::open(file).unwrap()
+    }
+
+    /// Opens a delete bitset given its file.
+    pub fn open(file: FileSlice) -> crate::Result<DeleteBitSet> {
+        let bytes = file.read_bytes()?;
+        let num_deleted: usize = bytes
             .as_slice()
             .iter()
             .map(|b| b.count_ones() as usize)
             .sum();
-        DeleteBitSet {
+        Ok(DeleteBitSet {
-            data,
+            data: bytes,
             len: num_deleted,
-        }
+        })
     }
 
     /// Returns true iff the document is still "alive". In other words, if it has not been deleted.
@@ -64,7 +86,7 @@ impl DeleteBitSet {
     #[inline(always)]
     pub fn is_deleted(&self, doc: DocId) -> bool {
         let byte_offset = doc / 8u32;
-        let b: u8 = (*self.data)[byte_offset as usize];
+        let b: u8 = self.data.as_slice()[byte_offset as usize];
         let shift = (doc & 7u32) as u8;
         b & (1u8 << shift) != 0
     }
@@ -83,42 +105,35 @@ impl HasLen for DeleteBitSet {
 
 #[cfg(test)]
 mod tests {
-    use super::*;
+    use super::DeleteBitSet;
-    use crate::directory::*;
+    use crate::common::HasLen;
-    use std::path::PathBuf;
 
-    fn test_delete_bitset_helper(bitset: &BitSet, max_doc: u32) {
+    #[test]
-        let test_path = PathBuf::from("test");
+    fn test_delete_bitset_empty() {
-        let mut directory = RAMDirectory::create();
+        let delete_bitset = DeleteBitSet::for_test(&[], 10);
-        {
+        for doc in 0..10 {
-            let mut writer = directory.open_write(&*test_path).unwrap();
+            assert_eq!(delete_bitset.is_deleted(doc), !delete_bitset.is_alive(doc));
-            write_delete_bitset(bitset, max_doc, &mut writer).unwrap();
-            writer.terminate().unwrap();
         }
-        let source = directory.open_read(&test_path).unwrap();
+        assert_eq!(delete_bitset.len(), 0);
-        let delete_bitset = DeleteBitSet::open(source);
-        for doc in 0..max_doc {
-            assert_eq!(bitset.contains(doc), delete_bitset.is_deleted(doc as DocId));
-        }
-        assert_eq!(delete_bitset.len(), bitset.len());
     }
 
     #[test]
     fn test_delete_bitset() {
-        {
+        let delete_bitset = DeleteBitSet::for_test(&[1, 9], 10);
-            let mut bitset = BitSet::with_max_value(10);
+        assert!(delete_bitset.is_alive(0));
-            bitset.insert(1);
+        assert!(delete_bitset.is_deleted(1));
-            bitset.insert(9);
+        assert!(delete_bitset.is_alive(2));
-            test_delete_bitset_helper(&bitset, 10);
+        assert!(delete_bitset.is_alive(3));
-        }
+        assert!(delete_bitset.is_alive(4));
-        {
+        assert!(delete_bitset.is_alive(5));
-            let mut bitset = BitSet::with_max_value(8);
+        assert!(delete_bitset.is_alive(6));
-            bitset.insert(1);
+        assert!(delete_bitset.is_alive(6));
-            bitset.insert(2);
+        assert!(delete_bitset.is_alive(7));
-            bitset.insert(3);
+        assert!(delete_bitset.is_alive(8));
-            bitset.insert(5);
+        assert!(delete_bitset.is_deleted(9));
-            bitset.insert(7);
+        for doc in 0..10 {
-            test_delete_bitset_helper(&bitset, 8);
+            assert_eq!(delete_bitset.is_deleted(doc), !delete_bitset.is_alive(doc));
         }
+        assert_eq!(delete_bitset.len(), 2);
     }
 }

src/fastfield/error.rs

@@ -4,8 +4,8 @@ use std::result;
 /// `FastFieldNotAvailableError` is returned when the
 /// user requested for a fast field reader, and the field was not
 /// defined in the schema as a fast field.
-#[derive(Debug, Fail)]
+#[derive(Debug, Error)]
-#[fail(display = "Fast field not available: '{:?}'", field_name)]
+#[error("Fast field not available: '{field_name:?}'")]
 pub struct FastFieldNotAvailableError {
     field_name: String,
 }

src/fastfield/facet_reader.rs

@@ -73,7 +73,61 @@ impl FacetReader {
     }
 
     /// Return the list of facet ordinals associated to a document.
-    pub fn facet_ords(&mut self, doc: DocId, output: &mut Vec<u64>) {
+    pub fn facet_ords(&self, doc: DocId, output: &mut Vec<u64>) {
         self.term_ords.get_vals(doc, output);
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use crate::Index;
+    use crate::{
+        schema::{Facet, SchemaBuilder},
+        Document,
+    };
+
+    #[test]
+    fn test_facet_not_populated_for_all_docs() -> crate::Result<()> {
+        let mut schema_builder = SchemaBuilder::default();
+        let facet_field = schema_builder.add_facet_field("facet");
+        let schema = schema_builder.build();
+        let index = Index::create_in_ram(schema);
+        let mut index_writer = index.writer_for_tests()?;
+        index_writer.add_document(doc!(facet_field=>Facet::from_text("/a/b")));
+        index_writer.add_document(Document::default());
+        index_writer.commit()?;
+        let searcher = index.reader()?.searcher();
+        let facet_reader = searcher
+            .segment_reader(0u32)
+            .facet_reader(facet_field)
+            .unwrap();
+        let mut facet_ords = Vec::new();
+        facet_reader.facet_ords(0u32, &mut facet_ords);
+        assert_eq!(&facet_ords, &[2u64]);
+        facet_reader.facet_ords(1u32, &mut facet_ords);
+        assert!(facet_ords.is_empty());
+        Ok(())
+    }
+    #[test]
+    fn test_facet_not_populated_for_any_docs() -> crate::Result<()> {
+        let mut schema_builder = SchemaBuilder::default();
+        let facet_field = schema_builder.add_facet_field("facet");
+        let schema = schema_builder.build();
+        let index = Index::create_in_ram(schema);
+        let mut index_writer = index.writer_for_tests()?;
+        index_writer.add_document(Document::default());
+        index_writer.add_document(Document::default());
+        index_writer.commit()?;
+        let searcher = index.reader()?.searcher();
+        let facet_reader = searcher
+            .segment_reader(0u32)
+            .facet_reader(facet_field)
+            .unwrap();
+        let mut facet_ords = Vec::new();
+        facet_reader.facet_ords(0u32, &mut facet_ords);
+        assert!(facet_ords.is_empty());
+        facet_reader.facet_ords(1u32, &mut facet_ords);
+        assert!(facet_ords.is_empty());
+        Ok(())
+    }
+}

src/fastfield/mod.rs

@@ -33,11 +33,14 @@ pub use self::reader::FastFieldReader;
 pub use self::readers::FastFieldReaders;
 pub use self::serializer::FastFieldSerializer;
 pub use self::writer::{FastFieldsWriter, IntFastFieldWriter};
-use crate::chrono::{NaiveDateTime, Utc};
 use crate::common;
 use crate::schema::Cardinality;
 use crate::schema::FieldType;
 use crate::schema::Value;
+use crate::{
+    chrono::{NaiveDateTime, Utc},
+    schema::Type,
+};
 
 mod bytes;
 mod delete;
@@ -76,6 +79,9 @@ pub trait FastValue: Clone + Copy + Send + Sync + PartialOrd {
     fn make_zero() -> Self {
         Self::from_u64(0i64.to_u64())
     }
+
+    /// Returns the `schema::Type` for this FastValue.
+    fn to_type() -> Type;
 }
 
 impl FastValue for u64 {
@@ -98,6 +104,10 @@ impl FastValue for u64 {
     fn as_u64(&self) -> u64 {
         *self
     }
+
+    fn to_type() -> Type {
+        Type::U64
+    }
 }
 
 impl FastValue for i64 {
@@ -119,6 +129,10 @@ impl FastValue for i64 {
     fn as_u64(&self) -> u64 {
         *self as u64
     }
+
+    fn to_type() -> Type {
+        Type::I64
+    }
 }
 
 impl FastValue for f64 {
@@ -140,6 +154,10 @@ impl FastValue for f64 {
     fn as_u64(&self) -> u64 {
         self.to_bits()
     }
+
+    fn to_type() -> Type {
+        Type::F64
+    }
 }
 
 impl FastValue for crate::DateTime {
@@ -162,6 +180,10 @@ impl FastValue for crate::DateTime {
     fn as_u64(&self) -> u64 {
         self.timestamp().as_u64()
     }
+
+    fn to_type() -> Type {
+        Type::Date
+    }
 }
 
 fn value_to_u64(value: &Value) -> u64 {
@@ -187,6 +209,7 @@ mod tests {
     use crate::schema::FAST;
     use crate::schema::{Document, IntOptions};
     use crate::{Index, SegmentId, SegmentReader};
+    use common::HasLen;
     use once_cell::sync::Lazy;
     use rand::prelude::SliceRandom;
     use rand::rngs::StdRng;
@@ -217,9 +240,9 @@ mod tests {
     }
 
     #[test]
-    fn test_intfastfield_small() {
+    fn test_intfastfield_small() -> crate::Result<()> {
         let path = Path::new("test");
-        let mut directory: RAMDirectory = RAMDirectory::create();
+        let directory: RAMDirectory = RAMDirectory::create();
         {
             let write: WritePtr = directory.open_write(Path::new("test")).unwrap();
             let mut serializer = FastFieldSerializer::from_write(write).unwrap();
@@ -232,27 +255,24 @@ mod tests {
                 .unwrap();
             serializer.close().unwrap();
         }
-        let source = directory.open_read(&path).unwrap();
+        let file = directory.open_read(&path).unwrap();
-        {
+        assert_eq!(file.len(), 36 as usize);
-            assert_eq!(source.len(), 36 as usize);
+        let composite_file = CompositeFile::open(&file)?;
-        }
+        let file = composite_file.open_read(*FIELD).unwrap();
-        {
+        let fast_field_reader = FastFieldReader::<u64>::open(file)?;
-            let composite_file = CompositeFile::open(&source).unwrap();
+        assert_eq!(fast_field_reader.get(0), 13u64);
-            let field_source = composite_file.open_read(*FIELD).unwrap();
+        assert_eq!(fast_field_reader.get(1), 14u64);
-            let fast_field_reader = FastFieldReader::<u64>::open(field_source);
+        assert_eq!(fast_field_reader.get(2), 2u64);
-            assert_eq!(fast_field_reader.get(0), 13u64);
+        Ok(())
-            assert_eq!(fast_field_reader.get(1), 14u64);
-            assert_eq!(fast_field_reader.get(2), 2u64);
-        }
     }
 
     #[test]
-    fn test_intfastfield_large() {
+    fn test_intfastfield_large() -> crate::Result<()> {
         let path = Path::new("test");
-        let mut directory: RAMDirectory = RAMDirectory::create();
+        let directory: RAMDirectory = RAMDirectory::create();
         {
-            let write: WritePtr = directory.open_write(Path::new("test")).unwrap();
+            let write: WritePtr = directory.open_write(Path::new("test"))?;
-            let mut serializer = FastFieldSerializer::from_write(write).unwrap();
+            let mut serializer = FastFieldSerializer::from_write(write)?;
             let mut fast_field_writers = FastFieldsWriter::from_schema(&SCHEMA);
             fast_field_writers.add_document(&doc!(*FIELD=>4u64));
             fast_field_writers.add_document(&doc!(*FIELD=>14_082_001u64));
@@ -263,19 +283,15 @@ mod tests {
             fast_field_writers.add_document(&doc!(*FIELD=>1_002u64));
             fast_field_writers.add_document(&doc!(*FIELD=>1_501u64));
             fast_field_writers.add_document(&doc!(*FIELD=>215u64));
-            fast_field_writers
+            fast_field_writers.serialize(&mut serializer, &HashMap::new())?;
-                .serialize(&mut serializer, &HashMap::new())
+            serializer.close()?;
-                .unwrap();
-            serializer.close().unwrap();
         }
-        let source = directory.open_read(&path).unwrap();
+        let file = directory.open_read(&path)?;
+        assert_eq!(file.len(), 61 as usize);
         {
-            assert_eq!(source.len(), 61 as usize);
+            let fast_fields_composite = CompositeFile::open(&file)?;
-        }
-        {
-            let fast_fields_composite = CompositeFile::open(&source).unwrap();
             let data = fast_fields_composite.open_read(*FIELD).unwrap();
-            let fast_field_reader = FastFieldReader::<u64>::open(data);
+            let fast_field_reader = FastFieldReader::<u64>::open(data)?;
             assert_eq!(fast_field_reader.get(0), 4u64);
             assert_eq!(fast_field_reader.get(1), 14_082_001u64);
             assert_eq!(fast_field_reader.get(2), 3_052u64);
@@ -286,12 +302,13 @@ mod tests {
             assert_eq!(fast_field_reader.get(7), 1_501u64);
             assert_eq!(fast_field_reader.get(8), 215u64);
         }
+        Ok(())
     }
 
     #[test]
-    fn test_intfastfield_null_amplitude() {
+    fn test_intfastfield_null_amplitude() -> crate::Result<()> {
         let path = Path::new("test");
-        let mut directory: RAMDirectory = RAMDirectory::create();
+        let directory: RAMDirectory = RAMDirectory::create();
 
         {
             let write: WritePtr = directory.open_write(Path::new("test")).unwrap();
@@ -305,24 +322,23 @@ mod tests {
                 .unwrap();
             serializer.close().unwrap();
         }
-        let source = directory.open_read(&path).unwrap();
+        let file = directory.open_read(&path).unwrap();
+        assert_eq!(file.len(), 34 as usize);
         {
-            assert_eq!(source.len(), 34 as usize);
+            let fast_fields_composite = CompositeFile::open(&file).unwrap();
-        }
-        {
-            let fast_fields_composite = CompositeFile::open(&source).unwrap();
             let data = fast_fields_composite.open_read(*FIELD).unwrap();
-            let fast_field_reader = FastFieldReader::<u64>::open(data);
+            let fast_field_reader = FastFieldReader::<u64>::open(data)?;
             for doc in 0..10_000 {
                 assert_eq!(fast_field_reader.get(doc), 100_000u64);
             }
         }
+        Ok(())
     }
 
     #[test]
-    fn test_intfastfield_large_numbers() {
+    fn test_intfastfield_large_numbers() -> crate::Result<()> {
         let path = Path::new("test");
-        let mut directory: RAMDirectory = RAMDirectory::create();
+        let directory: RAMDirectory = RAMDirectory::create();
 
         {
             let write: WritePtr = directory.open_write(Path::new("test")).unwrap();
@@ -338,14 +354,12 @@ mod tests {
                 .unwrap();
             serializer.close().unwrap();
         }
-        let source = directory.open_read(&path).unwrap();
+        let file = directory.open_read(&path).unwrap();
+        assert_eq!(file.len(), 80042 as usize);
         {
-            assert_eq!(source.len(), 80042 as usize);
+            let fast_fields_composite = CompositeFile::open(&file)?;
-        }
-        {
-            let fast_fields_composite = CompositeFile::open(&source).unwrap();
             let data = fast_fields_composite.open_read(*FIELD).unwrap();
-            let fast_field_reader = FastFieldReader::<u64>::open(data);
+            let fast_field_reader = FastFieldReader::<u64>::open(data)?;
             assert_eq!(fast_field_reader.get(0), 0u64);
             for doc in 1..10_001 {
                 assert_eq!(
@@ -354,12 +368,13 @@ mod tests {
                 );
             }
         }
+        Ok(())
     }
 
     #[test]
-    fn test_signed_intfastfield() {
+    fn test_signed_intfastfield() -> crate::Result<()> {
         let path = Path::new("test");
-        let mut directory: RAMDirectory = RAMDirectory::create();
+        let directory: RAMDirectory = RAMDirectory::create();
         let mut schema_builder = Schema::builder();
 
         let i64_field = schema_builder.add_i64_field("field", FAST);
@@ -378,14 +393,12 @@ mod tests {
                 .unwrap();
             serializer.close().unwrap();
         }
-        let source = directory.open_read(&path).unwrap();
+        let file = directory.open_read(&path).unwrap();
+        assert_eq!(file.len(), 17709 as usize);
         {
-            assert_eq!(source.len(), 17709 as usize);
+            let fast_fields_composite = CompositeFile::open(&file)?;
-        }
-        {
-            let fast_fields_composite = CompositeFile::open(&source).unwrap();
             let data = fast_fields_composite.open_read(i64_field).unwrap();
-            let fast_field_reader = FastFieldReader::<i64>::open(data);
+            let fast_field_reader = FastFieldReader::<i64>::open(data)?;
 
             assert_eq!(fast_field_reader.min_value(), -100i64);
             assert_eq!(fast_field_reader.max_value(), 9_999i64);
@@ -398,12 +411,13 @@ mod tests {
                 assert_eq!(buffer[i], -100i64 + 53i64 + i as i64);
             }
         }
+        Ok(())
     }
 
     #[test]
-    fn test_signed_intfastfield_default_val() {
+    fn test_signed_intfastfield_default_val() -> crate::Result<()> {
         let path = Path::new("test");
-        let mut directory: RAMDirectory = RAMDirectory::create();
+        let directory: RAMDirectory = RAMDirectory::create();
         let mut schema_builder = Schema::builder();
         let i64_field = schema_builder.add_i64_field("field", FAST);
         let schema = schema_builder.build();
@@ -420,13 +434,14 @@ mod tests {
             serializer.close().unwrap();
         }
 
-        let source = directory.open_read(&path).unwrap();
+        let file = directory.open_read(&path).unwrap();
         {
-            let fast_fields_composite = CompositeFile::open(&source).unwrap();
+            let fast_fields_composite = CompositeFile::open(&file).unwrap();
             let data = fast_fields_composite.open_read(i64_field).unwrap();
-            let fast_field_reader = FastFieldReader::<i64>::open(data);
+            let fast_field_reader = FastFieldReader::<i64>::open(data)?;
             assert_eq!(fast_field_reader.get(0u32), 0i64);
         }
+        Ok(())
     }
 
     // Warning: this generates the same permutation at each call
@@ -437,28 +452,26 @@ mod tests {
     }
 
     #[test]
-    fn test_intfastfield_permutation() {
+    fn test_intfastfield_permutation() -> crate::Result<()> {
         let path = Path::new("test");
         let permutation = generate_permutation();
         let n = permutation.len();
-        let mut directory = RAMDirectory::create();
+        let directory = RAMDirectory::create();
         {
-            let write: WritePtr = directory.open_write(Path::new("test")).unwrap();
+            let write: WritePtr = directory.open_write(Path::new("test"))?;
-            let mut serializer = FastFieldSerializer::from_write(write).unwrap();
+            let mut serializer = FastFieldSerializer::from_write(write)?;
             let mut fast_field_writers = FastFieldsWriter::from_schema(&SCHEMA);
             for &x in &permutation {
                 fast_field_writers.add_document(&doc!(*FIELD=>x));
             }
-            fast_field_writers
+            fast_field_writers.serialize(&mut serializer, &HashMap::new())?;
-                .serialize(&mut serializer, &HashMap::new())
+            serializer.close()?;
-                .unwrap();
-            serializer.close().unwrap();
         }
-        let source = directory.open_read(&path).unwrap();
+        let file = directory.open_read(&path)?;
         {
-            let fast_fields_composite = CompositeFile::open(&source).unwrap();
+            let fast_fields_composite = CompositeFile::open(&file)?;
             let data = fast_fields_composite.open_read(*FIELD).unwrap();
-            let fast_field_reader = FastFieldReader::<u64>::open(data);
+            let fast_field_reader = FastFieldReader::<u64>::open(data)?;
 
             let mut a = 0u64;
             for _ in 0..n {
@@ -466,6 +479,7 @@ mod tests {
                 a = fast_field_reader.get(a as u32);
             }
         }
+        Ok(())
     }
 
     #[test]
@@ -474,7 +488,7 @@ mod tests {
         let date_field = schema_builder.add_date_field("date", FAST);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests().unwrap();
         index_writer.set_merge_policy(Box::new(NoMergePolicy));
         index_writer.add_document(doc!(date_field =>crate::chrono::prelude::Utc::now()));
         index_writer.commit().unwrap();
@@ -511,7 +525,7 @@ mod tests {
         );
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests().unwrap();
         index_writer.set_merge_policy(Box::new(NoMergePolicy));
         index_writer.add_document(doc!(
             date_field => crate::DateTime::from_u64(1i64.to_u64()),
@@ -598,7 +612,7 @@ mod bench {
     fn bench_intfastfield_linear_fflookup(b: &mut Bencher) {
         let path = Path::new("test");
         let permutation = generate_permutation();
-        let mut directory: RAMDirectory = RAMDirectory::create();
+        let directory: RAMDirectory = RAMDirectory::create();
         {
             let write: WritePtr = directory.open_write(Path::new("test")).unwrap();
             let mut serializer = FastFieldSerializer::from_write(write).unwrap();
@@ -611,9 +625,9 @@ mod bench {
                 .unwrap();
             serializer.close().unwrap();
         }
-        let source = directory.open_read(&path).unwrap();
+        let file = directory.open_read(&path).unwrap();
         {
-            let fast_fields_composite = CompositeFile::open(&source).unwrap();
+            let fast_fields_composite = CompositeFile::open(&file).unwrap();
             let data = fast_fields_composite.open_read(*FIELD).unwrap();
             let fast_field_reader = FastFieldReader::<u64>::open(data);
 
@@ -632,7 +646,7 @@ mod bench {
     fn bench_intfastfield_fflookup(b: &mut Bencher) {
         let path = Path::new("test");
         let permutation = generate_permutation();
-        let mut directory: RAMDirectory = RAMDirectory::create();
+        let directory: RAMDirectory = RAMDirectory::create();
         {
             let write: WritePtr = directory.open_write(Path::new("test")).unwrap();
             let mut serializer = FastFieldSerializer::from_write(write).unwrap();
@@ -645,9 +659,9 @@ mod bench {
                 .unwrap();
             serializer.close().unwrap();
         }
-        let source = directory.open_read(&path).unwrap();
+        let file = directory.open_read(&path).unwrap();
         {
-            let fast_fields_composite = CompositeFile::open(&source).unwrap();
+            let fast_fields_composite = CompositeFile::open(&file).unwrap();
             let data = fast_fields_composite.open_read(*FIELD).unwrap();
             let fast_field_reader = FastFieldReader::<u64>::open(data);
 

src/fastfield/multivalued/mod.rs

@@ -25,7 +25,7 @@ mod tests {
         );
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests().unwrap();
         index_writer.add_document(doc!(field=>1u64, field=>3u64));
         index_writer.add_document(doc!());
         index_writer.add_document(doc!(field=>4u64));
@@ -64,7 +64,7 @@ mod tests {
             schema_builder.add_i64_field("time_stamp_i", IntOptions::default().set_stored());
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests().unwrap();
         let first_time_stamp = chrono::Utc::now();
         index_writer.add_document(
             doc!(date_field=>first_time_stamp, date_field=>first_time_stamp, time_i=>1i64),
@@ -100,6 +100,7 @@ mod tests {
                         .get_first(date_field)
                         .expect("cannot find value")
                         .date_value()
+                        .unwrap()
                         .timestamp(),
                     first_time_stamp.timestamp()
                 );
@@ -108,7 +109,7 @@ mod tests {
                         .get_first(time_i)
                         .expect("cannot find value")
                         .i64_value(),
-                    1i64
+                    Some(1i64)
                 );
             }
         }
@@ -131,6 +132,7 @@ mod tests {
                         .get_first(date_field)
                         .expect("cannot find value")
                         .date_value()
+                        .unwrap()
                         .timestamp(),
                     two_secs_ahead.timestamp()
                 );
@@ -139,7 +141,7 @@ mod tests {
                         .get_first(time_i)
                         .expect("cannot find value")
                         .i64_value(),
-                    3i64
+                    Some(3i64)
                 );
             }
         }
@@ -186,7 +188,7 @@ mod tests {
         );
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests().unwrap();
         index_writer.add_document(doc!(field=> 1i64, field => 3i64));
         index_writer.add_document(doc!());
         index_writer.add_document(doc!(field=> -4i64));
@@ -197,22 +199,14 @@ mod tests {
         let segment_reader = searcher.segment_reader(0);
         let mut vals = Vec::new();
         let multi_value_reader = segment_reader.fast_fields().i64s(field).unwrap();
-        {
+        multi_value_reader.get_vals(2, &mut vals);
-            multi_value_reader.get_vals(2, &mut vals);
+        assert_eq!(&vals, &[-4i64]);
-            assert_eq!(&vals, &[-4i64]);
+        multi_value_reader.get_vals(0, &mut vals);
-        }
+        assert_eq!(&vals, &[1i64, 3i64]);
-        {
+        multi_value_reader.get_vals(1, &mut vals);
-            multi_value_reader.get_vals(0, &mut vals);
+        assert!(vals.is_empty());
-            assert_eq!(&vals, &[1i64, 3i64]);
+        multi_value_reader.get_vals(3, &mut vals);
-        }
+        assert_eq!(&vals, &[-5i64, -20i64, 1i64]);
-        {
-            multi_value_reader.get_vals(1, &mut vals);
-            assert!(vals.is_empty());
-        }
-        {
-            multi_value_reader.get_vals(3, &mut vals);
-            assert_eq!(&vals, &[-5i64, -20i64, 1i64]);
-        }
     }
     #[test]
     #[ignore]
@@ -221,7 +215,7 @@ mod tests {
         let field = schema_builder.add_facet_field("facetfield");
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests().unwrap();
         for i in 0..100_000 {
             index_writer.add_document(doc!(field=> Facet::from(format!("/lang/{}", i).as_str())));
         }

src/fastfield/multivalued/reader.rs

@@ -74,7 +74,7 @@ mod tests {
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
         let mut index_writer = index
-            .writer_with_num_threads(1, 30_000_000)
+            .writer_for_tests()
             .expect("Failed to create index writer.");
         index_writer.add_document(doc!(
             facet_field => Facet::from("/category/cat2"),

src/fastfield/multivalued/writer.rs

@@ -143,7 +143,7 @@ impl MultiValueIntFastFieldWriter {
                             .iter()
                             .map(|val| *mapping.get(val).expect("Missing term ordinal"));
                         doc_vals.extend(remapped_vals);
-                        doc_vals.sort();
+                        doc_vals.sort_unstable();
                         for &val in &doc_vals {
                             value_serializer.add_val(val)?;
                         }

src/fastfield/reader.rs

@@ -3,13 +3,12 @@ use crate::common::bitpacker::BitUnpacker;
 use crate::common::compute_num_bits;
 use crate::common::BinarySerializable;
 use crate::common::CompositeFile;
-use crate::directory::ReadOnlySource;
+use crate::directory::FileSlice;
 use crate::directory::{Directory, RAMDirectory, WritePtr};
 use crate::fastfield::{FastFieldSerializer, FastFieldsWriter};
 use crate::schema::Schema;
 use crate::schema::FAST;
 use crate::DocId;
-use owning_ref::OwningRef;
 use std::collections::HashMap;
 use std::marker::PhantomData;
 use std::path::Path;
@@ -20,34 +19,27 @@ use std::path::Path;
 /// fast field is required.
 #[derive(Clone)]
 pub struct FastFieldReader<Item: FastValue> {
-    bit_unpacker: BitUnpacker<OwningRef<ReadOnlySource, [u8]>>,
+    bit_unpacker: BitUnpacker,
     min_value_u64: u64,
     max_value_u64: u64,
     _phantom: PhantomData<Item>,
 }
 
 impl<Item: FastValue> FastFieldReader<Item> {
-    /// Opens a fast field given a source.
+    /// Opens a fast field given a file.
-    pub fn open(data: ReadOnlySource) -> Self {
+    pub fn open(file: FileSlice) -> crate::Result<Self> {
-        let min_value: u64;
+        let mut bytes = file.read_bytes()?;
-        let amplitude: u64;
+        let min_value = u64::deserialize(&mut bytes)?;
-        {
+        let amplitude = u64::deserialize(&mut bytes)?;
-            let mut cursor = data.as_slice();
-            min_value =
-                u64::deserialize(&mut cursor).expect("Failed to read the min_value of fast field.");
-            amplitude =
-                u64::deserialize(&mut cursor).expect("Failed to read the amplitude of fast field.");
-        }
         let max_value = min_value + amplitude;
         let num_bits = compute_num_bits(amplitude);
-        let owning_ref = OwningRef::new(data).map(|data| &data[16..]);
+        let bit_unpacker = BitUnpacker::new(bytes, num_bits);
-        let bit_unpacker = BitUnpacker::new(owning_ref, num_bits);
+        Ok(FastFieldReader {
-        FastFieldReader {
             min_value_u64: min_value,
             max_value_u64: max_value,
             bit_unpacker,
             _phantom: PhantomData,
-        }
+        })
     }
 
     pub(crate) fn into_u64_reader(self) -> FastFieldReader<u64> {
@@ -135,7 +127,7 @@ impl<Item: FastValue> From<Vec<Item>> for FastFieldReader<Item> {
         let field = schema_builder.add_u64_field("field", FAST);
         let schema = schema_builder.build();
         let path = Path::new("__dummy__");
-        let mut directory: RAMDirectory = RAMDirectory::create();
+        let directory: RAMDirectory = RAMDirectory::create();
         {
             let write: WritePtr = directory
                 .open_write(path)
@@ -157,12 +149,11 @@ impl<Item: FastValue> From<Vec<Item>> for FastFieldReader<Item> {
             serializer.close().unwrap();
         }
 
-        let source = directory.open_read(path).expect("Failed to open the file");
+        let file = directory.open_read(path).expect("Failed to open the file");
-        let composite_file =
+        let composite_file = CompositeFile::open(&file).expect("Failed to read the composite file");
-            CompositeFile::open(&source).expect("Failed to read the composite file");
+        let field_file = composite_file
-        let field_source = composite_file
             .open_read(field)
             .expect("File component not found");
-        FastFieldReader::open(field_source)
+        FastFieldReader::open(field_file).unwrap()
     }
 }

src/fastfield/readers.rs

@@ -68,45 +68,52 @@ impl FastFieldReaders {
         };
         for (field, field_entry) in schema.fields() {
             let field_type = field_entry.field_type();
-            if field_type == &FieldType::Bytes {
+            if let FieldType::Bytes(bytes_option) = field_type {
-                let idx_reader = fast_fields_composite
+                if !bytes_option.is_fast() {
+                    continue;
+                }
+                let fast_field_idx_file = fast_fields_composite
                     .open_read_with_idx(field, 0)
-                    .ok_or_else(|| FastFieldNotAvailableError::new(field_entry))
+                    .ok_or_else(|| FastFieldNotAvailableError::new(field_entry))?;
-                    .map(FastFieldReader::open)?;
+                let idx_reader = FastFieldReader::open(fast_field_idx_file)?;
                 let data = fast_fields_composite
                     .open_read_with_idx(field, 1)
                     .ok_or_else(|| FastFieldNotAvailableError::new(field_entry))?;
+                let bytes_fast_field_reader = BytesFastFieldReader::open(idx_reader, data)?;
                 fast_field_readers
                     .fast_bytes
-                    .insert(field, BytesFastFieldReader::open(idx_reader, data));
+                    .insert(field, bytes_fast_field_reader);
             } else if let Some((fast_type, cardinality)) = type_and_cardinality(field_type) {
                 match cardinality {
                     Cardinality::SingleValue => {
                         if let Some(fast_field_data) = fast_fields_composite.open_read(field) {
                             match fast_type {
                                 FastType::U64 => {
-                                    let fast_field_reader = FastFieldReader::open(fast_field_data);
+                                    let fast_field_reader = FastFieldReader::open(fast_field_data)?;
                                     fast_field_readers
                                         .fast_field_u64
                                         .insert(field, fast_field_reader);
                                 }
                                 FastType::I64 => {
-                                    fast_field_readers.fast_field_i64.insert(
+                                    let fast_field_reader =
-                                        field,
+                                        FastFieldReader::open(fast_field_data.clone())?;
-                                        FastFieldReader::open(fast_field_data.clone()),
+                                    fast_field_readers
-                                    );
+                                        .fast_field_i64
+                                        .insert(field, fast_field_reader);
                                 }
                                 FastType::F64 => {
-                                    fast_field_readers.fast_field_f64.insert(
+                                    let fast_field_reader =
-                                        field,
+                                        FastFieldReader::open(fast_field_data.clone())?;
-                                        FastFieldReader::open(fast_field_data.clone()),
+                                    fast_field_readers
-                                    );
+                                        .fast_field_f64
+                                        .insert(field, fast_field_reader);
                                 }
                                 FastType::Date => {
-                                    fast_field_readers.fast_field_date.insert(
+                                    let fast_field_reader =
-                                        field,
+                                        FastFieldReader::open(fast_field_data.clone())?;
-                                        FastFieldReader::open(fast_field_data.clone()),
+                                    fast_field_readers
-                                    );
+                                        .fast_field_date
+                                        .insert(field, fast_field_reader);
                                 }
                             }
                         } else {
@@ -117,10 +124,10 @@ impl FastFieldReaders {
                         let idx_opt = fast_fields_composite.open_read_with_idx(field, 0);
                         let data_opt = fast_fields_composite.open_read_with_idx(field, 1);
                         if let (Some(fast_field_idx), Some(fast_field_data)) = (idx_opt, data_opt) {
-                            let idx_reader = FastFieldReader::open(fast_field_idx);
+                            let idx_reader = FastFieldReader::open(fast_field_idx)?;
                             match fast_type {
                                 FastType::I64 => {
-                                    let vals_reader = FastFieldReader::open(fast_field_data);
+                                    let vals_reader = FastFieldReader::open(fast_field_data)?;
                                     let multivalued_int_fast_field =
                                         MultiValueIntFastFieldReader::open(idx_reader, vals_reader);
                                     fast_field_readers
@@ -128,7 +135,7 @@ impl FastFieldReaders {
                                         .insert(field, multivalued_int_fast_field);
                                 }
                                 FastType::U64 => {
-                                    let vals_reader = FastFieldReader::open(fast_field_data);
+                                    let vals_reader = FastFieldReader::open(fast_field_data)?;
                                     let multivalued_int_fast_field =
                                         MultiValueIntFastFieldReader::open(idx_reader, vals_reader);
                                     fast_field_readers
@@ -136,7 +143,7 @@ impl FastFieldReaders {
                                         .insert(field, multivalued_int_fast_field);
                                 }
                                 FastType::F64 => {
-                                    let vals_reader = FastFieldReader::open(fast_field_data);
+                                    let vals_reader = FastFieldReader::open(fast_field_data)?;
                                     let multivalued_int_fast_field =
                                         MultiValueIntFastFieldReader::open(idx_reader, vals_reader);
                                     fast_field_readers
@@ -144,7 +151,7 @@ impl FastFieldReaders {
                                         .insert(field, multivalued_int_fast_field);
                                 }
                                 FastType::Date => {
-                                    let vals_reader = FastFieldReader::open(fast_field_data);
+                                    let vals_reader = FastFieldReader::open(fast_field_data)?;
                                     let multivalued_int_fast_field =
                                         MultiValueIntFastFieldReader::open(idx_reader, vals_reader);
                                     fast_field_readers

src/fastfield/writer.rs

@@ -33,7 +33,7 @@ impl FastFieldsWriter {
         let mut bytes_value_writers = Vec::new();
 
         for (field, field_entry) in schema.fields() {
-            match *field_entry.field_type() {
+            match field_entry.field_type() {
                 FieldType::I64(ref int_options)
                 | FieldType::U64(ref int_options)
                 | FieldType::F64(ref int_options)
@@ -56,9 +56,11 @@ impl FastFieldsWriter {
                     let fast_field_writer = MultiValueIntFastFieldWriter::new(field, true);
                     multi_values_writers.push(fast_field_writer);
                 }
-                FieldType::Bytes => {
+                FieldType::Bytes(bytes_option) => {
-                    let fast_field_writer = BytesFastFieldWriter::new(field);
+                    if bytes_option.is_fast() {
-                    bytes_value_writers.push(fast_field_writer);
+                        let fast_field_writer = BytesFastFieldWriter::new(field);
+                        bytes_value_writers.push(fast_field_writer);
+                    }
                 }
                 _ => {}
             }
@@ -126,6 +128,7 @@ impl FastFieldsWriter {
         for field_writer in &self.single_value_writers {
             field_writer.serialize(serializer)?;
         }
+
         for field_writer in &self.multi_values_writers {
             let field = field_writer.field();
             field_writer.serialize(serializer, mapping.get(&field))?;

src/fieldnorm/mod.rs

@@ -21,7 +21,7 @@ mod reader;
 mod serializer;
 mod writer;
 
-pub use self::reader::FieldNormReader;
+pub use self::reader::{FieldNormReader, FieldNormReaders};
 pub use self::serializer::FieldNormsSerializer;
 pub use self::writer::FieldNormsWriter;
 

src/fieldnorm/reader.rs

@@ -1,6 +1,47 @@
 use super::{fieldnorm_to_id, id_to_fieldnorm};
-use crate::directory::ReadOnlySource;
+use crate::common::CompositeFile;
+use crate::directory::FileSlice;
+use crate::directory::OwnedBytes;
+use crate::schema::Field;
+use crate::space_usage::PerFieldSpaceUsage;
 use crate::DocId;
+use std::sync::Arc;
+
+/// Reader for the fieldnorm (for each document, the number of tokens indexed in the
+/// field) of all indexed fields in the index.
+///
+/// Each fieldnorm is approximately compressed over one byte. We refer to this byte as
+/// `fieldnorm_id`.
+/// The mapping from `fieldnorm` to `fieldnorm_id` is given by monotonic.
+#[derive(Clone)]
+pub struct FieldNormReaders {
+    data: Arc<CompositeFile>,
+}
+
+impl FieldNormReaders {
+    /// Creates a field norm reader.
+    pub fn open(file: FileSlice) -> crate::Result<FieldNormReaders> {
+        let data = CompositeFile::open(&file)?;
+        Ok(FieldNormReaders {
+            data: Arc::new(data),
+        })
+    }
+
+    /// Returns the FieldNormReader for a specific field.
+    pub fn get_field(&self, field: Field) -> crate::Result<Option<FieldNormReader>> {
+        if let Some(file) = self.data.open_read(field) {
+            let fieldnorm_reader = FieldNormReader::open(file)?;
+            Ok(Some(fieldnorm_reader))
+        } else {
+            Ok(None)
+        }
+    }
+
+    /// Return a break down of the space usage per field.
+    pub fn space_usage(&self) -> PerFieldSpaceUsage {
+        self.data.space_usage()
+    }
+}
 
 /// Reads the fieldnorm associated to a document.
 /// The fieldnorm represents the length associated to
@@ -8,7 +49,7 @@ use crate::DocId;
 ///
 /// This metric is important to compute the score of a
 /// document : a document having a query word in one its short fields
-/// (e.g. title)  is likely to be more relevant than in one of its longer field
+/// (e.g. title)is likely to be more relevant than in one of its longer field
 /// (e.g. body).
 ///
 /// tantivy encodes `fieldnorm` on one byte with some precision loss,
@@ -19,14 +60,32 @@ use crate::DocId;
 /// Apart from compression, this scale also makes it possible to
 /// precompute computationally expensive functions of the fieldnorm
 /// in a very short array.
-pub struct FieldNormReader {
+#[derive(Clone)]
-    data: ReadOnlySource,
+pub enum FieldNormReader {
+    ConstFieldNorm { fieldnorm_id: u8, num_docs: u32 },
+    OneByte(OwnedBytes),
 }
 
 impl FieldNormReader {
-    /// Opens a field norm reader given its data source.
+    pub fn const_fieldnorm_id(fieldnorm_id: u8, num_docs: u32) -> FieldNormReader {
-    pub fn open(data: ReadOnlySource) -> Self {
+        FieldNormReader::ConstFieldNorm {
-        FieldNormReader { data }
+            fieldnorm_id,
+            num_docs,
+        }
+    }
+
+    /// Opens a field norm reader given its file.
+    pub fn open(fieldnorm_file: FileSlice) -> crate::Result<Self> {
+        let data = fieldnorm_file.read_bytes()?;
+        Ok(FieldNormReader::OneByte(data))
+    }
+
+    /// Returns the number of documents in this segment.
+    pub fn num_docs(&self) -> u32 {
+        match self {
+            Self::ConstFieldNorm { num_docs, .. } => *num_docs,
+            FieldNormReader::OneByte(vals) => vals.len() as u32,
+        }
     }
 
     /// Returns the `fieldnorm` associated to a doc id.
@@ -38,6 +97,7 @@ impl FieldNormReader {
     ///
     /// The fieldnorm is effectively decoded from the
     /// `fieldnorm_id` by doing a simple table lookup.
+    #[inline(always)]
     pub fn fieldnorm(&self, doc_id: DocId) -> u32 {
         let fieldnorm_id = self.fieldnorm_id(doc_id);
         id_to_fieldnorm(fieldnorm_id)
@@ -46,8 +106,11 @@ impl FieldNormReader {
     /// Returns the `fieldnorm_id` associated to a document.
     #[inline(always)]
     pub fn fieldnorm_id(&self, doc_id: DocId) -> u8 {
-        let fielnorms_data = self.data.as_slice();
+        match self {
-        fielnorms_data[doc_id as usize]
+            FieldNormReader::ConstFieldNorm { fieldnorm_id, .. } => *fieldnorm_id,
+
+            FieldNormReader::OneByte(data) => data.as_slice()[doc_id as usize],
+        }
     }
 
     /// Converts a `fieldnorm_id` into a fieldnorm.
@@ -62,18 +125,32 @@ impl FieldNormReader {
     pub fn fieldnorm_to_id(fieldnorm: u32) -> u8 {
         fieldnorm_to_id(fieldnorm)
     }
+
+    #[cfg(test)]
+    pub fn for_test(field_norms: &[u32]) -> FieldNormReader {
+        let field_norms_id = field_norms
+            .iter()
+            .cloned()
+            .map(FieldNormReader::fieldnorm_to_id)
+            .collect::<Vec<u8>>();
+        let field_norms_data = OwnedBytes::new(field_norms_id);
+        FieldNormReader::OneByte(field_norms_data)
+    }
 }
 
 #[cfg(test)]
-impl From<Vec<u32>> for FieldNormReader {
+mod tests {
-    fn from(field_norms: Vec<u32>) -> FieldNormReader {
+    use crate::fieldnorm::FieldNormReader;
-        let field_norms_id = field_norms
+
-            .into_iter()
+    #[test]
-            .map(FieldNormReader::fieldnorm_to_id)
+    fn test_from_fieldnorms_array() {
-            .collect::<Vec<u8>>();
+        let fieldnorms = &[1, 2, 3, 4, 1_000_000];
-        let field_norms_data = ReadOnlySource::from(field_norms_id);
+        let fieldnorm_reader = FieldNormReader::for_test(fieldnorms);
-        FieldNormReader {
+        assert_eq!(fieldnorm_reader.num_docs(), 5);
-            data: field_norms_data,
+        assert_eq!(fieldnorm_reader.fieldnorm(0), 1);
-        }
+        assert_eq!(fieldnorm_reader.fieldnorm(1), 2);
+        assert_eq!(fieldnorm_reader.fieldnorm(2), 3);
+        assert_eq!(fieldnorm_reader.fieldnorm(3), 4);
+        assert_eq!(fieldnorm_reader.fieldnorm(4), 983_064);
     }
 }

src/fieldnorm/writer.rs

@@ -13,7 +13,7 @@ use std::io;
 /// byte per document per field.
 pub struct FieldNormsWriter {
     fields: Vec<Field>,
-    fieldnorms_buffer: Vec<Vec<u8>>,
+    fieldnorms_buffer: Vec<Option<Vec<u8>>>,
 }
 
 impl FieldNormsWriter {
@@ -23,7 +23,7 @@ impl FieldNormsWriter {
         schema
             .fields()
             .filter_map(|(field, field_entry)| {
-                if field_entry.is_indexed() {
+                if field_entry.has_fieldnorms() {
                     Some(field)
                 } else {
                     None
@@ -36,15 +36,14 @@ impl FieldNormsWriter {
     /// specified in the schema.
     pub fn for_schema(schema: &Schema) -> FieldNormsWriter {
         let fields = FieldNormsWriter::fields_with_fieldnorm(schema);
-        let max_field = fields
+        let num_fields = schema.num_fields();
-            .iter()
+        let mut fieldnorms_buffer: Vec<Option<Vec<u8>>> = vec![None; num_fields];
-            .map(Field::field_id)
+        for field in &fields {
-            .max()
+            fieldnorms_buffer[field.field_id() as usize] = Some(Vec::new());
-            .map(|max_field_id| max_field_id as usize + 1)
+        }
-            .unwrap_or(0);
         FieldNormsWriter {
             fields,
-            fieldnorms_buffer: (0..max_field).map(|_| Vec::new()).collect::<Vec<_>>(),
+            fieldnorms_buffer,
         }
     }
 
@@ -53,8 +52,10 @@ impl FieldNormsWriter {
     ///
     /// Will extend with 0-bytes for documents that have not been seen.
     pub fn fill_up_to_max_doc(&mut self, max_doc: DocId) {
-        for field in self.fields.iter() {
+        for buffer_opt in self.fieldnorms_buffer.iter_mut() {
-            self.fieldnorms_buffer[field.field_id() as usize].resize(max_doc as usize, 0u8);
+            if let Some(buffer) = buffer_opt {
+                buffer.resize(max_doc as usize, 0u8);
+            }
         }
     }
 
@@ -67,22 +68,24 @@ impl FieldNormsWriter {
     /// * field     - the field being set
     /// * fieldnorm - the number of terms present in document `doc` in field `field`
     pub fn record(&mut self, doc: DocId, field: Field, fieldnorm: u32) {
-        let fieldnorm_buffer: &mut Vec<u8> = &mut self.fieldnorms_buffer[field.field_id() as usize];
+        if let Some(fieldnorm_buffer) = self.fieldnorms_buffer[field.field_id() as usize].as_mut() {
-        assert!(
+            assert!(
-            fieldnorm_buffer.len() <= doc as usize,
+                fieldnorm_buffer.len() <= doc as usize,
-            "Cannot register a given fieldnorm twice"
+                "Cannot register a given fieldnorm twice" // we fill intermediary `DocId` as  having a fieldnorm of 0.
-        );
+            );
-        // we fill intermediary `DocId` as  having a fieldnorm of 0.
+            fieldnorm_buffer.resize(doc as usize + 1, 0u8);
-        fieldnorm_buffer.resize(doc as usize + 1, 0u8);
+            fieldnorm_buffer[doc as usize] = fieldnorm_to_id(fieldnorm);
-        fieldnorm_buffer[doc as usize] = fieldnorm_to_id(fieldnorm);
+        }
     }
 
     /// Serialize the seen fieldnorm values to the serializer for all fields.
-    pub fn serialize(&self, fieldnorms_serializer: &mut FieldNormsSerializer) -> io::Result<()> {
+    pub fn serialize(&self, mut fieldnorms_serializer: FieldNormsSerializer) -> io::Result<()> {
         for &field in self.fields.iter() {
-            let fieldnorm_values: &[u8] = &self.fieldnorms_buffer[field.field_id() as usize][..];
+            if let Some(buffer) = self.fieldnorms_buffer[field.field_id() as usize].as_ref() {
-            fieldnorms_serializer.serialize_field(field, fieldnorm_values)?;
+                fieldnorms_serializer.serialize_field(field, &buffer[..])?;
+            }
         }
+        fieldnorms_serializer.close()?;
         Ok(())
     }
 }

src/indexer/index_writer.rs

@@ -108,9 +108,9 @@ fn compute_deleted_bitset(
         // Limit doc helps identify the first document
         // that may be affected by the delete operation.
         let limit_doc = doc_opstamps.compute_doc_limit(delete_op.opstamp);
-        let inverted_index = segment_reader.inverted_index(delete_op.term.field());
+        let inverted_index = segment_reader.inverted_index(delete_op.term.field())?;
         if let Some(mut docset) =
-            inverted_index.read_postings(&delete_op.term, IndexRecordOption::Basic)
+            inverted_index.read_postings(&delete_op.term, IndexRecordOption::Basic)?
         {
             let mut deleted_doc = docset.doc();
             while deleted_doc != TERMINATED {
@@ -536,6 +536,7 @@ impl IndexWriter {
     /// when no documents are remaining.
     ///
     /// Returns the former segment_ready channel.
+    #[allow(unused_must_use)]
     fn recreate_document_channel(&mut self) -> OperationReceiver {
         let (document_sender, document_receiver): (OperationSender, OperationReceiver) =
             channel::bounded(PIPELINE_MAX_SIZE_IN_DOCS);
@@ -575,7 +576,7 @@ impl IndexWriter {
         //
         // This will drop the document queue, and the thread
         // should terminate.
-        mem::replace(self, new_index_writer);
+        *self = new_index_writer;
 
         // Drains the document receiver pipeline :
         // Workers don't need to index the pending documents.
@@ -799,7 +800,7 @@ mod tests {
         let mut schema_builder = schema::Schema::builder();
         let text_field = schema_builder.add_text_field("text", schema::TEXT);
         let index = Index::create_in_ram(schema_builder.build());
-        let index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let index_writer = index.writer_for_tests().unwrap();
         let operations = vec![
             UserOperation::Add(doc!(text_field=>"a")),
             UserOperation::Add(doc!(text_field=>"b")),
@@ -814,7 +815,7 @@ mod tests {
         let text_field = schema_builder.add_text_field("text", schema::TEXT);
         let index = Index::create_in_ram(schema_builder.build());
 
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests().unwrap();
         index_writer.add_document(doc!(text_field => "hello1"));
         index_writer.add_document(doc!(text_field => "hello2"));
         assert!(index_writer.commit().is_ok());
@@ -863,7 +864,7 @@ mod tests {
             .reload_policy(ReloadPolicy::Manual)
             .try_into()
             .unwrap();
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests().unwrap();
         let a_term = Term::from_field_text(text_field, "a");
         let b_term = Term::from_field_text(text_field, "b");
         let operations = vec![
@@ -925,8 +926,8 @@ mod tests {
     fn test_lockfile_already_exists_error_msg() {
         let schema_builder = schema::Schema::builder();
         let index = Index::create_in_ram(schema_builder.build());
-        let _index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let _index_writer = index.writer_for_tests().unwrap();
-        match index.writer_with_num_threads(1, 3_000_000) {
+        match index.writer_for_tests() {
             Err(err) => {
                 let err_msg = err.to_string();
                 assert!(err_msg.contains("already an `IndexWriter`"));
@@ -978,7 +979,7 @@ mod tests {
         let num_docs_containing = |s: &str| {
             let searcher = reader.searcher();
             let term = Term::from_field_text(text_field, s);
-            searcher.doc_freq(&term)
+            searcher.doc_freq(&term).unwrap()
         };
 
         {
@@ -1014,7 +1015,7 @@ mod tests {
             .unwrap();
         let num_docs_containing = |s: &str| {
             let term_a = Term::from_field_text(text_field, s);
-            reader.searcher().doc_freq(&term_a)
+            reader.searcher().doc_freq(&term_a).unwrap()
         };
         {
             // writing the segment
@@ -1109,6 +1110,7 @@ mod tests {
                 .unwrap()
                 .searcher()
                 .doc_freq(&term_a)
+                .unwrap()
         };
         assert_eq!(num_docs_containing("a"), 0);
         assert_eq!(num_docs_containing("b"), 100);
@@ -1128,7 +1130,7 @@ mod tests {
             reader.reload().unwrap();
             let searcher = reader.searcher();
             let term = Term::from_field_text(text_field, s);
-            searcher.doc_freq(&term)
+            searcher.doc_freq(&term).unwrap()
         };
         let mut index_writer = index.writer_with_num_threads(4, 12_000_000).unwrap();
 
@@ -1179,7 +1181,15 @@ mod tests {
 
         // working with an empty index == no documents
         let term_b = Term::from_field_text(text_field, "b");
-        assert_eq!(index.reader().unwrap().searcher().doc_freq(&term_b), 0);
+        assert_eq!(
+            index
+                .reader()
+                .unwrap()
+                .searcher()
+                .doc_freq(&term_b)
+                .unwrap(),
+            0
+        );
     }
 
     #[test]
@@ -1199,7 +1209,15 @@ mod tests {
 
         let term_a = Term::from_field_text(text_field, "a");
         // expect the document with that term to be in the index
-        assert_eq!(index.reader().unwrap().searcher().doc_freq(&term_a), 1);
+        assert_eq!(
+            index
+                .reader()
+                .unwrap()
+                .searcher()
+                .doc_freq(&term_a)
+                .unwrap(),
+            1
+        );
     }
 
     #[test]
@@ -1225,7 +1243,15 @@ mod tests {
         // Find original docs in the index
         let term_a = Term::from_field_text(text_field, "a");
         // expect the document with that term to be in the index
-        assert_eq!(index.reader().unwrap().searcher().doc_freq(&term_a), 1);
+        assert_eq!(
+            index
+                .reader()
+                .unwrap()
+                .searcher()
+                .doc_freq(&term_a)
+                .unwrap(),
+            1
+        );
     }
 
     #[test]
@@ -1260,7 +1286,7 @@ mod tests {
         let idfield = schema_builder.add_text_field("id", STRING);
         schema_builder.add_text_field("optfield", STRING);
         let index = Index::create_in_ram(schema_builder.build());
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests().unwrap();
         index_writer.add_document(doc!(idfield=>"myid"));
         let commit = index_writer.commit();
         assert!(commit.is_ok());

src/indexer/mod.rs

@@ -29,8 +29,9 @@ pub use self::segment_writer::SegmentWriter;
 /// Alias for the default merge policy, which is the `LogMergePolicy`.
 pub type DefaultMergePolicy = LogMergePolicy;
 
+#[cfg(feature = "mmap")]
 #[cfg(test)]
-mod tests {
+mod tests_mmap {
     use crate::schema::{self, Schema};
     use crate::{Index, Term};
 
@@ -39,7 +40,7 @@ mod tests {
         let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", schema::TEXT);
         let index = Index::create_from_tempdir(schema_builder.build()).unwrap();
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests().unwrap();
         // there must be one deleted document in the segment
         index_writer.add_document(doc!(text_field=>"b"));
         index_writer.delete_term(Term::from_field_text(text_field, "b"));

src/indexer/segment_serializer.rs

@@ -8,15 +8,16 @@ use crate::store::StoreWriter;
 /// Segment serializer is in charge of laying out on disk
 /// the data accumulated and sorted by the `SegmentWriter`.
 pub struct SegmentSerializer {
+    segment: Segment,
     store_writer: StoreWriter,
     fast_field_serializer: FastFieldSerializer,
-    fieldnorms_serializer: FieldNormsSerializer,
+    fieldnorms_serializer: Option<FieldNormsSerializer>,
     postings_serializer: InvertedIndexSerializer,
 }
 
 impl SegmentSerializer {
     /// Creates a new `SegmentSerializer`.
-    pub fn for_segment(segment: &mut Segment) -> crate::Result<SegmentSerializer> {
+    pub fn for_segment(mut segment: Segment) -> crate::Result<SegmentSerializer> {
         let store_write = segment.open_write(SegmentComponent::STORE)?;
 
         let fast_field_write = segment.open_write(SegmentComponent::FASTFIELDS)?;
@@ -25,15 +26,20 @@ impl SegmentSerializer {
         let fieldnorms_write = segment.open_write(SegmentComponent::FIELDNORMS)?;
         let fieldnorms_serializer = FieldNormsSerializer::from_write(fieldnorms_write)?;
 
-        let postings_serializer = InvertedIndexSerializer::open(segment)?;
+        let postings_serializer = InvertedIndexSerializer::open(&mut segment)?;
         Ok(SegmentSerializer {
+            segment,
             store_writer: StoreWriter::new(store_write),
             fast_field_serializer,
-            fieldnorms_serializer,
+            fieldnorms_serializer: Some(fieldnorms_serializer),
             postings_serializer,
         })
     }
 
+    pub fn segment(&self) -> &Segment {
+        &self.segment
+    }
+
     /// Accessor to the `PostingsSerializer`.
     pub fn get_postings_serializer(&mut self) -> &mut InvertedIndexSerializer {
         &mut self.postings_serializer
@@ -44,9 +50,11 @@ impl SegmentSerializer {
         &mut self.fast_field_serializer
     }
 
-    /// Accessor to the field norm serializer.
+    /// Extract the field norm serializer.
-    pub fn get_fieldnorms_serializer(&mut self) -> &mut FieldNormsSerializer {
+    ///
-        &mut self.fieldnorms_serializer
+    /// Note the fieldnorms serializer can only be extracted once.
+    pub fn extract_fieldnorms_serializer(&mut self) -> Option<FieldNormsSerializer> {
+        self.fieldnorms_serializer.take()
     }
 
     /// Accessor to the `StoreWriter`.
@@ -55,11 +63,13 @@ impl SegmentSerializer {
     }
 
     /// Finalize the segment serialization.
-    pub fn close(self) -> crate::Result<()> {
+    pub fn close(mut self) -> crate::Result<()> {
+        if let Some(fieldnorms_serializer) = self.extract_fieldnorms_serializer() {
+            fieldnorms_serializer.close()?;
+        }
         self.fast_field_serializer.close()?;
         self.postings_serializer.close()?;
         self.store_writer.close()?;
-        self.fieldnorms_serializer.close()?;
         Ok(())
     }
 }

src/indexer/segment_updater.rs

@@ -43,7 +43,7 @@ const NUM_MERGE_THREADS: usize = 4;
 /// and flushed.
 ///
 /// This method is not part of tantivy's public API
-pub fn save_new_metas(schema: Schema, directory: &mut dyn Directory) -> crate::Result<()> {
+pub fn save_new_metas(schema: Schema, directory: &dyn Directory) -> crate::Result<()> {
     save_metas(
         &IndexMeta {
             segments: Vec::new(),
@@ -64,7 +64,7 @@ pub fn save_new_metas(schema: Schema, directory: &mut dyn Directory) -> crate::R
 /// and flushed.
 ///
 /// This method is not part of tantivy's public API
-fn save_metas(metas: &IndexMeta, directory: &mut dyn Directory) -> crate::Result<()> {
+fn save_metas(metas: &IndexMeta, directory: &dyn Directory) -> crate::Result<()> {
     info!("save metas");
     let mut buffer = serde_json::to_vec_pretty(metas)?;
     // Just adding a new line at the end of the buffer.
@@ -112,7 +112,7 @@ fn merge(
     target_opstamp: Opstamp,
 ) -> crate::Result<SegmentEntry> {
     // first we need to apply deletes to our segment.
-    let mut merged_segment = index.new_segment();
+    let merged_segment = index.new_segment();
 
     // First we apply all of the delet to the merged segment, up to the target opstamp.
     for segment_entry in &mut segment_entries {
@@ -131,12 +131,13 @@ fn merge(
     let merger: IndexMerger = IndexMerger::open(index.schema(), &segments[..])?;
 
     // ... we just serialize this index merger in our new segment to merge the two segments.
-    let segment_serializer = SegmentSerializer::for_segment(&mut merged_segment)?;
+    let segment_serializer = SegmentSerializer::for_segment(merged_segment.clone())?;
 
     let num_docs = merger.write(segment_serializer)?;
 
-    let segment_meta = index.new_segment_meta(merged_segment.id(), num_docs);
+    let merged_segment_id = merged_segment.id();
 
+    let segment_meta = index.new_segment_meta(merged_segment_id, num_docs);
     Ok(SegmentEntry::new(segment_meta, delete_cursor, None))
 }
 
@@ -449,9 +450,8 @@ impl SegmentUpdater {
             .into_iter()
             .map(|merge_candidate: MergeCandidate| {
                 MergeOperation::new(&self.merge_operations, commit_opstamp, merge_candidate.0)
-            })
+            });
-            .collect::<Vec<_>>();
+        merge_candidates.extend(committed_merge_candidates);
-        merge_candidates.extend(committed_merge_candidates.into_iter());
 
         for merge_operation in merge_candidates {
             if let Err(err) = self.start_merge(merge_operation) {
@@ -521,7 +521,7 @@ impl SegmentUpdater {
     ///
     /// Upon termination of the current merging threads,
     /// merge opportunity may appear.
-    //
+    ///
     /// We keep waiting until the merge policy judges that
     /// no opportunity is available.
     ///
@@ -554,7 +554,7 @@ mod tests {
         let index = Index::create_in_ram(schema);
 
         // writing the segment
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests().unwrap();
         index_writer.set_merge_policy(Box::new(MergeWheneverPossible));
 
         {
@@ -607,7 +607,7 @@ mod tests {
         let index = Index::create_in_ram(schema);
 
         // writing the segment
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests().unwrap();
 
         {
             for _ in 0..100 {
@@ -678,7 +678,7 @@ mod tests {
         let index = Index::create_in_ram(schema);
 
         // writing the segment
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests().unwrap();
 
         {
             for _ in 0..100 {

src/indexer/segment_writer.rs

@@ -2,7 +2,7 @@ use super::operation::AddOperation;
 use crate::core::Segment;
 use crate::core::SerializableSegment;
 use crate::fastfield::FastFieldsWriter;
-use crate::fieldnorm::FieldNormsWriter;
+use crate::fieldnorm::{FieldNormReaders, FieldNormsWriter};
 use crate::indexer::segment_serializer::SegmentSerializer;
 use crate::postings::compute_table_size;
 use crate::postings::MultiFieldPostingsWriter;
@@ -14,10 +14,8 @@ use crate::schema::{Field, FieldEntry};
 use crate::tokenizer::{BoxTokenStream, PreTokenizedStream};
 use crate::tokenizer::{FacetTokenizer, TextAnalyzer};
 use crate::tokenizer::{TokenStreamChain, Tokenizer};
-use crate::DocId;
 use crate::Opstamp;
-use std::io;
+use crate::{DocId, SegmentComponent};
-use std::str;
 
 /// Computes the initial size of the hash table.
 ///
@@ -48,6 +46,7 @@ pub struct SegmentWriter {
     fieldnorms_writer: FieldNormsWriter,
     doc_opstamps: Vec<Opstamp>,
     tokenizers: Vec<Option<TextAnalyzer>>,
+    term_buffer: Term,
 }
 
 impl SegmentWriter {
@@ -62,11 +61,12 @@ impl SegmentWriter {
     /// - schema
     pub fn for_segment(
         memory_budget: usize,
-        mut segment: Segment,
+        segment: Segment,
         schema: &Schema,
     ) -> crate::Result<SegmentWriter> {
+        let tokenizer_manager = segment.index().tokenizers().clone();
         let table_num_bits = initial_table_size(memory_budget)?;
-        let segment_serializer = SegmentSerializer::for_segment(&mut segment)?;
+        let segment_serializer = SegmentSerializer::for_segment(segment)?;
         let multifield_postings = MultiFieldPostingsWriter::new(schema, table_num_bits);
         let tokenizers = schema
             .fields()
@@ -76,7 +76,7 @@ impl SegmentWriter {
                         .get_indexing_options()
                         .and_then(|text_index_option| {
                             let tokenizer_name = &text_index_option.tokenizer();
-                            segment.index().tokenizers().get(tokenizer_name)
+                            tokenizer_manager.get(tokenizer_name)
                         }),
                     _ => None,
                 },
@@ -90,6 +90,7 @@ impl SegmentWriter {
             fast_field_writers: FastFieldsWriter::from_schema(schema),
             doc_opstamps: Vec::with_capacity(1_000),
             tokenizers,
+            term_buffer: Term::new(),
         })
     }
 
@@ -115,7 +116,11 @@ impl SegmentWriter {
     /// Indexes a new document
     ///
     /// As a user, you should rather use `IndexWriter`'s add_document.
-    pub fn add_document(&mut self, add_operation: AddOperation, schema: &Schema) -> io::Result<()> {
+    pub fn add_document(
+        &mut self,
+        add_operation: AddOperation,
+        schema: &Schema,
+    ) -> crate::Result<()> {
         let doc_id = self.max_doc;
         let mut doc = add_operation.document;
         self.doc_opstamps.push(add_operation.opstamp);
@@ -123,34 +128,45 @@ impl SegmentWriter {
         self.fast_field_writers.add_document(&doc);
 
         for (field, field_values) in doc.get_sorted_field_values() {
-            let field_options = schema.get_field_entry(field);
+            let field_entry = schema.get_field_entry(field);
-            if !field_options.is_indexed() {
+            let make_schema_error = || {
+                crate::TantivyError::SchemaError(format!(
+                    "Expected a {:?} for field {:?}",
+                    field_entry.field_type().value_type(),
+                    field_entry.name()
+                ))
+            };
+            if !field_entry.is_indexed() {
                 continue;
             }
-            match *field_options.field_type() {
+            let (term_buffer, multifield_postings) =
+                (&mut self.term_buffer, &mut self.multifield_postings);
+            match *field_entry.field_type() {
                 FieldType::HierarchicalFacet => {
-                    let facets: Vec<&str> = field_values
+                    term_buffer.set_field(field);
-                        .iter()
+                    let facets =
-                        .flat_map(|field_value| match *field_value.value() {
+                        field_values
-                            Value::Facet(ref facet) => Some(facet.encoded_str()),
+                            .iter()
-                            _ => {
+                            .flat_map(|field_value| match *field_value.value() {
-                                panic!("Expected hierarchical facet");
+                                Value::Facet(ref facet) => Some(facet.encoded_str()),
-                            }
+                                _ => {
-                        })
+                                    panic!("Expected hierarchical facet");
-                        .collect();
+                                }
-                    let mut term = Term::for_field(field); // we set the Term
+                            });
-                    for fake_str in facets {
+                    for facet_str in facets {
                         let mut unordered_term_id_opt = None;
-                        FacetTokenizer.token_stream(fake_str).process(&mut |token| {
+                        FacetTokenizer
-                            term.set_text(&token.text);
+                            .token_stream(facet_str)
-                            let unordered_term_id =
+                            .process(&mut |token| {
-                                self.multifield_postings.subscribe(doc_id, &term);
+                                term_buffer.set_text(&token.text);
-                            unordered_term_id_opt = Some(unordered_term_id);
+                                let unordered_term_id =
-                        });
+                                    multifield_postings.subscribe(doc_id, &term_buffer);
+                                unordered_term_id_opt = Some(unordered_term_id);
+                            });
                         if let Some(unordered_term_id) = unordered_term_id_opt {
                             self.fast_field_writers
                                 .get_multivalue_writer(field)
-                                .expect("multified writer for facet missing")
+                                .expect("writer for facet missing")
                                 .add_val(unordered_term_id);
                         }
                     }
@@ -167,7 +183,6 @@ impl SegmentWriter {
                                 if let Some(last_token) = tok_str.tokens.last() {
                                     total_offset += last_token.offset_to;
                                 }
-
                                 token_streams
                                     .push(PreTokenizedStream::from(tok_str.clone()).into());
                             }
@@ -177,7 +192,6 @@ impl SegmentWriter {
                                 {
                                     offsets.push(total_offset);
                                     total_offset += text.len();
-
                                     token_streams.push(tokenizer.token_stream(text));
                                 }
                             }
@@ -189,8 +203,12 @@ impl SegmentWriter {
                         0
                     } else {
                         let mut token_stream = TokenStreamChain::new(offsets, token_streams);
-                        self.multifield_postings
+                        multifield_postings.index_text(
-                            .index_text(doc_id, field, &mut token_stream)
+                            doc_id,
+                            field,
+                            &mut token_stream,
+                            term_buffer,
+                        )
                     };
 
                     self.fieldnorms_writer.record(doc_id, field, num_tokens);
@@ -198,49 +216,67 @@ impl SegmentWriter {
                 FieldType::U64(ref int_option) => {
                     if int_option.is_indexed() {
                         for field_value in field_values {
-                            let term = Term::from_field_u64(
+                            term_buffer.set_field(field_value.field());
-                                field_value.field(),
+                            let u64_val = field_value
-                                field_value.value().u64_value(),
+                                .value()
-                            );
+                                .u64_value()
-                            self.multifield_postings.subscribe(doc_id, &term);
+                                .ok_or_else(make_schema_error)?;
+                            term_buffer.set_u64(u64_val);
+                            multifield_postings.subscribe(doc_id, &term_buffer);
                         }
                     }
                 }
                 FieldType::Date(ref int_option) => {
                     if int_option.is_indexed() {
                         for field_value in field_values {
-                            let term = Term::from_field_i64(
+                            term_buffer.set_field(field_value.field());
-                                field_value.field(),
+                            let date_val = field_value
-                                field_value.value().date_value().timestamp(),
+                                .value()
-                            );
+                                .date_value()
-                            self.multifield_postings.subscribe(doc_id, &term);
+                                .ok_or_else(make_schema_error)?;
+                            term_buffer.set_i64(date_val.timestamp());
+                            multifield_postings.subscribe(doc_id, &term_buffer);
                         }
                     }
                 }
                 FieldType::I64(ref int_option) => {
                     if int_option.is_indexed() {
                         for field_value in field_values {
-                            let term = Term::from_field_i64(
+                            term_buffer.set_field(field_value.field());
-                                field_value.field(),
+                            let i64_val = field_value
-                                field_value.value().i64_value(),
+                                .value()
-                            );
+                                .i64_value()
-                            self.multifield_postings.subscribe(doc_id, &term);
+                                .ok_or_else(make_schema_error)?;
+                            term_buffer.set_i64(i64_val);
+                            multifield_postings.subscribe(doc_id, &term_buffer);
                         }
                     }
                 }
                 FieldType::F64(ref int_option) => {
                     if int_option.is_indexed() {
                         for field_value in field_values {
-                            let term = Term::from_field_f64(
+                            term_buffer.set_field(field_value.field());
-                                field_value.field(),
+                            let f64_val = field_value
-                                field_value.value().f64_value(),
+                                .value()
-                            );
+                                .f64_value()
-                            self.multifield_postings.subscribe(doc_id, &term);
+                                .ok_or_else(make_schema_error)?;
+                            term_buffer.set_f64(f64_val);
+                            multifield_postings.subscribe(doc_id, &term_buffer);
                         }
                     }
                 }
-                FieldType::Bytes => {
+                FieldType::Bytes(ref option) => {
-                    // Do nothing. Bytes only supports fast fields.
+                    if option.is_indexed() {
+                        for field_value in field_values {
+                            term_buffer.set_field(field_value.field());
+                            let bytes = field_value
+                                .value()
+                                .bytes_value()
+                                .ok_or_else(make_schema_error)?;
+                            term_buffer.set_bytes(bytes);
+                            self.multifield_postings.subscribe(doc_id, &term_buffer);
+                        }
+                    }
                 }
             }
         }
@@ -280,9 +316,16 @@ fn write(
     fieldnorms_writer: &FieldNormsWriter,
     mut serializer: SegmentSerializer,
 ) -> crate::Result<()> {
-    let term_ord_map = multifield_postings.serialize(serializer.get_postings_serializer())?;
+    if let Some(fieldnorms_serializer) = serializer.extract_fieldnorms_serializer() {
+        fieldnorms_writer.serialize(fieldnorms_serializer)?;
+    }
+    let fieldnorm_data = serializer
+        .segment()
+        .open_read(SegmentComponent::FIELDNORMS)?;
+    let fieldnorm_readers = FieldNormReaders::open(fieldnorm_data)?;
+    let term_ord_map =
+        multifield_postings.serialize(serializer.get_postings_serializer(), fieldnorm_readers)?;
     fast_field_writers.serialize(serializer.get_fast_field_serializer(), &term_ord_map)?;
-    fieldnorms_writer.serialize(serializer.get_fieldnorms_serializer())?;
     serializer.close()?;
     Ok(())
 }

src/lib.rs

@@ -105,7 +105,7 @@ extern crate serde_json;
 extern crate log;
 
 #[macro_use]
-extern crate failure;
+extern crate thiserror;
 
 #[cfg(all(test, feature = "unstable"))]
 extern crate test;
@@ -134,7 +134,7 @@ mod core;
 mod indexer;
 
 #[allow(unused_doc_comments)]
-mod error;
+pub mod error;
 pub mod tokenizer;
 
 pub mod collector;
@@ -157,6 +157,7 @@ pub use self::snippet::{Snippet, SnippetGenerator};
 
 mod docset;
 pub use self::docset::{DocSet, TERMINATED};
+pub use crate::common::HasLen;
 pub use crate::common::{f64_to_u64, i64_to_u64, u64_to_f64, u64_to_i64};
 pub use crate::core::{Executor, SegmentComponent};
 pub use crate::core::{Index, IndexMeta, Searcher, Segment, SegmentId, SegmentMeta};
@@ -173,7 +174,7 @@ use once_cell::sync::Lazy;
 use serde::{Deserialize, Serialize};
 
 /// Index format version.
-const INDEX_FORMAT_VERSION: u32 = 1;
+const INDEX_FORMAT_VERSION: u32 = 2;
 
 /// Structure version for the index.
 #[derive(Clone, PartialEq, Eq, Serialize, Deserialize)]
@@ -245,11 +246,10 @@ pub type DocId = u32;
 /// with opstamp `n+1`.
 pub type Opstamp = u64;
 
-/// A f32 that represents the relevance of the document to the query
+/// A Score that represents the relevance of the document to the query
 ///
-/// This is modelled internally as a `f32`. The
+/// This is modelled internally as a `f32`. The larger the number, the more relevant
-/// larger the number, the more relevant the document
+/// the document to the search query.
-/// to the search
 pub type Score = f32;
 
 /// A `SegmentLocalId` identifies a segment.
@@ -277,12 +277,11 @@ impl DocAddress {
 ///
 /// The id used for the segment is actually an ordinal
 /// in the list of `Segment`s held by a `Searcher`.
-#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
 pub struct DocAddress(pub SegmentLocalId, pub DocId);
 
 #[cfg(test)]
 mod tests {
-
     use crate::collector::tests::TEST_COLLECTOR_WITH_SCORE;
     use crate::core::SegmentReader;
     use crate::docset::{DocSet, TERMINATED};
@@ -290,7 +289,6 @@ mod tests {
     use crate::schema::*;
     use crate::DocAddress;
     use crate::Index;
-    use crate::IndexWriter;
     use crate::Postings;
     use crate::ReloadPolicy;
     use rand::distributions::Bernoulli;
@@ -298,17 +296,26 @@ mod tests {
     use rand::rngs::StdRng;
     use rand::{Rng, SeedableRng};
 
-    pub fn assert_nearly_equals(expected: f32, val: f32) {
+    /// Checks if left and right are close one to each other.
-        assert!(
+    /// Panics if the two values are more than 0.5% apart.
-            nearly_equals(val, expected),
+    #[macro_export]
-            "Got {}, expected {}.",
+    macro_rules! assert_nearly_equals {
-            val,
+        ($left:expr, $right:expr) => {{
-            expected
+            match (&$left, &$right) {
-        );
+                (left_val, right_val) => {
-    }
+                    let diff = (left_val - right_val).abs();
-
+                    let add = left_val.abs() + right_val.abs();
-    pub fn nearly_equals(a: f32, b: f32) -> bool {
+                    if diff > 0.0005 * add {
-        (a - b).abs() < 0.0005 * (a + b).abs()
+                        panic!(
+                            r#"assertion failed: `(left ~= right)`
+  left: `{:?}`,
+ right: `{:?}`"#,
+                            &*left_val, &*right_val
+                        )
+                    }
+                }
+            }
+        }};
     }
 
     pub fn generate_nonunique_unsorted(max_value: u32, n_elems: usize) -> Vec<u32> {
@@ -346,14 +353,14 @@ mod tests {
 
     #[test]
     #[cfg(feature = "mmap")]
-    fn test_indexing() {
+    fn test_indexing() -> crate::Result<()> {
         let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", TEXT);
         let schema = schema_builder.build();
         let index = Index::create_from_tempdir(schema).unwrap();
         {
             // writing the segment
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+            let mut index_writer = index.writer_for_tests()?;
             {
                 let doc = doc!(text_field=>"af b");
                 index_writer.add_document(doc);
@@ -368,100 +375,76 @@ mod tests {
             }
             assert!(index_writer.commit().is_ok());
         }
+        Ok(())
     }
 
     #[test]
-    fn test_docfreq1() {
+    fn test_docfreq1() -> crate::Result<()> {
         let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", TEXT);
         let index = Index::create_in_ram(schema_builder.build());
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests()?;
-        {
+        index_writer.add_document(doc!(text_field=>"a b c"));
-            index_writer.add_document(doc!(text_field=>"a b c"));
+        index_writer.commit()?;
-            index_writer.commit().unwrap();
+        index_writer.add_document(doc!(text_field=>"a"));
-        }
+        index_writer.add_document(doc!(text_field=>"a a"));
-        {
+        index_writer.commit()?;
-            index_writer.add_document(doc!(text_field=>"a"));
+        index_writer.add_document(doc!(text_field=>"c"));
-            index_writer.add_document(doc!(text_field=>"a a"));
+        index_writer.commit()?;
-            index_writer.commit().unwrap();
+        let reader = index.reader()?;
-        }
+        let searcher = reader.searcher();
-        {
+        let term_a = Term::from_field_text(text_field, "a");
-            index_writer.add_document(doc!(text_field=>"c"));
+        assert_eq!(searcher.doc_freq(&term_a)?, 3);
-            index_writer.commit().unwrap();
+        let term_b = Term::from_field_text(text_field, "b");
-        }
+        assert_eq!(searcher.doc_freq(&term_b)?, 1);
-        {
+        let term_c = Term::from_field_text(text_field, "c");
-            let reader = index.reader().unwrap();
+        assert_eq!(searcher.doc_freq(&term_c)?, 2);
-            let searcher = reader.searcher();
+        let term_d = Term::from_field_text(text_field, "d");
-            let term_a = Term::from_field_text(text_field, "a");
+        assert_eq!(searcher.doc_freq(&term_d)?, 0);
-            assert_eq!(searcher.doc_freq(&term_a), 3);
+        Ok(())
-            let term_b = Term::from_field_text(text_field, "b");
-            assert_eq!(searcher.doc_freq(&term_b), 1);
-            let term_c = Term::from_field_text(text_field, "c");
-            assert_eq!(searcher.doc_freq(&term_c), 2);
-            let term_d = Term::from_field_text(text_field, "d");
-            assert_eq!(searcher.doc_freq(&term_d), 0);
-        }
     }
 
     #[test]
-    fn test_fieldnorm_no_docs_with_field() {
+    fn test_fieldnorm_no_docs_with_field() -> crate::Result<()> {
         let mut schema_builder = Schema::builder();
         let title_field = schema_builder.add_text_field("title", TEXT);
         let text_field = schema_builder.add_text_field("text", TEXT);
         let index = Index::create_in_ram(schema_builder.build());
+        let mut index_writer = index.writer_for_tests()?;
+        index_writer.add_document(doc!(text_field=>"a b c"));
+        index_writer.commit()?;
+        let index_reader = index.reader()?;
+        let searcher = index_reader.searcher();
+        let reader = searcher.segment_reader(0);
         {
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+            let fieldnorm_reader = reader.get_fieldnorms_reader(text_field)?;
-            {
+            assert_eq!(fieldnorm_reader.fieldnorm(0), 3);
-                let doc = doc!(text_field=>"a b c");
-                index_writer.add_document(doc);
-            }
-            index_writer.commit().unwrap();
         }
         {
-            let index_reader = index.reader().unwrap();
+            let fieldnorm_reader = reader.get_fieldnorms_reader(title_field)?;
-            let searcher = index_reader.searcher();
+            assert_eq!(fieldnorm_reader.fieldnorm_id(0), 0);
-            let reader = searcher.segment_reader(0);
-            {
-                let fieldnorm_reader = reader.get_fieldnorms_reader(text_field);
-                assert_eq!(fieldnorm_reader.fieldnorm(0), 3);
-            }
-            {
-                let fieldnorm_reader = reader.get_fieldnorms_reader(title_field);
-                assert_eq!(fieldnorm_reader.fieldnorm_id(0), 0);
-            }
         }
+        Ok(())
     }
 
     #[test]
-    fn test_fieldnorm() {
+    fn test_fieldnorm() -> crate::Result<()> {
         let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", TEXT);
         let index = Index::create_in_ram(schema_builder.build());
-        {
+        let mut index_writer = index.writer_for_tests()?;
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        index_writer.add_document(doc!(text_field=>"a b c"));
-            {
+        index_writer.add_document(doc!());
-                let doc = doc!(text_field=>"a b c");
+        index_writer.add_document(doc!(text_field=>"a b"));
-                index_writer.add_document(doc);
+        index_writer.commit()?;
-            }
+        let reader = index.reader()?;
-            {
+        let searcher = reader.searcher();
-                let doc = doc!();
+        let segment_reader: &SegmentReader = searcher.segment_reader(0);
-                index_writer.add_document(doc);
+        let fieldnorms_reader = segment_reader.get_fieldnorms_reader(text_field)?;
-            }
+        assert_eq!(fieldnorms_reader.fieldnorm(0), 3);
-            {
+        assert_eq!(fieldnorms_reader.fieldnorm(1), 0);
-                let doc = doc!(text_field=>"a b");
+        assert_eq!(fieldnorms_reader.fieldnorm(2), 2);
-                index_writer.add_document(doc);
+        Ok(())
-            }
-            index_writer.commit().unwrap();
-        }
-        {
-            let reader = index.reader().unwrap();
-            let searcher = reader.searcher();
-            let segment_reader: &SegmentReader = searcher.segment_reader(0);
-            let fieldnorms_reader = segment_reader.get_fieldnorms_reader(text_field);
-            assert_eq!(fieldnorms_reader.fieldnorm(0), 3);
-            assert_eq!(fieldnorms_reader.fieldnorm(1), 0);
-            assert_eq!(fieldnorms_reader.fieldnorm(2), 2);
-        }
     }
 
     fn advance_undeleted(docset: &mut dyn DocSet, reader: &SegmentReader) -> bool {
@@ -476,7 +459,7 @@ mod tests {
     }
 
     #[test]
-    fn test_delete_postings1() {
+    fn test_delete_postings1() -> crate::Result<()> {
         let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", TEXT);
         let term_abcd = Term::from_field_text(text_field, "abcd");
@@ -492,7 +475,7 @@ mod tests {
             .unwrap();
         {
             // writing the segment
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+            let mut index_writer = index.writer_for_tests()?;
             // 0
             index_writer.add_document(doc!(text_field=>"a b"));
             // 1
@@ -508,19 +491,19 @@ mod tests {
             index_writer.add_document(doc!(text_field=>" b c"));
             // 5
             index_writer.add_document(doc!(text_field=>" a"));
-            index_writer.commit().unwrap();
+            index_writer.commit()?;
         }
         {
-            reader.reload().unwrap();
+            reader.reload()?;
             let searcher = reader.searcher();
             let segment_reader = searcher.segment_reader(0);
-            let inverted_index = segment_reader.inverted_index(text_field);
+            let inverted_index = segment_reader.inverted_index(text_field)?;
             assert!(inverted_index
-                .read_postings(&term_abcd, IndexRecordOption::WithFreqsAndPositions)
+                .read_postings(&term_abcd, IndexRecordOption::WithFreqsAndPositions)?
                 .is_none());
             {
                 let mut postings = inverted_index
-                    .read_postings(&term_a, IndexRecordOption::WithFreqsAndPositions)
+                    .read_postings(&term_a, IndexRecordOption::WithFreqsAndPositions)?
                     .unwrap();
                 assert!(advance_undeleted(&mut postings, segment_reader));
                 assert_eq!(postings.doc(), 5);
@@ -528,7 +511,7 @@ mod tests {
             }
             {
                 let mut postings = inverted_index
-                    .read_postings(&term_b, IndexRecordOption::WithFreqsAndPositions)
+                    .read_postings(&term_b, IndexRecordOption::WithFreqsAndPositions)?
                     .unwrap();
                 assert!(advance_undeleted(&mut postings, segment_reader));
                 assert_eq!(postings.doc(), 3);
@@ -539,25 +522,25 @@ mod tests {
         }
         {
             // writing the segment
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+            let mut index_writer = index.writer_for_tests()?;
             // 0
             index_writer.add_document(doc!(text_field=>"a b"));
             // 1
             index_writer.delete_term(Term::from_field_text(text_field, "c"));
-            index_writer.rollback().unwrap();
+            index_writer.rollback()?;
         }
         {
-            reader.reload().unwrap();
+            reader.reload()?;
             let searcher = reader.searcher();
             let seg_reader = searcher.segment_reader(0);
-            let inverted_index = seg_reader.inverted_index(term_abcd.field());
+            let inverted_index = seg_reader.inverted_index(term_abcd.field())?;
 
             assert!(inverted_index
-                .read_postings(&term_abcd, IndexRecordOption::WithFreqsAndPositions)
+                .read_postings(&term_abcd, IndexRecordOption::WithFreqsAndPositions)?
                 .is_none());
             {
                 let mut postings = inverted_index
-                    .read_postings(&term_a, IndexRecordOption::WithFreqsAndPositions)
+                    .read_postings(&term_a, IndexRecordOption::WithFreqsAndPositions)?
                     .unwrap();
                 assert!(advance_undeleted(&mut postings, seg_reader));
                 assert_eq!(postings.doc(), 5);
@@ -565,7 +548,7 @@ mod tests {
             }
             {
                 let mut postings = inverted_index
-                    .read_postings(&term_b, IndexRecordOption::WithFreqsAndPositions)
+                    .read_postings(&term_b, IndexRecordOption::WithFreqsAndPositions)?
                     .unwrap();
                 assert!(advance_undeleted(&mut postings, seg_reader));
                 assert_eq!(postings.doc(), 3);
@@ -576,30 +559,30 @@ mod tests {
         }
         {
             // writing the segment
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+            let mut index_writer = index.writer_for_tests()?;
             index_writer.add_document(doc!(text_field=>"a b"));
             index_writer.delete_term(Term::from_field_text(text_field, "c"));
-            index_writer.rollback().unwrap();
+            index_writer.rollback()?;
             index_writer.delete_term(Term::from_field_text(text_field, "a"));
-            index_writer.commit().unwrap();
+            index_writer.commit()?;
         }
         {
-            reader.reload().unwrap();
+            reader.reload()?;
             let searcher = reader.searcher();
             let segment_reader = searcher.segment_reader(0);
-            let inverted_index = segment_reader.inverted_index(term_abcd.field());
+            let inverted_index = segment_reader.inverted_index(term_abcd.field())?;
             assert!(inverted_index
-                .read_postings(&term_abcd, IndexRecordOption::WithFreqsAndPositions)
+                .read_postings(&term_abcd, IndexRecordOption::WithFreqsAndPositions)?
                 .is_none());
             {
                 let mut postings = inverted_index
-                    .read_postings(&term_a, IndexRecordOption::WithFreqsAndPositions)
+                    .read_postings(&term_a, IndexRecordOption::WithFreqsAndPositions)?
                     .unwrap();
                 assert!(!advance_undeleted(&mut postings, segment_reader));
             }
             {
                 let mut postings = inverted_index
-                    .read_postings(&term_b, IndexRecordOption::WithFreqsAndPositions)
+                    .read_postings(&term_b, IndexRecordOption::WithFreqsAndPositions)?
                     .unwrap();
                 assert!(advance_undeleted(&mut postings, segment_reader));
                 assert_eq!(postings.doc(), 3);
@@ -609,101 +592,107 @@ mod tests {
             }
             {
                 let mut postings = inverted_index
-                    .read_postings(&term_c, IndexRecordOption::WithFreqsAndPositions)
+                    .read_postings(&term_c, IndexRecordOption::WithFreqsAndPositions)?
                     .unwrap();
                 assert!(advance_undeleted(&mut postings, segment_reader));
                 assert_eq!(postings.doc(), 4);
                 assert!(!advance_undeleted(&mut postings, segment_reader));
             }
         }
+        Ok(())
     }
 
     #[test]
-    fn test_indexed_u64() {
+    fn test_indexed_u64() -> crate::Result<()> {
         let mut schema_builder = Schema::builder();
         let field = schema_builder.add_u64_field("value", INDEXED);
         let schema = schema_builder.build();
 
         let index = Index::create_in_ram(schema);
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests()?;
         index_writer.add_document(doc!(field=>1u64));
-        index_writer.commit().unwrap();
+        index_writer.commit()?;
-        let reader = index.reader().unwrap();
+        let reader = index.reader()?;
         let searcher = reader.searcher();
         let term = Term::from_field_u64(field, 1u64);
         let mut postings = searcher
             .segment_reader(0)
-            .inverted_index(term.field())
+            .inverted_index(term.field())?
-            .read_postings(&term, IndexRecordOption::Basic)
+            .read_postings(&term, IndexRecordOption::Basic)?
             .unwrap();
         assert_eq!(postings.doc(), 0);
         assert_eq!(postings.advance(), TERMINATED);
+        Ok(())
     }
 
     #[test]
-    fn test_indexed_i64() {
+    fn test_indexed_i64() -> crate::Result<()> {
         let mut schema_builder = Schema::builder();
         let value_field = schema_builder.add_i64_field("value", INDEXED);
         let schema = schema_builder.build();
 
         let index = Index::create_in_ram(schema);
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests()?;
         let negative_val = -1i64;
         index_writer.add_document(doc!(value_field => negative_val));
-        index_writer.commit().unwrap();
+        index_writer.commit()?;
-        let reader = index.reader().unwrap();
+        let reader = index.reader()?;
         let searcher = reader.searcher();
         let term = Term::from_field_i64(value_field, negative_val);
         let mut postings = searcher
             .segment_reader(0)
-            .inverted_index(term.field())
+            .inverted_index(term.field())?
-            .read_postings(&term, IndexRecordOption::Basic)
+            .read_postings(&term, IndexRecordOption::Basic)?
             .unwrap();
         assert_eq!(postings.doc(), 0);
         assert_eq!(postings.advance(), TERMINATED);
+        Ok(())
     }
 
     #[test]
-    fn test_indexed_f64() {
+    fn test_indexed_f64() -> crate::Result<()> {
         let mut schema_builder = Schema::builder();
         let value_field = schema_builder.add_f64_field("value", INDEXED);
         let schema = schema_builder.build();
 
         let index = Index::create_in_ram(schema);
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests()?;
         let val = std::f64::consts::PI;
         index_writer.add_document(doc!(value_field => val));
-        index_writer.commit().unwrap();
+        index_writer.commit()?;
-        let reader = index.reader().unwrap();
+        let reader = index.reader()?;
         let searcher = reader.searcher();
         let term = Term::from_field_f64(value_field, val);
         let mut postings = searcher
             .segment_reader(0)
-            .inverted_index(term.field())
+            .inverted_index(term.field())?
-            .read_postings(&term, IndexRecordOption::Basic)
+            .read_postings(&term, IndexRecordOption::Basic)?
             .unwrap();
         assert_eq!(postings.doc(), 0);
         assert_eq!(postings.advance(), TERMINATED);
+        Ok(())
     }
 
     #[test]
-    fn test_indexedfield_not_in_documents() {
+    fn test_indexedfield_not_in_documents() -> crate::Result<()> {
         let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", TEXT);
         let absent_field = schema_builder.add_text_field("text", TEXT);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
-        let mut index_writer = index.writer_with_num_threads(2, 6_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests()?;
         index_writer.add_document(doc!(text_field=>"a"));
         assert!(index_writer.commit().is_ok());
-        let reader = index.reader().unwrap();
+        let reader = index.reader()?;
         let searcher = reader.searcher();
         let segment_reader = searcher.segment_reader(0);
-        segment_reader.inverted_index(absent_field); //< should not panic
+        let inverted_index = segment_reader.inverted_index(absent_field)?;
+        assert_eq!(inverted_index.terms().num_terms(), 0);
+        Ok(())
     }
 
     #[test]
-    fn test_delete_postings2() {
+    fn test_delete_postings2() -> crate::Result<()> {
         let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", TEXT);
         let schema = schema_builder.build();
@@ -711,125 +700,112 @@ mod tests {
         let reader = index
             .reader_builder()
             .reload_policy(ReloadPolicy::Manual)
-            .try_into()
+            .try_into()?;
-            .unwrap();
 
         // writing the segment
-        let mut index_writer = index.writer_with_num_threads(2, 6_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests()?;
-
+        index_writer.add_document(doc!(text_field=>"63"));
-        let add_document = |index_writer: &mut IndexWriter, val: &'static str| {
+        index_writer.add_document(doc!(text_field=>"70"));
-            let doc = doc!(text_field=>val);
+        index_writer.add_document(doc!(text_field=>"34"));
-            index_writer.add_document(doc);
+        index_writer.add_document(doc!(text_field=>"1"));
-        };
+        index_writer.add_document(doc!(text_field=>"38"));
-
+        index_writer.add_document(doc!(text_field=>"33"));
-        let remove_document = |index_writer: &mut IndexWriter, val: &'static str| {
+        index_writer.add_document(doc!(text_field=>"40"));
-            let delterm = Term::from_field_text(text_field, val);
+        index_writer.add_document(doc!(text_field=>"17"));
-            index_writer.delete_term(delterm);
+        index_writer.delete_term(Term::from_field_text(text_field, "38"));
-        };
+        index_writer.delete_term(Term::from_field_text(text_field, "34"));
-
+        index_writer.commit()?;
-        add_document(&mut index_writer, "63");
+        reader.reload()?;
-        add_document(&mut index_writer, "70");
+        assert_eq!(reader.searcher().num_docs(), 6);
-        add_document(&mut index_writer, "34");
+        Ok(())
-        add_document(&mut index_writer, "1");
-        add_document(&mut index_writer, "38");
-        add_document(&mut index_writer, "33");
-        add_document(&mut index_writer, "40");
-        add_document(&mut index_writer, "17");
-        remove_document(&mut index_writer, "38");
-        remove_document(&mut index_writer, "34");
-        index_writer.commit().unwrap();
-        reader.reload().unwrap();
-        let searcher = reader.searcher();
-        assert_eq!(searcher.num_docs(), 6);
     }
 
     #[test]
-    fn test_termfreq() {
+    fn test_termfreq() -> crate::Result<()> {
         let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", TEXT);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
         {
             // writing the segment
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+            let mut index_writer = index.writer_for_tests()?;
-            let doc = doc!(text_field=>"af af af bc bc");
+            index_writer.add_document(doc!(text_field=>"af af af bc bc"));
-            index_writer.add_document(doc);
+            index_writer.commit()?;
-            index_writer.commit().unwrap();
         }
         {
-            let index_reader = index.reader().unwrap();
+            let index_reader = index.reader()?;
             let searcher = index_reader.searcher();
             let reader = searcher.segment_reader(0);
-            let inverted_index = reader.inverted_index(text_field);
+            let inverted_index = reader.inverted_index(text_field)?;
             let term_abcd = Term::from_field_text(text_field, "abcd");
             assert!(inverted_index
-                .read_postings(&term_abcd, IndexRecordOption::WithFreqsAndPositions)
+                .read_postings(&term_abcd, IndexRecordOption::WithFreqsAndPositions)?
                 .is_none());
             let term_af = Term::from_field_text(text_field, "af");
             let mut postings = inverted_index
-                .read_postings(&term_af, IndexRecordOption::WithFreqsAndPositions)
+                .read_postings(&term_af, IndexRecordOption::WithFreqsAndPositions)?
                 .unwrap();
             assert_eq!(postings.doc(), 0);
             assert_eq!(postings.term_freq(), 3);
             assert_eq!(postings.advance(), TERMINATED);
         }
+        Ok(())
     }
 
     #[test]
-    fn test_searcher_1() {
+    fn test_searcher_1() -> crate::Result<()> {
         let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", TEXT);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
-        let reader = index.reader().unwrap();
+        let reader = index.reader()?;
-        {
+        // writing the segment
-            // writing the segment
+        let mut index_writer = index.writer_for_tests()?;
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        index_writer.add_document(doc!(text_field=>"af af af b"));
-            index_writer.add_document(doc!(text_field=>"af af af b"));
+        index_writer.add_document(doc!(text_field=>"a b c"));
-            index_writer.add_document(doc!(text_field=>"a b c"));
+        index_writer.add_document(doc!(text_field=>"a b c d"));
-            index_writer.add_document(doc!(text_field=>"a b c d"));
+        index_writer.commit()?;
-            index_writer.commit().unwrap();
+
-        }
+        reader.reload()?;
-        {
+        let searcher = reader.searcher();
-            reader.reload().unwrap();
+        let get_doc_ids = |terms: Vec<Term>| {
-            let searcher = reader.searcher();
+            let query = BooleanQuery::new_multiterms_query(terms);
-            let get_doc_ids = |terms: Vec<Term>| {
+            searcher
-                let query = BooleanQuery::new_multiterms_query(terms);
+                .search(&query, &TEST_COLLECTOR_WITH_SCORE)
-                let topdocs = searcher.search(&query, &TEST_COLLECTOR_WITH_SCORE).unwrap();
+                .map(|topdocs| topdocs.docs().to_vec())
-                topdocs.docs().to_vec()
+        };
-            };
+        assert_eq!(
-            assert_eq!(
+            get_doc_ids(vec![Term::from_field_text(text_field, "a")])?,
-                get_doc_ids(vec![Term::from_field_text(text_field, "a")]),
+            vec![DocAddress(0, 1), DocAddress(0, 2)]
-                vec![DocAddress(0, 1), DocAddress(0, 2)]
+        );
-            );
+        assert_eq!(
-            assert_eq!(
+            get_doc_ids(vec![Term::from_field_text(text_field, "af")])?,
-                get_doc_ids(vec![Term::from_field_text(text_field, "af")]),
+            vec![DocAddress(0, 0)]
-                vec![DocAddress(0, 0)]
+        );
-            );
+        assert_eq!(
-            assert_eq!(
+            get_doc_ids(vec![Term::from_field_text(text_field, "b")])?,
-                get_doc_ids(vec![Term::from_field_text(text_field, "b")]),
+            vec![DocAddress(0, 0), DocAddress(0, 1), DocAddress(0, 2)]
-                vec![DocAddress(0, 0), DocAddress(0, 1), DocAddress(0, 2)]
+        );
-            );
+        assert_eq!(
-            assert_eq!(
+            get_doc_ids(vec![Term::from_field_text(text_field, "c")])?,
-                get_doc_ids(vec![Term::from_field_text(text_field, "c")]),
+            vec![DocAddress(0, 1), DocAddress(0, 2)]
-                vec![DocAddress(0, 1), DocAddress(0, 2)]
+        );
-            );
+        assert_eq!(
-            assert_eq!(
+            get_doc_ids(vec![Term::from_field_text(text_field, "d")])?,
-                get_doc_ids(vec![Term::from_field_text(text_field, "d")]),
+            vec![DocAddress(0, 2)]
-                vec![DocAddress(0, 2)]
+        );
-            );
+        assert_eq!(
-            assert_eq!(
+            get_doc_ids(vec![
-                get_doc_ids(vec![
+                Term::from_field_text(text_field, "b"),
-                    Term::from_field_text(text_field, "b"),
+                Term::from_field_text(text_field, "a"),
-                    Term::from_field_text(text_field, "a"),
+            ])?,
-                ]),
+            vec![DocAddress(0, 0), DocAddress(0, 1), DocAddress(0, 2)]
-                vec![DocAddress(0, 0), DocAddress(0, 1), DocAddress(0, 2)]
+        );
-            );
+        Ok(())
-        }
     }
 
     #[test]
-    fn test_searcher_2() {
+    fn test_searcher_2() -> crate::Result<()> {
         let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", TEXT);
         let schema = schema_builder.build();
@@ -837,19 +813,17 @@ mod tests {
         let reader = index
             .reader_builder()
             .reload_policy(ReloadPolicy::Manual)
-            .try_into()
+            .try_into()?;
-            .unwrap();
         assert_eq!(reader.searcher().num_docs(), 0u64);
-        {
+        // writing the segment
-            // writing the segment
+        let mut index_writer = index.writer_for_tests()?;
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        index_writer.add_document(doc!(text_field=>"af b"));
-            index_writer.add_document(doc!(text_field=>"af b"));
+        index_writer.add_document(doc!(text_field=>"a b c"));
-            index_writer.add_document(doc!(text_field=>"a b c"));
+        index_writer.add_document(doc!(text_field=>"a b c d"));
-            index_writer.add_document(doc!(text_field=>"a b c d"));
+        index_writer.commit()?;
-            index_writer.commit().unwrap();
+        reader.reload()?;
-        }
-        reader.reload().unwrap();
         assert_eq!(reader.searcher().num_docs(), 3u64);
+        Ok(())
     }
 
     #[test]
@@ -861,17 +835,17 @@ mod tests {
                             text_field => "some other value",
                             other_text_field => "short");
         assert_eq!(document.len(), 3);
-        let values = document.get_all(text_field);
+        let values: Vec<&Value> = document.get_all(text_field).collect();
         assert_eq!(values.len(), 2);
         assert_eq!(values[0].text(), Some("tantivy"));
         assert_eq!(values[1].text(), Some("some other value"));
-        let values = document.get_all(other_text_field);
+        let values: Vec<&Value> = document.get_all(other_text_field).collect();
         assert_eq!(values.len(), 1);
         assert_eq!(values[0].text(), Some("short"));
     }
 
     #[test]
-    fn test_wrong_fast_field_type() {
+    fn test_wrong_fast_field_type() -> crate::Result<()> {
         let mut schema_builder = Schema::builder();
         let fast_field_unsigned = schema_builder.add_u64_field("unsigned", FAST);
         let fast_field_signed = schema_builder.add_i64_field("signed", FAST);
@@ -881,14 +855,14 @@ mod tests {
         let schema = schema_builder.build();
 
         let index = Index::create_in_ram(schema);
-        let mut index_writer = index.writer_with_num_threads(1, 50_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests()?;
         {
             let document =
                 doc!(fast_field_unsigned => 4u64, fast_field_signed=>4i64, fast_field_float=>4f64);
             index_writer.add_document(document);
-            index_writer.commit().unwrap();
+            index_writer.commit()?;
         }
-        let reader = index.reader().unwrap();
+        let reader = index.reader()?;
         let searcher = reader.searcher();
         let segment_reader: &SegmentReader = searcher.segment_reader(0);
         {
@@ -927,11 +901,12 @@ mod tests {
             let fast_field_reader = fast_field_reader_opt.unwrap();
             assert_eq!(fast_field_reader.get(0), 4f64)
         }
+        Ok(())
     }
 
     // motivated by #729
     #[test]
-    fn test_update_via_delete_insert() {
+    fn test_update_via_delete_insert() -> crate::Result<()> {
         use crate::collector::Count;
         use crate::indexer::NoMergePolicy;
         use crate::query::AllQuery;
@@ -945,17 +920,17 @@ mod tests {
         let schema = schema_builder.build();
 
         let index = Index::create_in_ram(schema.clone());
-        let index_reader = index.reader().unwrap();
+        let index_reader = index.reader()?;
 
-        let mut index_writer = index.writer(3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests()?;
         index_writer.set_merge_policy(Box::new(NoMergePolicy));
 
         for doc_id in 0u64..DOC_COUNT {
             index_writer.add_document(doc!(id => doc_id));
         }
-        index_writer.commit().unwrap();
+        index_writer.commit()?;
 
-        index_reader.reload().unwrap();
+        index_reader.reload()?;
         let searcher = index_reader.searcher();
 
         assert_eq!(
@@ -966,12 +941,11 @@ mod tests {
         // update the 10 elements by deleting and re-adding
         for doc_id in 0u64..DOC_COUNT {
             index_writer.delete_term(Term::from_field_u64(id, doc_id));
-            index_writer.commit().unwrap();
+            index_writer.commit()?;
-            index_reader.reload().unwrap();
+            index_reader.reload()?;
-            let doc = doc!(id =>  doc_id);
+            index_writer.add_document(doc!(id =>  doc_id));
-            index_writer.add_document(doc);
+            index_writer.commit()?;
-            index_writer.commit().unwrap();
+            index_reader.reload()?;
-            index_reader.reload().unwrap();
             let searcher = index_reader.searcher();
             // The number of document should be stable.
             assert_eq!(
@@ -980,7 +954,7 @@ mod tests {
             );
         }
 
-        index_reader.reload().unwrap();
+        index_reader.reload()?;
         let searcher = index_reader.searcher();
         let segment_ids: Vec<SegmentId> = searcher
             .segment_readers()
@@ -989,12 +963,18 @@ mod tests {
             .collect();
         block_on(index_writer.merge(&segment_ids)).unwrap();
 
-        index_reader.reload().unwrap();
+        index_reader.reload()?;
         let searcher = index_reader.searcher();
+        assert_eq!(searcher.search(&AllQuery, &Count)?, DOC_COUNT as usize);
+        Ok(())
+    }
 
-        assert_eq!(
+    #[test]
-            searcher.search(&AllQuery, &Count).unwrap(),
+    fn test_validate_checksum() -> crate::Result<()> {
-            DOC_COUNT as usize
+        let index_path = tempfile::tempdir().expect("dir");
-        );
+        let schema = Schema::builder().build();
+        let index = Index::create_in_dir(&index_path, schema)?;
+        assert!(index.validate_checksum()?.is_empty());
+        Ok(())
     }
 }

src/positions/mod.rs

@@ -38,11 +38,11 @@ const LONG_SKIP_INTERVAL: u64 = (LONG_SKIP_IN_BLOCKS * COMPRESSION_BLOCK_SIZE) a
 pub mod tests {
 
     use super::PositionSerializer;
-    use crate::directory::ReadOnlySource;
     use crate::positions::reader::PositionReader;
+    use crate::{common::HasLen, directory::FileSlice};
     use std::iter;
 
-    fn create_stream_buffer(vals: &[u32]) -> (ReadOnlySource, ReadOnlySource) {
+    fn create_stream_buffer(vals: &[u32]) -> (FileSlice, FileSlice) {
         let mut skip_buffer = vec![];
         let mut stream_buffer = vec![];
         {
@@ -53,10 +53,7 @@ pub mod tests {
             }
             serializer.close().unwrap();
         }
-        (
+        (FileSlice::from(stream_buffer), FileSlice::from(skip_buffer))
-            ReadOnlySource::from(stream_buffer),
-            ReadOnlySource::from(skip_buffer),
-        )
     }
 
     #[test]
@@ -65,7 +62,7 @@ pub mod tests {
         let (stream, skip) = create_stream_buffer(&v[..]);
         assert_eq!(skip.len(), 12);
         assert_eq!(stream.len(), 1168);
-        let mut position_reader = PositionReader::new(stream, skip, 0u64);
+        let mut position_reader = PositionReader::new(stream, skip, 0u64).unwrap();
         for &n in &[1, 10, 127, 128, 130, 312] {
             let mut v = vec![0u32; n];
             position_reader.read(0, &mut v[..]);
@@ -81,7 +78,7 @@ pub mod tests {
         let (stream, skip) = create_stream_buffer(&v[..]);
         assert_eq!(skip.len(), 12);
         assert_eq!(stream.len(), 1168);
-        let mut position_reader = PositionReader::new(stream, skip, 0u64);
+        let mut position_reader = PositionReader::new(stream, skip, 0u64).unwrap();
         for &offset in &[1u64, 10u64, 127u64, 128u64, 130u64, 312u64] {
             for &len in &[1, 10, 130, 500] {
                 let mut v = vec![0u32; len];
@@ -100,7 +97,7 @@ pub mod tests {
         assert_eq!(skip.len(), 12);
         assert_eq!(stream.len(), 1168);
 
-        let mut position_reader = PositionReader::new(stream, skip, 0u64);
+        let mut position_reader = PositionReader::new(stream, skip, 0u64).unwrap();
         let mut buf = [0u32; 7];
         let mut c = 0;
 
@@ -122,7 +119,7 @@ pub mod tests {
         let (stream, skip) = create_stream_buffer(&v[..]);
         assert_eq!(skip.len(), 15_749);
         assert_eq!(stream.len(), 4_987_872);
-        let mut position_reader = PositionReader::new(stream.clone(), skip.clone(), 0);
+        let mut position_reader = PositionReader::new(stream.clone(), skip.clone(), 0).unwrap();
         let mut buf = [0u32; 256];
         position_reader.read(128, &mut buf);
         for i in 0..256 {
@@ -142,7 +139,8 @@ pub mod tests {
         assert_eq!(skip.len(), 15_749);
         assert_eq!(stream.len(), 4_987_872);
         let mut buf = [0u32; 1];
-        let mut position_reader = PositionReader::new(stream.clone(), skip.clone(), 200_000);
+        let mut position_reader =
+            PositionReader::new(stream.clone(), skip.clone(), 200_000).unwrap();
         position_reader.read(230, &mut buf);
         position_reader.read(9, &mut buf);
     }
@@ -157,7 +155,7 @@ pub mod tests {
         }
         let (stream, skip) = create_stream_buffer(&v[..]);
         let mut buf = Vec::new();
-        let mut position_reader = PositionReader::new(stream.clone(), skip.clone(), 0);
+        let mut position_reader = PositionReader::new(stream.clone(), skip.clone(), 0).unwrap();
         let mut offset = 0;
         for i in 1..24 {
             buf.resize(i, 0);
@@ -175,7 +173,7 @@ pub mod tests {
         let (stream, skip) = create_stream_buffer(&v[..]);
         assert_eq!(skip.len(), 15_749);
         assert_eq!(stream.len(), 1_000_000);
-        let mut position_reader = PositionReader::new(stream, skip, 128 * 1024);
+        let mut position_reader = PositionReader::new(stream, skip, 128 * 1024).unwrap();
         let mut buf = [0u32; 1];
         position_reader.read(0, &mut buf);
         assert_eq!(buf[0], CONST_VAL);
@@ -194,7 +192,8 @@ pub mod tests {
             128 * 1024 + 7,
             128 * 10 * 1024 + 10,
         ] {
-            let mut position_reader = PositionReader::new(stream.clone(), skip.clone(), offset);
+            let mut position_reader =
+                PositionReader::new(stream.clone(), skip.clone(), offset).unwrap();
             let mut buf = [0u32; 1];
             position_reader.read(0, &mut buf);
             assert_eq!(buf[0], offset as u32);

src/positions/reader.rs

@@ -1,8 +1,13 @@
+use std::io;
+
 use crate::common::{BinarySerializable, FixedSize};
-use crate::directory::ReadOnlySource;
+use crate::directory::FileSlice;
+use crate::directory::OwnedBytes;
 use crate::positions::COMPRESSION_BLOCK_SIZE;
 use crate::positions::LONG_SKIP_INTERVAL;
 use crate::positions::LONG_SKIP_IN_BLOCKS;
+use bitpacking::{BitPacker, BitPacker4x};
+
 /// Positions works as a long sequence of compressed block.
 /// All terms are chained one after the other.
 ///
@@ -23,28 +28,28 @@ use crate::positions::LONG_SKIP_IN_BLOCKS;
 /// A given block obviously takes `(128 x  num_bit_for_the_block / num_bits_in_a_byte)`,
 /// so skipping a block without decompressing it is just a matter of advancing that many
 /// bytes.
-use bitpacking::{BitPacker, BitPacker4x};
-use owned_read::OwnedRead;
 
 struct Positions {
     bit_packer: BitPacker4x,
-    skip_source: ReadOnlySource,
+    skip_file: FileSlice,
-    position_source: ReadOnlySource,
+    position_file: FileSlice,
-    long_skip_source: ReadOnlySource,
+    long_skip_data: OwnedBytes,
 }
 
 impl Positions {
-    pub fn new(position_source: ReadOnlySource, skip_source: ReadOnlySource) -> Positions {
+    pub fn new(position_file: FileSlice, skip_file: FileSlice) -> io::Result<Positions> {
-        let (body, footer) = skip_source.split_from_end(u32::SIZE_IN_BYTES);
+        let (body, footer) = skip_file.split_from_end(u32::SIZE_IN_BYTES);
-        let num_long_skips = u32::deserialize(&mut footer.as_slice()).expect("Index corrupted");
+        let footer_data = footer.read_bytes()?;
-        let (skip_source, long_skip_source) =
+        let num_long_skips = u32::deserialize(&mut footer_data.as_slice())?;
+        let (skip_file, long_skip_file) =
             body.split_from_end(u64::SIZE_IN_BYTES * (num_long_skips as usize));
-        Positions {
+        let long_skip_data = long_skip_file.read_bytes()?;
+        Ok(Positions {
             bit_packer: BitPacker4x::new(),
-            skip_source,
+            skip_file,
-            long_skip_source,
+            long_skip_data,
-            position_source,
+            position_file,
-        }
+        })
     }
 
     /// Returns the offset of the block associated to the given `long_skip_id`.
@@ -54,19 +59,23 @@ impl Positions {
         if long_skip_id == 0 {
             return 0;
         }
-        let long_skip_slice = self.long_skip_source.as_slice();
+        let long_skip_slice = self.long_skip_data.as_slice();
         let mut long_skip_blocks: &[u8] = &long_skip_slice[(long_skip_id - 1) * 8..][..8];
         u64::deserialize(&mut long_skip_blocks).expect("Index corrupted")
     }
 
-    fn reader(&self, offset: u64) -> PositionReader {
+    fn reader(&self, offset: u64) -> io::Result<PositionReader> {
         let long_skip_id = (offset / LONG_SKIP_INTERVAL) as usize;
         let offset_num_bytes: u64 = self.long_skip(long_skip_id);
-        let mut position_read = OwnedRead::new(self.position_source.clone());
+        let position_read = self
-        position_read.advance(offset_num_bytes as usize);
+            .position_file
-        let mut skip_read = OwnedRead::new(self.skip_source.clone());
+            .slice_from(offset_num_bytes as usize)
-        skip_read.advance(long_skip_id * LONG_SKIP_IN_BLOCKS);
+            .read_bytes()?;
-        PositionReader {
+        let skip_read = self
+            .skip_file
+            .slice_from(long_skip_id * LONG_SKIP_IN_BLOCKS)
+            .read_bytes()?;
+        Ok(PositionReader {
             bit_packer: self.bit_packer,
             skip_read,
             position_read,
@@ -74,13 +83,14 @@ impl Positions {
             block_offset: std::i64::MAX as u64,
             anchor_offset: (long_skip_id as u64) * LONG_SKIP_INTERVAL,
             abs_offset: offset,
-        }
+        })
     }
 }
 
+#[derive(Clone)]
 pub struct PositionReader {
-    skip_read: OwnedRead,
+    skip_read: OwnedBytes,
-    position_read: OwnedRead,
+    position_read: OwnedBytes,
     bit_packer: BitPacker4x,
     buffer: Box<[u32; COMPRESSION_BLOCK_SIZE]>,
 
@@ -92,11 +102,12 @@ pub struct PositionReader {
 
 impl PositionReader {
     pub fn new(
-        position_source: ReadOnlySource,
+        position_file: FileSlice,
-        skip_source: ReadOnlySource,
+        skip_file: FileSlice,
         offset: u64,
-    ) -> PositionReader {
+    ) -> io::Result<PositionReader> {
-        Positions::new(position_source, skip_source).reader(offset)
+        let positions = Positions::new(position_file, skip_file)?;
+        positions.reader(offset)
     }
 
     fn advance_num_blocks(&mut self, num_blocks: usize) {
@@ -130,7 +141,7 @@ impl PositionReader {
             self.advance_num_blocks(num_blocks_to_skip);
             self.anchor_offset = offset - (offset % COMPRESSION_BLOCK_SIZE as u64);
             self.block_offset = self.anchor_offset;
-            let num_bits = self.skip_read.get(0);
+            let num_bits = self.skip_read.as_slice()[0];
             self.bit_packer
                 .decompress(self.position_read.as_ref(), self.buffer.as_mut(), num_bits);
         } else {
@@ -140,7 +151,7 @@ impl PositionReader {
             self.anchor_offset = self.block_offset;
         }
 
-        let mut num_bits = self.skip_read.get(0);
+        let mut num_bits = self.skip_read.as_slice()[0];
         let mut position_data = self.position_read.as_ref();
 
         for i in 1.. {
@@ -154,7 +165,7 @@ impl PositionReader {
             output = &mut output[remaining_in_block..];
             offset += remaining_in_block as u64;
             position_data = &position_data[(num_bits as usize * COMPRESSION_BLOCK_SIZE / 8)..];
-            num_bits = self.skip_read.get(i);
+            num_bits = self.skip_read.as_slice()[i];
             self.bit_packer
                 .decompress(position_data, self.buffer.as_mut(), num_bits);
             self.block_offset += COMPRESSION_BLOCK_SIZE as u64;

src/postings/block_segment_postings.rs

@@ -1,11 +1,24 @@
+use std::io;
+
 use crate::common::{BinarySerializable, VInt};
-use crate::directory::ReadOnlySource;
+use crate::directory::FileSlice;
+use crate::directory::OwnedBytes;
+use crate::fieldnorm::FieldNormReader;
 use crate::postings::compression::{
     AlignedBuffer, BlockDecoder, VIntDecoder, COMPRESSION_BLOCK_SIZE,
 };
 use crate::postings::{BlockInfo, FreqReadingOption, SkipReader};
+use crate::query::BM25Weight;
 use crate::schema::IndexRecordOption;
-use crate::{DocId, TERMINATED};
+use crate::{DocId, Score, TERMINATED};
+
+fn max_score<I: Iterator<Item = Score>>(mut it: I) -> Option<Score> {
+    if let Some(first) = it.next() {
+        Some(it.fold(first, Score::max))
+    } else {
+        None
+    }
+}
 
 /// `BlockSegmentPostings` is a cursor iterating over blocks
 /// of documents.
@@ -14,16 +27,18 @@ use crate::{DocId, TERMINATED};
 ///
 /// While it is useful for some very specific high-performance
 /// use cases, you should prefer using `SegmentPostings` for most usage.
+#[derive(Clone)]
 pub struct BlockSegmentPostings {
     pub(crate) doc_decoder: BlockDecoder,
     loaded_offset: usize,
     freq_decoder: BlockDecoder,
     freq_reading_option: FreqReadingOption,
+    block_max_score_cache: Option<Score>,
 
-    doc_freq: usize,
+    doc_freq: u32,
 
-    data: ReadOnlySource,
+    data: OwnedBytes,
-    skip_reader: SkipReader,
+    pub(crate) skip_reader: SkipReader,
 }
 
 fn decode_bitpacked_block(
@@ -47,60 +62,104 @@ fn decode_vint_block(
     doc_offset: DocId,
     num_vint_docs: usize,
 ) {
-    doc_decoder.clear();
+    let num_consumed_bytes =
-    let num_consumed_bytes = doc_decoder.uncompress_vint_sorted(data, doc_offset, num_vint_docs);
+        doc_decoder.uncompress_vint_sorted(data, doc_offset, num_vint_docs, TERMINATED);
     if let Some(freq_decoder) = freq_decoder_opt {
-        freq_decoder.uncompress_vint_unsorted(&data[num_consumed_bytes..], num_vint_docs);
+        freq_decoder.uncompress_vint_unsorted(
+            &data[num_consumed_bytes..],
+            num_vint_docs,
+            TERMINATED,
+        );
     }
 }
 
 fn split_into_skips_and_postings(
     doc_freq: u32,
-    data: ReadOnlySource,
+    mut bytes: OwnedBytes,
-) -> (Option<ReadOnlySource>, ReadOnlySource) {
+) -> (Option<OwnedBytes>, OwnedBytes) {
     if doc_freq < COMPRESSION_BLOCK_SIZE as u32 {
-        return (None, data);
+        return (None, bytes);
     }
-    let mut data_byte_arr = data.as_slice();
+    let skip_len = VInt::deserialize(&mut bytes).expect("Data corrupted").0 as usize;
-    let skip_len = VInt::deserialize(&mut data_byte_arr)
+    let (skip_data, postings_data) = bytes.split(skip_len);
-        .expect("Data corrupted")
-        .0 as usize;
-    let vint_len = data.len() - data_byte_arr.len();
-    let (skip_data, postings_data) = data.slice_from(vint_len).split(skip_len);
     (Some(skip_data), postings_data)
 }
 
 impl BlockSegmentPostings {
-    pub(crate) fn from_data(
+    pub(crate) fn open(
         doc_freq: u32,
-        data: ReadOnlySource,
+        data: FileSlice,
         record_option: IndexRecordOption,
         requested_option: IndexRecordOption,
-    ) -> BlockSegmentPostings {
+    ) -> io::Result<BlockSegmentPostings> {
         let freq_reading_option = match (record_option, requested_option) {
             (IndexRecordOption::Basic, _) => FreqReadingOption::NoFreq,
             (_, IndexRecordOption::Basic) => FreqReadingOption::SkipFreq,
             (_, _) => FreqReadingOption::ReadFreq,
         };
 
-        let (skip_data_opt, postings_data) = split_into_skips_and_postings(doc_freq, data);
+        let (skip_data_opt, postings_data) =
+            split_into_skips_and_postings(doc_freq, data.read_bytes()?);
         let skip_reader = match skip_data_opt {
             Some(skip_data) => SkipReader::new(skip_data, doc_freq, record_option),
-            None => SkipReader::new(ReadOnlySource::empty(), doc_freq, record_option),
+            None => SkipReader::new(OwnedBytes::empty(), doc_freq, record_option),
         };
 
-        let doc_freq = doc_freq as usize;
         let mut block_segment_postings = BlockSegmentPostings {
             doc_decoder: BlockDecoder::with_val(TERMINATED),
             loaded_offset: std::usize::MAX,
             freq_decoder: BlockDecoder::with_val(1),
             freq_reading_option,
+            block_max_score_cache: None,
             doc_freq,
             data: postings_data,
             skip_reader,
         };
-        block_segment_postings.advance();
+        block_segment_postings.load_block();
-        block_segment_postings
+        Ok(block_segment_postings)
+    }
+
+    /// Returns the block_max_score for the current block.
+    /// It does not require the block to be loaded. For instance, it is ok to call this method
+    /// after having called `.shallow_advance(..)`.
+    ///
+    /// See `TermScorer::block_max_score(..)` for more information.
+    pub fn block_max_score(
+        &mut self,
+        fieldnorm_reader: &FieldNormReader,
+        bm25_weight: &BM25Weight,
+    ) -> Score {
+        if let Some(score) = self.block_max_score_cache {
+            return score;
+        }
+        if let Some(skip_reader_max_score) = self.skip_reader.block_max_score(bm25_weight) {
+            // if we are on a full block, the skip reader should have the block max information
+            // for us
+            self.block_max_score_cache = Some(skip_reader_max_score);
+            return skip_reader_max_score;
+        }
+        // this is the last block of the segment posting list.
+        // If it is actually loaded, we can compute block max manually.
+        if self.block_is_loaded() {
+            let docs = self.doc_decoder.output_array().iter().cloned();
+            let freqs = self.freq_decoder.output_array().iter().cloned();
+            let bm25_scores = docs.zip(freqs).map(|(doc, term_freq)| {
+                let fieldnorm_id = fieldnorm_reader.fieldnorm_id(doc);
+                bm25_weight.score(fieldnorm_id, term_freq)
+            });
+            let block_max_score = max_score(bm25_scores).unwrap_or(0.0);
+            self.block_max_score_cache = Some(block_max_score);
+            return block_max_score;
+        }
+        // We do not have access to any good block max value. We return bm25_weight.max_score()
+        // as it is a valid upperbound.
+        //
+        // We do not cache it however, so that it gets computed when once block is loaded.
+        bm25_weight.max_score()
+    }
+
+    pub(crate) fn freq_reading_option(&self) -> FreqReadingOption {
+        self.freq_reading_option
     }
 
     // Resets the block segment postings on another position
@@ -113,24 +172,26 @@ impl BlockSegmentPostings {
     // # Warning
     //
     // This does not reset the positions list.
-    pub(crate) fn reset(&mut self, doc_freq: u32, postings_data: ReadOnlySource) {
+    pub(crate) fn reset(&mut self, doc_freq: u32, postings_data: OwnedBytes) {
         let (skip_data_opt, postings_data) = split_into_skips_and_postings(doc_freq, postings_data);
-        self.data = ReadOnlySource::new(postings_data);
+        self.data = postings_data;
-        self.loaded_offset = std::usize::MAX;
+        self.block_max_score_cache = None;
         self.loaded_offset = std::usize::MAX;
         if let Some(skip_data) = skip_data_opt {
             self.skip_reader.reset(skip_data, doc_freq);
         } else {
-            self.skip_reader.reset(ReadOnlySource::empty(), doc_freq);
+            self.skip_reader.reset(OwnedBytes::empty(), doc_freq);
         }
-        self.doc_freq = doc_freq as usize;
+        self.doc_freq = doc_freq;
+        self.load_block();
     }
 
-    /// Returns the document frequency associated to this block postings.
+    /// Returns the overall number of documents in the block postings.
+    /// It does not take in account whether documents are deleted or not.
     ///
     /// This `doc_freq` is simply the sum of the length of all of the blocks
     /// length, and it does not take in account deleted documents.
-    pub fn doc_freq(&self) -> usize {
+    pub fn doc_freq(&self) -> u32 {
         self.doc_freq
     }
 
@@ -140,11 +201,20 @@ impl BlockSegmentPostings {
     /// returned by `.docs()` is empty.
     #[inline]
     pub fn docs(&self) -> &[DocId] {
+        debug_assert!(self.block_is_loaded());
         self.doc_decoder.output_array()
     }
 
+    /// Returns a full block, regardless of whetehr the block is complete or incomplete (
+    /// as it happens for the last block of the posting list).
+    ///
+    /// In the latter case, the block is guaranteed to be padded with the sentinel value:
+    /// `TERMINATED`. The array is also guaranteed to be aligned on 16 bytes = 128 bits.
+    ///
+    /// This method is useful to run SSE2 linear search.
     #[inline(always)]
     pub(crate) fn docs_aligned(&self) -> &AlignedBuffer {
+        debug_assert!(self.block_is_loaded());
         self.doc_decoder.output_aligned()
     }
 
@@ -157,12 +227,14 @@ impl BlockSegmentPostings {
     /// Return the array of `term freq` in the block.
     #[inline]
     pub fn freqs(&self) -> &[u32] {
+        debug_assert!(self.block_is_loaded());
         self.freq_decoder.output_array()
     }
 
     /// Return the frequency at index `idx` of the block.
     #[inline]
     pub fn freq(&self, idx: usize) -> u32 {
+        debug_assert!(self.block_is_loaded());
         self.freq_decoder.output(idx)
     }
 
@@ -173,23 +245,40 @@ impl BlockSegmentPostings {
     /// of any number between 1 and `NUM_DOCS_PER_BLOCK - 1`
     #[inline]
     pub fn block_len(&self) -> usize {
+        debug_assert!(self.block_is_loaded());
         self.doc_decoder.output_len
     }
 
-    pub(crate) fn position_offset(&self) -> u64 {
-        self.skip_reader.position_offset()
-    }
-
     /// Position on a block that may contains `target_doc`.
     ///
     /// If all docs are smaller than target, the block loaded may be empty,
     /// or be the last an incomplete VInt block.
     pub fn seek(&mut self, target_doc: DocId) {
-        self.skip_reader.seek(target_doc);
+        self.shallow_seek(target_doc);
         self.load_block();
     }
 
-    fn load_block(&mut self) {
+    pub(crate) fn position_offset(&self) -> u64 {
+        self.skip_reader.position_offset()
+    }
+
+    /// Dangerous API! This calls seek on the skip list,
+    /// but does not `.load_block()` afterwards.
+    ///
+    /// `.load_block()` needs to be called manually afterwards.
+    /// If all docs are smaller than target, the block loaded may be empty,
+    /// or be the last an incomplete VInt block.
+    pub(crate) fn shallow_seek(&mut self, target_doc: DocId) {
+        if self.skip_reader.seek(target_doc) {
+            self.block_max_score_cache = None;
+        }
+    }
+
+    pub(crate) fn block_is_loaded(&self) -> bool {
+        self.loaded_offset == self.skip_reader.byte_offset()
+    }
+
+    pub(crate) fn load_block(&mut self) {
         let offset = self.skip_reader.byte_offset();
         if self.loaded_offset == offset {
             return;
@@ -214,7 +303,14 @@ impl BlockSegmentPostings {
                     tf_num_bits,
                 );
             }
-            BlockInfo::VInt(num_vint_docs) => {
+            BlockInfo::VInt { num_docs } => {
+                let data = {
+                    if num_docs == 0 {
+                        &[]
+                    } else {
+                        &self.data.as_slice()[offset..]
+                    }
+                };
                 decode_vint_block(
                     &mut self.doc_decoder,
                     if let FreqReadingOption::ReadFreq = self.freq_reading_option {
@@ -222,9 +318,9 @@ impl BlockSegmentPostings {
                     } else {
                         None
                     },
-                    &self.data.as_slice()[offset..],
+                    data,
                     self.skip_reader.last_doc_in_previous_block,
-                    num_vint_docs as usize,
+                    num_docs as usize,
                 );
             }
         }
@@ -233,24 +329,23 @@ impl BlockSegmentPostings {
     /// Advance to the next block.
     ///
     /// Returns false iff there was no remaining blocks.
-    pub fn advance(&mut self) -> bool {
+    pub fn advance(&mut self) {
-        if !self.skip_reader.advance() {
+        self.skip_reader.advance();
-            return false;
+        self.block_max_score_cache = None;
-        }
         self.load_block();
-        true
     }
 
     /// Returns an empty segment postings object
     pub fn empty() -> BlockSegmentPostings {
         BlockSegmentPostings {
             doc_decoder: BlockDecoder::with_val(TERMINATED),
-            loaded_offset: std::usize::MAX,
+            loaded_offset: 0,
             freq_decoder: BlockDecoder::with_val(1),
             freq_reading_option: FreqReadingOption::NoFreq,
+            block_max_score_cache: None,
             doc_freq: 0,
-            data: ReadOnlySource::new(vec![]),
+            data: OwnedBytes::empty(),
-            skip_reader: SkipReader::new(ReadOnlySource::new(vec![]), 0, IndexRecordOption::Basic),
+            skip_reader: SkipReader::new(OwnedBytes::empty(), 0, IndexRecordOption::Basic),
         }
     }
 }
@@ -273,8 +368,10 @@ mod tests {
     #[test]
     fn test_empty_segment_postings() {
         let mut postings = SegmentPostings::empty();
+        assert_eq!(postings.doc(), TERMINATED);
         assert_eq!(postings.advance(), TERMINATED);
         assert_eq!(postings.advance(), TERMINATED);
+        assert_eq!(postings.doc_freq(), 0);
         assert_eq!(postings.len(), 0);
     }
 
@@ -294,7 +391,10 @@ mod tests {
     #[test]
     fn test_empty_block_segment_postings() {
         let mut postings = BlockSegmentPostings::empty();
-        assert!(!postings.advance());
+        assert!(postings.docs().is_empty());
+        assert_eq!(postings.doc_freq(), 0);
+        postings.advance();
+        assert!(postings.docs().is_empty());
         assert_eq!(postings.doc_freq(), 0);
     }
 
@@ -306,13 +406,14 @@ mod tests {
         assert_eq!(block_segments.doc_freq(), 100_000);
         loop {
             let block = block_segments.docs();
+            if block.is_empty() {
+                break;
+            }
             for (i, doc) in block.iter().cloned().enumerate() {
                 assert_eq!(offset + (i as u32), doc);
             }
             offset += block.len() as u32;
-            if block_segments.advance() {
+            block_segments.advance();
-                break;
-            }
         }
     }
 
@@ -354,7 +455,7 @@ mod tests {
         let int_field = schema_builder.add_u64_field("id", INDEXED);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests().unwrap();
         let mut last_doc = 0u32;
         for &doc in docs {
             for _ in last_doc..doc {
@@ -366,14 +467,16 @@ mod tests {
         index_writer.commit().unwrap();
         let searcher = index.reader().unwrap().searcher();
         let segment_reader = searcher.segment_reader(0);
-        let inverted_index = segment_reader.inverted_index(int_field);
+        let inverted_index = segment_reader.inverted_index(int_field).unwrap();
         let term = Term::from_field_u64(int_field, 0u64);
         let term_info = inverted_index.get_term_info(&term).unwrap();
-        inverted_index.read_block_postings_from_terminfo(&term_info, IndexRecordOption::Basic)
+        inverted_index
+            .read_block_postings_from_terminfo(&term_info, IndexRecordOption::Basic)
+            .unwrap()
     }
 
     #[test]
-    fn test_block_segment_postings_skip2() {
+    fn test_block_segment_postings_seek() {
         let mut docs = vec![0];
         for i in 0..1300 {
             docs.push((i * i / 100) + i);
@@ -390,38 +493,38 @@ mod tests {
     }
 
     #[test]
-    fn test_reset_block_segment_postings() {
+    fn test_reset_block_segment_postings() -> crate::Result<()> {
         let mut schema_builder = Schema::builder();
         let int_field = schema_builder.add_u64_field("id", INDEXED);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests()?;
         // create two postings list, one containg even number,
         // the other containing odd numbers.
         for i in 0..6 {
             let doc = doc!(int_field=> (i % 2) as u64);
             index_writer.add_document(doc);
         }
-        index_writer.commit().unwrap();
+        index_writer.commit()?;
-        let searcher = index.reader().unwrap().searcher();
+        let searcher = index.reader()?.searcher();
         let segment_reader = searcher.segment_reader(0);
 
         let mut block_segments;
         {
             let term = Term::from_field_u64(int_field, 0u64);
-            let inverted_index = segment_reader.inverted_index(int_field);
+            let inverted_index = segment_reader.inverted_index(int_field)?;
             let term_info = inverted_index.get_term_info(&term).unwrap();
             block_segments = inverted_index
-                .read_block_postings_from_terminfo(&term_info, IndexRecordOption::Basic);
+                .read_block_postings_from_terminfo(&term_info, IndexRecordOption::Basic)?;
         }
         assert_eq!(block_segments.docs(), &[0, 2, 4]);
         {
             let term = Term::from_field_u64(int_field, 1u64);
-            let inverted_index = segment_reader.inverted_index(int_field);
+            let inverted_index = segment_reader.inverted_index(int_field)?;
             let term_info = inverted_index.get_term_info(&term).unwrap();
-            inverted_index.reset_block_postings_from_terminfo(&term_info, &mut block_segments);
+            inverted_index.reset_block_postings_from_terminfo(&term_info, &mut block_segments)?;
         }
-        assert!(block_segments.advance());
         assert_eq!(block_segments.docs(), &[1, 3, 5]);
+        Ok(())
     }
 }

src/postings/compression/mod.rs

@@ -1,5 +1,4 @@
 use crate::common::FixedSize;
-use crate::docset::TERMINATED;
 use bitpacking::{BitPacker, BitPacker4x};
 
 pub const COMPRESSION_BLOCK_SIZE: usize = BitPacker4x::BLOCK_LEN;
@@ -53,8 +52,10 @@ impl BlockEncoder {
 /// We ensure that the OutputBuffer is align on 128 bits
 /// in order to run SSE2 linear search on it.
 #[repr(align(128))]
+#[derive(Clone)]
 pub(crate) struct AlignedBuffer(pub [u32; COMPRESSION_BLOCK_SIZE]);
 
+#[derive(Clone)]
 pub struct BlockDecoder {
     bitpacker: BitPacker4x,
     output: AlignedBuffer,
@@ -107,10 +108,6 @@ impl BlockDecoder {
     pub fn output(&self, idx: usize) -> u32 {
         self.output.0[idx]
     }
-
-    pub fn clear(&mut self) {
-        self.output.0.iter_mut().for_each(|el| *el = TERMINATED);
-    }
 }
 
 pub trait VIntEncoder {
@@ -147,11 +144,14 @@ pub trait VIntDecoder {
     /// For instance, if delta encoded are `1, 3, 9`, and the
     /// `offset` is 5, then the output will be:
     /// `5 + 1 = 6, 6 + 3= 9, 9 + 9 = 18`
+    ///
+    /// The value given in `padding` will be used to fill the remaining `128 - num_els` values.
     fn uncompress_vint_sorted(
         &mut self,
         compressed_data: &[u8],
         offset: u32,
         num_els: usize,
+        padding: u32,
     ) -> usize;
 
     /// Uncompress an array of `u32s`, compressed using variable
@@ -159,7 +159,14 @@ pub trait VIntDecoder {
     ///
     /// The method takes a number of int to decompress, and returns
     /// the amount of bytes that were read to decompress them.
-    fn uncompress_vint_unsorted(&mut self, compressed_data: &[u8], num_els: usize) -> usize;
+    ///
+    /// The value given in `padding` will be used to fill the remaining `128 - num_els` values.
+    fn uncompress_vint_unsorted(
+        &mut self,
+        compressed_data: &[u8],
+        num_els: usize,
+        padding: u32,
+    ) -> usize;
 }
 
 impl VIntEncoder for BlockEncoder {
@@ -178,13 +185,21 @@ impl VIntDecoder for BlockDecoder {
         compressed_data: &[u8],
         offset: u32,
         num_els: usize,
+        padding: u32,
     ) -> usize {
         self.output_len = num_els;
+        self.output.0.iter_mut().for_each(|el| *el = padding);
         vint::uncompress_sorted(compressed_data, &mut self.output.0[..num_els], offset)
     }
 
-    fn uncompress_vint_unsorted(&mut self, compressed_data: &[u8], num_els: usize) -> usize {
+    fn uncompress_vint_unsorted(
+        &mut self,
+        compressed_data: &[u8],
+        num_els: usize,
+        padding: u32,
+    ) -> usize {
         self.output_len = num_els;
+        self.output.0.iter_mut().for_each(|el| *el = padding);
         vint::uncompress_unsorted(compressed_data, &mut self.output.0[..num_els])
     }
 }
@@ -193,6 +208,7 @@ impl VIntDecoder for BlockDecoder {
 pub mod tests {
 
     use super::*;
+    use crate::TERMINATED;
 
     #[test]
     fn test_encode_sorted_block() {
@@ -271,18 +287,20 @@ pub mod tests {
     }
     #[test]
     fn test_encode_vint() {
-        {
+        const PADDING_VALUE: u32 = 234_234_345u32;
-            let expected_length = 154;
+        let expected_length = 154;
-            let mut encoder = BlockEncoder::new();
+        let mut encoder = BlockEncoder::new();
-            let input: Vec<u32> = (0u32..123u32).map(|i| 4 + i * 7 / 2).into_iter().collect();
+        let input: Vec<u32> = (0u32..123u32).map(|i| 4 + i * 7 / 2).into_iter().collect();
-            for offset in &[0u32, 1u32, 2u32] {
+        for offset in &[0u32, 1u32, 2u32] {
-                let encoded_data = encoder.compress_vint_sorted(&input, *offset);
+            let encoded_data = encoder.compress_vint_sorted(&input, *offset);
-                assert!(encoded_data.len() <= expected_length);
+            assert!(encoded_data.len() <= expected_length);
-                let mut decoder = BlockDecoder::default();
+            let mut decoder = BlockDecoder::default();
-                let consumed_num_bytes =
+            let consumed_num_bytes =
-                    decoder.uncompress_vint_sorted(&encoded_data, *offset, input.len());
+                decoder.uncompress_vint_sorted(&encoded_data, *offset, input.len(), PADDING_VALUE);
-                assert_eq!(consumed_num_bytes, encoded_data.len());
+            assert_eq!(consumed_num_bytes, encoded_data.len());
-                assert_eq!(input, decoder.output_array());
+            assert_eq!(input, decoder.output_array());
+            for i in input.len()..COMPRESSION_BLOCK_SIZE {
+                assert_eq!(decoder.output(i), PADDING_VALUE);
             }
         }
     }
@@ -292,6 +310,7 @@ pub mod tests {
 mod bench {
 
     use super::*;
+    use crate::TERMINATED;
     use rand::rngs::StdRng;
     use rand::Rng;
     use rand::SeedableRng;
@@ -322,7 +341,7 @@ mod bench {
         let mut encoder = BlockEncoder::new();
         let data = generate_array(COMPRESSION_BLOCK_SIZE, 0.1);
         let (num_bits, compressed) = encoder.compress_block_sorted(&data, 0u32);
-        let mut decoder = BlockDecoder::new();
+        let mut decoder = BlockDecoder::default();
         b.iter(|| {
             decoder.uncompress_block_sorted(compressed, 0u32, num_bits);
         });
@@ -357,9 +376,9 @@ mod bench {
         let mut encoder = BlockEncoder::new();
         let data = generate_array(NUM_INTS_BENCH_VINT, 0.001);
         let compressed = encoder.compress_vint_sorted(&data, 0u32);
-        let mut decoder = BlockDecoder::new();
+        let mut decoder = BlockDecoder::default();
         b.iter(|| {
-            decoder.uncompress_vint_sorted(compressed, 0u32, NUM_INTS_BENCH_VINT);
+            decoder.uncompress_vint_sorted(compressed, 0u32, NUM_INTS_BENCH_VINT, TERMINATED);
         });
     }
 }

src/postings/mod.rs

@@ -28,8 +28,6 @@ pub use self::segment_postings::SegmentPostings;
 
 pub(crate) use self::stacker::compute_table_size;
 
-pub use crate::common::HasLen;
-
 pub(crate) type UnorderedTermId = u64;
 
 #[cfg_attr(feature = "cargo-clippy", allow(clippy::enum_variant_names))]
@@ -42,8 +40,8 @@ pub(crate) enum FreqReadingOption {
 
 #[cfg(test)]
 pub mod tests {
-
+    use super::InvertedIndexSerializer;
-    use super::*;
+    use super::Postings;
     use crate::core::Index;
     use crate::core::SegmentComponent;
     use crate::core::SegmentReader;
@@ -58,6 +56,7 @@ pub mod tests {
     use crate::schema::{IndexRecordOption, TextFieldIndexing};
     use crate::tokenizer::{SimpleTokenizer, MAX_TOKEN_LEN};
     use crate::DocId;
+    use crate::HasLen;
     use crate::Score;
     use once_cell::sync::Lazy;
     use rand::rngs::StdRng;
@@ -65,51 +64,48 @@ pub mod tests {
     use std::iter;
 
     #[test]
-    pub fn test_position_write() {
+    pub fn test_position_write() -> crate::Result<()> {
         let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", TEXT);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
         let mut segment = index.new_segment();
-        let mut posting_serializer = InvertedIndexSerializer::open(&mut segment).unwrap();
+        let mut posting_serializer = InvertedIndexSerializer::open(&mut segment)?;
-        {
+        let mut field_serializer = posting_serializer.new_field(text_field, 120 * 4, None)?;
-            let mut field_serializer = posting_serializer.new_field(text_field, 120 * 4).unwrap();
+        field_serializer.new_term("abc".as_bytes(), 12u32)?;
-            field_serializer.new_term("abc".as_bytes()).unwrap();
+        for doc_id in 0u32..120u32 {
-            for doc_id in 0u32..120u32 {
+            let delta_positions = vec![1, 2, 3, 2];
-                let delta_positions = vec![1, 2, 3, 2];
+            field_serializer.write_doc(doc_id, 4, &delta_positions)?;
-                field_serializer
-                    .write_doc(doc_id, 4, &delta_positions)
-                    .unwrap();
-            }
-            field_serializer.close_term().unwrap();
         }
-        posting_serializer.close().unwrap();
+        field_serializer.close_term()?;
-        let read = segment.open_read(SegmentComponent::POSITIONS).unwrap();
+        posting_serializer.close()?;
+        let read = segment.open_read(SegmentComponent::POSITIONS)?;
         assert!(read.len() <= 140);
+        Ok(())
     }
 
     #[test]
-    pub fn test_skip_positions() {
+    pub fn test_skip_positions() -> crate::Result<()> {
         let mut schema_builder = Schema::builder();
         let title = schema_builder.add_text_field("title", TEXT);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
-        let mut index_writer = index.writer_with_num_threads(1, 30_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests()?;
         index_writer.add_document(doc!(title => r#"abc abc abc"#));
         index_writer.add_document(doc!(title => r#"abc be be be be abc"#));
         for _ in 0..1_000 {
             index_writer.add_document(doc!(title => r#"abc abc abc"#));
         }
         index_writer.add_document(doc!(title => r#"abc be be be be abc"#));
-        index_writer.commit().unwrap();
+        index_writer.commit()?;
 
-        let searcher = index.reader().unwrap().searcher();
+        let searcher = index.reader()?.searcher();
-        let inverted_index = searcher.segment_reader(0u32).inverted_index(title);
+        let inverted_index = searcher.segment_reader(0u32).inverted_index(title)?;
         let term = Term::from_field_text(title, "abc");
         let mut positions = Vec::new();
         {
             let mut postings = inverted_index
-                .read_postings(&term, IndexRecordOption::WithFreqsAndPositions)
+                .read_postings(&term, IndexRecordOption::WithFreqsAndPositions)?
                 .unwrap();
             assert_eq!(postings.doc(), 0);
             postings.positions(&mut positions);
@@ -123,7 +119,7 @@ pub mod tests {
         }
         {
             let mut postings = inverted_index
-                .read_postings(&term, IndexRecordOption::WithFreqsAndPositions)
+                .read_postings(&term, IndexRecordOption::WithFreqsAndPositions)?
                 .unwrap();
             assert_eq!(postings.doc(), 0);
             assert_eq!(postings.advance(), 1);
@@ -132,7 +128,7 @@ pub mod tests {
         }
         {
             let mut postings = inverted_index
-                .read_postings(&term, IndexRecordOption::WithFreqsAndPositions)
+                .read_postings(&term, IndexRecordOption::WithFreqsAndPositions)?
                 .unwrap();
             assert_eq!(postings.seek(1), 1);
             assert_eq!(postings.doc(), 1);
@@ -141,7 +137,7 @@ pub mod tests {
         }
         {
             let mut postings = inverted_index
-                .read_postings(&term, IndexRecordOption::WithFreqsAndPositions)
+                .read_postings(&term, IndexRecordOption::WithFreqsAndPositions)?
                 .unwrap();
             assert_eq!(postings.seek(1002), 1002);
             assert_eq!(postings.doc(), 1002);
@@ -150,7 +146,7 @@ pub mod tests {
         }
         {
             let mut postings = inverted_index
-                .read_postings(&term, IndexRecordOption::WithFreqsAndPositions)
+                .read_postings(&term, IndexRecordOption::WithFreqsAndPositions)?
                 .unwrap();
             assert_eq!(postings.seek(100), 100);
             assert_eq!(postings.seek(1002), 1002);
@@ -158,10 +154,11 @@ pub mod tests {
             postings.positions(&mut positions);
             assert_eq!(&[0, 5], &positions[..]);
         }
+        Ok(())
     }
 
     #[test]
-    pub fn test_drop_token_that_are_too_long() {
+    pub fn test_drop_token_that_are_too_long() -> crate::Result<()> {
         let ok_token_text: String = iter::repeat('A').take(MAX_TOKEN_LEN).collect();
         let mut exceeding_token_text: String = iter::repeat('A').take(MAX_TOKEN_LEN + 1).collect();
         exceeding_token_text.push_str(" hello");
@@ -178,7 +175,7 @@ pub mod tests {
             .tokenizers()
             .register("simple_no_truncation", SimpleTokenizer);
         let reader = index.reader().unwrap();
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests().unwrap();
         index_writer.set_merge_policy(Box::new(NoMergePolicy));
         {
             index_writer.add_document(doc!(text_field=>exceeding_token_text));
@@ -186,7 +183,7 @@ pub mod tests {
             reader.reload().unwrap();
             let searcher = reader.searcher();
             let segment_reader = searcher.segment_reader(0u32);
-            let inverted_index = segment_reader.inverted_index(text_field);
+            let inverted_index = segment_reader.inverted_index(text_field)?;
             assert_eq!(inverted_index.terms().num_terms(), 1);
             let mut bytes = vec![];
             assert!(inverted_index.terms().ord_to_term(0, &mut bytes));
@@ -198,16 +195,17 @@ pub mod tests {
             reader.reload().unwrap();
             let searcher = reader.searcher();
             let segment_reader = searcher.segment_reader(1u32);
-            let inverted_index = segment_reader.inverted_index(text_field);
+            let inverted_index = segment_reader.inverted_index(text_field)?;
             assert_eq!(inverted_index.terms().num_terms(), 1);
             let mut bytes = vec![];
             assert!(inverted_index.terms().ord_to_term(0, &mut bytes));
             assert_eq!(&bytes[..], ok_token_text.as_bytes());
         }
+        Ok(())
     }
 
     #[test]
-    pub fn test_position_and_fieldnorm1() {
+    pub fn test_position_and_fieldnorm1() -> crate::Result<()> {
         let mut positions = Vec::new();
         let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", TEXT);
@@ -219,42 +217,38 @@ pub mod tests {
             let mut segment_writer =
                 SegmentWriter::for_segment(3_000_000, segment.clone(), &schema).unwrap();
             {
-                let mut doc = Document::default();
                 // checking that position works if the field has two values
-                doc.add_text(text_field, "a b a c a d a a.");
-                doc.add_text(text_field, "d d d d a");
                 let op = AddOperation {
                     opstamp: 0u64,
-                    document: doc,
+                    document: doc!(
+                       text_field => "a b a c a d a a.",
+                       text_field => "d d d d a"
+                    ),
                 };
-                segment_writer.add_document(op, &schema).unwrap();
+                segment_writer.add_document(op, &schema)?;
             }
             {
-                let mut doc = Document::default();
-                doc.add_text(text_field, "b a");
                 let op = AddOperation {
                     opstamp: 1u64,
-                    document: doc,
+                    document: doc!(text_field => "b a"),
                 };
                 segment_writer.add_document(op, &schema).unwrap();
             }
             for i in 2..1000 {
-                let mut doc = Document::default();
+                let mut text: String = iter::repeat("e ").take(i).collect();
-                let mut text = iter::repeat("e ").take(i).collect::<String>();
                 text.push_str(" a");
-                doc.add_text(text_field, &text);
                 let op = AddOperation {
                     opstamp: 2u64,
-                    document: doc,
+                    document: doc!(text_field => text),
                 };
                 segment_writer.add_document(op, &schema).unwrap();
             }
-            segment_writer.finalize().unwrap();
+            segment_writer.finalize()?;
         }
         {
-            let segment_reader = SegmentReader::open(&segment).unwrap();
+            let segment_reader = SegmentReader::open(&segment)?;
             {
-                let fieldnorm_reader = segment_reader.get_fieldnorms_reader(text_field);
+                let fieldnorm_reader = segment_reader.get_fieldnorms_reader(text_field)?;
                 assert_eq!(fieldnorm_reader.fieldnorm(0), 8 + 5);
                 assert_eq!(fieldnorm_reader.fieldnorm(1), 2);
                 for i in 2..1000 {
@@ -267,15 +261,15 @@ pub mod tests {
             {
                 let term_a = Term::from_field_text(text_field, "abcdef");
                 assert!(segment_reader
-                    .inverted_index(term_a.field())
+                    .inverted_index(term_a.field())?
-                    .read_postings(&term_a, IndexRecordOption::WithFreqsAndPositions)
+                    .read_postings(&term_a, IndexRecordOption::WithFreqsAndPositions)?
                     .is_none());
             }
             {
                 let term_a = Term::from_field_text(text_field, "a");
                 let mut postings_a = segment_reader
-                    .inverted_index(term_a.field())
+                    .inverted_index(term_a.field())?
-                    .read_postings(&term_a, IndexRecordOption::WithFreqsAndPositions)
+                    .read_postings(&term_a, IndexRecordOption::WithFreqsAndPositions)?
                     .unwrap();
                 assert_eq!(postings_a.len(), 1000);
                 assert_eq!(postings_a.doc(), 0);
@@ -297,8 +291,8 @@ pub mod tests {
             {
                 let term_e = Term::from_field_text(text_field, "e");
                 let mut postings_e = segment_reader
-                    .inverted_index(term_e.field())
+                    .inverted_index(term_e.field())?
-                    .read_postings(&term_e, IndexRecordOption::WithFreqsAndPositions)
+                    .read_postings(&term_e, IndexRecordOption::WithFreqsAndPositions)?
                     .unwrap();
                 assert_eq!(postings_e.len(), 1000 - 2);
                 for i in 2u32..1000u32 {
@@ -314,17 +308,18 @@ pub mod tests {
                 assert_eq!(postings_e.doc(), TERMINATED);
             }
         }
+        Ok(())
     }
 
     #[test]
-    pub fn test_position_and_fieldnorm2() {
+    pub fn test_position_and_fieldnorm2() -> crate::Result<()> {
         let mut positions: Vec<u32> = Vec::new();
         let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", TEXT);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
         {
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+            let mut index_writer = index.writer_for_tests().unwrap();
             index_writer.add_document(doc!(text_field => "g b b d c g c"));
             index_writer.add_document(doc!(text_field => "g a b b a d c g c"));
             assert!(index_writer.commit().is_ok());
@@ -333,16 +328,17 @@ pub mod tests {
         let searcher = index.reader().unwrap().searcher();
         let segment_reader = searcher.segment_reader(0);
         let mut postings = segment_reader
-            .inverted_index(text_field)
+            .inverted_index(text_field)?
-            .read_postings(&term_a, IndexRecordOption::WithFreqsAndPositions)
+            .read_postings(&term_a, IndexRecordOption::WithFreqsAndPositions)?
             .unwrap();
         assert_eq!(postings.doc(), 1u32);
         postings.positions(&mut positions);
         assert_eq!(&positions[..], &[1u32, 4]);
+        Ok(())
     }
 
     #[test]
-    fn test_skip_next() {
+    fn test_skip_next() -> crate::Result<()> {
         let term_0 = Term::from_field_u64(Field::from_field_id(0), 0);
         let term_1 = Term::from_field_u64(Field::from_field_id(0), 1);
         let term_2 = Term::from_field_u64(Field::from_field_id(0), 2);
@@ -353,10 +349,9 @@ pub mod tests {
             let mut schema_builder = Schema::builder();
             let value_field = schema_builder.add_u64_field("value", INDEXED);
             let schema = schema_builder.build();
-
             let index = Index::create_in_ram(schema);
             {
-                let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+                let mut index_writer = index.writer_for_tests()?;
                 for i in 0u64..num_docs as u64 {
                     let doc = doc!(value_field => 2u64, value_field => i % 2u64);
                     index_writer.add_document(doc);
@@ -365,15 +360,15 @@ pub mod tests {
             }
             index
         };
-        let searcher = index.reader().unwrap().searcher();
+        let searcher = index.reader()?.searcher();
         let segment_reader = searcher.segment_reader(0);
 
         // check that the basic usage works
         for i in 0..num_docs - 1 {
             for j in i + 1..num_docs {
                 let mut segment_postings = segment_reader
-                    .inverted_index(term_2.field())
+                    .inverted_index(term_2.field())?
-                    .read_postings(&term_2, IndexRecordOption::Basic)
+                    .read_postings(&term_2, IndexRecordOption::Basic)?
                     .unwrap();
                 assert_eq!(segment_postings.seek(i), i);
                 assert_eq!(segment_postings.doc(), i);
@@ -385,8 +380,8 @@ pub mod tests {
 
         {
             let mut segment_postings = segment_reader
-                .inverted_index(term_2.field())
+                .inverted_index(term_2.field())?
-                .read_postings(&term_2, IndexRecordOption::Basic)
+                .read_postings(&term_2, IndexRecordOption::Basic)?
                 .unwrap();
 
             // check that `skip_next` advances the iterator
@@ -405,8 +400,8 @@ pub mod tests {
         // check that filtering works
         {
             let mut segment_postings = segment_reader
-                .inverted_index(term_0.field())
+                .inverted_index(term_0.field())?
-                .read_postings(&term_0, IndexRecordOption::Basic)
+                .read_postings(&term_0, IndexRecordOption::Basic)?
                 .unwrap();
 
             for i in 0..num_docs / 2 {
@@ -415,8 +410,8 @@ pub mod tests {
             }
 
             let mut segment_postings = segment_reader
-                .inverted_index(term_0.field())
+                .inverted_index(term_0.field())?
-                .read_postings(&term_0, IndexRecordOption::Basic)
+                .read_postings(&term_0, IndexRecordOption::Basic)?
                 .unwrap();
 
             for i in 0..num_docs / 2 - 1 {
@@ -427,19 +422,19 @@ pub mod tests {
 
         // delete some of the documents
         {
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+            let mut index_writer = index.writer_for_tests()?;
             index_writer.delete_term(term_0);
             assert!(index_writer.commit().is_ok());
         }
-        let searcher = index.reader().unwrap().searcher();
+        let searcher = index.reader()?.searcher();
         assert_eq!(searcher.segment_readers().len(), 1);
         let segment_reader = searcher.segment_reader(0);
 
         // make sure seeking still works
         for i in 0..num_docs {
             let mut segment_postings = segment_reader
-                .inverted_index(term_2.field())
+                .inverted_index(term_2.field())?
-                .read_postings(&term_2, IndexRecordOption::Basic)
+                .read_postings(&term_2, IndexRecordOption::Basic)?
                 .unwrap();
 
             if i % 2 == 0 {
@@ -455,8 +450,8 @@ pub mod tests {
         // now try with a longer sequence
         {
             let mut segment_postings = segment_reader
-                .inverted_index(term_2.field())
+                .inverted_index(term_2.field())?
-                .read_postings(&term_2, IndexRecordOption::Basic)
+                .read_postings(&term_2, IndexRecordOption::Basic)?
                 .unwrap();
 
             let mut last = 2; // start from 5 to avoid seeking to 3 twice
@@ -481,20 +476,19 @@ pub mod tests {
 
         // delete everything else
         {
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+            let mut index_writer = index.writer_for_tests()?;
             index_writer.delete_term(term_1);
             assert!(index_writer.commit().is_ok());
         }
-        let searcher = index.reader().unwrap().searcher();
+        let searcher = index.reader()?.searcher();
 
         // finally, check that it's empty
         {
-            let searchable_segment_ids = index
+            let searchable_segment_ids = index.searchable_segment_ids()?;
-                .searchable_segment_ids()
-                .expect("could not get index segment ids");
             assert!(searchable_segment_ids.is_empty());
             assert_eq!(searcher.num_docs(), 0);
         }
+        Ok(())
     }
 
     pub static TERM_A: Lazy<Term> = Lazy::new(|| {
@@ -524,7 +518,7 @@ pub mod tests {
         let index = Index::create_in_ram(schema);
         let posting_list_size = 1_000_000;
         {
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+            let mut index_writer = index.writer_for_tests().unwrap();
             for _ in 0..posting_list_size {
                 let mut doc = Document::default();
                 if rng.gen_bool(1f64 / 15f64) {
@@ -582,6 +576,9 @@ pub mod tests {
     ) {
         for target in targets {
             let mut postings_opt = postings_factory();
+            if target < postings_opt.doc() {
+                continue;
+            }
             let mut postings_unopt = UnoptimizedDocSet::wrap(postings_factory());
             let skip_result_opt = postings_opt.seek(target);
             let skip_result_unopt = postings_unopt.seek(target);
@@ -623,7 +620,7 @@ mod bench {
         b.iter(|| {
             let mut segment_postings = segment_reader
                 .inverted_index(TERM_A.field())
-                .read_postings(&*TERM_A, IndexRecordOption::Basic)
+                .read_postings(&*TERM_A, IndexRecordOption::Basic)?
                 .unwrap();
             while segment_postings.advance() != TERMINATED {}
         });
@@ -638,18 +635,22 @@ mod bench {
             let segment_postings_a = segment_reader
                 .inverted_index(TERM_A.field())
                 .read_postings(&*TERM_A, IndexRecordOption::Basic)
+                .unwrap()
                 .unwrap();
             let segment_postings_b = segment_reader
                 .inverted_index(TERM_B.field())
                 .read_postings(&*TERM_B, IndexRecordOption::Basic)
+                .unwrap()
                 .unwrap();
             let segment_postings_c = segment_reader
                 .inverted_index(TERM_C.field())
                 .read_postings(&*TERM_C, IndexRecordOption::Basic)
+                .unwrap()
                 .unwrap();
             let segment_postings_d = segment_reader
                 .inverted_index(TERM_D.field())
                 .read_postings(&*TERM_D, IndexRecordOption::Basic)
+                .unwrap()
                 .unwrap();
             let mut intersection = Intersection::new(vec![
                 segment_postings_a,
@@ -670,6 +671,7 @@ mod bench {
         let mut segment_postings = segment_reader
             .inverted_index(TERM_A.field())
             .read_postings(&*TERM_A, IndexRecordOption::Basic)
+            .unwrap()
             .unwrap();
 
         let mut existing_docs = Vec::new();
@@ -729,7 +731,7 @@ mod bench {
             let mut s = 0u32;
             while segment_postings.doc() != TERMINATED {
                 s += (segment_postings.doc() & n) % 1024;
-                segment_postings.advance()
+                segment_postings.advance();
             }
             s
         });

src/postings/postings_writer.rs

@@ -1,5 +1,6 @@
 use super::stacker::{Addr, MemoryArena, TermHashMap};
 
+use crate::fieldnorm::FieldNormReaders;
 use crate::postings::recorder::{
     BufferLender, NothingRecorder, Recorder, TFAndPositionRecorder, TermFrequencyRecorder,
 };
@@ -37,12 +38,8 @@ fn posting_from_field_entry(field_entry: &FieldEntry) -> Box<dyn PostingsWriter>
         | FieldType::I64(_)
         | FieldType::F64(_)
         | FieldType::Date(_)
+        | FieldType::Bytes(_)
         | FieldType::HierarchicalFacet => SpecializedPostingsWriter::<NothingRecorder>::new_boxed(),
-        FieldType::Bytes => {
-            // FieldType::Bytes cannot actually be indexed.
-            // TODO fix during the indexer refactoring described in #276
-            SpecializedPostingsWriter::<NothingRecorder>::new_boxed()
-        }
     }
 }
 
@@ -104,6 +101,7 @@ impl MultiFieldPostingsWriter {
         doc: DocId,
         field: Field,
         token_stream: &mut dyn TokenStream,
+        term_buffer: &mut Term,
     ) -> u32 {
         let postings_writer =
             self.per_field_postings_writers[field.field_id() as usize].deref_mut();
@@ -113,6 +111,7 @@ impl MultiFieldPostingsWriter {
             field,
             token_stream,
             &mut self.heap,
+            term_buffer,
         )
     }
 
@@ -128,6 +127,7 @@ impl MultiFieldPostingsWriter {
     pub fn serialize(
         &self,
         serializer: &mut InvertedIndexSerializer,
+        fieldnorm_readers: FieldNormReaders,
     ) -> crate::Result<HashMap<Field, FnvHashMap<UnorderedTermId, TermOrdinal>>> {
         let mut term_offsets: Vec<(&[u8], Addr, UnorderedTermId)> =
             self.term_index.iter().collect();
@@ -157,12 +157,17 @@ impl MultiFieldPostingsWriter {
                     unordered_term_mappings.insert(field, mapping);
                 }
                 FieldType::U64(_) | FieldType::I64(_) | FieldType::F64(_) | FieldType::Date(_) => {}
-                FieldType::Bytes => {}
+                FieldType::Bytes(_) => {}
             }
 
-            let postings_writer = &self.per_field_postings_writers[field.field_id() as usize];
+            let postings_writer =
-            let mut field_serializer =
+                self.per_field_postings_writers[field.field_id() as usize].as_ref();
-                serializer.new_field(field, postings_writer.total_num_tokens())?;
+            let fieldnorm_reader = fieldnorm_readers.get_field(field)?;
+            let mut field_serializer = serializer.new_field(
+                field,
+                postings_writer.total_num_tokens(),
+                fieldnorm_reader,
+            )?;
             postings_writer.serialize(
                 &term_offsets[start..stop],
                 &mut field_serializer,
@@ -214,13 +219,20 @@ pub trait PostingsWriter {
         field: Field,
         token_stream: &mut dyn TokenStream,
         heap: &mut MemoryArena,
+        term_buffer: &mut Term,
     ) -> u32 {
-        let mut term = Term::for_field(field);
+        term_buffer.set_field(field);
         let mut sink = |token: &Token| {
             // We skip all tokens with a len greater than u16.
             if token.text.len() <= MAX_TOKEN_LEN {
-                term.set_text(token.text.as_str());
+                term_buffer.set_text(token.text.as_str());
-                self.subscribe(term_index, doc_id, token.position as u32, &term, heap);
+                self.subscribe(
+                    term_index,
+                    doc_id,
+                    token.position as u32,
+                    &term_buffer,
+                    heap,
+                );
             } else {
                 info!(
                     "A token exceeding MAX_TOKEN_LEN ({}>{}) was dropped. Search for \
@@ -297,7 +309,8 @@ impl<Rec: Recorder + 'static> PostingsWriter for SpecializedPostingsWriter<Rec>
         let mut buffer_lender = BufferLender::default();
         for &(term_bytes, addr, _) in term_addrs {
             let recorder: Rec = termdict_heap.read(addr);
-            serializer.new_term(&term_bytes[4..])?;
+            let term_doc_freq = recorder.term_doc_freq().unwrap_or(0u32);
+            serializer.new_term(&term_bytes[4..], term_doc_freq)?;
             recorder.serialize(&mut buffer_lender, serializer, heap)?;
             serializer.close_term()?;
         }

src/postings/recorder.rs

@@ -75,6 +75,10 @@ pub(crate) trait Recorder: Copy + 'static {
         serializer: &mut FieldSerializer<'_>,
         heap: &MemoryArena,
     ) -> io::Result<()>;
+    /// Returns the number of document containing this term.
+    ///
+    /// Returns `None` if not available.
+    fn term_doc_freq(&self) -> Option<u32>;
 }
 
 /// Only records the doc ids
@@ -113,11 +117,16 @@ impl Recorder for NothingRecorder {
     ) -> io::Result<()> {
         let buffer = buffer_lender.lend_u8();
         self.stack.read_to_end(heap, buffer);
+        // TODO avoid reading twice.
         for doc in VInt32Reader::new(&buffer[..]) {
             serializer.write_doc(doc as u32, 0u32, &[][..])?;
         }
         Ok(())
     }
+
+    fn term_doc_freq(&self) -> Option<u32> {
+        None
+    }
 }
 
 /// Recorder encoding document ids, and term frequencies
@@ -126,6 +135,7 @@ pub struct TermFrequencyRecorder {
     stack: ExpUnrolledLinkedList,
     current_doc: DocId,
     current_tf: u32,
+    term_doc_freq: u32,
 }
 
 impl Recorder for TermFrequencyRecorder {
@@ -134,6 +144,7 @@ impl Recorder for TermFrequencyRecorder {
             stack: ExpUnrolledLinkedList::new(),
             current_doc: u32::max_value(),
             current_tf: 0u32,
+            term_doc_freq: 0u32,
         }
     }
 
@@ -142,6 +153,7 @@ impl Recorder for TermFrequencyRecorder {
     }
 
     fn new_doc(&mut self, doc: DocId, heap: &mut MemoryArena) {
+        self.term_doc_freq += 1;
         self.current_doc = doc;
         let _ = write_u32_vint(doc, &mut self.stack.writer(heap));
     }
@@ -172,6 +184,10 @@ impl Recorder for TermFrequencyRecorder {
 
         Ok(())
     }
+
+    fn term_doc_freq(&self) -> Option<u32> {
+        Some(self.term_doc_freq)
+    }
 }
 
 /// Recorder encoding term frequencies as well as positions.
@@ -179,12 +195,14 @@ impl Recorder for TermFrequencyRecorder {
 pub struct TFAndPositionRecorder {
     stack: ExpUnrolledLinkedList,
     current_doc: DocId,
+    term_doc_freq: u32,
 }
 impl Recorder for TFAndPositionRecorder {
     fn new() -> Self {
         TFAndPositionRecorder {
             stack: ExpUnrolledLinkedList::new(),
             current_doc: u32::max_value(),
+            term_doc_freq: 0u32,
         }
     }
 
@@ -194,6 +212,7 @@ impl Recorder for TFAndPositionRecorder {
 
     fn new_doc(&mut self, doc: DocId, heap: &mut MemoryArena) {
         self.current_doc = doc;
+        self.term_doc_freq += 1u32;
         let _ = write_u32_vint(doc, &mut self.stack.writer(heap));
     }
 
@@ -233,6 +252,10 @@ impl Recorder for TFAndPositionRecorder {
         }
         Ok(())
     }
+
+    fn term_doc_freq(&self) -> Option<u32> {
+        Some(self.term_doc_freq)
+    }
 }
 
 #[cfg(test)]

src/postings/segment_postings.rs

@@ -1,27 +1,24 @@
 use crate::common::HasLen;
-
+use crate::directory::FileSlice;
 use crate::docset::DocSet;
+use crate::fastfield::DeleteBitSet;
 use crate::positions::PositionReader;
-
 use crate::postings::compression::COMPRESSION_BLOCK_SIZE;
 use crate::postings::serializer::PostingsSerializer;
 use crate::postings::BlockSearcher;
-
-use crate::postings::Postings;
-
-use crate::schema::IndexRecordOption;
-use crate::DocId;
-
-use crate::directory::ReadOnlySource;
 use crate::postings::BlockSegmentPostings;
+use crate::postings::Postings;
+use crate::schema::IndexRecordOption;
+use crate::{DocId, TERMINATED};
 
 /// `SegmentPostings` represents the inverted list or postings associated to
 /// a term in a `Segment`.
 ///
 /// As we iterate through the `SegmentPostings`, the frequencies are optionally decoded.
 /// Positions on the other hand, are optionally entirely decoded upfront.
+#[derive(Clone)]
 pub struct SegmentPostings {
-    block_cursor: BlockSegmentPostings,
+    pub(crate) block_cursor: BlockSegmentPostings,
     cur: usize,
     position_reader: Option<PositionReader>,
     block_searcher: BlockSearcher,
@@ -38,6 +35,31 @@ impl SegmentPostings {
         }
     }
 
+    /// Compute the number of non-deleted documents.
+    ///
+    /// This method will clone and scan through the posting lists.
+    /// (this is a rather expensive operation).
+    pub fn doc_freq_given_deletes(&self, delete_bitset: &DeleteBitSet) -> u32 {
+        let mut docset = self.clone();
+        let mut doc_freq = 0;
+        loop {
+            let doc = docset.doc();
+            if doc == TERMINATED {
+                return doc_freq;
+            }
+            if delete_bitset.is_alive(doc) {
+                doc_freq += 1u32;
+            }
+            docset.advance();
+        }
+    }
+
+    /// Returns the overall number of documents in the block postings.
+    /// It does not take in account whether documents are deleted or not.
+    pub fn doc_freq(&self) -> u32 {
+        self.block_cursor.doc_freq()
+    }
+
     /// Creates a segment postings object with the given documents
     /// and no frequency encoded.
     ///
@@ -49,7 +71,9 @@ impl SegmentPostings {
     pub fn create_from_docs(docs: &[u32]) -> SegmentPostings {
         let mut buffer = Vec::new();
         {
-            let mut postings_serializer = PostingsSerializer::new(&mut buffer, false, false);
+            let mut postings_serializer =
+                PostingsSerializer::new(&mut buffer, 0.0, IndexRecordOption::Basic, None);
+            postings_serializer.new_term(docs.len() as u32);
             for &doc in docs {
                 postings_serializer.write_doc(doc, 1u32);
             }
@@ -57,12 +81,58 @@ impl SegmentPostings {
                 .close_term(docs.len() as u32)
                 .expect("In memory Serialization should never fail.");
         }
-        let block_segment_postings = BlockSegmentPostings::from_data(
+        let block_segment_postings = BlockSegmentPostings::open(
             docs.len() as u32,
-            ReadOnlySource::from(buffer),
+            FileSlice::from(buffer),
             IndexRecordOption::Basic,
             IndexRecordOption::Basic,
+        )
+        .unwrap();
+        SegmentPostings::from_block_postings(block_segment_postings, None)
+    }
+
+    /// Helper functions to create `SegmentPostings` for tests.
+    #[cfg(test)]
+    pub fn create_from_docs_and_tfs(
+        doc_and_tfs: &[(u32, u32)],
+        fieldnorms: Option<&[u32]>,
+    ) -> SegmentPostings {
+        use crate::fieldnorm::FieldNormReader;
+        use crate::Score;
+        let mut buffer: Vec<u8> = Vec::new();
+        let fieldnorm_reader = fieldnorms.map(FieldNormReader::for_test);
+        let average_field_norm = fieldnorms
+            .map(|fieldnorms| {
+                if fieldnorms.len() == 0 {
+                    return 0.0;
+                }
+                let total_num_tokens: u64 = fieldnorms
+                    .iter()
+                    .map(|&fieldnorm| fieldnorm as u64)
+                    .sum::<u64>();
+                total_num_tokens as Score / fieldnorms.len() as Score
+            })
+            .unwrap_or(0.0);
+        let mut postings_serializer = PostingsSerializer::new(
+            &mut buffer,
+            average_field_norm,
+            IndexRecordOption::WithFreqs,
+            fieldnorm_reader,
         );
+        postings_serializer.new_term(doc_and_tfs.len() as u32);
+        for &(doc, tf) in doc_and_tfs {
+            postings_serializer.write_doc(doc, tf);
+        }
+        postings_serializer
+            .close_term(doc_and_tfs.len() as u32)
+            .unwrap();
+        let block_segment_postings = BlockSegmentPostings::open(
+            doc_and_tfs.len() as u32,
+            FileSlice::from(buffer),
+            IndexRecordOption::WithFreqs,
+            IndexRecordOption::WithFreqs,
+        )
+        .unwrap();
         SegmentPostings::from_block_postings(block_segment_postings, None)
     }
 
@@ -90,6 +160,7 @@ impl DocSet for SegmentPostings {
     // next needs to be called a first time to point to the correct element.
     #[inline]
     fn advance(&mut self) -> DocId {
+        debug_assert!(self.block_cursor.block_is_loaded());
         if self.cur == COMPRESSION_BLOCK_SIZE - 1 {
             self.cur = 0;
             self.block_cursor.advance();
@@ -100,14 +171,15 @@ impl DocSet for SegmentPostings {
     }
 
     fn seek(&mut self, target: DocId) -> DocId {
-        if self.doc() == target {
+        debug_assert!(self.doc() <= target);
-            return target;
+        if self.doc() >= target {
+            return self.doc();
         }
+
         self.block_cursor.seek(target);
 
         // At this point we are on the block, that might contain our document.
         let output = self.block_cursor.docs_aligned();
-
         self.cur = self.block_searcher.search_in_block(&output, target);
 
         // The last block is not full and padded with the value TERMINATED,
@@ -123,11 +195,12 @@ impl DocSet for SegmentPostings {
         // After the search, the cursor should point to the first value of TERMINATED.
         let doc = output.0[self.cur];
         debug_assert!(doc >= target);
+        debug_assert_eq!(doc, self.doc());
         doc
     }
 
     /// Return the current document's `DocId`.
-    #[inline]
+    #[inline(always)]
     fn doc(&self) -> DocId {
         self.block_cursor.doc(self.cur)
     }
@@ -139,7 +212,7 @@ impl DocSet for SegmentPostings {
 
 impl HasLen for SegmentPostings {
     fn len(&self) -> usize {
-        self.block_cursor.doc_freq()
+        self.block_cursor.doc_freq() as usize
     }
 }
 
@@ -194,6 +267,7 @@ mod tests {
     use crate::common::HasLen;
 
     use crate::docset::{DocSet, TERMINATED};
+    use crate::fastfield::DeleteBitSet;
     use crate::postings::postings::Postings;
 
     #[test]
@@ -216,4 +290,14 @@ mod tests {
         let postings = SegmentPostings::empty();
         assert_eq!(postings.term_freq(), 1);
     }
+
+    #[test]
+    fn test_doc_freq() {
+        let docs = SegmentPostings::create_from_docs(&[0, 2, 10]);
+        assert_eq!(docs.doc_freq(), 3);
+        let delete_bitset = DeleteBitSet::for_test(&[2], 12);
+        assert_eq!(docs.doc_freq_given_deletes(&delete_bitset), 2);
+        let all_deleted = DeleteBitSet::for_test(&[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11], 12);
+        assert_eq!(docs.doc_freq_given_deletes(&all_deleted), 0);
+    }
 }

src/postings/serializer.rs

@@ -3,13 +3,16 @@ use crate::common::{BinarySerializable, VInt};
 use crate::common::{CompositeWrite, CountingWriter};
 use crate::core::Segment;
 use crate::directory::WritePtr;
+use crate::fieldnorm::FieldNormReader;
 use crate::positions::PositionSerializer;
 use crate::postings::compression::{BlockEncoder, VIntEncoder, COMPRESSION_BLOCK_SIZE};
 use crate::postings::skip::SkipSerializer;
-use crate::schema::Schema;
+use crate::query::BM25Weight;
 use crate::schema::{Field, FieldEntry, FieldType};
+use crate::schema::{IndexRecordOption, Schema};
 use crate::termdict::{TermDictionaryBuilder, TermOrdinal};
-use crate::DocId;
+use crate::{DocId, Score};
+use std::cmp::Ordering;
 use std::io::{self, Write};
 
 /// `InvertedIndexSerializer` is in charge of serializing
@@ -89,20 +92,22 @@ impl InvertedIndexSerializer {
         &mut self,
         field: Field,
         total_num_tokens: u64,
+        fieldnorm_reader: Option<FieldNormReader>,
     ) -> io::Result<FieldSerializer<'_>> {
         let field_entry: &FieldEntry = self.schema.get_field_entry(field);
         let term_dictionary_write = self.terms_write.for_field(field);
         let postings_write = self.postings_write.for_field(field);
-        total_num_tokens.serialize(postings_write)?;
         let positions_write = self.positions_write.for_field(field);
         let positionsidx_write = self.positionsidx_write.for_field(field);
         let field_type: FieldType = (*field_entry.field_type()).clone();
         FieldSerializer::create(
             &field_type,
+            total_num_tokens,
             term_dictionary_write,
             postings_write,
             positions_write,
             positionsidx_write,
+            fieldnorm_reader,
         )
     }
 
@@ -130,26 +135,32 @@ pub struct FieldSerializer<'a> {
 impl<'a> FieldSerializer<'a> {
     fn create(
         field_type: &FieldType,
+        total_num_tokens: u64,
         term_dictionary_write: &'a mut CountingWriter<WritePtr>,
         postings_write: &'a mut CountingWriter<WritePtr>,
         positions_write: &'a mut CountingWriter<WritePtr>,
         positionsidx_write: &'a mut CountingWriter<WritePtr>,
+        fieldnorm_reader: Option<FieldNormReader>,
     ) -> io::Result<FieldSerializer<'a>> {
-        let (term_freq_enabled, position_enabled): (bool, bool) = match field_type {
+        total_num_tokens.serialize(postings_write)?;
+        let mode = match field_type {
             FieldType::Str(ref text_options) => {
                 if let Some(text_indexing_options) = text_options.get_indexing_options() {
-                    let index_option = text_indexing_options.index_option();
+                    text_indexing_options.index_option()
-                    (index_option.has_freq(), index_option.has_positions())
                 } else {
-                    (false, false)
+                    IndexRecordOption::Basic
                 }
             }
-            _ => (false, false),
+            _ => IndexRecordOption::Basic,
         };
         let term_dictionary_builder = TermDictionaryBuilder::create(term_dictionary_write)?;
+        let average_fieldnorm = fieldnorm_reader
+            .as_ref()
+            .map(|ff_reader| (total_num_tokens as Score / ff_reader.num_docs() as Score))
+            .unwrap_or(0.0);
         let postings_serializer =
-            PostingsSerializer::new(postings_write, term_freq_enabled, position_enabled);
+            PostingsSerializer::new(postings_write, average_fieldnorm, mode, fieldnorm_reader);
-        let positions_serializer_opt = if position_enabled {
+        let positions_serializer_opt = if mode.has_positions() {
             Some(PositionSerializer::new(positions_write, positionsidx_write))
         } else {
             None
@@ -181,18 +192,20 @@ impl<'a> FieldSerializer<'a> {
     /// Starts the postings for a new term.
     /// * term - the term. It needs to come after the previous term according
     ///   to the lexicographical order.
-    /// * doc_freq - return the number of document containing the term.
+    /// * term_doc_freq - return the number of document containing the term.
-    pub fn new_term(&mut self, term: &[u8]) -> io::Result<TermOrdinal> {
+    pub fn new_term(&mut self, term: &[u8], term_doc_freq: u32) -> io::Result<TermOrdinal> {
         assert!(
             !self.term_open,
             "Called new_term, while the previous term was not closed."
         );
+
         self.term_open = true;
         self.postings_serializer.clear();
         self.current_term_info = self.current_term_info();
         self.term_dictionary_builder.insert_key(term)?;
         let term_ordinal = self.num_terms;
         self.num_terms += 1;
+        self.postings_serializer.new_term(term_doc_freq);
         Ok(term_ordinal)
     }
 
@@ -304,15 +317,21 @@ pub struct PostingsSerializer<W: Write> {
     postings_write: Vec<u8>,
     skip_write: SkipSerializer,
 
-    termfreq_enabled: bool,
+    mode: IndexRecordOption,
-    termfreq_sum_enabled: bool,
+    fieldnorm_reader: Option<FieldNormReader>,
+
+    bm25_weight: Option<BM25Weight>,
+
+    avg_fieldnorm: Score, // Average number of term in the field for that segment.
+                          // this value is used to compute the block wand information.
 }
 
 impl<W: Write> PostingsSerializer<W> {
     pub fn new(
         write: W,
-        termfreq_enabled: bool,
+        avg_fieldnorm: Score,
-        termfreq_sum_enabled: bool,
+        mode: IndexRecordOption,
+        fieldnorm_reader: Option<FieldNormReader>,
     ) -> PostingsSerializer<W> {
         PostingsSerializer {
             output_write: CountingWriter::wrap(write),
@@ -324,11 +343,32 @@ impl<W: Write> PostingsSerializer<W> {
             skip_write: SkipSerializer::new(),
 
             last_doc_id_encoded: 0u32,
-            termfreq_enabled,
+            mode,
-            termfreq_sum_enabled,
+
+            fieldnorm_reader,
+            bm25_weight: None,
+
+            avg_fieldnorm,
         }
     }
 
+    /// Returns the number of documents in the segment currently being serialized.
+    /// This function may return `None` if there are no fieldnorm for that field.
+    fn num_docs_in_segment(&self) -> Option<u32> {
+        self.fieldnorm_reader
+            .as_ref()
+            .map(|reader| reader.num_docs())
+    }
+
+    pub fn new_term(&mut self, term_doc_freq: u32) {
+        if self.mode.has_freq() {
+            return;
+        }
+        self.bm25_weight = self.num_docs_in_segment().map(|num_docs| {
+            BM25Weight::for_one_term(term_doc_freq as u64, num_docs as u64, self.avg_fieldnorm)
+        });
+    }
+
     fn write_block(&mut self) {
         {
             // encode the doc ids
@@ -341,17 +381,43 @@ impl<W: Write> PostingsSerializer<W> {
             // last el block 0, offset block 1,
             self.postings_write.extend(block_encoded);
         }
-        if self.termfreq_enabled {
+        if self.mode.has_freq() {
-            // encode the term_freqs
             let (num_bits, block_encoded): (u8, &[u8]) = self
                 .block_encoder
                 .compress_block_unsorted(&self.block.term_freqs());
             self.postings_write.extend(block_encoded);
             self.skip_write.write_term_freq(num_bits);
-            if self.termfreq_sum_enabled {
+            if self.mode.has_positions() {
+                // We serialize the sum of term freqs within the skip information
+                // in order to navigate through positions.
                 let sum_freq = self.block.term_freqs().iter().cloned().sum();
                 self.skip_write.write_total_term_freq(sum_freq);
             }
+            let mut blockwand_params = (0u8, 0u32);
+            if let Some(bm25_weight) = self.bm25_weight.as_ref() {
+                if let Some(fieldnorm_reader) = self.fieldnorm_reader.as_ref() {
+                    let docs = self.block.doc_ids().iter().cloned();
+                    let term_freqs = self.block.term_freqs().iter().cloned();
+                    let fieldnorms = docs.map(|doc| fieldnorm_reader.fieldnorm_id(doc));
+                    blockwand_params = fieldnorms
+                        .zip(term_freqs)
+                        .max_by(
+                            |(left_fieldnorm_id, left_term_freq),
+                             (right_fieldnorm_id, right_term_freq)| {
+                                let left_score =
+                                    bm25_weight.tf_factor(*left_fieldnorm_id, *left_term_freq);
+                                let right_score =
+                                    bm25_weight.tf_factor(*right_fieldnorm_id, *right_term_freq);
+                                left_score
+                                    .partial_cmp(&right_score)
+                                    .unwrap_or(Ordering::Equal)
+                            },
+                        )
+                        .unwrap();
+                }
+            }
+            let (fieldnorm_id, term_freq) = blockwand_params;
+            self.skip_write.write_blockwand_max(fieldnorm_id, term_freq);
         }
         self.block.clear();
     }
@@ -382,7 +448,7 @@ impl<W: Write> PostingsSerializer<W> {
                 self.postings_write.write_all(block_encoded)?;
             }
             // ... Idem for term frequencies
-            if self.termfreq_enabled {
+            if self.mode.has_freq() {
                 let block_encoded = self
                     .block_encoder
                     .compress_vint_unsorted(self.block.term_freqs());
@@ -400,6 +466,7 @@ impl<W: Write> PostingsSerializer<W> {
         }
         self.skip_write.clear();
         self.postings_write.clear();
+        self.bm25_weight = None;
         Ok(())
     }
 

src/postings/skip.rs

@@ -1,9 +1,9 @@
-use crate::common::BinarySerializable;
+use crate::common::{read_u32_vint_no_advance, serialize_vint_u32, BinarySerializable};
-use crate::directory::ReadOnlySource;
+use crate::directory::OwnedBytes;
 use crate::postings::compression::{compressed_block_size, COMPRESSION_BLOCK_SIZE};
+use crate::query::BM25Weight;
 use crate::schema::IndexRecordOption;
-use crate::{DocId, TERMINATED};
+use crate::{DocId, Score, TERMINATED};
-use owned_read::OwnedRead;
 
 pub struct SkipSerializer {
     buffer: Vec<u8>,
@@ -40,6 +40,13 @@ impl SkipSerializer {
             .expect("Should never fail");
     }
 
+    pub fn write_blockwand_max(&mut self, fieldnorm_id: u8, term_freq: u32) {
+        self.buffer.push(fieldnorm_id);
+        let mut buf = [0u8; 8];
+        let bytes = serialize_vint_u32(term_freq, &mut buf);
+        self.buffer.extend_from_slice(bytes);
+    }
+
     pub fn data(&self) -> &[u8] {
         &self.buffer[..]
     }
@@ -50,10 +57,11 @@ impl SkipSerializer {
     }
 }
 
+#[derive(Clone)]
 pub(crate) struct SkipReader {
     last_doc_in_block: DocId,
     pub(crate) last_doc_in_previous_block: DocId,
-    owned_read: OwnedRead,
+    owned_read: OwnedBytes,
     skip_info: IndexRecordOption,
     byte_offset: usize,
     remaining_docs: u32, // number of docs remaining, including the
@@ -69,41 +77,74 @@ pub(crate) enum BlockInfo {
         doc_num_bits: u8,
         tf_num_bits: u8,
         tf_sum: u32,
+        block_wand_fieldnorm_id: u8,
+        block_wand_term_freq: u32,
+    },
+    VInt {
+        num_docs: u32,
     },
-    VInt(u32),
 }
 
 impl Default for BlockInfo {
     fn default() -> Self {
-        BlockInfo::VInt(0)
+        BlockInfo::VInt { num_docs: 0u32 }
     }
 }
 
 impl SkipReader {
-    pub fn new(data: ReadOnlySource, doc_freq: u32, skip_info: IndexRecordOption) -> SkipReader {
+    pub fn new(data: OwnedBytes, doc_freq: u32, skip_info: IndexRecordOption) -> SkipReader {
-        SkipReader {
+        let mut skip_reader = SkipReader {
-            last_doc_in_block: 0u32,
+            last_doc_in_block: if doc_freq >= COMPRESSION_BLOCK_SIZE as u32 {
+                0
+            } else {
+                TERMINATED
+            },
             last_doc_in_previous_block: 0u32,
-            owned_read: OwnedRead::new(data),
+            owned_read: data,
             skip_info,
-            block_info: BlockInfo::default(),
+            block_info: BlockInfo::VInt { num_docs: doc_freq },
             byte_offset: 0,
             remaining_docs: doc_freq,
             position_offset: 0u64,
+        };
+        if doc_freq >= COMPRESSION_BLOCK_SIZE as u32 {
+            skip_reader.read_block_info();
+        }
+        skip_reader
+    }
+
+    pub fn reset(&mut self, data: OwnedBytes, doc_freq: u32) {
+        self.last_doc_in_block = if doc_freq >= COMPRESSION_BLOCK_SIZE as u32 {
+            0
+        } else {
+            TERMINATED
+        };
+        self.last_doc_in_previous_block = 0u32;
+        self.owned_read = data;
+        self.block_info = BlockInfo::VInt { num_docs: doc_freq };
+        self.byte_offset = 0;
+        self.remaining_docs = doc_freq;
+        self.position_offset = 0u64;
+        if doc_freq >= COMPRESSION_BLOCK_SIZE as u32 {
+            self.read_block_info();
         }
     }
 
-    pub fn reset(&mut self, data: ReadOnlySource, doc_freq: u32) {
+    // Returns the block max score for this block if available.
-        self.last_doc_in_block = 0u32;
+    //
-        self.last_doc_in_previous_block = 0u32;
+    // The block max score is available for all full bitpacked block,
-        self.owned_read = OwnedRead::new(data);
+    // but no available for the last VInt encoded incomplete block.
-        self.block_info = BlockInfo::default();
+    pub fn block_max_score(&self, bm25_weight: &BM25Weight) -> Option<Score> {
-        self.byte_offset = 0;
+        match self.block_info {
-        self.remaining_docs = doc_freq;
+            BlockInfo::BitPacked {
+                block_wand_fieldnorm_id,
+                block_wand_term_freq,
+                ..
+            } => Some(bm25_weight.score(block_wand_fieldnorm_id, block_wand_term_freq)),
+            BlockInfo::VInt { .. } => None,
+        }
     }
 
-    #[cfg(test)]
-    #[inline(always)]
     pub(crate) fn last_doc_in_block(&self) -> DocId {
         self.last_doc_in_block
     }
@@ -112,40 +153,63 @@ impl SkipReader {
         self.position_offset
     }
 
+    #[inline(always)]
     pub fn byte_offset(&self) -> usize {
         self.byte_offset
     }
 
     fn read_block_info(&mut self) {
-        let doc_delta = u32::deserialize(&mut self.owned_read).expect("Skip data corrupted");
+        let doc_delta = {
+            let bytes = self.owned_read.as_slice();
+            let mut buf = [0; 4];
+            buf.copy_from_slice(&bytes[..4]);
+            u32::from_le_bytes(buf)
+        };
         self.last_doc_in_block += doc_delta as DocId;
-        let doc_num_bits = self.owned_read.get(0);
+        let doc_num_bits = self.owned_read.as_slice()[4];
+
         match self.skip_info {
             IndexRecordOption::Basic => {
-                self.owned_read.advance(1);
+                self.owned_read.advance(5);
                 self.block_info = BlockInfo::BitPacked {
                     doc_num_bits,
                     tf_num_bits: 0,
                     tf_sum: 0,
+                    block_wand_fieldnorm_id: 0,
+                    block_wand_term_freq: 0,
                 };
             }
             IndexRecordOption::WithFreqs => {
-                let tf_num_bits = self.owned_read.get(1);
+                let bytes = self.owned_read.as_slice();
+                let tf_num_bits = bytes[5];
+                let block_wand_fieldnorm_id = bytes[6];
+                let (block_wand_term_freq, num_bytes) = read_u32_vint_no_advance(&bytes[7..]);
+                self.owned_read.advance(7 + num_bytes);
                 self.block_info = BlockInfo::BitPacked {
                     doc_num_bits,
                     tf_num_bits,
                     tf_sum: 0,
+                    block_wand_fieldnorm_id,
+                    block_wand_term_freq,
                 };
-                self.owned_read.advance(2);
             }
             IndexRecordOption::WithFreqsAndPositions => {
-                let tf_num_bits = self.owned_read.get(1);
+                let bytes = self.owned_read.as_slice();
-                self.owned_read.advance(2);
+                let tf_num_bits = bytes[5];
-                let tf_sum = u32::deserialize(&mut self.owned_read).expect("Failed reading tf_sum");
+                let tf_sum = {
+                    let mut buf = [0; 4];
+                    buf.copy_from_slice(&bytes[6..10]);
+                    u32::from_le_bytes(buf)
+                };
+                let block_wand_fieldnorm_id = bytes[10];
+                let (block_wand_term_freq, num_bytes) = read_u32_vint_no_advance(&bytes[11..]);
+                self.owned_read.advance(11 + num_bytes);
                 self.block_info = BlockInfo::BitPacked {
                     doc_num_bits,
                     tf_num_bits,
                     tf_sum,
+                    block_wand_fieldnorm_id,
+                    block_wand_term_freq,
                 };
             }
         }
@@ -159,35 +223,44 @@ impl SkipReader {
     ///
     /// If the target is larger than all documents, the skip_reader
     /// then advance to the last Variable In block.
-    pub fn seek(&mut self, target: DocId) {
+    pub fn seek(&mut self, target: DocId) -> bool {
-        while self.last_doc_in_block < target {
+        if self.last_doc_in_block() >= target {
+            return false;
+        }
+        loop {
             self.advance();
+            if self.last_doc_in_block() >= target {
+                return true;
+            }
         }
     }
 
-    pub fn advance(&mut self) -> bool {
+    pub fn advance(&mut self) {
         match self.block_info {
             BlockInfo::BitPacked {
                 doc_num_bits,
                 tf_num_bits,
                 tf_sum,
+                ..
             } => {
                 self.remaining_docs -= COMPRESSION_BLOCK_SIZE as u32;
                 self.byte_offset += compressed_block_size(doc_num_bits + tf_num_bits);
                 self.position_offset += tf_sum as u64;
             }
-            BlockInfo::VInt(num_vint_docs) => {
+            BlockInfo::VInt { num_docs } => {
-                self.remaining_docs -= num_vint_docs;
+                debug_assert_eq!(num_docs, self.remaining_docs);
+                self.remaining_docs = 0;
+                self.byte_offset = std::usize::MAX;
             }
         }
         self.last_doc_in_previous_block = self.last_doc_in_block;
         if self.remaining_docs >= COMPRESSION_BLOCK_SIZE as u32 {
             self.read_block_info();
-            true
         } else {
             self.last_doc_in_block = TERMINATED;
-            self.block_info = BlockInfo::VInt(self.remaining_docs);
+            self.block_info = BlockInfo::VInt {
-            self.remaining_docs > 0
+                num_docs: self.remaining_docs,
+            };
         }
     }
 }
@@ -198,7 +271,7 @@ mod tests {
     use super::BlockInfo;
     use super::IndexRecordOption;
     use super::{SkipReader, SkipSerializer};
-    use crate::directory::ReadOnlySource;
+    use crate::directory::OwnedBytes;
     use crate::postings::compression::COMPRESSION_BLOCK_SIZE;
 
     #[test]
@@ -207,39 +280,44 @@ mod tests {
             let mut skip_serializer = SkipSerializer::new();
             skip_serializer.write_doc(1u32, 2u8);
             skip_serializer.write_term_freq(3u8);
+            skip_serializer.write_blockwand_max(13u8, 3u32);
             skip_serializer.write_doc(5u32, 5u8);
             skip_serializer.write_term_freq(2u8);
+            skip_serializer.write_blockwand_max(8u8, 2u32);
             skip_serializer.data().to_owned()
         };
         let doc_freq = 3u32 + (COMPRESSION_BLOCK_SIZE * 2) as u32;
-        let mut skip_reader = SkipReader::new(
+        let mut skip_reader =
-            ReadOnlySource::new(buf),
+            SkipReader::new(OwnedBytes::new(buf), doc_freq, IndexRecordOption::WithFreqs);
-            doc_freq,
-            IndexRecordOption::WithFreqs,
-        );
-        assert!(skip_reader.advance());
         assert_eq!(skip_reader.last_doc_in_block(), 1u32);
         assert_eq!(
-            skip_reader.block_info(),
+            skip_reader.block_info,
             BlockInfo::BitPacked {
                 doc_num_bits: 2u8,
                 tf_num_bits: 3u8,
-                tf_sum: 0
+                tf_sum: 0,
+                block_wand_fieldnorm_id: 13,
+                block_wand_term_freq: 3
             }
         );
-        assert!(skip_reader.advance());
+        skip_reader.advance();
         assert_eq!(skip_reader.last_doc_in_block(), 5u32);
         assert_eq!(
             skip_reader.block_info(),
             BlockInfo::BitPacked {
                 doc_num_bits: 5u8,
                 tf_num_bits: 2u8,
-                tf_sum: 0
+                tf_sum: 0,
+                block_wand_fieldnorm_id: 8,
+                block_wand_term_freq: 2
             }
         );
-        assert!(skip_reader.advance());
+        skip_reader.advance();
-        assert_eq!(skip_reader.block_info(), BlockInfo::VInt(3u32));
+        assert_eq!(skip_reader.block_info(), BlockInfo::VInt { num_docs: 3u32 });
-        assert!(!skip_reader.advance());
+        skip_reader.advance();
+        assert_eq!(skip_reader.block_info(), BlockInfo::VInt { num_docs: 0u32 });
+        skip_reader.advance();
+        assert_eq!(skip_reader.block_info(), BlockInfo::VInt { num_docs: 0u32 });
     }
 
     #[test]
@@ -251,34 +329,37 @@ mod tests {
             skip_serializer.data().to_owned()
         };
         let doc_freq = 3u32 + (COMPRESSION_BLOCK_SIZE * 2) as u32;
-        let mut skip_reader = SkipReader::new(
+        let mut skip_reader =
-            ReadOnlySource::from(buf),
+            SkipReader::new(OwnedBytes::new(buf), doc_freq, IndexRecordOption::Basic);
-            doc_freq,
-            IndexRecordOption::Basic,
-        );
-        assert!(skip_reader.advance());
         assert_eq!(skip_reader.last_doc_in_block(), 1u32);
         assert_eq!(
             skip_reader.block_info(),
             BlockInfo::BitPacked {
                 doc_num_bits: 2u8,
                 tf_num_bits: 0,
-                tf_sum: 0u32
+                tf_sum: 0u32,
+                block_wand_fieldnorm_id: 0,
+                block_wand_term_freq: 0
             }
         );
-        assert!(skip_reader.advance());
+        skip_reader.advance();
         assert_eq!(skip_reader.last_doc_in_block(), 5u32);
         assert_eq!(
             skip_reader.block_info(),
             BlockInfo::BitPacked {
                 doc_num_bits: 5u8,
                 tf_num_bits: 0,
-                tf_sum: 0u32
+                tf_sum: 0u32,
+                block_wand_fieldnorm_id: 0,
+                block_wand_term_freq: 0
             }
         );
-        assert!(skip_reader.advance());
+        skip_reader.advance();
-        assert_eq!(skip_reader.block_info(), BlockInfo::VInt(3u32));
+        assert_eq!(skip_reader.block_info(), BlockInfo::VInt { num_docs: 3u32 });
-        assert!(!skip_reader.advance());
+        skip_reader.advance();
+        assert_eq!(skip_reader.block_info(), BlockInfo::VInt { num_docs: 0u32 });
+        skip_reader.advance();
+        assert_eq!(skip_reader.block_info(), BlockInfo::VInt { num_docs: 0u32 });
     }
 
     #[test]
@@ -289,21 +370,20 @@ mod tests {
             skip_serializer.data().to_owned()
         };
         let doc_freq = COMPRESSION_BLOCK_SIZE as u32;
-        let mut skip_reader = SkipReader::new(
+        let mut skip_reader =
-            ReadOnlySource::from(buf),
+            SkipReader::new(OwnedBytes::new(buf), doc_freq, IndexRecordOption::Basic);
-            doc_freq,
-            IndexRecordOption::Basic,
-        );
-        assert!(skip_reader.advance());
         assert_eq!(skip_reader.last_doc_in_block(), 1u32);
         assert_eq!(
             skip_reader.block_info(),
             BlockInfo::BitPacked {
                 doc_num_bits: 2u8,
                 tf_num_bits: 0,
-                tf_sum: 0u32
+                tf_sum: 0u32,
+                block_wand_fieldnorm_id: 0,
+                block_wand_term_freq: 0
             }
         );
-        assert!(!skip_reader.advance());
+        skip_reader.advance();
+        assert_eq!(skip_reader.block_info(), BlockInfo::VInt { num_docs: 0u32 });
     }
 }

src/postings/stacker/expull.rs

@@ -206,8 +206,8 @@ mod tests {
     fn test_stack_long() {
         let mut heap = MemoryArena::new();
         let mut stack = ExpUnrolledLinkedList::new();
-        let source: Vec<u32> = (0..100).collect();
+        let data: Vec<u32> = (0..100).collect();
-        for &el in &source {
+        for &el in &data {
             assert!(stack
                 .writer(&mut heap)
                 .write_u32::<LittleEndian>(el)
@@ -221,7 +221,7 @@ mod tests {
             result.push(LittleEndian::read_u32(&remaining[..4]));
             remaining = &remaining[4..];
         }
-        assert_eq!(&result[..], &source[..]);
+        assert_eq!(&result[..], &data[..]);
     }
 
     #[test]

src/query/all_query.rs

@@ -9,7 +9,7 @@ use crate::Score;
 
 /// Query that matches all of the documents.
 ///
-/// All of the document get the score 1f32.
+/// All of the document get the score 1.0.
 #[derive(Clone, Debug)]
 pub struct AllQuery;
 
@@ -23,7 +23,7 @@ impl Query for AllQuery {
 pub struct AllWeight;
 
 impl Weight for AllWeight {
-    fn scorer(&self, reader: &SegmentReader, boost: f32) -> crate::Result<Box<dyn Scorer>> {
+    fn scorer(&self, reader: &SegmentReader, boost: Score) -> crate::Result<Box<dyn Scorer>> {
         let all_scorer = AllScorer {
             doc: 0u32,
             max_doc: reader.max_doc(),
@@ -35,7 +35,7 @@ impl Weight for AllWeight {
         if doc >= reader.max_doc() {
             return Err(does_not_match(doc));
         }
-        Ok(Explanation::new("AllQuery", 1f32))
+        Ok(Explanation::new("AllQuery", 1.0))
     }
 }
 
@@ -66,7 +66,7 @@ impl DocSet for AllScorer {
 
 impl Scorer for AllScorer {
     fn score(&mut self) -> Score {
-        1f32
+        1.0
     }
 }
 
@@ -83,7 +83,7 @@ mod tests {
         let field = schema_builder.add_text_field("text", TEXT);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
-        let mut index_writer = index.writer_with_num_threads(1, 10_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests().unwrap();
         index_writer.add_document(doc!(field=>"aaa"));
         index_writer.add_document(doc!(field=>"bbb"));
         index_writer.commit().unwrap();
@@ -100,7 +100,7 @@ mod tests {
         let weight = AllQuery.weight(&searcher, false).unwrap();
         {
             let reader = searcher.segment_reader(0);
-            let mut scorer = weight.scorer(reader, 1.0f32).unwrap();
+            let mut scorer = weight.scorer(reader, 1.0).unwrap();
             assert_eq!(scorer.doc(), 0u32);
             assert_eq!(scorer.advance(), 1u32);
             assert_eq!(scorer.doc(), 1u32);
@@ -108,7 +108,7 @@ mod tests {
         }
         {
             let reader = searcher.segment_reader(1);
-            let mut scorer = weight.scorer(reader, 1.0f32).unwrap();
+            let mut scorer = weight.scorer(reader, 1.0).unwrap();
             assert_eq!(scorer.doc(), 0u32);
             assert_eq!(scorer.advance(), TERMINATED);
         }
@@ -122,14 +122,14 @@ mod tests {
         let weight = AllQuery.weight(&searcher, false).unwrap();
         let reader = searcher.segment_reader(0);
         {
-            let mut scorer = weight.scorer(reader, 2.0f32).unwrap();
+            let mut scorer = weight.scorer(reader, 2.0).unwrap();
             assert_eq!(scorer.doc(), 0u32);
-            assert_eq!(scorer.score(), 2.0f32);
+            assert_eq!(scorer.score(), 2.0);
         }
         {
-            let mut scorer = weight.scorer(reader, 1.5f32).unwrap();
+            let mut scorer = weight.scorer(reader, 1.5).unwrap();
             assert_eq!(scorer.doc(), 0u32);
-            assert_eq!(scorer.score(), 1.5f32);
+            assert_eq!(scorer.score(), 1.5);
         }
     }
 }

src/query/automaton_weight.rs

@@ -5,9 +5,8 @@ use crate::query::{BitSetDocSet, Explanation};
 use crate::query::{Scorer, Weight};
 use crate::schema::{Field, IndexRecordOption};
 use crate::termdict::{TermDictionary, TermStreamer};
-use crate::DocId;
-use crate::Result;
 use crate::TantivyError;
+use crate::{DocId, Score};
 use std::sync::Arc;
 use tantivy_fst::Automaton;
 
@@ -40,24 +39,25 @@ impl<A> Weight for AutomatonWeight<A>
 where
     A: Automaton + Send + Sync + 'static,
 {
-    fn scorer(&self, reader: &SegmentReader, boost: f32) -> Result<Box<dyn Scorer>> {
+    fn scorer(&self, reader: &SegmentReader, boost: Score) -> crate::Result<Box<dyn Scorer>> {
         let max_doc = reader.max_doc();
         let mut doc_bitset = BitSet::with_max_value(max_doc);
-
+        let inverted_index = reader.inverted_index(self.field)?;
-        let inverted_index = reader.inverted_index(self.field);
         let term_dict = inverted_index.terms();
         let mut term_stream = self.automaton_stream(term_dict);
         while term_stream.advance() {
             let term_info = term_stream.value();
             let mut block_segment_postings = inverted_index
-                .read_block_postings_from_terminfo(term_info, IndexRecordOption::Basic);
+                .read_block_postings_from_terminfo(term_info, IndexRecordOption::Basic)?;
             loop {
-                for &doc in block_segment_postings.docs() {
+                let docs = block_segment_postings.docs();
-                    doc_bitset.insert(doc);
+                if docs.is_empty() {
-                }
-                if !block_segment_postings.advance() {
                     break;
                 }
+                for &doc in docs {
+                    doc_bitset.insert(doc);
+                }
+                block_segment_postings.advance();
             }
         }
         let doc_bitset = BitSetDocSet::from(doc_bitset);
@@ -65,10 +65,10 @@ where
         Ok(Box::new(const_scorer))
     }
 
-    fn explain(&self, reader: &SegmentReader, doc: DocId) -> Result<Explanation> {
+    fn explain(&self, reader: &SegmentReader, doc: DocId) -> crate::Result<Explanation> {
-        let mut scorer = self.scorer(reader, 1.0f32)?;
+        let mut scorer = self.scorer(reader, 1.0)?;
         if scorer.seek(doc) == doc {
-            Ok(Explanation::new("AutomatonScorer", 1.0f32))
+            Ok(Explanation::new("AutomatonScorer", 1.0))
         } else {
             Err(TantivyError::InvalidArgument(
                 "Document does not exist".to_string(),
@@ -90,7 +90,7 @@ mod tests {
         let mut schema = Schema::builder();
         let title = schema.add_text_field("title", STRING);
         let index = Index::create_in_ram(schema.build());
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests().unwrap();
         index_writer.add_document(doc!(title=>"abc"));
         index_writer.add_document(doc!(title=>"bcd"));
         index_writer.add_document(doc!(title=>"abcd"));
@@ -143,13 +143,13 @@ mod tests {
         let reader = index.reader().unwrap();
         let searcher = reader.searcher();
         let mut scorer = automaton_weight
-            .scorer(searcher.segment_reader(0u32), 1.0f32)
+            .scorer(searcher.segment_reader(0u32), 1.0)
             .unwrap();
         assert_eq!(scorer.doc(), 0u32);
-        assert_eq!(scorer.score(), 1.0f32);
+        assert_eq!(scorer.score(), 1.0);
         assert_eq!(scorer.advance(), 2u32);
         assert_eq!(scorer.doc(), 2u32);
-        assert_eq!(scorer.score(), 1.0f32);
+        assert_eq!(scorer.score(), 1.0);
         assert_eq!(scorer.advance(), TERMINATED);
     }
 
@@ -161,9 +161,9 @@ mod tests {
         let reader = index.reader().unwrap();
         let searcher = reader.searcher();
         let mut scorer = automaton_weight
-            .scorer(searcher.segment_reader(0u32), 1.32f32)
+            .scorer(searcher.segment_reader(0u32), 1.32)
             .unwrap();
         assert_eq!(scorer.doc(), 0u32);
-        assert_eq!(scorer.score(), 1.32f32);
+        assert_eq!(scorer.score(), 1.32);
     }
 }

src/query/bitset/mod.rs

@@ -61,21 +61,23 @@ impl DocSet for BitSetDocSet {
     }
 
     fn seek(&mut self, target: DocId) -> DocId {
+        if target >= self.docs.max_value() {
+            self.doc = TERMINATED;
+            return TERMINATED;
+        }
         let target_bucket = target / 64u32;
-
-        // Mask for all of the bits greater or equal
-        // to our target document.
         if target_bucket > self.cursor_bucket {
             self.go_to_bucket(target_bucket);
             let greater_filter: TinySet = TinySet::range_greater_or_equal(target);
             self.cursor_tinybitset = self.cursor_tinybitset.intersect(greater_filter);
-            self.advance();
+            self.advance()
+        } else {
+            let mut doc = self.doc();
+            while doc < target {
+                doc = self.advance();
+            }
+            doc
         }
-        let mut doc = self.doc();
-        while doc < target {
-            doc = self.advance();
-        }
-        doc
     }
 
     /// Returns the current document
@@ -114,6 +116,13 @@ mod tests {
         assert_eq!(empty.advance(), TERMINATED)
     }
 
+    #[test]
+    fn test_seek_terminated() {
+        let bitset = BitSet::with_max_value(1000);
+        let mut empty = BitSetDocSet::from(bitset);
+        assert_eq!(empty.seek(TERMINATED), TERMINATED)
+    }
+
     fn test_go_through_sequential(docs: &[DocId]) {
         let mut docset = create_docbitset(docs, 1_000u32);
         for &doc in docs {

src/query/bm25.rs

@@ -3,21 +3,24 @@ use crate::query::Explanation;
 use crate::Score;
 use crate::Searcher;
 use crate::Term;
+use serde::Deserialize;
+use serde::Serialize;
 
-const K1: f32 = 1.2;
+const K1: Score = 1.2;
-const B: f32 = 0.75;
+const B: Score = 0.75;
 
-fn idf(doc_freq: u64, doc_count: u64) -> f32 {
+fn idf(doc_freq: u64, doc_count: u64) -> Score {
-    let x = ((doc_count - doc_freq) as f32 + 0.5) / (doc_freq as f32 + 0.5);
+    assert!(doc_count >= doc_freq, "{} >= {}", doc_count, doc_freq);
-    (1f32 + x).ln()
+    let x = ((doc_count - doc_freq) as Score + 0.5) / (doc_freq as Score + 0.5);
+    (1.0 + x).ln()
 }
 
-fn cached_tf_component(fieldnorm: u32, average_fieldnorm: f32) -> f32 {
+fn cached_tf_component(fieldnorm: u32, average_fieldnorm: Score) -> Score {
-    K1 * (1f32 - B + B * fieldnorm as f32 / average_fieldnorm)
+    K1 * (1.0 - B + B * fieldnorm as Score / average_fieldnorm)
 }
 
-fn compute_tf_cache(average_fieldnorm: f32) -> [f32; 256] {
+fn compute_tf_cache(average_fieldnorm: Score) -> [Score; 256] {
-    let mut cache = [0f32; 256];
+    let mut cache: [Score; 256] = [0.0; 256];
     for (fieldnorm_id, cache_mut) in cache.iter_mut().enumerate() {
         let fieldnorm = FieldNormReader::id_to_fieldnorm(fieldnorm_id as u8);
         *cache_mut = cached_tf_component(fieldnorm, average_fieldnorm);
@@ -25,15 +28,22 @@ fn compute_tf_cache(average_fieldnorm: f32) -> [f32; 256] {
     cache
 }
 
+#[derive(Clone, PartialEq, Debug, Serialize, Deserialize)]
+pub struct BM25Params {
+    pub idf: Score,
+    pub avg_fieldnorm: Score,
+}
+
+#[derive(Clone)]
 pub struct BM25Weight {
     idf_explain: Explanation,
-    weight: f32,
+    weight: Score,
-    cache: [f32; 256],
+    cache: [Score; 256],
-    average_fieldnorm: f32,
+    average_fieldnorm: Score,
 }
 
 impl BM25Weight {
-    pub fn boost_by(&self, boost: f32) -> BM25Weight {
+    pub fn boost_by(&self, boost: Score) -> BM25Weight {
         BM25Weight {
             idf_explain: self.idf_explain.clone(),
             weight: self.weight * boost,
@@ -42,7 +52,7 @@ impl BM25Weight {
         }
     }
 
-    pub fn for_terms(searcher: &Searcher, terms: &[Term]) -> BM25Weight {
+    pub fn for_terms(searcher: &Searcher, terms: &[Term]) -> crate::Result<BM25Weight> {
         assert!(!terms.is_empty(), "BM25 requires at least one term");
         let field = terms[0].field();
         for term in &terms[1..] {
@@ -56,38 +66,48 @@ impl BM25Weight {
         let mut total_num_tokens = 0u64;
         let mut total_num_docs = 0u64;
         for segment_reader in searcher.segment_readers() {
-            let inverted_index = segment_reader.inverted_index(field);
+            let inverted_index = segment_reader.inverted_index(field)?;
             total_num_tokens += inverted_index.total_num_tokens();
             total_num_docs += u64::from(segment_reader.max_doc());
         }
-        let average_fieldnorm = total_num_tokens as f32 / total_num_docs as f32;
+        let average_fieldnorm = total_num_tokens as Score / total_num_docs as Score;
 
-        let mut idf_explain: Explanation;
         if terms.len() == 1 {
-            let term_doc_freq = searcher.doc_freq(&terms[0]);
+            let term_doc_freq = searcher.doc_freq(&terms[0])?;
-            let idf = idf(term_doc_freq, total_num_docs);
+            Ok(BM25Weight::for_one_term(
-            idf_explain =
+                term_doc_freq,
-                Explanation::new("idf, computed as log(1 + (N - n + 0.5) / (n + 0.5))", idf);
+                total_num_docs,
-            idf_explain.add_const(
+                average_fieldnorm,
-                "n, number of docs containing this term",
+            ))
-                term_doc_freq as f32,
-            );
-            idf_explain.add_const("N, total number of docs", total_num_docs as f32);
         } else {
-            let idf = terms
+            let mut idf_sum: Score = 0.0;
-                .iter()
+            for term in terms {
-                .map(|term| {
+                let term_doc_freq = searcher.doc_freq(term)?;
-                    let term_doc_freq = searcher.doc_freq(term);
+                idf_sum += idf(term_doc_freq, total_num_docs);
-                    idf(term_doc_freq, total_num_docs)
+            }
-                })
+            let idf_explain = Explanation::new("idf", idf_sum);
-                .sum::<f32>();
+            Ok(BM25Weight::new(idf_explain, average_fieldnorm))
-            idf_explain = Explanation::new("idf", idf);
         }
-        BM25Weight::new(idf_explain, average_fieldnorm)
     }
 
-    fn new(idf_explain: Explanation, average_fieldnorm: f32) -> BM25Weight {
+    pub fn for_one_term(
-        let weight = idf_explain.value() * (1f32 + K1);
+        term_doc_freq: u64,
+        total_num_docs: u64,
+        avg_fieldnorm: Score,
+    ) -> BM25Weight {
+        let idf = idf(term_doc_freq, total_num_docs);
+        let mut idf_explain =
+            Explanation::new("idf, computed as log(1 + (N - n + 0.5) / (n + 0.5))", idf);
+        idf_explain.add_const(
+            "n, number of docs containing this term",
+            term_doc_freq as Score,
+        );
+        idf_explain.add_const("N, total number of docs", total_num_docs as Score);
+        BM25Weight::new(idf_explain, avg_fieldnorm)
+    }
+
+    fn new(idf_explain: Explanation, average_fieldnorm: Score) -> BM25Weight {
+        let weight = idf_explain.value() * (1.0 + K1);
         BM25Weight {
             idf_explain,
             weight,
@@ -98,19 +118,27 @@ impl BM25Weight {
 
     #[inline(always)]
     pub fn score(&self, fieldnorm_id: u8, term_freq: u32) -> Score {
+        self.weight * self.tf_factor(fieldnorm_id, term_freq)
+    }
+
+    pub fn max_score(&self) -> Score {
+        self.score(255u8, 2_013_265_944)
+    }
+
+    #[inline(always)]
+    pub(crate) fn tf_factor(&self, fieldnorm_id: u8, term_freq: u32) -> Score {
+        let term_freq = term_freq as Score;
         let norm = self.cache[fieldnorm_id as usize];
-        let term_freq = term_freq as f32;
+        term_freq / (term_freq + norm)
-        self.weight * term_freq / (term_freq + norm)
     }
 
     pub fn explain(&self, fieldnorm_id: u8, term_freq: u32) -> Explanation {
         // The explain format is directly copied from Lucene's.
         // (So, Kudos to Lucene)
-
         let score = self.score(fieldnorm_id, term_freq);
 
         let norm = self.cache[fieldnorm_id as usize];
-        let term_freq = term_freq as f32;
+        let term_freq = term_freq as Score;
         let right_factor = term_freq / (term_freq + norm);
 
         let mut tf_explanation = Explanation::new(
@@ -123,12 +151,12 @@ impl BM25Weight {
         tf_explanation.add_const("b, length normalization parameter", B);
         tf_explanation.add_const(
             "dl, length of field",
-            FieldNormReader::id_to_fieldnorm(fieldnorm_id) as f32,
+            FieldNormReader::id_to_fieldnorm(fieldnorm_id) as Score,
         );
         tf_explanation.add_const("avgdl, average length of field", self.average_fieldnorm);
 
         let mut explanation = Explanation::new("TermQuery, product of...", score);
-        explanation.add_detail(Explanation::new("(K1+1)", K1 + 1f32));
+        explanation.add_detail(Explanation::new("(K1+1)", K1 + 1.0));
         explanation.add_detail(self.idf_explain.clone());
         explanation.add_detail(tf_explanation);
         explanation
@@ -139,10 +167,11 @@ impl BM25Weight {
 mod tests {
 
     use super::idf;
-    use crate::tests::assert_nearly_equals;
+    use crate::{assert_nearly_equals, Score};
 
     #[test]
     fn test_idf() {
-        assert_nearly_equals(idf(1, 2), 0.6931472);
+        let score: Score = 2.0;
+        assert_nearly_equals!(idf(1, 2), score.ln());
     }
 }

src/query/boolean_query/block_wand.rs

@@ -0,0 +1,434 @@
+use crate::query::term_query::TermScorer;
+use crate::query::Scorer;
+use crate::{DocId, DocSet, Score, TERMINATED};
+use std::ops::Deref;
+use std::ops::DerefMut;
+
+/// Takes a term_scorers sorted by their current doc() and a threshold and returns
+/// Returns (pivot_len, pivot_ord) defined as follows:
+/// - `pivot_doc` lowest document that has a chance of exceeding (>) the threshold score.
+/// - `before_pivot_len` number of term_scorers such that term_scorer.doc() < pivot.
+/// - `pivot_len` number of term_scorers such that term_scorer.doc() <= pivot.
+///
+/// We always have `before_pivot_len` < `pivot_len`.
+///
+/// None is returned if we establish that no document can exceed the threshold.
+fn find_pivot_doc(
+    term_scorers: &[TermScorerWithMaxScore],
+    threshold: Score,
+) -> Option<(usize, usize, DocId)> {
+    let mut max_score = 0.0;
+    let mut before_pivot_len = 0;
+    let mut pivot_doc = TERMINATED;
+    while before_pivot_len < term_scorers.len() {
+        let term_scorer = &term_scorers[before_pivot_len];
+        max_score += term_scorer.max_score;
+        if max_score > threshold {
+            pivot_doc = term_scorer.doc();
+            break;
+        }
+        before_pivot_len += 1;
+    }
+    if pivot_doc == TERMINATED {
+        return None;
+    }
+    // Right now i is an ordinal, we want a len.
+    let mut pivot_len = before_pivot_len + 1;
+    // Some other term_scorer may be positioned on the same document.
+    pivot_len += term_scorers[pivot_len..]
+        .iter()
+        .take_while(|term_scorer| term_scorer.doc() == pivot_doc)
+        .count();
+    Some((before_pivot_len, pivot_len, pivot_doc))
+}
+
+// Before and after calling this method, scorers need to be sorted by their `.doc()`.
+fn block_max_was_too_low_advance_one_scorer(
+    scorers: &mut Vec<TermScorerWithMaxScore>,
+    pivot_len: usize,
+) {
+    debug_assert!(is_sorted(scorers.iter().map(|scorer| scorer.doc())));
+    let mut scorer_to_seek = pivot_len - 1;
+    let mut doc_to_seek_after = scorers[scorer_to_seek].doc();
+    for scorer_ord in (0..pivot_len - 1).rev() {
+        let scorer = &scorers[scorer_ord];
+        if scorer.last_doc_in_block() <= doc_to_seek_after {
+            doc_to_seek_after = scorer.last_doc_in_block();
+            scorer_to_seek = scorer_ord;
+        }
+    }
+    for scorer in &scorers[pivot_len..] {
+        if scorer.doc() <= doc_to_seek_after {
+            doc_to_seek_after = scorer.doc();
+        }
+    }
+    scorers[scorer_to_seek].seek(doc_to_seek_after + 1);
+    restore_ordering(scorers, scorer_to_seek);
+    debug_assert!(is_sorted(scorers.iter().map(|scorer| scorer.doc())));
+}
+
+// Given a list of term_scorers and a `ord` and assuming that `term_scorers[ord]` is sorted
+// except term_scorers[ord] that might be in advance compared to its ranks,
+// bubble up term_scorers[ord] in order to restore the ordering.
+fn restore_ordering(term_scorers: &mut Vec<TermScorerWithMaxScore>, ord: usize) {
+    let doc = term_scorers[ord].doc();
+    for i in ord + 1..term_scorers.len() {
+        if term_scorers[i].doc() >= doc {
+            break;
+        }
+        term_scorers.swap(i, i - 1);
+    }
+    debug_assert!(is_sorted(term_scorers.iter().map(|scorer| scorer.doc())));
+}
+
+// Attempts to advance all term_scorers between `&term_scorers[0..before_len]` to the pivot.
+// If this works, return true.
+// If this fails (ie: one of the term_scorer does not contain `pivot_doc` and seek goes past the
+// pivot), reorder the term_scorers to ensure the list is still sorted and returns `false`.
+// If a term_scorer reach TERMINATED in the process return false remove the term_scorer and return.
+fn align_scorers(
+    term_scorers: &mut Vec<TermScorerWithMaxScore>,
+    pivot_doc: DocId,
+    before_pivot_len: usize,
+) -> bool {
+    debug_assert_ne!(pivot_doc, TERMINATED);
+    for i in (0..before_pivot_len).rev() {
+        let new_doc = term_scorers[i].seek(pivot_doc);
+        if new_doc != pivot_doc {
+            if new_doc == TERMINATED {
+                term_scorers.swap_remove(i);
+            }
+            // We went past the pivot.
+            // We just go through the outer loop mechanic (Note that pivot is
+            // still a possible candidate).
+            //
+            // Termination is still guaranteed since we can only consider the same
+            // pivot at most term_scorers.len() - 1 times.
+            restore_ordering(term_scorers, i);
+            return false;
+        }
+    }
+    true
+}
+
+// Assumes terms_scorers[..pivot_len] are positioned on the same doc (pivot_doc).
+// Advance term_scorers[..pivot_len] and out of these removes the terminated scores.
+// Restores the ordering of term_scorers.
+fn advance_all_scorers_on_pivot(term_scorers: &mut Vec<TermScorerWithMaxScore>, pivot_len: usize) {
+    for term_scorer in &mut term_scorers[..pivot_len] {
+        term_scorer.advance();
+    }
+    // TODO use drain_filter when available.
+    let mut i = 0;
+    while i != term_scorers.len() {
+        if term_scorers[i].doc() == TERMINATED {
+            term_scorers.swap_remove(i);
+        } else {
+            i += 1;
+        }
+    }
+    term_scorers.sort_by_key(|scorer| scorer.doc());
+}
+
+pub fn block_wand(
+    mut scorers: Vec<TermScorer>,
+    mut threshold: Score,
+    callback: &mut dyn FnMut(u32, Score) -> Score,
+) {
+    let mut scorers: Vec<TermScorerWithMaxScore> = scorers
+        .iter_mut()
+        .map(TermScorerWithMaxScore::from)
+        .collect();
+    scorers.sort_by_key(|scorer| scorer.doc());
+    // At this point we need to ensure that the scorers are sorted!
+    debug_assert!(is_sorted(scorers.iter().map(|scorer| scorer.doc())));
+    while let Some((before_pivot_len, pivot_len, pivot_doc)) =
+        find_pivot_doc(&scorers[..], threshold)
+    {
+        debug_assert!(is_sorted(scorers.iter().map(|scorer| scorer.doc())));
+        debug_assert_ne!(pivot_doc, TERMINATED);
+        debug_assert!(before_pivot_len < pivot_len);
+
+        let block_max_score_upperbound: Score = scorers[..pivot_len]
+            .iter_mut()
+            .map(|scorer| {
+                scorer.shallow_seek(pivot_doc);
+                scorer.block_max_score()
+            })
+            .sum();
+
+        // Beware after shallow advance, skip readers can be in advance compared to
+        // the segment posting lists.
+        //
+        // `block_segment_postings.load_block()` need to be called separately.
+        if block_max_score_upperbound <= threshold {
+            // Block max condition was not reached
+            // We could get away by simply advancing the scorers to DocId + 1 but it would
+            // be inefficient. The optimization requires proper explanation and was
+            // isolated in a different function.
+            block_max_was_too_low_advance_one_scorer(&mut scorers, pivot_len);
+            continue;
+        }
+
+        // Block max condition is observed.
+        //
+        // Let's try and advance all scorers before the pivot to the pivot.
+        if !align_scorers(&mut scorers, pivot_doc, before_pivot_len) {
+            // At least of the scorer does not contain the pivot.
+            //
+            // Let's stop scoring this pivot and go through the pivot selection again.
+            // Note that the current pivot is not necessarily a bad candidate and it
+            // may be picked again.
+            continue;
+        }
+
+        // At this point, all scorers are positioned on the doc.
+        let score = scorers[..pivot_len]
+            .iter_mut()
+            .map(|scorer| scorer.score())
+            .sum();
+        if score > threshold {
+            threshold = callback(pivot_doc, score);
+        }
+        // let's advance all of the scorers that are currently positioned on the pivot.
+        advance_all_scorers_on_pivot(&mut scorers, pivot_len);
+    }
+}
+
+struct TermScorerWithMaxScore<'a> {
+    scorer: &'a mut TermScorer,
+    max_score: Score,
+}
+
+impl<'a> From<&'a mut TermScorer> for TermScorerWithMaxScore<'a> {
+    fn from(scorer: &'a mut TermScorer) -> Self {
+        let max_score = scorer.max_score();
+        TermScorerWithMaxScore { scorer, max_score }
+    }
+}
+
+impl<'a> Deref for TermScorerWithMaxScore<'a> {
+    type Target = TermScorer;
+
+    fn deref(&self) -> &Self::Target {
+        self.scorer
+    }
+}
+
+impl<'a> DerefMut for TermScorerWithMaxScore<'a> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        self.scorer
+    }
+}
+
+fn is_sorted<I: Iterator<Item = DocId>>(mut it: I) -> bool {
+    if let Some(first) = it.next() {
+        let mut prev = first;
+        for doc in it {
+            if doc < prev {
+                return false;
+            }
+            prev = doc;
+        }
+    }
+    true
+}
+#[cfg(test)]
+mod tests {
+    use crate::query::score_combiner::SumCombiner;
+    use crate::query::term_query::TermScorer;
+    use crate::query::Union;
+    use crate::query::{BM25Weight, Scorer};
+    use crate::{DocId, DocSet, Score, TERMINATED};
+    use proptest::prelude::*;
+    use std::cmp::Ordering;
+    use std::collections::BinaryHeap;
+    use std::iter;
+
+    struct Float(Score);
+
+    impl Eq for Float {}
+
+    impl PartialEq for Float {
+        fn eq(&self, other: &Self) -> bool {
+            self.cmp(&other) == Ordering::Equal
+        }
+    }
+
+    impl PartialOrd for Float {
+        fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+            Some(self.cmp(other))
+        }
+    }
+
+    impl Ord for Float {
+        fn cmp(&self, other: &Self) -> Ordering {
+            other.0.partial_cmp(&self.0).unwrap_or(Ordering::Equal)
+        }
+    }
+
+    fn nearly_equals(left: Score, right: Score) -> bool {
+        (left - right).abs() < 0.000001 * (left + right).abs()
+    }
+
+    fn compute_checkpoints_for_each_pruning(
+        term_scorers: Vec<TermScorer>,
+        n: usize,
+    ) -> Vec<(DocId, Score)> {
+        let mut heap: BinaryHeap<Float> = BinaryHeap::with_capacity(n);
+        let mut checkpoints: Vec<(DocId, Score)> = Vec::new();
+        let mut limit: Score = 0.0;
+        super::block_wand(term_scorers, Score::MIN, &mut |doc, score| {
+            heap.push(Float(score));
+            if heap.len() > n {
+                heap.pop().unwrap();
+            }
+            if heap.len() == n {
+                limit = heap.peek().unwrap().0;
+            }
+            if !nearly_equals(score, limit) {
+                checkpoints.push((doc, score));
+            }
+            return limit;
+        });
+        checkpoints
+    }
+
+    fn compute_checkpoints_manual(term_scorers: Vec<TermScorer>, n: usize) -> Vec<(DocId, Score)> {
+        let mut heap: BinaryHeap<Float> = BinaryHeap::with_capacity(n);
+        let mut checkpoints: Vec<(DocId, Score)> = Vec::new();
+        let mut scorer: Union<TermScorer, SumCombiner> = Union::from(term_scorers);
+
+        let mut limit = Score::MIN;
+        loop {
+            if scorer.doc() == TERMINATED {
+                break;
+            }
+            let doc = scorer.doc();
+            let score = scorer.score();
+            if score > limit {
+                heap.push(Float(score));
+                if heap.len() > n {
+                    heap.pop().unwrap();
+                }
+                if heap.len() == n {
+                    limit = heap.peek().unwrap().0;
+                }
+                if !nearly_equals(score, limit) {
+                    checkpoints.push((doc, score));
+                }
+            }
+            scorer.advance();
+        }
+        checkpoints
+    }
+
+    const MAX_TERM_FREQ: u32 = 100u32;
+
+    fn posting_list(max_doc: u32) -> BoxedStrategy<Vec<(DocId, u32)>> {
+        (1..max_doc + 1)
+            .prop_flat_map(move |doc_freq| {
+                (
+                    proptest::bits::bitset::sampled(doc_freq as usize, 0..max_doc as usize),
+                    proptest::collection::vec(1u32..MAX_TERM_FREQ, doc_freq as usize),
+                )
+            })
+            .prop_map(|(docset, term_freqs)| {
+                docset
+                    .iter()
+                    .map(|doc| doc as u32)
+                    .zip(term_freqs.iter().cloned())
+                    .collect::<Vec<_>>()
+            })
+            .boxed()
+    }
+
+    fn gen_term_scorers(num_scorers: usize) -> BoxedStrategy<(Vec<Vec<(DocId, u32)>>, Vec<u32>)> {
+        (1u32..100u32)
+            .prop_flat_map(move |max_doc: u32| {
+                (
+                    proptest::collection::vec(posting_list(max_doc), num_scorers),
+                    proptest::collection::vec(2u32..10u32 * MAX_TERM_FREQ, max_doc as usize),
+                )
+            })
+            .boxed()
+    }
+
+    fn test_block_wand_aux(posting_lists: &[Vec<(DocId, u32)>], fieldnorms: &[u32]) {
+        // We virtually repeat all docs 64 times in order to emulate blocks of 2 documents
+        // and surface blogs more easily.
+        const REPEAT: usize = 64;
+        let fieldnorms_expanded = fieldnorms
+            .iter()
+            .cloned()
+            .flat_map(|fieldnorm| iter::repeat(fieldnorm).take(REPEAT))
+            .collect::<Vec<u32>>();
+
+        let postings_lists_expanded: Vec<Vec<(DocId, u32)>> = posting_lists
+            .iter()
+            .map(|posting_list| {
+                posting_list
+                    .into_iter()
+                    .cloned()
+                    .flat_map(|(doc, term_freq)| {
+                        (0 as u32..REPEAT as u32).map(move |offset| {
+                            (
+                                doc * (REPEAT as u32) + offset,
+                                if offset == 0 { term_freq } else { 1 },
+                            )
+                        })
+                    })
+                    .collect::<Vec<(DocId, u32)>>()
+            })
+            .collect::<Vec<_>>();
+
+        let total_fieldnorms: u64 = fieldnorms_expanded
+            .iter()
+            .cloned()
+            .map(|fieldnorm| fieldnorm as u64)
+            .sum();
+        let average_fieldnorm = (total_fieldnorms as Score) / (fieldnorms_expanded.len() as Score);
+        let max_doc = fieldnorms_expanded.len();
+
+        let term_scorers: Vec<TermScorer> = postings_lists_expanded
+            .iter()
+            .map(|postings| {
+                let bm25_weight = BM25Weight::for_one_term(
+                    postings.len() as u64,
+                    max_doc as u64,
+                    average_fieldnorm,
+                );
+                TermScorer::create_for_test(postings, &fieldnorms_expanded[..], bm25_weight)
+            })
+            .collect();
+        for top_k in 1..4 {
+            let checkpoints_for_each_pruning =
+                compute_checkpoints_for_each_pruning(term_scorers.clone(), top_k);
+            let checkpoints_manual = compute_checkpoints_manual(term_scorers.clone(), top_k);
+            assert_eq!(checkpoints_for_each_pruning.len(), checkpoints_manual.len());
+            for (&(left_doc, left_score), &(right_doc, right_score)) in checkpoints_for_each_pruning
+                .iter()
+                .zip(checkpoints_manual.iter())
+            {
+                assert_eq!(left_doc, right_doc);
+                assert!(nearly_equals(left_score, right_score));
+            }
+        }
+    }
+
+    proptest! {
+        #![proptest_config(ProptestConfig::with_cases(500))]
+        #[test]
+        fn test_block_wand_two_term_scorers((posting_lists, fieldnorms) in gen_term_scorers(2)) {
+            test_block_wand_aux(&posting_lists[..], &fieldnorms[..]);
+        }
+    }
+
+    proptest! {
+        #![proptest_config(ProptestConfig::with_cases(500))]
+        #[test]
+        fn test_block_wand_three_term_scorers((posting_lists, fieldnorms) in gen_term_scorers(3)) {
+            test_block_wand_aux(&posting_lists[..], &fieldnorms[..]);
+        }
+    }
+}

src/query/boolean_query/boolean_query.rs

@@ -83,7 +83,7 @@ use std::collections::BTreeSet;
 ///    ];
 ///    // Make a BooleanQuery equivalent to
 ///    // title:+diary title:-girl
-///    let diary_must_and_girl_mustnot = BooleanQuery::from(queries_with_occurs1);
+///    let diary_must_and_girl_mustnot = BooleanQuery::new(queries_with_occurs1);
 ///    let count1 = searcher.search(&diary_must_and_girl_mustnot, &Count)?;
 ///    assert_eq!(count1, 1);
 ///
@@ -93,7 +93,7 @@ use std::collections::BTreeSet;
 ///        IndexRecordOption::Basic,
 ///    ));
 ///    // "title:diary OR title:cow"
-///    let title_diary_or_cow = BooleanQuery::from(vec![
+///    let title_diary_or_cow = BooleanQuery::new(vec![
 ///        (Occur::Should, diary_term_query.box_clone()),
 ///        (Occur::Should, cow_term_query),
 ///    ]);
@@ -108,7 +108,7 @@ use std::collections::BTreeSet;
 ///    // You can combine subqueries of different types into 1 BooleanQuery:
 ///    // `TermQuery` and `PhraseQuery`
 ///    // "title:diary OR "dairy cow"
-///    let term_of_phrase_query = BooleanQuery::from(vec![
+///    let term_of_phrase_query = BooleanQuery::new(vec![
 ///        (Occur::Should, diary_term_query.box_clone()),
 ///        (Occur::Should, phrase_query.box_clone()),
 ///    ]);
@@ -117,7 +117,7 @@ use std::collections::BTreeSet;
 ///
 ///    // You can nest one BooleanQuery inside another
 ///    // body:found AND ("title:diary OR "dairy cow")
-///    let nested_query = BooleanQuery::from(vec![
+///    let nested_query = BooleanQuery::new(vec![
 ///        (Occur::Must, body_term_query),
 ///        (Occur::Must, Box::new(term_of_phrase_query))
 ///    ]);
@@ -143,7 +143,7 @@ impl Clone for BooleanQuery {
 
 impl From<Vec<(Occur, Box<dyn Query>)>> for BooleanQuery {
     fn from(subqueries: Vec<(Occur, Box<dyn Query>)>) -> BooleanQuery {
-        BooleanQuery { subqueries }
+        BooleanQuery::new(subqueries)
     }
 }
 
@@ -167,6 +167,23 @@ impl Query for BooleanQuery {
 }
 
 impl BooleanQuery {
+    /// Creates a new boolean query.
+    pub fn new(subqueries: Vec<(Occur, Box<dyn Query>)>) -> BooleanQuery {
+        BooleanQuery { subqueries }
+    }
+
+    /// Returns the intersection of the queries.
+    pub fn intersection(queries: Vec<Box<dyn Query>>) -> BooleanQuery {
+        let subqueries = queries.into_iter().map(|s| (Occur::Must, s)).collect();
+        BooleanQuery::new(subqueries)
+    }
+
+    /// Returns the union of the queries.
+    pub fn union(queries: Vec<Box<dyn Query>>) -> BooleanQuery {
+        let subqueries = queries.into_iter().map(|s| (Occur::Should, s)).collect();
+        BooleanQuery::new(subqueries)
+    }
+
     /// Helper method to create a boolean query matching a given list of terms.
     /// The resulting query is a disjunction of the terms.
     pub fn new_multiterms_query(terms: Vec<Term>) -> BooleanQuery {
@@ -178,7 +195,7 @@ impl BooleanQuery {
                 (Occur::Should, term_query)
             })
             .collect();
-        BooleanQuery::from(occur_term_queries)
+        BooleanQuery::new(occur_term_queries)
     }
 
     /// Deconstructed view of the clauses making up this query.
@@ -186,3 +203,77 @@ impl BooleanQuery {
         &self.subqueries[..]
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::BooleanQuery;
+    use crate::collector::DocSetCollector;
+    use crate::query::{QueryClone, TermQuery};
+    use crate::schema::{IndexRecordOption, Schema, TEXT};
+    use crate::{DocAddress, Index, Term};
+
+    fn create_test_index() -> crate::Result<Index> {
+        let mut schema_builder = Schema::builder();
+        let text = schema_builder.add_text_field("text", TEXT);
+        let schema = schema_builder.build();
+        let index = Index::create_in_ram(schema);
+        let mut writer = index.writer_for_tests().unwrap();
+        writer.add_document(doc!(text=>"b c"));
+        writer.add_document(doc!(text=>"a c"));
+        writer.add_document(doc!(text=>"a b"));
+        writer.add_document(doc!(text=>"a d"));
+        writer.commit()?;
+        Ok(index)
+    }
+
+    #[test]
+    fn test_union() -> crate::Result<()> {
+        let index = create_test_index()?;
+        let searcher = index.reader()?.searcher();
+        let text = index.schema().get_field("text").unwrap();
+        let term_a = TermQuery::new(Term::from_field_text(text, "a"), IndexRecordOption::Basic);
+        let term_d = TermQuery::new(Term::from_field_text(text, "d"), IndexRecordOption::Basic);
+        let union_ad = BooleanQuery::union(vec![term_a.box_clone(), term_d.box_clone()]);
+        let docs = searcher.search(&union_ad, &DocSetCollector)?;
+        assert_eq!(
+            docs,
+            vec![
+                DocAddress(0u32, 1u32),
+                DocAddress(0u32, 2u32),
+                DocAddress(0u32, 3u32)
+            ]
+            .into_iter()
+            .collect()
+        );
+        Ok(())
+    }
+
+    #[test]
+    fn test_intersection() -> crate::Result<()> {
+        let index = create_test_index()?;
+        let searcher = index.reader()?.searcher();
+        let text = index.schema().get_field("text").unwrap();
+        let term_a = TermQuery::new(Term::from_field_text(text, "a"), IndexRecordOption::Basic);
+        let term_b = TermQuery::new(Term::from_field_text(text, "b"), IndexRecordOption::Basic);
+        let term_c = TermQuery::new(Term::from_field_text(text, "c"), IndexRecordOption::Basic);
+        let intersection_ab =
+            BooleanQuery::intersection(vec![term_a.box_clone(), term_b.box_clone()]);
+        let intersection_ac =
+            BooleanQuery::intersection(vec![term_a.box_clone(), term_c.box_clone()]);
+        let intersection_bc =
+            BooleanQuery::intersection(vec![term_b.box_clone(), term_c.box_clone()]);
+        {
+            let docs = searcher.search(&intersection_ab, &DocSetCollector)?;
+            assert_eq!(docs, vec![DocAddress(0u32, 2u32)].into_iter().collect());
+        }
+        {
+            let docs = searcher.search(&intersection_ac, &DocSetCollector)?;
+            assert_eq!(docs, vec![DocAddress(0u32, 1u32)].into_iter().collect());
+        }
+        {
+            let docs = searcher.search(&intersection_bc, &DocSetCollector)?;
+            assert_eq!(docs, vec![DocAddress(0u32, 0u32)].into_iter().collect());
+        }
+        Ok(())
+    }
+}

src/query/boolean_query/boolean_weight.rs

@@ -1,4 +1,5 @@
 use crate::core::SegmentReader;
+use crate::postings::FreqReadingOption;
 use crate::query::explanation::does_not_match;
 use crate::query::score_combiner::{DoNothingCombiner, ScoreCombiner, SumWithCoordsCombiner};
 use crate::query::term_query::TermScorer;
@@ -14,12 +15,12 @@ use crate::query::{intersect_scorers, Explanation};
 use crate::{DocId, Score};
 use std::collections::HashMap;
 
-enum SpecializedScorer<TScoreCombiner: ScoreCombiner> {
+enum SpecializedScorer {
-    TermUnion(Union<TermScorer, TScoreCombiner>),
+    TermUnion(Vec<TermScorer>),
     Other(Box<dyn Scorer>),
 }
 
-fn scorer_union<TScoreCombiner>(scorers: Vec<Box<dyn Scorer>>) -> SpecializedScorer<TScoreCombiner>
+fn scorer_union<TScoreCombiner>(scorers: Vec<Box<dyn Scorer>>) -> SpecializedScorer
 where
     TScoreCombiner: ScoreCombiner,
 {
@@ -35,20 +36,29 @@ where
                 .into_iter()
                 .map(|scorer| *(scorer.downcast::<TermScorer>().map_err(|_| ()).unwrap()))
                 .collect();
-            return SpecializedScorer::TermUnion(Union::<TermScorer, TScoreCombiner>::from(
+            if scorers
-                scorers,
+                .iter()
-            ));
+                .all(|scorer| scorer.freq_reading_option() == FreqReadingOption::ReadFreq)
+            {
+                // Block wand is only available iff we read frequencies.
+                return SpecializedScorer::TermUnion(scorers);
+            } else {
+                return SpecializedScorer::Other(Box::new(Union::<_, TScoreCombiner>::from(
+                    scorers,
+                )));
+            }
         }
     }
     SpecializedScorer::Other(Box::new(Union::<_, TScoreCombiner>::from(scorers)))
 }
 
-impl<TScoreCombiner: ScoreCombiner> Into<Box<dyn Scorer>> for SpecializedScorer<TScoreCombiner> {
+fn into_box_scorer<TScoreCombiner: ScoreCombiner>(scorer: SpecializedScorer) -> Box<dyn Scorer> {
-    fn into(self) -> Box<dyn Scorer> {
+    match scorer {
-        match self {
+        SpecializedScorer::TermUnion(term_scorers) => {
-            Self::TermUnion(union) => Box::new(union),
+            let union_scorer = Union::<TermScorer, TScoreCombiner>::from(term_scorers);
-            Self::Other(scorer) => scorer,
+            Box::new(union_scorer)
         }
+        SpecializedScorer::Other(scorer) => scorer,
     }
 }
 
@@ -68,7 +78,7 @@ impl BooleanWeight {
     fn per_occur_scorers(
         &self,
         reader: &SegmentReader,
-        boost: f32,
+        boost: Score,
     ) -> crate::Result<HashMap<Occur, Vec<Box<dyn Scorer>>>> {
         let mut per_occur_scorers: HashMap<Occur, Vec<Box<dyn Scorer>>> = HashMap::new();
         for &(ref occur, ref subweight) in &self.weights {
@@ -84,47 +94,48 @@ impl BooleanWeight {
     fn complex_scorer<TScoreCombiner: ScoreCombiner>(
         &self,
         reader: &SegmentReader,
-        boost: f32,
+        boost: Score,
-    ) -> crate::Result<SpecializedScorer<TScoreCombiner>> {
+    ) -> crate::Result<SpecializedScorer> {
         let mut per_occur_scorers = self.per_occur_scorers(reader, boost)?;
 
-        let should_scorer_opt: Option<SpecializedScorer<TScoreCombiner>> = per_occur_scorers
+        let should_scorer_opt: Option<SpecializedScorer> = per_occur_scorers
             .remove(&Occur::Should)
             .map(scorer_union::<TScoreCombiner>);
 
         let exclude_scorer_opt: Option<Box<dyn Scorer>> = per_occur_scorers
             .remove(&Occur::MustNot)
-            .map(scorer_union::<TScoreCombiner>)
+            .map(scorer_union::<DoNothingCombiner>)
-            .map(Into::into);
+            .map(into_box_scorer::<DoNothingCombiner>);
 
         let must_scorer_opt: Option<Box<dyn Scorer>> = per_occur_scorers
             .remove(&Occur::Must)
             .map(intersect_scorers);
 
-        let positive_scorer: SpecializedScorer<TScoreCombiner> =
+        let positive_scorer: SpecializedScorer = match (should_scorer_opt, must_scorer_opt) {
-            match (should_scorer_opt, must_scorer_opt) {
+            (Some(should_scorer), Some(must_scorer)) => {
-                (Some(should_scorer), Some(must_scorer)) => {
+                if self.scoring_enabled {
-                    if self.scoring_enabled {
+                    SpecializedScorer::Other(Box::new(RequiredOptionalScorer::<
-                        SpecializedScorer::Other(Box::new(RequiredOptionalScorer::<
+                        Box<dyn Scorer>,
-                            Box<dyn Scorer>,
+                        Box<dyn Scorer>,
-                            Box<dyn Scorer>,
+                        TScoreCombiner,
-                            TScoreCombiner,
+                    >::new(
-                        >::new(
+                        must_scorer,
-                            must_scorer, should_scorer.into()
+                        into_box_scorer::<TScoreCombiner>(should_scorer),
-                        )))
+                    )))
-                    } else {
+                } else {
-                        SpecializedScorer::Other(must_scorer)
+                    SpecializedScorer::Other(must_scorer)
-                    }
                 }
-                (None, Some(must_scorer)) => SpecializedScorer::Other(must_scorer),
+            }
-                (Some(should_scorer), None) => should_scorer,
+            (None, Some(must_scorer)) => SpecializedScorer::Other(must_scorer),
-                (None, None) => {
+            (Some(should_scorer), None) => should_scorer,
-                    return Ok(SpecializedScorer::Other(Box::new(EmptyScorer)));
+            (None, None) => {
-                }
+                return Ok(SpecializedScorer::Other(Box::new(EmptyScorer)));
-            };
+            }
+        };
 
         if let Some(exclude_scorer) = exclude_scorer_opt {
-            let positive_scorer_boxed: Box<dyn Scorer> = positive_scorer.into();
+            let positive_scorer_boxed: Box<dyn Scorer> =
+                into_box_scorer::<TScoreCombiner>(positive_scorer);
             Ok(SpecializedScorer::Other(Box::new(Exclude::new(
                 positive_scorer_boxed,
                 exclude_scorer,
@@ -136,7 +147,7 @@ impl BooleanWeight {
 }
 
 impl Weight for BooleanWeight {
-    fn scorer(&self, reader: &SegmentReader, boost: f32) -> crate::Result<Box<dyn Scorer>> {
+    fn scorer(&self, reader: &SegmentReader, boost: Score) -> crate::Result<Box<dyn Scorer>> {
         if self.weights.is_empty() {
             Ok(Box::new(EmptyScorer))
         } else if self.weights.len() == 1 {
@@ -148,20 +159,22 @@ impl Weight for BooleanWeight {
             }
         } else if self.scoring_enabled {
             self.complex_scorer::<SumWithCoordsCombiner>(reader, boost)
-                .map(Into::into)
+                .map(|specialized_scorer| {
+                    into_box_scorer::<SumWithCoordsCombiner>(specialized_scorer)
+                })
         } else {
             self.complex_scorer::<DoNothingCombiner>(reader, boost)
-                .map(Into::into)
+                .map(into_box_scorer::<DoNothingCombiner>)
         }
     }
 
     fn explain(&self, reader: &SegmentReader, doc: DocId) -> crate::Result<Explanation> {
-        let mut scorer = self.scorer(reader, 1.0f32)?;
+        let mut scorer = self.scorer(reader, 1.0)?;
         if scorer.seek(doc) != doc {
             return Err(does_not_match(doc));
         }
         if !self.scoring_enabled {
-            return Ok(Explanation::new("BooleanQuery with no scoring", 1f32));
+            return Ok(Explanation::new("BooleanQuery with no scoring", 1.0));
         }
 
         let mut explanation = Explanation::new("BooleanClause. Sum of ...", scorer.score());
@@ -180,9 +193,11 @@ impl Weight for BooleanWeight {
         reader: &SegmentReader,
         callback: &mut dyn FnMut(DocId, Score),
     ) -> crate::Result<()> {
-        let scorer = self.complex_scorer::<SumWithCoordsCombiner>(reader, 1.0f32)?;
+        let scorer = self.complex_scorer::<SumWithCoordsCombiner>(reader, 1.0)?;
         match scorer {
-            SpecializedScorer::TermUnion(mut union_scorer) => {
+            SpecializedScorer::TermUnion(term_scorers) => {
+                let mut union_scorer =
+                    Union::<TermScorer, SumWithCoordsCombiner>::from(term_scorers);
                 for_each_scorer(&mut union_scorer, callback);
             }
             SpecializedScorer::Other(mut scorer) => {
@@ -204,14 +219,14 @@ impl Weight for BooleanWeight {
     /// important optimization (e.g. BlockWAND for union).
     fn for_each_pruning(
         &self,
-        threshold: f32,
+        threshold: Score,
         reader: &SegmentReader,
         callback: &mut dyn FnMut(DocId, Score) -> Score,
     ) -> crate::Result<()> {
-        let scorer = self.complex_scorer::<SumWithCoordsCombiner>(reader, 1.0f32)?;
+        let scorer = self.complex_scorer::<SumWithCoordsCombiner>(reader, 1.0)?;
         match scorer {
-            SpecializedScorer::TermUnion(mut union_scorer) => {
+            SpecializedScorer::TermUnion(term_scorers) => {
-                for_each_pruning_scorer(&mut union_scorer, threshold, callback);
+                super::block_wand(term_scorers, threshold, callback);
             }
             SpecializedScorer::Other(mut scorer) => {
                 for_each_pruning_scorer(scorer.as_mut(), threshold, callback);

src/query/boolean_query/mod.rs

@@ -1,13 +1,17 @@
+mod block_wand;
 mod boolean_query;
 mod boolean_weight;
 
+pub(crate) use self::block_wand::block_wand;
 pub use self::boolean_query::BooleanQuery;
 
 #[cfg(test)]
 mod tests {
 
     use super::*;
+    use crate::assert_nearly_equals;
     use crate::collector::tests::TEST_COLLECTOR_WITH_SCORE;
+    use crate::collector::TopDocs;
     use crate::query::score_combiner::SumWithCoordsCombiner;
     use crate::query::term_query::TermScorer;
     use crate::query::Intersection;
@@ -18,9 +22,8 @@ mod tests {
     use crate::query::Scorer;
     use crate::query::TermQuery;
     use crate::schema::*;
-    use crate::tests::assert_nearly_equals;
     use crate::Index;
-    use crate::{DocAddress, DocId};
+    use crate::{DocAddress, DocId, Score};
 
     fn aux_test_helper() -> (Index, Field) {
         let mut schema_builder = Schema::builder();
@@ -29,14 +32,12 @@ mod tests {
         let index = Index::create_in_ram(schema);
         {
             // writing the segment
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+            let mut index_writer = index.writer_for_tests().unwrap();
-            {
+            index_writer.add_document(doc!(text_field => "a b c"));
-                index_writer.add_document(doc!(text_field => "a b c"));
+            index_writer.add_document(doc!(text_field => "a c"));
-                index_writer.add_document(doc!(text_field => "a c"));
+            index_writer.add_document(doc!(text_field => "b c"));
-                index_writer.add_document(doc!(text_field => "b c"));
+            index_writer.add_document(doc!(text_field => "a b c d"));
-                index_writer.add_document(doc!(text_field => "a b c d"));
+            index_writer.add_document(doc!(text_field => "d"));
-                index_writer.add_document(doc!(text_field => "d"));
-            }
             assert!(index_writer.commit().is_ok());
         }
         (index, text_field)
@@ -58,9 +59,7 @@ mod tests {
         let query = query_parser.parse_query("+a").unwrap();
         let searcher = index.reader().unwrap().searcher();
         let weight = query.weight(&searcher, true).unwrap();
-        let scorer = weight
+        let scorer = weight.scorer(searcher.segment_reader(0u32), 1.0).unwrap();
-            .scorer(searcher.segment_reader(0u32), 1.0f32)
-            .unwrap();
         assert!(scorer.is::<TermScorer>());
     }
 
@@ -72,17 +71,13 @@ mod tests {
         {
             let query = query_parser.parse_query("+a +b +c").unwrap();
             let weight = query.weight(&searcher, true).unwrap();
-            let scorer = weight
+            let scorer = weight.scorer(searcher.segment_reader(0u32), 1.0).unwrap();
-                .scorer(searcher.segment_reader(0u32), 1.0f32)
-                .unwrap();
             assert!(scorer.is::<Intersection<TermScorer>>());
         }
         {
             let query = query_parser.parse_query("+a +(b c)").unwrap();
             let weight = query.weight(&searcher, true).unwrap();
-            let scorer = weight
+            let scorer = weight.scorer(searcher.segment_reader(0u32), 1.0).unwrap();
-                .scorer(searcher.segment_reader(0u32), 1.0f32)
-                .unwrap();
             assert!(scorer.is::<Intersection<Box<dyn Scorer>>>());
         }
     }
@@ -95,9 +90,7 @@ mod tests {
         {
             let query = query_parser.parse_query("+a b").unwrap();
             let weight = query.weight(&searcher, true).unwrap();
-            let scorer = weight
+            let scorer = weight.scorer(searcher.segment_reader(0u32), 1.0).unwrap();
-                .scorer(searcher.segment_reader(0u32), 1.0f32)
-                .unwrap();
             assert!(scorer.is::<RequiredOptionalScorer<
                 Box<dyn Scorer>,
                 Box<dyn Scorer>,
@@ -107,9 +100,7 @@ mod tests {
         {
             let query = query_parser.parse_query("+a b").unwrap();
             let weight = query.weight(&searcher, false).unwrap();
-            let scorer = weight
+            let scorer = weight.scorer(searcher.segment_reader(0u32), 1.0).unwrap();
-                .scorer(searcher.segment_reader(0u32), 1.0f32)
-                .unwrap();
             assert!(scorer.is::<TermScorer>());
         }
     }
@@ -140,31 +131,30 @@ mod tests {
                 .map(|doc| doc.1)
                 .collect::<Vec<DocId>>()
         };
-
         {
-            let boolean_query = BooleanQuery::from(vec![(Occur::Must, make_term_query("a"))]);
+            let boolean_query = BooleanQuery::new(vec![(Occur::Must, make_term_query("a"))]);
             assert_eq!(matching_docs(&boolean_query), vec![0, 1, 3]);
         }
         {
-            let boolean_query = BooleanQuery::from(vec![(Occur::Should, make_term_query("a"))]);
+            let boolean_query = BooleanQuery::new(vec![(Occur::Should, make_term_query("a"))]);
             assert_eq!(matching_docs(&boolean_query), vec![0, 1, 3]);
         }
         {
-            let boolean_query = BooleanQuery::from(vec![
+            let boolean_query = BooleanQuery::new(vec![
                 (Occur::Should, make_term_query("a")),
                 (Occur::Should, make_term_query("b")),
             ]);
             assert_eq!(matching_docs(&boolean_query), vec![0, 1, 2, 3]);
         }
         {
-            let boolean_query = BooleanQuery::from(vec![
+            let boolean_query = BooleanQuery::new(vec![
                 (Occur::Must, make_term_query("a")),
                 (Occur::Should, make_term_query("b")),
             ]);
             assert_eq!(matching_docs(&boolean_query), vec![0, 1, 3]);
         }
         {
-            let boolean_query = BooleanQuery::from(vec![
+            let boolean_query = BooleanQuery::new(vec![
                 (Occur::Must, make_term_query("a")),
                 (Occur::Should, make_term_query("b")),
                 (Occur::MustNot, make_term_query("d")),
@@ -172,11 +162,59 @@ mod tests {
             assert_eq!(matching_docs(&boolean_query), vec![0, 1]);
         }
         {
-            let boolean_query = BooleanQuery::from(vec![(Occur::MustNot, make_term_query("d"))]);
+            let boolean_query = BooleanQuery::new(vec![(Occur::MustNot, make_term_query("d"))]);
             assert_eq!(matching_docs(&boolean_query), Vec::<u32>::new());
         }
     }
 
+    #[test]
+    pub fn test_boolean_query_two_excluded() {
+        let (index, text_field) = aux_test_helper();
+
+        let make_term_query = |text: &str| {
+            let term_query = TermQuery::new(
+                Term::from_field_text(text_field, text),
+                IndexRecordOption::Basic,
+            );
+            let query: Box<dyn Query> = Box::new(term_query);
+            query
+        };
+
+        let reader = index.reader().unwrap();
+
+        let matching_topdocs = |query: &dyn Query| {
+            reader
+                .searcher()
+                .search(query, &TopDocs::with_limit(3))
+                .unwrap()
+        };
+
+        let score_doc_4: Score; // score of doc 4 should not be influenced by exclusion
+        {
+            let boolean_query_no_excluded =
+                BooleanQuery::new(vec![(Occur::Must, make_term_query("d"))]);
+            let topdocs_no_excluded = matching_topdocs(&boolean_query_no_excluded);
+            assert_eq!(topdocs_no_excluded.len(), 2);
+            let (top_score, top_doc) = topdocs_no_excluded[0];
+            assert_eq!(top_doc, DocAddress(0, 4));
+            assert_eq!(topdocs_no_excluded[1].1, DocAddress(0, 3)); // ignore score of doc 3.
+            score_doc_4 = top_score;
+        }
+
+        {
+            let boolean_query_two_excluded = BooleanQuery::new(vec![
+                (Occur::Must, make_term_query("d")),
+                (Occur::MustNot, make_term_query("a")),
+                (Occur::MustNot, make_term_query("b")),
+            ]);
+            let topdocs_excluded = matching_topdocs(&boolean_query_two_excluded);
+            assert_eq!(topdocs_excluded.len(), 1);
+            let (top_score, top_doc) = topdocs_excluded[0];
+            assert_eq!(top_doc, DocAddress(0, 4));
+            assert_eq!(top_score, score_doc_4);
+        }
+    }
+
     #[test]
     pub fn test_boolean_query_with_weight() {
         let mut schema_builder = Schema::builder();
@@ -184,7 +222,7 @@ mod tests {
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
         {
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+            let mut index_writer = index.writer_for_tests().unwrap();
             index_writer.add_document(doc!(text_field => "a b c"));
             index_writer.add_document(doc!(text_field => "a c"));
             index_writer.add_document(doc!(text_field => "b c"));
@@ -201,21 +239,21 @@ mod tests {
         let reader = index.reader().unwrap();
         let searcher = reader.searcher();
         let boolean_query =
-            BooleanQuery::from(vec![(Occur::Should, term_a), (Occur::Should, term_b)]);
+            BooleanQuery::new(vec![(Occur::Should, term_a), (Occur::Should, term_b)]);
         let boolean_weight = boolean_query.weight(&searcher, true).unwrap();
         {
             let mut boolean_scorer = boolean_weight
-                .scorer(searcher.segment_reader(0u32), 1.0f32)
+                .scorer(searcher.segment_reader(0u32), 1.0)
                 .unwrap();
             assert_eq!(boolean_scorer.doc(), 0u32);
-            assert_nearly_equals(boolean_scorer.score(), 0.84163445f32);
+            assert_nearly_equals!(boolean_scorer.score(), 0.84163445);
         }
         {
             let mut boolean_scorer = boolean_weight
-                .scorer(searcher.segment_reader(0u32), 2.0f32)
+                .scorer(searcher.segment_reader(0u32), 2.0)
                 .unwrap();
             assert_eq!(boolean_scorer.doc(), 0u32);
-            assert_nearly_equals(boolean_scorer.score(), 1.6832689f32);
+            assert_nearly_equals!(boolean_scorer.score(), 1.6832689);
         }
     }
 
@@ -241,174 +279,38 @@ mod tests {
         };
 
         {
-            let boolean_query = BooleanQuery::from(vec![
+            let boolean_query = BooleanQuery::new(vec![
                 (Occur::Must, make_term_query("a")),
                 (Occur::Must, make_term_query("b")),
             ]);
-            assert_eq!(score_docs(&boolean_query), vec![0.977973, 0.84699446]);
+            let scores = score_docs(&boolean_query);
+            assert_nearly_equals!(scores[0], 0.977973);
+            assert_nearly_equals!(scores[1], 0.84699446);
         }
     }
 
-    // motivated by #554
     #[test]
-    fn test_bm25_several_fields() {
+    pub fn test_explain() -> crate::Result<()> {
         let mut schema_builder = Schema::builder();
-        let title = schema_builder.add_text_field("title", TEXT);
+        let text = schema_builder.add_text_field("text", STRING);
-        let text = schema_builder.add_text_field("text", TEXT);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
-
+        let mut index_writer = index.writer_with_num_threads(1, 5_000_000)?;
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        index_writer.add_document(doc!(text=>"a"));
-        index_writer.add_document(doc!(
+        index_writer.add_document(doc!(text=>"b"));
-            // tf = 1 0
+        index_writer.commit()?;
-            title =>  "Законы притяжения   Оксана Кулакова",
+        let searcher = index.reader()?.searcher();
-            // tf = 1 0
+        let term_a: Box<dyn Query> = Box::new(TermQuery::new(
-            text => "Законы притяжения Оксана Кулакова]  \n\nТема: Сексуальное искусство, Женственность\nТип товара: Запись вебинара (аудио)\nПродолжительность: 1,5 часа\n\nСсылка на вебинар:\n  ",
+            Term::from_field_text(text, "a"),
+            IndexRecordOption::Basic,
         ));
-        index_writer.add_document(doc!(
+        let term_b: Box<dyn Query> = Box::new(TermQuery::new(
-            // tf = 1 0
+            Term::from_field_text(text, "b"),
-            title => "Любимые русские пироги (Оксана Путан)",
+            IndexRecordOption::Basic,
-            // tf = 2 0
-            text => "http://i95.fastpic.ru/big/2017/0628/9a/615b9c8504d94a3893d7f496ac53539a.jpg \n\nОт издателя\nОксана Путан   профессиональный повар, автор кулинарных книг и известный кулинарный блогер. Ее рецепты отличаются практичностью, доступностью и пользуются огромной популярностью в русскоязычном интернете. Это третья книга автора о самом вкусном и ароматном   настоящих русских пирогах и выпечке!\nДаже новички на кухне легко готовят по ее рецептам. Оксана описывает процесс приготовления настолько подробно и понятно, что вам остается только наслаждаться готовкой и не тратить время на лишние усилия. Готовьте легко и просто!\n\nhttps://www.ozon.ru/context/detail/id/139872462/"
         ));
-        index_writer.add_document(doc!(
+        let query = BooleanQuery::from(vec![(Occur::Should, term_a), (Occur::Should, term_b)]);
-            // tf = 1 1
+        let explanation = query.explain(&searcher, DocAddress(0, 0u32))?;
-            title =>  "PDF Мастер Класс \"Морячок\" (Оксана Лифенко)",
+        assert_nearly_equals!(explanation.value(), 0.6931472f32);
-            // tf = 0 0 
+        Ok(())
-            text => "https://i.ibb.co/pzvHrDN/I3d U T6 Gg TM.jpg\nhttps://i.ibb.co/NFrb6v6/N0ls Z9nwjb U.jpg\nВ описание входит штаны, кофта, берет, матросский воротник. Описание продается в формате PDF, состоит из 12 страниц формата А4 и может быть напечатано на любом принтере.\nОписание предназначено для кукол BJD RealPuki от FairyLand, но может подойти и другим подобным куклам. Также вы можете вязать этот наряд из обычной пряжи, и он подойдет для куколок побольше.\nhttps://vk.com/market 95724412?w=product 95724412_2212"
-        ));
-        for _ in 0..1_000 {
-            index_writer.add_document(doc!(
-                title =>  "a b d e f g",
-                text => "maitre corbeau sur un arbre perche tenait dans son bec un fromage Maitre rnard par lodeur alleche lui tint a peu pres ce langage."
-            ));
-        }
-        index_writer.commit().unwrap();
-        let reader = index.reader().unwrap();
-        let searcher = reader.searcher();
-        let query_parser = QueryParser::for_index(&index, vec![title, text]);
-        let query = query_parser.parse_query("Оксана Лифенко").unwrap();
-        let weight = query.weight(&searcher, true).unwrap();
-        let mut scorer = weight
-            .scorer(searcher.segment_reader(0u32), 1.0f32)
-            .unwrap();
-        scorer.advance();
-
-        let explanation = query.explain(&searcher, DocAddress(0u32, 0u32)).unwrap();
-        assert_eq!(
-            explanation.to_pretty_json(),
-            r#"{
-  "value": 12.997711,
-  "description": "BooleanClause. Sum of ...",
-  "details": [
-    {
-      "value": 12.997711,
-      "description": "BooleanClause. Sum of ...",
-      "details": [
-        {
-          "value": 6.551476,
-          "description": "TermQuery, product of...",
-          "details": [
-            {
-              "value": 2.2,
-              "description": "(K1+1)"
-            },
-            {
-              "value": 5.658984,
-              "description": "idf, computed as log(1 + (N - n + 0.5) / (n + 0.5))",
-              "details": [
-                {
-                  "value": 3.0,
-                  "description": "n, number of docs containing this term"
-                },
-                {
-                  "value": 1003.0,
-                  "description": "N, total number of docs"
-                }
-              ]
-            },
-            {
-              "value": 0.5262329,
-              "description": "freq / (freq + k1 * (1 - b + b * dl / avgdl))",
-              "details": [
-                {
-                  "value": 1.0,
-                  "description": "freq, occurrences of term within document"
-                },
-                {
-                  "value": 1.2,
-                  "description": "k1, term saturation parameter"
-                },
-                {
-                  "value": 0.75,
-                  "description": "b, length normalization parameter"
-                },
-                {
-                  "value": 4.0,
-                  "description": "dl, length of field"
-                },
-                {
-                  "value": 5.997009,
-                  "description": "avgdl, average length of field"
-                }
-              ]
-            }
-          ]
-        },
-        {
-          "value": 6.446235,
-          "description": "TermQuery, product of...",
-          "details": [
-            {
-              "value": 2.2,
-              "description": "(K1+1)"
-            },
-            {
-              "value": 5.9954567,
-              "description": "idf, computed as log(1 + (N - n + 0.5) / (n + 0.5))",
-              "details": [
-                {
-                  "value": 2.0,
-                  "description": "n, number of docs containing this term"
-                },
-                {
-                  "value": 1003.0,
-                  "description": "N, total number of docs"
-                }
-              ]
-            },
-            {
-              "value": 0.4887212,
-              "description": "freq / (freq + k1 * (1 - b + b * dl / avgdl))",
-              "details": [
-                {
-                  "value": 1.0,
-                  "description": "freq, occurrences of term within document"
-                },
-                {
-                  "value": 1.2,
-                  "description": "k1, term saturation parameter"
-                },
-                {
-                  "value": 0.75,
-                  "description": "b, length normalization parameter"
-                },
-                {
-                  "value": 20.0,
-                  "description": "dl, length of field"
-                },
-                {
-                  "value": 24.123629,
-                  "description": "avgdl, average length of field"
-                }
-              ]
-            }
-          ]
-        }
-      ]
-    }
-  ]
-}"#
-        );
     }
 }

src/query/boost_query.rs

@@ -1,7 +1,7 @@
 use crate::fastfield::DeleteBitSet;
 use crate::query::explanation::does_not_match;
 use crate::query::{Explanation, Query, Scorer, Weight};
-use crate::{DocId, DocSet, Searcher, SegmentReader, Term};
+use crate::{DocId, DocSet, Score, Searcher, SegmentReader, Term};
 use std::collections::BTreeSet;
 use std::fmt;
 
@@ -12,12 +12,12 @@ use std::fmt;
 /// factor.
 pub struct BoostQuery {
     query: Box<dyn Query>,
-    boost: f32,
+    boost: Score,
 }
 
 impl BoostQuery {
     /// Builds a boost query.
-    pub fn new(query: Box<dyn Query>, boost: f32) -> BoostQuery {
+    pub fn new(query: Box<dyn Query>, boost: Score) -> BoostQuery {
         BoostQuery { query, boost }
     }
 }
@@ -55,22 +55,22 @@ impl Query for BoostQuery {
 
 pub(crate) struct BoostWeight {
     weight: Box<dyn Weight>,
-    boost: f32,
+    boost: Score,
 }
 
 impl BoostWeight {
-    pub fn new(weight: Box<dyn Weight>, boost: f32) -> Self {
+    pub fn new(weight: Box<dyn Weight>, boost: Score) -> Self {
         BoostWeight { weight, boost }
     }
 }
 
 impl Weight for BoostWeight {
-    fn scorer(&self, reader: &SegmentReader, boost: f32) -> crate::Result<Box<dyn Scorer>> {
+    fn scorer(&self, reader: &SegmentReader, boost: Score) -> crate::Result<Box<dyn Scorer>> {
         self.weight.scorer(reader, boost * self.boost)
     }
 
     fn explain(&self, reader: &SegmentReader, doc: u32) -> crate::Result<Explanation> {
-        let mut scorer = self.scorer(reader, 1.0f32)?;
+        let mut scorer = self.scorer(reader, 1.0)?;
         if scorer.seek(doc) != doc {
             return Err(does_not_match(doc));
         }
@@ -88,11 +88,11 @@ impl Weight for BoostWeight {
 
 pub(crate) struct BoostScorer<S: Scorer> {
     underlying: S,
-    boost: f32,
+    boost: Score,
 }
 
 impl<S: Scorer> BoostScorer<S> {
-    pub fn new(underlying: S, boost: f32) -> BoostScorer<S> {
+    pub fn new(underlying: S, boost: Score) -> BoostScorer<S> {
         BoostScorer { underlying, boost }
     }
 }
@@ -128,7 +128,7 @@ impl<S: Scorer> DocSet for BoostScorer<S> {
 }
 
 impl<S: Scorer> Scorer for BoostScorer<S> {
-    fn score(&mut self) -> f32 {
+    fn score(&mut self) -> Score {
         self.underlying.score() * self.boost
     }
 }
@@ -144,7 +144,7 @@ mod tests {
     fn test_boost_query_explain() {
         let schema = Schema::builder().build();
         let index = Index::create_in_ram(schema);
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests().unwrap();
         index_writer.add_document(Document::new());
         assert!(index_writer.commit().is_ok());
         let reader = index.reader().unwrap();
@@ -153,7 +153,7 @@ mod tests {
         let explanation = query.explain(&searcher, DocAddress(0, 0u32)).unwrap();
         assert_eq!(
             explanation.to_pretty_json(),
-            "{\n  \"value\": 0.2,\n  \"description\": \"Boost x0.2 of ...\",\n  \"details\": [\n    {\n      \"value\": 1.0,\n      \"description\": \"AllQuery\"\n    }\n  ]\n}"
+            "{\n  \"value\": 0.2,\n  \"description\": \"Boost x0.2 of ...\",\n  \"details\": [\n    {\n      \"value\": 1.0,\n      \"description\": \"AllQuery\",\n      \"context\": []\n    }\n  ],\n  \"context\": []\n}"
         )
     }
 }

src/query/empty_query.rs

@@ -34,7 +34,7 @@ impl Query for EmptyQuery {
 /// It is useful for tests and handling edge cases.
 pub struct EmptyWeight;
 impl Weight for EmptyWeight {
-    fn scorer(&self, _reader: &SegmentReader, _boost: f32) -> crate::Result<Box<dyn Scorer>> {
+    fn scorer(&self, _reader: &SegmentReader, _boost: Score) -> crate::Result<Box<dyn Scorer>> {
         Ok(Box::new(EmptyScorer))
     }
 
@@ -64,7 +64,7 @@ impl DocSet for EmptyScorer {
 
 impl Scorer for EmptyScorer {
     fn score(&mut self) -> Score {
-        0f32
+        0.0
     }
 }
 

src/query/exclude.rs

@@ -3,6 +3,11 @@ use crate::query::Scorer;
 use crate::DocId;
 use crate::Score;
 
+#[inline(always)]
+fn is_within<TDocSetExclude: DocSet>(docset: &mut TDocSetExclude, doc: DocId) -> bool {
+    docset.doc() <= doc && docset.seek(doc) == doc
+}
+
 /// Filters a given `DocSet` by removing the docs from a given `DocSet`.
 ///
 /// The excluding docset has no impact on scoring.
@@ -23,8 +28,7 @@ where
     ) -> Exclude<TDocSet, TDocSetExclude> {
         while underlying_docset.doc() != TERMINATED {
             let target = underlying_docset.doc();
-            if excluding_docset.seek(target) != target {
+            if !is_within(&mut excluding_docset, target) {
-                // this document is not excluded.
                 break;
             }
             underlying_docset.advance();
@@ -36,42 +40,30 @@ where
     }
 }
 
-impl<TDocSet, TDocSetExclude> Exclude<TDocSet, TDocSetExclude>
-where
-    TDocSet: DocSet,
-    TDocSetExclude: DocSet,
-{
-    /// Returns true iff the doc is not removed.
-    ///
-    /// The method has to be called with non strictly
-    /// increasing `doc`.
-    fn accept(&mut self) -> bool {
-        let doc = self.underlying_docset.doc();
-        self.excluding_docset.seek(doc) != doc
-    }
-}
-
 impl<TDocSet, TDocSetExclude> DocSet for Exclude<TDocSet, TDocSetExclude>
 where
     TDocSet: DocSet,
     TDocSetExclude: DocSet,
 {
     fn advance(&mut self) -> DocId {
-        while self.underlying_docset.advance() != TERMINATED {
+        loop {
-            if self.accept() {
+            let candidate = self.underlying_docset.advance();
-                return self.doc();
+            if candidate == TERMINATED {
+                return TERMINATED;
+            }
+            if !is_within(&mut self.excluding_docset, candidate) {
+                return candidate;
             }
         }
-        TERMINATED
     }
 
     fn seek(&mut self, target: DocId) -> DocId {
-        let underlying_seek_result = self.underlying_docset.seek(target);
+        let candidate = self.underlying_docset.seek(target);
-        if underlying_seek_result == TERMINATED {
+        if candidate == TERMINATED {
             return TERMINATED;
         }
-        if self.accept() {
+        if !is_within(&mut self.excluding_docset, candidate) {
-            return underlying_seek_result;
+            return candidate;
         }
         self.advance()
     }
@@ -129,7 +121,7 @@ mod tests {
                     VecDocSet::from(vec![1, 2, 3, 10, 16, 24]),
                 ))
             },
-            vec![1, 2, 5, 8, 10, 15, 24],
+            vec![5, 8, 10, 15, 24],
         );
     }
 

src/query/explanation.rs

@@ -1,5 +1,6 @@
-use crate::{DocId, TantivyError};
+use crate::{DocId, Score, TantivyError};
 use serde::Serialize;
+use std::fmt;
 
 pub(crate) fn does_not_match(doc: DocId) -> TantivyError {
     TantivyError::InvalidArgument(format!("Document #({}) does not match", doc))
@@ -12,24 +13,32 @@ pub(crate) fn does_not_match(doc: DocId) -> TantivyError {
 /// representation of this tree when debugging a given score.
 #[derive(Clone, Serialize)]
 pub struct Explanation {
-    value: f32,
+    value: Score,
     description: String,
     #[serde(skip_serializing_if = "Vec::is_empty")]
     details: Vec<Explanation>,
+    context: Vec<String>,
+}
+
+impl fmt::Debug for Explanation {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "Explanation({})", self.to_pretty_json())
+    }
 }
 
 impl Explanation {
     /// Creates a new explanation object.
-    pub fn new<T: ToString>(description: T, value: f32) -> Explanation {
+    pub fn new<T: ToString>(description: T, value: Score) -> Explanation {
         Explanation {
             value,
             description: description.to_string(),
             details: vec![],
+            context: vec![],
         }
     }
 
     /// Returns the value associated to the current node.
-    pub fn value(&self) -> f32 {
+    pub fn value(&self) -> Score {
         self.value
     }
 
@@ -40,8 +49,13 @@ impl Explanation {
         self.details.push(child_explanation);
     }
 
+    /// Adds some extra context to the explanation.
+    pub fn add_context(&mut self, context: String) {
+        self.context.push(context);
+    }
+
     /// Shortcut for `self.details.push(Explanation::new(name, value));`
-    pub fn add_const<T: ToString>(&mut self, name: T, value: f32) {
+    pub fn add_const<T: ToString>(&mut self, name: T, value: Score) {
         self.details.push(Explanation::new(name, value));
     }
 

src/query/fuzzy_query.rs

@@ -163,10 +163,10 @@ impl Query for FuzzyTermQuery {
 #[cfg(test)]
 mod test {
     use super::FuzzyTermQuery;
+    use crate::assert_nearly_equals;
     use crate::collector::TopDocs;
     use crate::schema::Schema;
     use crate::schema::TEXT;
-    use crate::tests::assert_nearly_equals;
     use crate::Index;
     use crate::Term;
 
@@ -177,7 +177,7 @@ mod test {
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
         {
-            let mut index_writer = index.writer_with_num_threads(1, 10_000_000).unwrap();
+            let mut index_writer = index.writer_for_tests().unwrap();
             index_writer.add_document(doc!(
                 country_field => "japan",
             ));
@@ -199,7 +199,7 @@ mod test {
                 .unwrap();
             assert_eq!(top_docs.len(), 1, "Expected only 1 document");
             let (score, _) = top_docs[0];
-            assert_nearly_equals(1f32, score);
+            assert_nearly_equals!(1.0, score);
         }
 
         // fails because non-prefix Levenshtein distance is more than 1 (add 'a' and 'n')
@@ -223,7 +223,7 @@ mod test {
                 .unwrap();
             assert_eq!(top_docs.len(), 1, "Expected only 1 document");
             let (score, _) = top_docs[0];
-            assert_nearly_equals(1f32, score);
+            assert_nearly_equals!(1.0, score);
         }
     }
 }

src/query/intersection.rs

@@ -53,7 +53,8 @@ pub struct Intersection<TDocSet: DocSet, TOtherDocSet: DocSet = Box<dyn Scorer>>
 }
 
 fn go_to_first_doc<TDocSet: DocSet>(docsets: &mut [TDocSet]) -> DocId {
-    let mut candidate = 0;
+    assert!(!docsets.is_empty());
+    let mut candidate = docsets.iter().map(TDocSet::doc).max().unwrap();
     'outer: loop {
         for docset in docsets.iter_mut() {
             let seek_doc = docset.seek(candidate);
@@ -118,7 +119,9 @@ impl<TDocSet: DocSet, TOtherDocSet: DocSet> DocSet for Intersection<TDocSet, TOt
                     continue 'outer;
                 }
             }
-
+            debug_assert_eq!(candidate, self.left.doc());
+            debug_assert_eq!(candidate, self.right.doc());
+            debug_assert!(self.others.iter().all(|docset| docset.doc() == candidate));
             return candidate;
         }
     }
@@ -129,7 +132,10 @@ impl<TDocSet: DocSet, TOtherDocSet: DocSet> DocSet for Intersection<TDocSet, TOt
         for docset in &mut self.others {
             docsets.push(docset);
         }
-        go_to_first_doc(&mut docsets[..])
+        let doc = go_to_first_doc(&mut docsets[..]);
+        debug_assert!(docsets.iter().all(|docset| docset.doc() == doc));
+        debug_assert!(doc >= target);
+        doc
     }
 
     fn doc(&self) -> DocId {

src/query/mod.rs

@@ -26,6 +26,7 @@ mod weight;
 mod vec_docset;
 
 pub(crate) mod score_combiner;
+pub(crate) use self::bm25::BM25Weight;
 pub use self::intersection::Intersection;
 pub use self::union::Union;
 
@@ -45,7 +46,7 @@ pub(crate) use self::fuzzy_query::DFAWrapper;
 pub use self::fuzzy_query::FuzzyTermQuery;
 pub use self::intersection::intersect_scorers;
 pub use self::phrase_query::PhraseQuery;
-pub use self::query::Query;
+pub use self::query::{Query, QueryClone};
 pub use self::query_parser::QueryParser;
 pub use self::query_parser::QueryParserError;
 pub use self::range_query::RangeQuery;

src/query/phrase_query/mod.rs

@@ -10,12 +10,13 @@ pub use self::phrase_weight::PhraseWeight;
 pub mod tests {
 
     use super::*;
+    use crate::assert_nearly_equals;
     use crate::collector::tests::{TEST_COLLECTOR_WITHOUT_SCORE, TEST_COLLECTOR_WITH_SCORE};
     use crate::core::Index;
+    use crate::query::Weight;
     use crate::schema::{Schema, Term, TEXT};
-    use crate::tests::assert_nearly_equals;
-    use crate::DocAddress;
     use crate::DocId;
+    use crate::{DocAddress, TERMINATED};
 
     pub fn create_index(texts: &[&'static str]) -> Index {
         let mut schema_builder = Schema::builder();
@@ -23,7 +24,7 @@ pub mod tests {
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
         {
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+            let mut index_writer = index.writer_for_tests().unwrap();
             for &text in texts {
                 let doc = doc!(text_field=>text);
                 index_writer.add_document(doc);
@@ -67,6 +68,23 @@ pub mod tests {
         assert!(test_query(vec!["g", "a"]).is_empty());
     }
 
+    #[test]
+    pub fn test_phrase_query_simple() -> crate::Result<()> {
+        let index = create_index(&["a b b d c g c", "a b a b c"]);
+        let text_field = index.schema().get_field("text").unwrap();
+        let searcher = index.reader()?.searcher();
+        let terms: Vec<Term> = vec!["a", "b", "c"]
+            .iter()
+            .map(|text| Term::from_field_text(text_field, text))
+            .collect();
+        let phrase_query = PhraseQuery::new(terms);
+        let phrase_weight = phrase_query.phrase_weight(&searcher, false)?;
+        let mut phrase_scorer = phrase_weight.scorer(searcher.segment_reader(0), 1.0)?;
+        assert_eq!(phrase_scorer.doc(), 1);
+        assert_eq!(phrase_scorer.advance(), TERMINATED);
+        Ok(())
+    }
+
     #[test]
     pub fn test_phrase_query_no_score() {
         let index = create_index(&[
@@ -117,7 +135,7 @@ pub mod tests {
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
         {
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+            let mut index_writer = index.writer_for_tests().unwrap();
             index_writer.add_document(doc!(text_field=>"a b c"));
             assert!(index_writer.commit().is_ok());
         }
@@ -157,8 +175,8 @@ pub mod tests {
                 .to_vec()
         };
         let scores = test_query(vec!["a", "b"]);
-        assert_nearly_equals(scores[0], 0.40618482);
+        assert_nearly_equals!(scores[0], 0.40618482);
-        assert_nearly_equals(scores[1], 0.46844664);
+        assert_nearly_equals!(scores[1], 0.46844664);
     }
 
     #[test] // motivated by #234
@@ -168,7 +186,7 @@ pub mod tests {
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
         {
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+            let mut index_writer = index.writer_for_tests().unwrap();
             index_writer.add_document(doc!(text_field=>"b"));
             index_writer.add_document(doc!(text_field=>"a b"));
             index_writer.add_document(doc!(text_field=>"b a"));
@@ -199,7 +217,7 @@ pub mod tests {
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
         {
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+            let mut index_writer = index.writer_for_tests().unwrap();
             index_writer.add_document(doc!(text_field=>"a b c d e f g h"));
             assert!(index_writer.commit().is_ok());
         }

src/query/phrase_query/phrase_query.rs

@@ -95,7 +95,7 @@ impl PhraseQuery {
             )));
         }
         let terms = self.phrase_terms();
-        let bm25_weight = BM25Weight::for_terms(searcher, &terms);
+        let bm25_weight = BM25Weight::for_terms(searcher, &terms)?;
         Ok(PhraseWeight::new(
             self.phrase_terms.clone(),
             bm25_weight,

src/query/phrase_query/phrase_scorer.rs

@@ -3,7 +3,7 @@ use crate::fieldnorm::FieldNormReader;
 use crate::postings::Postings;
 use crate::query::bm25::BM25Weight;
 use crate::query::{Intersection, Scorer};
-use crate::DocId;
+use crate::{DocId, Score};
 use std::cmp::Ordering;
 
 struct PostingsWithOffset<TPostings> {
@@ -239,6 +239,7 @@ impl<TPostings: Postings> DocSet for PhraseScorer<TPostings> {
     }
 
     fn seek(&mut self, target: DocId) -> DocId {
+        debug_assert!(target >= self.doc());
         let doc = self.intersection_docset.seek(target);
         if doc == TERMINATED || self.phrase_match() {
             return doc;
@@ -256,7 +257,7 @@ impl<TPostings: Postings> DocSet for PhraseScorer<TPostings> {
 }
 
 impl<TPostings: Postings> Scorer for PhraseScorer<TPostings> {
-    fn score(&mut self) -> f32 {
+    fn score(&mut self) -> Score {
         let doc = self.doc();
         let fieldnorm_id = self.fieldnorm_reader.fieldnorm_id(doc);
         self.similarity_weight
@@ -266,7 +267,6 @@ impl<TPostings: Postings> Scorer for PhraseScorer<TPostings> {
 
 #[cfg(test)]
 mod tests {
-
     use super::{intersection, intersection_count};
 
     fn test_intersection_sym(left: &[u32], right: &[u32], expected: &[u32]) {