test store

Issue/969

CHANGELOG.md

@@ -7,6 +7,12 @@ Tantivy 0.14.0
 - Added support for Brotli compression in the DocStore. (@ppodolsky)
 - Added helper for building intersections and unions in BooleanQuery (@guilload)
 - Bugfix in `Query::explain`
+- Removed dependency on `notify` #924. Replaced with `FileWatcher` struct that polls meta file every 500ms in background thread. (@halvorboe @guilload)
+- Added `FilterCollector`, which wraps another collector and filters docs using a predicate over a fast field (@barrotsteindev)
+- Simplified the encoding of the skip reader struct. BlockWAND max tf is now encoded over a single byte. (@pmasurel)
+- `FilterCollector` now supports all Fast Field value types (@barrotsteindev)
+
+This version breaks compatibility and requires users to reindex everything.
 
 Tantivy 0.13.2
 ===================

Cargo.toml

@@ -30,7 +30,6 @@ serde_json = "1"
 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 = "0.8"
 futures = {version = "0.3",  features=["thread-pool"] }
@@ -48,15 +47,18 @@ murmurhash32 = "0.2"
 chrono = "0.4"
 smallvec = "1"
 rayon = "1"
+env_logger = "0.8"
+lru = "0.6"
 
 [target.'cfg(windows)'.dependencies]
 winapi = "0.3"
 
 [dev-dependencies]
-rand = "0.7"
+rand = "0.8"
 maplit = "1"
 matches = "0.1.8"
 proptest = "0.10"
+criterion = "0.3"
 
 [dev-dependencies.fail]
 version = "0.4"
@@ -73,7 +75,7 @@ overflow-checks = true
 
 [features]
 default = ["mmap"]
-mmap = ["fs2", "tempfile", "memmap", "notify"]
+mmap = ["fs2", "tempfile", "memmap"]
 brotli-compression = ["brotli"]
 lz4-compression = ["lz4"]
 failpoints = ["fail/failpoints"]
@@ -97,3 +99,7 @@ travis-ci = { repository = "tantivy-search/tantivy" }
 name = "failpoints"
 path = "tests/failpoints/mod.rs"
 required-features = ["fail/failpoints"]
+
+[[bench]]
+name = "analyzer"
+harness = false

benches/analyzer.rs

@@ -0,0 +1,22 @@
+use criterion::{criterion_group, criterion_main, Criterion};
+use tantivy::tokenizer::TokenizerManager;
+
+const ALICE_TXT: &'static str = include_str!("alice.txt");
+
+pub fn criterion_benchmark(c: &mut Criterion) {
+    let tokenizer_manager = TokenizerManager::default();
+    let tokenizer = tokenizer_manager.get("default").unwrap();
+    c.bench_function("default-tokenize-alice", |b| {
+        b.iter(|| {
+            let mut word_count = 0;
+            let mut token_stream = tokenizer.token_stream(ALICE_TXT);
+            while token_stream.advance() {
+                word_count += 1;
+            }
+            assert_eq!(word_count, 30_731);
+        })
+    });
+}
+
+criterion_group!(benches, criterion_benchmark);
+criterion_main!(benches);

examples/faceted_search_with_tweaked_score.rs

@@ -61,7 +61,7 @@ fn main() -> tantivy::Result<()> {
 
                 let query_ords: HashSet<u64> = facets
                     .iter()
-                    .filter_map(|key| facet_dict.term_ord(key.encoded_str()))
+                    .filter_map(|key| facet_dict.term_ord(key.encoded_str()).unwrap())
                     .collect();
 
                 let mut facet_ords_buffer: Vec<u64> = Vec::with_capacity(20);

src/collector/facet_collector.rs

@@ -274,7 +274,7 @@ impl Collector for FacetCollector {
         let mut collapse_facet_it = self.facets.iter().peekable();
         collapse_facet_ords.push(0);
         {
-            let mut facet_streamer = facet_reader.facet_dict().range().into_stream();
+            let mut facet_streamer = facet_reader.facet_dict().range().into_stream()?;
             if facet_streamer.advance() {
                 'outer: loop {
                     // at the begining of this loop, facet_streamer
@@ -368,9 +368,12 @@ impl SegmentCollector for FacetSegmentCollector {
             }
             let mut facet = vec![];
             let facet_ord = self.collapse_facet_ords[collapsed_facet_ord];
-            facet_dict.ord_to_term(facet_ord as u64, &mut facet);
-            // TODO
-            facet_counts.insert(Facet::from_encoded(facet).unwrap(), count);
+            // TODO handle errors.
+            if facet_dict.ord_to_term(facet_ord as u64, &mut facet).is_ok() {
+                if let Ok(facet) = Facet::from_encoded(facet) {
+                    facet_counts.insert(facet, count);
+                }
+            }
         }
         FacetCounts { facet_counts }
     }

src/collector/filter_collector_wrapper.rs

@@ -0,0 +1,189 @@
+// # Custom collector example
+//
+// This example shows how you can implement your own
+// collector. As an example, we will compute a collector
+// that computes the standard deviation of a given fast field.
+//
+// Of course, you can have a look at the tantivy's built-in collectors
+// such as the `CountCollector` for more examples.
+
+// ---
+// Importing tantivy...
+use std::marker::PhantomData;
+
+use crate::collector::{Collector, SegmentCollector};
+use crate::fastfield::{FastFieldReader, FastValue};
+use crate::schema::Field;
+use crate::{Score, SegmentReader, TantivyError};
+
+/// The `FilterCollector` collector filters docs using a u64 fast field value and a predicate.
+/// Only the documents for which the predicate returned "true" will be passed on to the next collector.
+///
+/// ```rust
+/// use tantivy::collector::{TopDocs, FilterCollector};
+/// use tantivy::query::QueryParser;
+/// use tantivy::schema::{Schema, TEXT, INDEXED, FAST};
+/// use tantivy::{doc, DocAddress, Index};
+///
+/// let mut schema_builder = Schema::builder();
+/// let title = schema_builder.add_text_field("title", TEXT);
+/// let price = schema_builder.add_u64_field("price", INDEXED | 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).unwrap();
+/// index_writer.add_document(doc!(title => "The Name of the Wind", price => 30_200u64));
+/// index_writer.add_document(doc!(title => "The Diary of Muadib", price => 29_240u64));
+/// index_writer.add_document(doc!(title => "A Dairy Cow", price => 21_240u64));
+/// index_writer.add_document(doc!(title => "The Diary of a Young Girl", price => 20_120u64));
+/// assert!(index_writer.commit().is_ok());
+///
+/// let reader = index.reader().unwrap();
+/// let searcher = reader.searcher();
+///
+/// let query_parser = QueryParser::for_index(&index, vec![title]);
+/// let query = query_parser.parse_query("diary").unwrap();
+/// let no_filter_collector = FilterCollector::new(price, &|value: u64| value > 20_120u64, TopDocs::with_limit(2));
+/// let top_docs = searcher.search(&query, &no_filter_collector).unwrap();
+///
+/// assert_eq!(top_docs.len(), 1);
+/// assert_eq!(top_docs[0].1, DocAddress(0, 1));
+///
+/// let filter_all_collector: FilterCollector<_, _, u64> = FilterCollector::new(price, &|value| value < 5u64, TopDocs::with_limit(2));
+/// let filtered_top_docs = searcher.search(&query, &filter_all_collector).unwrap();
+///
+/// assert_eq!(filtered_top_docs.len(), 0);
+/// ```
+pub struct FilterCollector<TCollector, TPredicate, TPredicateValue: FastValue>
+where
+    TPredicate: 'static,
+{
+    field: Field,
+    collector: TCollector,
+    predicate: &'static TPredicate,
+    t_predicate_value: PhantomData<TPredicateValue>,
+}
+
+impl<TCollector, TPredicate, TPredicateValue: FastValue>
+    FilterCollector<TCollector, TPredicate, TPredicateValue>
+where
+    TCollector: Collector + Send + Sync,
+    TPredicate: Fn(TPredicateValue) -> bool + Send + Sync,
+{
+    /// Create a new FilterCollector.
+    pub fn new(
+        field: Field,
+        predicate: &'static TPredicate,
+        collector: TCollector,
+    ) -> FilterCollector<TCollector, TPredicate, TPredicateValue> {
+        FilterCollector {
+            field,
+            predicate,
+            collector,
+            t_predicate_value: PhantomData,
+        }
+    }
+}
+
+impl<TCollector, TPredicate, TPredicateValue: FastValue> Collector
+    for FilterCollector<TCollector, TPredicate, TPredicateValue>
+where
+    TCollector: Collector + Send + Sync,
+    TPredicate: 'static + Fn(TPredicateValue) -> bool + Send + Sync,
+    TPredicateValue: 'static + FastValue,
+{
+    // That's the type of our result.
+    // Our standard deviation will be a float.
+    type Fruit = TCollector::Fruit;
+
+    type Child = FilterSegmentCollector<TCollector::Child, TPredicate, TPredicateValue>;
+
+    fn for_segment(
+        &self,
+        segment_local_id: u32,
+        segment_reader: &SegmentReader,
+    ) -> crate::Result<FilterSegmentCollector<TCollector::Child, TPredicate, TPredicateValue>> {
+        let schema = segment_reader.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 requested_type = TPredicateValue::to_type();
+        let field_schema_type = field_entry.field_type().value_type();
+        if requested_type != field_schema_type {
+            return Err(TantivyError::SchemaError(format!(
+                "Field {:?} is of type {:?}!={:?}",
+                field_entry.name(),
+                requested_type,
+                field_schema_type
+            )));
+        }
+
+        let fast_field_reader = segment_reader
+            .fast_fields()
+            .typed_fast_field_reader(self.field)
+            .ok_or_else(|| {
+                TantivyError::SchemaError(format!(
+                    "{:?} is not declared as a fast field in the schema.",
+                    self.field
+                ))
+            })?;
+
+        let segment_collector = self
+            .collector
+            .for_segment(segment_local_id, segment_reader)?;
+
+        Ok(FilterSegmentCollector {
+            fast_field_reader,
+            segment_collector,
+            predicate: self.predicate,
+            t_predicate_value: PhantomData,
+        })
+    }
+
+    fn requires_scoring(&self) -> bool {
+        self.collector.requires_scoring()
+    }
+
+    fn merge_fruits(
+        &self,
+        segment_fruits: Vec<<TCollector::Child as SegmentCollector>::Fruit>,
+    ) -> crate::Result<TCollector::Fruit> {
+        self.collector.merge_fruits(segment_fruits)
+    }
+}
+
+pub struct FilterSegmentCollector<TSegmentCollector, TPredicate, TPredicateValue>
+where
+    TPredicate: 'static,
+    TPredicateValue: 'static + FastValue,
+{
+    fast_field_reader: FastFieldReader<TPredicateValue>,
+    segment_collector: TSegmentCollector,
+    predicate: &'static TPredicate,
+    t_predicate_value: PhantomData<TPredicateValue>,
+}
+
+impl<TSegmentCollector, TPredicate, TPredicateValue> SegmentCollector
+    for FilterSegmentCollector<TSegmentCollector, TPredicate, TPredicateValue>
+where
+    TSegmentCollector: SegmentCollector,
+    TPredicate: 'static + Fn(TPredicateValue) -> bool + Send + Sync,
+    TPredicateValue: 'static + FastValue,
+{
+    type Fruit = TSegmentCollector::Fruit;
+
+    fn collect(&mut self, doc: u32, score: Score) {
+        let value = self.fast_field_reader.get(doc);
+        if (self.predicate)(value) {
+            self.segment_collector.collect(doc, score)
+        }
+    }
+
+    fn harvest(self) -> <TSegmentCollector as SegmentCollector>::Fruit {
+        self.segment_collector.harvest()
+    }
+}

src/collector/mod.rs

@@ -114,6 +114,9 @@ use crate::query::Weight;
 mod docset_collector;
 pub use self::docset_collector::DocSetCollector;
 
+mod filter_collector_wrapper;
+pub use self::filter_collector_wrapper::FilterCollector;
+
 /// `Fruit` is the type for the result of our collection.
 /// e.g. `usize` for the `Count` collector.
 pub trait Fruit: Send + downcast_rs::Downcast {}

src/collector/tests.rs

@@ -8,6 +8,13 @@ use crate::DocId;
 use crate::Score;
 use crate::SegmentLocalId;
 
+use crate::collector::{FilterCollector, TopDocs};
+use crate::query::QueryParser;
+use crate::schema::{Schema, FAST, TEXT};
+use crate::DateTime;
+use crate::{doc, Index};
+use std::str::FromStr;
+
 pub const TEST_COLLECTOR_WITH_SCORE: TestCollector = TestCollector {
     compute_score: true,
 };
@@ -16,6 +23,54 @@ pub const TEST_COLLECTOR_WITHOUT_SCORE: TestCollector = TestCollector {
     compute_score: true,
 };
 
+#[test]
+pub fn test_filter_collector() {
+    let mut schema_builder = Schema::builder();
+    let title = schema_builder.add_text_field("title", TEXT);
+    let price = schema_builder.add_u64_field("price", FAST);
+    let date = 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, 10_000_000).unwrap();
+    index_writer.add_document(doc!(title => "The Name of the Wind", price => 30_200u64, date => DateTime::from_str("1898-04-09T00:00:00+00:00").unwrap()));
+    index_writer.add_document(doc!(title => "The Diary of Muadib", price => 29_240u64, date => DateTime::from_str("2020-04-09T00:00:00+00:00").unwrap()));
+    index_writer.add_document(doc!(title => "The Diary of Anne Frank", price => 18_240u64, date => DateTime::from_str("2019-04-20T00:00:00+00:00").unwrap()));
+    index_writer.add_document(doc!(title => "A Dairy Cow", price => 21_240u64, date => DateTime::from_str("2019-04-09T00:00:00+00:00").unwrap()));
+    index_writer.add_document(doc!(title => "The Diary of a Young Girl", price => 20_120u64, date => DateTime::from_str("2018-04-09T00:00:00+00:00").unwrap()));
+    assert!(index_writer.commit().is_ok());
+
+    let reader = index.reader().unwrap();
+    let searcher = reader.searcher();
+
+    let query_parser = QueryParser::for_index(&index, vec![title]);
+    let query = query_parser.parse_query("diary").unwrap();
+    let filter_some_collector = FilterCollector::new(
+        price,
+        &|value: u64| value > 20_120u64,
+        TopDocs::with_limit(2),
+    );
+    let top_docs = searcher.search(&query, &filter_some_collector).unwrap();
+
+    assert_eq!(top_docs.len(), 1);
+    assert_eq!(top_docs[0].1, DocAddress(0, 1));
+
+    let filter_all_collector: FilterCollector<_, _, u64> =
+        FilterCollector::new(price, &|value| value < 5u64, TopDocs::with_limit(2));
+    let filtered_top_docs = searcher.search(&query, &filter_all_collector).unwrap();
+
+    assert_eq!(filtered_top_docs.len(), 0);
+
+    fn date_filter(value: DateTime) -> bool {
+        (value - DateTime::from_str("2019-04-09T00:00:00+00:00").unwrap()).num_weeks() > 0
+    }
+
+    let filter_dates_collector = FilterCollector::new(date, &date_filter, TopDocs::with_limit(5));
+    let filtered_date_docs = searcher.search(&query, &filter_dates_collector).unwrap();
+
+    assert_eq!(filtered_date_docs.len(), 2);
+}
+
 /// Stores all of the doc ids.
 /// This collector is only used for tests.
 /// It is unusable in pr

src/collector/top_score_collector.rs

@@ -728,7 +728,7 @@ mod tests {
     }
 
     #[test]
-    fn test_top_collector_not_at_capacity() {
+    fn test_top_collector_not_at_capacity_without_offset() {
         let index = make_index();
         let field = index.schema().get_field("text").unwrap();
         let query_parser = QueryParser::for_index(&index, vec![field]);

src/common/counting_writer.rs

@@ -20,9 +20,10 @@ impl<W: Write> CountingWriter<W> {
         self.written_bytes
     }
 
-    pub fn finish(mut self) -> io::Result<(W, u64)> {
-        self.flush()?;
-        Ok((self.underlying, self.written_bytes))
+    /// Returns the underlying write object.
+    /// Note that this method does not trigger any flushing.
+    pub fn finish(self) -> W {
+        self.underlying
     }
 }
 
@@ -46,7 +47,6 @@ impl<W: Write> Write for CountingWriter<W> {
 
 impl<W: TerminatingWrite> TerminatingWrite for CountingWriter<W> {
     fn terminate_ref(&mut self, token: AntiCallToken) -> io::Result<()> {
-        self.flush()?;
         self.underlying.terminate_ref(token)
     }
 }
@@ -63,8 +63,9 @@ mod test {
         let mut counting_writer = CountingWriter::wrap(buffer);
         let bytes = (0u8..10u8).collect::<Vec<u8>>();
         counting_writer.write_all(&bytes).unwrap();
-        let (w, len): (Vec<u8>, u64) = counting_writer.finish().unwrap();
+        let len = counting_writer.written_bytes();
+        let buffer_restituted: Vec<u8> = counting_writer.finish();
         assert_eq!(len, 10u64);
-        assert_eq!(w.len(), 10);
+        assert_eq!(buffer_restituted.len(), 10);
     }
 }

src/common/mod.rs

@@ -66,10 +66,6 @@ pub(crate) fn compute_num_bits(n: u64) -> u8 {
     }
 }
 
-pub(crate) fn is_power_of_2(n: usize) -> bool {
-    (n > 0) && (n & (n - 1) == 0)
-}
-
 /// Has length trait
 pub trait HasLen {
     /// Return length
@@ -119,11 +115,16 @@ pub fn u64_to_i64(val: u64) -> i64 {
 /// For simplicity, tantivy internally handles `f64` as `u64`.
 /// The mapping is defined by this function.
 ///
-/// Maps `f64` to `u64` so that lexical order is preserved.
+/// Maps `f64` to `u64` in a monotonic manner, so that bytes lexical order is preserved.
 ///
 /// This is more suited than simply casting (`val as u64`)
 /// which would truncate the result
 ///
+/// # Reference
+///
+/// Daniel Lemire's [blog post](https://lemire.me/blog/2020/12/14/converting-floating-point-numbers-to-integers-while-preserving-order/)
+/// explains the mapping in a clear manner.
+///
 /// # See also
 /// The [reverse mapping is `u64_to_f64`](./fn.u64_to_f64.html).
 #[inline(always)]
@@ -152,6 +153,7 @@ pub(crate) mod test {
     pub use super::minmax;
     pub use super::serialize::test::fixed_size_test;
     use super::{compute_num_bits, f64_to_u64, i64_to_u64, u64_to_f64, u64_to_i64};
+    use proptest::prelude::*;
     use std::f64;
 
     fn test_i64_converter_helper(val: i64) {
@@ -162,6 +164,15 @@ pub(crate) mod test {
         assert_eq!(u64_to_f64(f64_to_u64(val)), val);
     }
 
+    proptest! {
+        #[test]
+        fn test_f64_converter_monotonicity_proptest((left, right) in (proptest::num::f64::NORMAL, proptest::num::f64::NORMAL)) {
+            let left_u64 = f64_to_u64(left);
+            let right_u64 = f64_to_u64(right);
+            assert_eq!(left_u64 < right_u64,  left < right);
+        }
+    }
+
     #[test]
     fn test_i64_converter() {
         assert_eq!(i64_to_u64(i64::min_value()), u64::min_value());

src/core/index.rs

@@ -5,6 +5,7 @@ use crate::core::SegmentId;
 use crate::core::SegmentMeta;
 use crate::core::SegmentMetaInventory;
 use crate::core::META_FILEPATH;
+use crate::directory::error::OpenReadError;
 use crate::directory::ManagedDirectory;
 #[cfg(feature = "mmap")]
 use crate::directory::MmapDirectory;
@@ -34,12 +35,18 @@ fn load_metas(
     inventory: &SegmentMetaInventory,
 ) -> crate::Result<IndexMeta> {
     let meta_data = directory.atomic_read(&META_FILEPATH)?;
-    let meta_string = String::from_utf8_lossy(&meta_data);
+    let meta_string = String::from_utf8(meta_data)
+        .map_err(|utf8_err| {
+            DataCorruption::new(
+                META_FILEPATH.to_path_buf(),
+                format!("Meta file is not valid utf-8. {:?}", utf8_err)
+            )
+        })?;
     IndexMeta::deserialize(&meta_string, &inventory)
         .map_err(|e| {
             DataCorruption::new(
                 META_FILEPATH.to_path_buf(),
-                format!("Meta file cannot be deserialized. {:?}.", e),
+                format!("Meta file cannot be deserialized. {:?}. content = {}", e, meta_string),
             )
         })
         .map_err(From::from)
@@ -59,7 +66,7 @@ impl 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 {
+    pub fn exists<Dir: Directory>(dir: &Dir) -> Result<bool, OpenReadError> {
         dir.exists(&META_FILEPATH)
     }
 
@@ -106,7 +113,7 @@ impl Index {
         schema: Schema,
     ) -> crate::Result<Index> {
         let mmap_directory = MmapDirectory::open(directory_path)?;
-        if Index::exists(&mmap_directory) {
+        if Index::exists(&mmap_directory)? {
             return Err(TantivyError::IndexAlreadyExists);
         }
         Index::create(mmap_directory, schema)
@@ -114,7 +121,7 @@ impl Index {
 
     /// Opens or creates a new index in the provided directory
     pub fn open_or_create<Dir: Directory>(dir: Dir, schema: Schema) -> crate::Result<Index> {
-        if !Index::exists(&dir) {
+        if !Index::exists(&dir)? {
             return Index::create(dir, schema);
         }
         let index = Index::open(dir)?;
@@ -399,7 +406,7 @@ impl fmt::Debug for Index {
 
 #[cfg(test)]
 mod tests {
-    use crate::directory::RAMDirectory;
+    use crate::directory::{RAMDirectory, WatchCallback};
     use crate::schema::Field;
     use crate::schema::{Schema, INDEXED, TEXT};
     use crate::IndexReader;
@@ -423,24 +430,24 @@ mod tests {
     #[test]
     fn test_index_exists() {
         let directory = RAMDirectory::create();
-        assert!(!Index::exists(&directory));
+        assert!(!Index::exists(&directory).unwrap());
         assert!(Index::create(directory.clone(), throw_away_schema()).is_ok());
-        assert!(Index::exists(&directory));
+        assert!(Index::exists(&directory).unwrap());
     }
 
     #[test]
     fn open_or_create_should_create() {
         let directory = RAMDirectory::create();
-        assert!(!Index::exists(&directory));
+        assert!(!Index::exists(&directory).unwrap());
         assert!(Index::open_or_create(directory.clone(), throw_away_schema()).is_ok());
-        assert!(Index::exists(&directory));
+        assert!(Index::exists(&directory).unwrap());
     }
 
     #[test]
     fn open_or_create_should_open() {
         let directory = RAMDirectory::create();
         assert!(Index::create(directory.clone(), throw_away_schema()).is_ok());
-        assert!(Index::exists(&directory));
+        assert!(Index::exists(&directory).unwrap());
         assert!(Index::open_or_create(directory, throw_away_schema()).is_ok());
     }
 
@@ -448,7 +455,7 @@ mod tests {
     fn create_should_wipeoff_existing() {
         let directory = RAMDirectory::create();
         assert!(Index::create(directory.clone(), throw_away_schema()).is_ok());
-        assert!(Index::exists(&directory));
+        assert!(Index::exists(&directory).unwrap());
         assert!(Index::create(directory.clone(), Schema::builder().build()).is_ok());
     }
 
@@ -456,7 +463,7 @@ mod tests {
     fn open_or_create_exists_but_schema_does_not_match() {
         let directory = RAMDirectory::create();
         assert!(Index::create(directory.clone(), throw_away_schema()).is_ok());
-        assert!(Index::exists(&directory));
+        assert!(Index::exists(&directory).unwrap());
         assert!(Index::open_or_create(directory.clone(), throw_away_schema()).is_ok());
         let err = Index::open_or_create(directory, Schema::builder().build());
         assert_eq!(
@@ -510,28 +517,28 @@ mod tests {
         }
 
         #[test]
-        fn test_index_manual_policy_mmap() {
+        fn test_index_manual_policy_mmap() -> crate::Result<()> {
             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_for_tests().unwrap();
-            writer.commit().unwrap();
+            let mut index = Index::create_from_tempdir(schema)?;
+            let mut writer = index.writer_for_tests()?;
+            writer.commit()?;
             let reader = index
                 .reader_builder()
                 .reload_policy(ReloadPolicy::Manual)
-                .try_into()
-                .unwrap();
+                .try_into()?;
             assert_eq!(reader.searcher().num_docs(), 0);
             writer.add_document(doc!(field=>1u64));
             let (sender, receiver) = crossbeam::channel::unbounded();
-            let _handle = index.directory_mut().watch(Box::new(move || {
+            let _handle = index.directory_mut().watch(WatchCallback::new(move || {
                 let _ = sender.send(());
             }));
-            writer.commit().unwrap();
+            writer.commit()?;
             assert!(receiver.recv().is_ok());
             assert_eq!(reader.searcher().num_docs(), 0);
-            reader.reload().unwrap();
+            reader.reload()?;
             assert_eq!(reader.searcher().num_docs(), 1);
+            Ok(())
         }
 
         #[test]
@@ -554,9 +561,11 @@ mod tests {
     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 _watch_handle = reader_index
+            .directory_mut()
+            .watch(WatchCallback::new(move || {
+                let _ = sender.send(());
+            }));
         let mut writer = index.writer_for_tests().unwrap();
         assert_eq!(reader.searcher().num_docs(), 0);
         writer.add_document(doc!(field=>1u64));
@@ -595,7 +604,7 @@ mod tests {
             writer.add_document(doc!(field => i));
         }
         let (sender, receiver) = crossbeam::channel::unbounded();
-        let _handle = directory.watch(Box::new(move || {
+        let _handle = directory.watch(WatchCallback::new(move || {
             let _ = sender.send(());
         }));
         writer.commit().unwrap();

src/core/inverted_index_reader.rs

@@ -66,7 +66,7 @@ impl InvertedIndexReader {
     }
 
     /// Returns the term info associated with the term.
-    pub fn get_term_info(&self, term: &Term) -> Option<TermInfo> {
+    pub fn get_term_info(&self, term: &Term) -> io::Result<Option<TermInfo>> {
         self.termdict.get(term.value_bytes())
     }
 
@@ -90,9 +90,9 @@ impl InvertedIndexReader {
         term_info: &TermInfo,
         block_postings: &mut BlockSegmentPostings,
     ) -> io::Result<()> {
-        let postings_slice = self
-            .postings_file_slice
-            .slice_from(term_info.postings_offset as usize);
+        let start_offset = term_info.postings_start_offset as usize;
+        let stop_offset = term_info.postings_stop_offset as usize;
+        let postings_slice = self.postings_file_slice.slice(start_offset, stop_offset);
         block_postings.reset(term_info.doc_freq, postings_slice.read_bytes()?);
         Ok(())
     }
@@ -106,10 +106,9 @@ impl InvertedIndexReader {
         term: &Term,
         option: IndexRecordOption,
     ) -> io::Result<Option<BlockSegmentPostings>> {
-        Ok(self
-            .get_term_info(term)
+        self.get_term_info(term)?
             .map(move |term_info| self.read_block_postings_from_terminfo(&term_info, option))
-            .transpose()?)
+            .transpose()
     }
 
     /// Returns a block postings given a `term_info`.
@@ -121,8 +120,10 @@ impl InvertedIndexReader {
         term_info: &TermInfo,
         requested_option: IndexRecordOption,
     ) -> io::Result<BlockSegmentPostings> {
-        let offset = term_info.postings_offset as usize;
-        let postings_data = self.postings_file_slice.slice_from(offset);
+        let postings_data = self.postings_file_slice.slice(
+            term_info.postings_start_offset as usize,
+            term_info.postings_stop_offset as usize,
+        );
         BlockSegmentPostings::open(
             term_info.doc_freq,
             postings_data,
@@ -179,7 +180,7 @@ impl InvertedIndexReader {
         term: &Term,
         option: IndexRecordOption,
     ) -> io::Result<Option<SegmentPostings>> {
-        self.get_term_info(term)
+        self.get_term_info(term)?
             .map(move |term_info| self.read_postings_from_terminfo(&term_info, option))
             .transpose()
     }
@@ -189,7 +190,7 @@ impl InvertedIndexReader {
         term: &Term,
         option: IndexRecordOption,
     ) -> io::Result<Option<SegmentPostings>> {
-        self.get_term_info(term)
+        self.get_term_info(term)?
             .map(|term_info| self.read_postings_from_terminfo(&term_info, option))
             .transpose()
     }
@@ -197,7 +198,7 @@ impl InvertedIndexReader {
     /// Returns the number of documents containing the term.
     pub fn doc_freq(&self, term: &Term) -> io::Result<u32> {
         Ok(self
-            .get_term_info(term)
+            .get_term_info(term)?
             .map(|term_info| term_info.doc_freq)
             .unwrap_or(0u32))
     }

src/core/searcher.rs

@@ -1,17 +1,16 @@
 use crate::collector::Collector;
 use crate::core::Executor;
-use crate::core::InvertedIndexReader;
+
 use crate::core::SegmentReader;
 use crate::query::Query;
 use crate::schema::Document;
 use crate::schema::Schema;
-use crate::schema::{Field, Term};
+use crate::schema::Term;
 use crate::space_usage::SearcherSpaceUsage;
 use crate::store::StoreReader;
-use crate::termdict::TermMerger;
 use crate::DocAddress;
 use crate::Index;
-use std::sync::Arc;
+
 use std::{fmt, io};
 
 /// Holds a list of `SegmentReader`s ready for search.
@@ -148,16 +147,6 @@ impl Searcher {
         collector.merge_fruits(fruits)
     }
 
-    /// Return the field searcher associated to a `Field`.
-    pub fn field(&self, field: Field) -> crate::Result<FieldSearcher> {
-        let inv_index_readers: Vec<Arc<InvertedIndexReader>> = self
-            .segment_readers
-            .iter()
-            .map(|segment_reader| segment_reader.inverted_index(field))
-            .collect::<crate::Result<Vec<_>>>()?;
-        Ok(FieldSearcher::new(inv_index_readers))
-    }
-
     /// Summarize total space usage of this searcher.
     pub fn space_usage(&self) -> io::Result<SearcherSpaceUsage> {
         let mut space_usage = SearcherSpaceUsage::new();
@@ -168,27 +157,6 @@ impl Searcher {
     }
 }
 
-pub struct FieldSearcher {
-    inv_index_readers: Vec<Arc<InvertedIndexReader>>,
-}
-
-impl FieldSearcher {
-    fn new(inv_index_readers: Vec<Arc<InvertedIndexReader>>) -> FieldSearcher {
-        FieldSearcher { inv_index_readers }
-    }
-
-    /// Returns a Stream over all of the sorted unique terms of
-    /// for the given field.
-    pub fn terms(&self) -> TermMerger<'_> {
-        let term_streamers: Vec<_> = self
-            .inv_index_readers
-            .iter()
-            .map(|inverted_index| inverted_index.terms().stream())
-            .collect();
-        TermMerger::new(term_streamers)
-    }
-}
-
 impl fmt::Debug for Searcher {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         let segment_ids = self

src/directory/directory.rs

@@ -1,8 +1,8 @@
 use crate::directory::directory_lock::Lock;
 use crate::directory::error::LockError;
 use crate::directory::error::{DeleteError, OpenReadError, OpenWriteError};
-use crate::directory::WatchCallback;
 use crate::directory::WatchHandle;
+use crate::directory::{FileHandle, WatchCallback};
 use crate::directory::{FileSlice, WritePtr};
 use std::fmt;
 use std::io;
@@ -108,10 +108,13 @@ fn retry_policy(is_blocking: bool) -> RetryPolicy {
 /// should be your default choice.
 /// - The [`RAMDirectory`](struct.RAMDirectory.html), which
 /// should be used mostly for tests.
-///
 pub trait Directory: DirectoryClone + fmt::Debug + Send + Sync + 'static {
-    /// Opens a virtual file for read.
+    /// Opens a file and returns a boxed `FileHandle`.
     ///
+    /// Users of `Directory` should typically call `Directory::open_read(...)`,
+    /// while `Directory` implementor should implement `get_file_handle()`.
+    fn get_file_handle(&self, path: &Path) -> Result<Box<dyn FileHandle>, OpenReadError>;
+
     /// Once a virtual file is open, its data may not
     /// change.
     ///
@@ -119,7 +122,10 @@ pub trait Directory: DirectoryClone + fmt::Debug + Send + Sync + 'static {
     /// 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<FileSlice, OpenReadError>;
+    fn open_read(&self, path: &Path) -> Result<FileSlice, OpenReadError> {
+        let file_handle = self.get_file_handle(path)?;
+        Ok(FileSlice::new(file_handle))
+    }
 
     /// Removes a file
     ///
@@ -131,7 +137,7 @@ pub trait Directory: DirectoryClone + fmt::Debug + Send + Sync + 'static {
     fn delete(&self, path: &Path) -> Result<(), DeleteError>;
 
     /// Returns true iff the file exists
-    fn exists(&self, path: &Path) -> bool;
+    fn exists(&self, path: &Path) -> Result<bool, OpenReadError>;
 
     /// Opens a writer for the *virtual file* associated with
     /// a Path.

src/directory/error.rs

@@ -58,7 +58,8 @@ pub enum OpenWriteError {
 }
 
 impl OpenWriteError {
-    pub(crate) fn wrap_io_error(io_error: io::Error, filepath: PathBuf) -> Self {
+    /// Wraps an io error.
+    pub fn wrap_io_error(io_error: io::Error, filepath: PathBuf) -> Self {
         Self::IOError { io_error, filepath }
     }
 }
@@ -143,7 +144,8 @@ pub enum OpenReadError {
 }
 
 impl OpenReadError {
-    pub(crate) fn wrap_io_error(io_error: io::Error, filepath: PathBuf) -> Self {
+    /// Wraps an io error.
+    pub fn wrap_io_error(io_error: io::Error, filepath: PathBuf) -> Self {
         Self::IOError { io_error, filepath }
     }
 }

src/directory/file_slice.rs

@@ -2,10 +2,11 @@ use stable_deref_trait::StableDeref;
 
 use crate::common::HasLen;
 use crate::directory::OwnedBytes;
-use std::sync::Arc;
+use std::sync::{Arc, Weak};
 use std::{io, ops::Deref};
 
-pub type BoxedData = Box<dyn Deref<Target = [u8]> + Send + Sync + 'static>;
+pub type ArcBytes = Arc<dyn Deref<Target = [u8]> + Send + Sync + 'static>;
+pub type WeakArcBytes = Weak<dyn Deref<Target = [u8]> + Send + Sync + 'static>;
 
 /// Objects that represents files sections in tantivy.
 ///
@@ -40,7 +41,7 @@ where
     B: StableDeref + Deref<Target = [u8]> + 'static + Send + Sync,
 {
     fn from(bytes: B) -> FileSlice {
-        FileSlice::new(OwnedBytes::new(bytes))
+        FileSlice::new(Box::new(OwnedBytes::new(bytes)))
     }
 }
 
@@ -50,22 +51,25 @@ where
 ///
 #[derive(Clone)]
 pub struct FileSlice {
-    data: Arc<Box<dyn FileHandle>>,
+    data: Arc<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();
+    pub fn new(file_handle: Box<dyn FileHandle>) -> Self {
+        let num_bytes = file_handle.len();
+        FileSlice::new_with_num_bytes(file_handle, num_bytes)
+    }
+
+    /// Wraps a FileHandle.
+    #[doc(hidden)]
+    pub fn new_with_num_bytes(file_handle: Box<dyn FileHandle>, num_bytes: usize) -> Self {
         FileSlice {
-            data: Arc::new(Box::new(data)),
+            data: Arc::from(file_handle),
             start: 0,
-            stop: len,
+            stop: num_bytes,
         }
     }
 
@@ -146,6 +150,12 @@ impl FileSlice {
     }
 }
 
+impl FileHandle for FileSlice {
+    fn read_bytes(&self, from: usize, to: usize) -> io::Result<OwnedBytes> {
+        self.read_bytes_slice(from, to)
+    }
+}
+
 impl HasLen for FileSlice {
     fn len(&self) -> usize {
         self.stop - self.start
@@ -160,7 +170,7 @@ mod tests {
 
     #[test]
     fn test_file_slice() -> io::Result<()> {
-        let file_slice = FileSlice::new(b"abcdef".as_ref());
+        let file_slice = FileSlice::new(Box::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");
@@ -204,7 +214,7 @@ mod tests {
 
     #[test]
     fn test_slice_simple_read() -> io::Result<()> {
-        let slice = FileSlice::new(&b"abcdef"[..]);
+        let slice = FileSlice::new(Box::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");
@@ -213,7 +223,7 @@ mod tests {
 
     #[test]
     fn test_slice_read_slice() -> io::Result<()> {
-        let slice_deref = FileSlice::new(&b"abcdef"[..]);
+        let slice_deref = FileSlice::new(Box::new(&b"abcdef"[..]));
         assert_eq!(slice_deref.read_bytes_slice(1, 4)?.as_ref(), b"bcd");
         Ok(())
     }
@@ -221,14 +231,14 @@ mod tests {
     #[test]
     #[should_panic(expected = "assertion failed: from <= to")]
     fn test_slice_read_slice_invalid_range() {
-        let slice_deref = FileSlice::new(&b"abcdef"[..]);
+        let slice_deref = FileSlice::new(Box::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"[..]);
+        let slice_deref = FileSlice::new(Box::new(&b"abcdef"[..]));
         assert_eq!(
             slice_deref.read_bytes_slice(0, 10).unwrap().as_ref(),
             b"bcd"

src/directory/file_watcher.rs

@@ -0,0 +1,178 @@
+use crate::directory::{WatchCallback, WatchCallbackList, WatchHandle};
+use crc32fast::Hasher;
+use std::fs;
+use std::io;
+use std::io::BufRead;
+use std::path::Path;
+use std::sync::atomic::{AtomicUsize, Ordering};
+use std::sync::Arc;
+use std::thread;
+use std::time::Duration;
+
+pub const POLLING_INTERVAL: Duration = Duration::from_millis(if cfg!(test) { 1 } else { 500 });
+
+// Watches a file and executes registered callbacks when the file is modified.
+pub struct FileWatcher {
+    path: Arc<Path>,
+    callbacks: Arc<WatchCallbackList>,
+    state: Arc<AtomicUsize>, // 0: new, 1: runnable, 2: terminated
+}
+
+impl FileWatcher {
+    pub fn new(path: &Path) -> FileWatcher {
+        FileWatcher {
+            path: Arc::from(path),
+            callbacks: Default::default(),
+            state: Default::default(),
+        }
+    }
+
+    pub fn spawn(&self) {
+        if self.state.compare_and_swap(0, 1, Ordering::SeqCst) > 0 {
+            return;
+        }
+
+        let path = self.path.clone();
+        let callbacks = self.callbacks.clone();
+        let state = self.state.clone();
+
+        thread::Builder::new()
+            .name("thread-tantivy-meta-file-watcher".to_string())
+            .spawn(move || {
+                let mut current_checksum = None;
+
+                while state.load(Ordering::SeqCst) == 1 {
+                    if let Ok(checksum) = FileWatcher::compute_checksum(&path) {
+                        // `None.unwrap_or_else(|| !checksum) != checksum` evaluates to `true`
+                        if current_checksum.unwrap_or_else(|| !checksum) != checksum {
+                            info!("Meta file {:?} was modified", path);
+                            current_checksum = Some(checksum);
+                            futures::executor::block_on(callbacks.broadcast());
+                        }
+                    }
+
+                    thread::sleep(POLLING_INTERVAL);
+                }
+            })
+            .expect("Failed to spawn meta file watcher thread");
+    }
+
+    pub fn watch(&self, callback: WatchCallback) -> WatchHandle {
+        let handle = self.callbacks.subscribe(callback);
+        self.spawn();
+        handle
+    }
+
+    fn compute_checksum(path: &Path) -> Result<u32, io::Error> {
+        let reader = match fs::File::open(path) {
+            Ok(f) => io::BufReader::new(f),
+            Err(e) => {
+                warn!("Failed to open meta file {:?}: {:?}", path, e);
+                return Err(e);
+            }
+        };
+
+        let mut hasher = Hasher::new();
+
+        for line in reader.lines() {
+            hasher.update(line?.as_bytes())
+        }
+
+        Ok(hasher.finalize())
+    }
+}
+
+impl Drop for FileWatcher {
+    fn drop(&mut self) {
+        self.state.store(2, Ordering::SeqCst);
+    }
+}
+
+#[cfg(test)]
+mod tests {
+
+    use std::mem;
+
+    use crate::directory::mmap_directory::atomic_write;
+
+    use super::*;
+
+    #[test]
+    fn test_file_watcher_drop_watcher() -> crate::Result<()> {
+        let tmp_dir = tempfile::TempDir::new()?;
+        let tmp_file = tmp_dir.path().join("watched.txt");
+
+        let counter: Arc<AtomicUsize> = Default::default();
+        let (tx, rx) = crossbeam::channel::unbounded();
+        let timeout = Duration::from_millis(100);
+
+        let watcher = FileWatcher::new(&tmp_file);
+
+        let state = watcher.state.clone();
+        assert_eq!(state.load(Ordering::SeqCst), 0);
+
+        let counter_clone = counter.clone();
+
+        let _handle = watcher.watch(WatchCallback::new(move || {
+            let val = counter_clone.fetch_add(1, Ordering::SeqCst);
+            tx.send(val + 1).unwrap();
+        }));
+
+        assert_eq!(counter.load(Ordering::SeqCst), 0);
+        assert_eq!(state.load(Ordering::SeqCst), 1);
+
+        atomic_write(&tmp_file, b"foo")?;
+        assert_eq!(rx.recv_timeout(timeout), Ok(1));
+
+        atomic_write(&tmp_file, b"foo")?;
+        assert!(rx.recv_timeout(timeout).is_err());
+
+        atomic_write(&tmp_file, b"bar")?;
+        assert_eq!(rx.recv_timeout(timeout), Ok(2));
+
+        mem::drop(watcher);
+
+        atomic_write(&tmp_file, b"qux")?;
+        thread::sleep(Duration::from_millis(10));
+        assert_eq!(counter.load(Ordering::SeqCst), 2);
+        assert_eq!(state.load(Ordering::SeqCst), 2);
+
+        Ok(())
+    }
+
+    #[test]
+    fn test_file_watcher_drop_handle() -> crate::Result<()> {
+        let tmp_dir = tempfile::TempDir::new()?;
+        let tmp_file = tmp_dir.path().join("watched.txt");
+
+        let counter: Arc<AtomicUsize> = Default::default();
+        let (tx, rx) = crossbeam::channel::unbounded();
+        let timeout = Duration::from_millis(100);
+
+        let watcher = FileWatcher::new(&tmp_file);
+
+        let state = watcher.state.clone();
+        assert_eq!(state.load(Ordering::SeqCst), 0);
+
+        let counter_clone = counter.clone();
+
+        let handle = watcher.watch(WatchCallback::new(move || {
+            let val = counter_clone.fetch_add(1, Ordering::SeqCst);
+            tx.send(val + 1).unwrap();
+        }));
+
+        assert_eq!(counter.load(Ordering::SeqCst), 0);
+        assert_eq!(state.load(Ordering::SeqCst), 1);
+
+        atomic_write(&tmp_file, b"foo")?;
+        assert_eq!(rx.recv_timeout(timeout), Ok(1));
+
+        mem::drop(handle);
+
+        atomic_write(&tmp_file, b"qux")?;
+        assert_eq!(counter.load(Ordering::SeqCst), 1);
+        assert_eq!(state.load(Ordering::SeqCst), 1);
+
+        Ok(())
+    }
+}

src/directory/footer.rs

@@ -115,6 +115,18 @@ impl Footer {
                 }
                 Ok(())
             }
+            VersionedFooter::V3 {
+                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(())
+            }
             VersionedFooter::UnknownVersion => Err(Incompatibility::IndexMismatch {
                 library_version: library_version.clone(),
                 index_version: self.version.clone(),
@@ -136,24 +148,31 @@ pub enum VersionedFooter {
         crc32: CrcHashU32,
         store_compression: String,
     },
+    // Block wand max termfred on 1 byte
+    V3 {
+        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::V2 {
+            VersionedFooter::V3 {
                 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(&2u32, &mut buf)?;
+                BinarySerializable::serialize(&3u32, &mut buf)?;
                 BinarySerializable::serialize(crc32, &mut buf)?;
                 BinarySerializable::serialize(compression, &mut buf)?;
             }
-            VersionedFooter::V1 { .. } | VersionedFooter::UnknownVersion => {
+            VersionedFooter::V2 { .. }
+            | VersionedFooter::V1 { .. }
+            | VersionedFooter::UnknownVersion => {
                 return Err(io::Error::new(
                     io::ErrorKind::InvalidInput,
                     "Cannot serialize an unknown versioned footer ",
@@ -182,7 +201,7 @@ impl BinarySerializable for VersionedFooter {
         reader.read_exact(&mut buf[..])?;
         let mut cursor = &buf[..];
         let version = u32::deserialize(&mut cursor)?;
-        if version != 1 && version != 2 {
+        if version > 3 {
             return Ok(VersionedFooter::UnknownVersion);
         }
         let crc32 = u32::deserialize(&mut cursor)?;
@@ -192,12 +211,17 @@ impl BinarySerializable for VersionedFooter {
                 crc32,
                 store_compression,
             }
-        } else {
-            assert_eq!(version, 2);
+        } else if version == 2 {
             VersionedFooter::V2 {
                 crc32,
                 store_compression,
             }
+        } else {
+            assert_eq!(version, 3);
+            VersionedFooter::V3 {
+                crc32,
+                store_compression,
+            }
         })
     }
 }
@@ -205,6 +229,7 @@ impl BinarySerializable for VersionedFooter {
 impl VersionedFooter {
     pub fn crc(&self) -> Option<CrcHashU32> {
         match self {
+            VersionedFooter::V3 { crc32, .. } => Some(*crc32),
             VersionedFooter::V2 { crc32, .. } => Some(*crc32),
             VersionedFooter::V1 { crc32, .. } => Some(*crc32),
             VersionedFooter::UnknownVersion { .. } => None,
@@ -243,7 +268,7 @@ 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::V2 {
+        let footer = Footer::new(VersionedFooter::V3 {
             crc32,
             store_compression: crate::store::COMPRESSION.to_string(),
         });
@@ -278,7 +303,7 @@ mod tests {
         let footer = Footer::deserialize(&mut &vec[..]).unwrap();
         assert!(matches!(
            footer.versioned_footer,
-           VersionedFooter::V2 { store_compression, .. }
+           VersionedFooter::V3 { store_compression, .. }
            if store_compression == crate::store::COMPRESSION
         ));
         assert_eq!(&footer.version, crate::version());
@@ -288,7 +313,7 @@ mod tests {
     fn test_serialize_deserialize_footer() {
         let mut buffer = Vec::new();
         let crc32 = 123456u32;
-        let footer: Footer = Footer::new(VersionedFooter::V2 {
+        let footer: Footer = Footer::new(VersionedFooter::V3 {
             crc32,
             store_compression: "lz4".to_string(),
         });
@@ -300,7 +325,7 @@ mod tests {
     #[test]
     fn footer_length() {
         let crc32 = 1111111u32;
-        let versioned_footer = VersionedFooter::V2 {
+        let versioned_footer = VersionedFooter::V3 {
             crc32,
             store_compression: "lz4".to_string(),
         };
@@ -321,7 +346,7 @@ mod tests {
             // versionned footer length
             12 | 128,
             // index format version
-            2,
+            3,
             0,
             0,
             0,
@@ -340,7 +365,7 @@ 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::V2 {
+        let expected_versioned_footer: VersionedFooter = VersionedFooter::V3 {
             crc32: expected_crc,
             store_compression: "lz4".to_string(),
         };

src/directory/managed_directory.rs

@@ -1,10 +1,10 @@
 use crate::core::{MANAGED_FILEPATH, META_FILEPATH};
 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::{DirectoryLock, FileHandle};
 use crate::directory::{FileSlice, WritePtr};
 use crate::directory::{WatchCallback, WatchHandle};
 use crate::error::DataCorruption;
@@ -274,6 +274,11 @@ impl ManagedDirectory {
 }
 
 impl Directory for ManagedDirectory {
+    fn get_file_handle(&self, path: &Path) -> Result<Box<dyn FileHandle>, OpenReadError> {
+        let file_slice = self.open_read(path)?;
+        Ok(Box::new(file_slice))
+    }
+
     fn open_read(&self, path: &Path) -> result::Result<FileSlice, OpenReadError> {
         let file_slice = self.directory.open_read(path)?;
         let (footer, reader) = Footer::extract_footer(file_slice)
@@ -307,7 +312,7 @@ impl Directory for ManagedDirectory {
         self.directory.delete(path)
     }
 
-    fn exists(&self, path: &Path) -> bool {
+    fn exists(&self, path: &Path) -> Result<bool, OpenReadError> {
         self.directory.exists(path)
     }
 
@@ -355,22 +360,22 @@ mod tests_mmap_specific {
             managed_directory
                 .atomic_write(test_path2, &[0u8, 1u8])
                 .unwrap();
-            assert!(managed_directory.exists(test_path1));
-            assert!(managed_directory.exists(test_path2));
+            assert!(managed_directory.exists(test_path1).unwrap());
+            assert!(managed_directory.exists(test_path2).unwrap());
             let living_files: HashSet<PathBuf> = [test_path1.to_owned()].iter().cloned().collect();
             assert!(managed_directory.garbage_collect(|| living_files).is_ok());
-            assert!(managed_directory.exists(test_path1));
-            assert!(!managed_directory.exists(test_path2));
+            assert!(managed_directory.exists(test_path1).unwrap());
+            assert!(!managed_directory.exists(test_path2).unwrap());
         }
         {
             let mmap_directory = MmapDirectory::open(&tempdir_path).unwrap();
             let mut managed_directory = ManagedDirectory::wrap(mmap_directory).unwrap();
-            assert!(managed_directory.exists(test_path1));
-            assert!(!managed_directory.exists(test_path2));
+            assert!(managed_directory.exists(test_path1).unwrap());
+            assert!(!managed_directory.exists(test_path2).unwrap());
             let living_files: HashSet<PathBuf> = HashSet::new();
             assert!(managed_directory.garbage_collect(|| living_files).is_ok());
-            assert!(!managed_directory.exists(test_path1));
-            assert!(!managed_directory.exists(test_path2));
+            assert!(!managed_directory.exists(test_path1).unwrap());
+            assert!(!managed_directory.exists(test_path2).unwrap());
         }
     }
 
@@ -387,7 +392,7 @@ mod tests_mmap_specific {
         let mut write = managed_directory.open_write(test_path1).unwrap();
         write.write_all(&[0u8, 1u8]).unwrap();
         write.terminate().unwrap();
-        assert!(managed_directory.exists(test_path1));
+        assert!(managed_directory.exists(test_path1).unwrap());
 
         let _mmap_read = managed_directory.open_read(test_path1).unwrap();
         assert!(managed_directory
@@ -395,15 +400,15 @@ mod tests_mmap_specific {
             .is_ok());
         if cfg!(target_os = "windows") {
             // On Windows, gc should try and fail the file as it is mmapped.
-            assert!(managed_directory.exists(test_path1));
+            assert!(managed_directory.exists(test_path1).unwrap());
             // unmap should happen here.
             drop(_mmap_read);
             // The file should still be in the list of managed file and
             // eventually be deleted once mmap is released.
             assert!(managed_directory.garbage_collect(|| living_files).is_ok());
-            assert!(!managed_directory.exists(test_path1));
+            assert!(!managed_directory.exists(test_path1).unwrap());
         } else {
-            assert!(!managed_directory.exists(test_path1));
+            assert!(!managed_directory.exists(test_path1).unwrap());
         }
     }
 

src/directory/mmap_directory.rs

@@ -1,21 +1,17 @@
 use crate::core::META_FILEPATH;
 use crate::directory::error::LockError;
 use crate::directory::error::{DeleteError, OpenDirectoryError, OpenReadError, OpenWriteError};
-use crate::directory::AntiCallToken;
-use crate::directory::BoxedData;
+use crate::directory::file_watcher::FileWatcher;
 use crate::directory::Directory;
 use crate::directory::DirectoryLock;
-use crate::directory::FileSlice;
 use crate::directory::Lock;
 use crate::directory::WatchCallback;
-use crate::directory::WatchCallbackList;
 use crate::directory::WatchHandle;
+use crate::directory::{AntiCallToken, FileHandle, OwnedBytes};
+use crate::directory::{ArcBytes, WeakArcBytes};
 use crate::directory::{TerminatingWrite, WritePtr};
 use fs2::FileExt;
 use memmap::Mmap;
-use notify::RawEvent;
-use notify::RecursiveMode;
-use notify::Watcher;
 use serde::{Deserialize, Serialize};
 use stable_deref_trait::StableDeref;
 use std::convert::From;
@@ -26,12 +22,8 @@ use std::io::{self, Seek, SeekFrom};
 use std::io::{BufWriter, Read, Write};
 use std::path::{Path, PathBuf};
 use std::result;
-use std::sync::mpsc::{channel, Receiver, Sender};
 use std::sync::Arc;
-use std::sync::Mutex;
 use std::sync::RwLock;
-use std::sync::Weak;
-use std::thread;
 use std::{collections::HashMap, ops::Deref};
 use tempfile::TempDir;
 
@@ -84,7 +76,7 @@ pub struct CacheInfo {
 
 struct MmapCache {
     counters: CacheCounters,
-    cache: HashMap<PathBuf, Weak<BoxedData>>,
+    cache: HashMap<PathBuf, WeakArcBytes>,
 }
 
 impl Default for MmapCache {
@@ -118,7 +110,7 @@ impl MmapCache {
     }
 
     // Returns None if the file exists but as a len of 0 (and hence is not mmappable).
-    fn get_mmap(&mut self, full_path: &Path) -> Result<Option<Arc<BoxedData>>, OpenReadError> {
+    fn get_mmap(&mut self, full_path: &Path) -> Result<Option<ArcBytes>, OpenReadError> {
         if let Some(mmap_weak) = self.cache.get(full_path) {
             if let Some(mmap_arc) = mmap_weak.upgrade() {
                 self.counters.hit += 1;
@@ -129,7 +121,7 @@ impl MmapCache {
         self.counters.miss += 1;
         let mmap_opt = open_mmap(full_path)?;
         Ok(mmap_opt.map(|mmap| {
-            let mmap_arc: Arc<BoxedData> = Arc::new(Box::new(mmap));
+            let mmap_arc: ArcBytes = Arc::new(mmap);
             let mmap_weak = Arc::downgrade(&mmap_arc);
             self.cache.insert(full_path.to_owned(), mmap_weak);
             mmap_arc
@@ -137,67 +129,6 @@ impl MmapCache {
     }
 }
 
-struct WatcherWrapper {
-    _watcher: Mutex<notify::RecommendedWatcher>,
-    watcher_router: Arc<WatchCallbackList>,
-}
-
-impl WatcherWrapper {
-    pub fn new(path: &Path) -> Result<Self, OpenDirectoryError> {
-        let (tx, watcher_recv): (Sender<RawEvent>, Receiver<RawEvent>) = channel();
-        // We need to initialize the
-        let watcher = notify::raw_watcher(tx)
-            .and_then(|mut watcher| {
-                watcher.watch(path, RecursiveMode::Recursive)?;
-                Ok(watcher)
-            })
-            .map_err(|err| match err {
-                notify::Error::PathNotFound => OpenDirectoryError::DoesNotExist(path.to_owned()),
-                _ => {
-                    panic!("Unknown error while starting watching directory {:?}", path);
-                }
-            })?;
-        let watcher_router: Arc<WatchCallbackList> = Default::default();
-        let watcher_router_clone = watcher_router.clone();
-        thread::Builder::new()
-            .name("meta-file-watch-thread".to_string())
-            .spawn(move || {
-                loop {
-                    match watcher_recv.recv().map(|evt| evt.path) {
-                        Ok(Some(changed_path)) => {
-                            // ... Actually subject to false positive.
-                            // We might want to be more accurate than this at one point.
-                            if let Some(filename) = changed_path.file_name() {
-                                if filename == *META_FILEPATH {
-                                    let _ = watcher_router_clone.broadcast();
-                                }
-                            }
-                        }
-                        Ok(None) => {
-                            // not an event we are interested in.
-                        }
-                        Err(_e) => {
-                            // the watch send channel was dropped
-                            break;
-                        }
-                    }
-                }
-            })
-            .map_err(|io_error| OpenDirectoryError::IoError {
-                io_error,
-                directory_path: path.to_path_buf(),
-            })?;
-        Ok(WatcherWrapper {
-            _watcher: Mutex::new(watcher),
-            watcher_router,
-        })
-    }
-
-    pub fn watch(&mut self, watch_callback: WatchCallback) -> WatchHandle {
-        self.watcher_router.subscribe(watch_callback)
-    }
-}
-
 /// Directory storing data in files, read via mmap.
 ///
 /// The Mmap object are cached to limit the
@@ -219,40 +150,21 @@ struct MmapDirectoryInner {
     root_path: PathBuf,
     mmap_cache: RwLock<MmapCache>,
     _temp_directory: Option<TempDir>,
-    watcher: RwLock<Option<WatcherWrapper>>,
+    watcher: FileWatcher,
 }
 
 impl MmapDirectoryInner {
     fn new(root_path: PathBuf, temp_directory: Option<TempDir>) -> MmapDirectoryInner {
         MmapDirectoryInner {
-            root_path,
             mmap_cache: Default::default(),
             _temp_directory: temp_directory,
-            watcher: RwLock::new(None),
+            watcher: FileWatcher::new(&root_path.join(*META_FILEPATH)),
+            root_path,
         }
     }
 
-    fn watch(&self, watch_callback: WatchCallback) -> crate::Result<WatchHandle> {
-        // a lot of juggling here, to ensure we don't do anything that panics
-        // while the rwlock is held. That way we ensure that the rwlock cannot
-        // be poisoned.
-        //
-        // The downside is that we might create a watch wrapper that is not useful.
-        let need_initialization = self.watcher.read().unwrap().is_none();
-        if need_initialization {
-            let watch_wrapper = WatcherWrapper::new(&self.root_path)?;
-            let mut watch_wlock = self.watcher.write().unwrap();
-            // the watcher could have been initialized when we released the lock, and
-            // we do not want to lose the watched files that were set.
-            if watch_wlock.is_none() {
-                *watch_wlock = Some(watch_wrapper);
-            }
-        }
-        if let Some(watch_wrapper) = self.watcher.write().unwrap().as_mut() {
-            Ok(watch_wrapper.watch(watch_callback))
-        } else {
-            unreachable!("At this point, watch wrapper is supposed to be initialized");
-        }
+    fn watch(&self, callback: WatchCallback) -> crate::Result<WatchHandle> {
+        Ok(self.watcher.watch(callback))
     }
 }
 
@@ -402,7 +314,7 @@ impl TerminatingWrite for SafeFileWriter {
 }
 
 #[derive(Clone)]
-struct MmapArc(Arc<Box<dyn Deref<Target = [u8]> + Send + Sync>>);
+struct MmapArc(Arc<dyn Deref<Target = [u8]> + Send + Sync>);
 
 impl Deref for MmapArc {
     type Target = [u8];
@@ -413,8 +325,26 @@ impl Deref for MmapArc {
 }
 unsafe impl StableDeref for MmapArc {}
 
+/// Writes a file in an atomic manner.
+pub(crate) fn atomic_write(path: &Path, content: &[u8]) -> io::Result<()> {
+    // We create the temporary file in the same directory as the target file.
+    // Indeed the canonical temp directory and the target file might sit in different
+    // filesystem, in which case the atomic write may actually not work.
+    let parent_path = path.parent().ok_or_else(|| {
+        io::Error::new(
+            io::ErrorKind::InvalidInput,
+            "Path {:?} does not have parent directory.",
+        )
+    })?;
+    let mut tempfile = tempfile::Builder::new().tempfile_in(&parent_path)?;
+    tempfile.write_all(content)?;
+    tempfile.flush()?;
+    tempfile.into_temp_path().persist(path)?;
+    Ok(())
+}
+
 impl Directory for MmapDirectory {
-    fn open_read(&self, path: &Path) -> result::Result<FileSlice, OpenReadError> {
+    fn get_file_handle(&self, path: &Path) -> result::Result<Box<dyn FileHandle>, OpenReadError> {
         debug!("Open Read {:?}", path);
         let full_path = self.resolve_path(path);
 
@@ -427,11 +357,16 @@ impl Directory for MmapDirectory {
             let io_err = make_io_err(msg);
             OpenReadError::wrap_io_error(io_err, path.to_path_buf())
         })?;
-        if let Some(mmap_arc) = mmap_cache.get_mmap(&full_path)? {
-            Ok(FileSlice::from(MmapArc(mmap_arc)))
-        } else {
-            Ok(FileSlice::empty())
-        }
+
+        let owned_bytes = mmap_cache
+            .get_mmap(&full_path)?
+            .map(|mmap_arc| {
+                let mmap_arc_obj = MmapArc(mmap_arc);
+                OwnedBytes::new(mmap_arc_obj)
+            })
+            .unwrap_or_else(OwnedBytes::empty);
+
+        Ok(Box::new(owned_bytes))
     }
 
     /// Any entry associated to the path in the mmap will be
@@ -456,9 +391,9 @@ impl Directory for MmapDirectory {
         }
     }
 
-    fn exists(&self, path: &Path) -> bool {
+    fn exists(&self, path: &Path) -> Result<bool, OpenReadError> {
         let full_path = self.resolve_path(path);
-        full_path.exists()
+        Ok(full_path.exists())
     }
 
     fn open_write(&self, path: &Path) -> Result<WritePtr, OpenWriteError> {
@@ -513,12 +448,9 @@ impl Directory for MmapDirectory {
 
     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);
-        tempfile.into_temp_path().persist(full_path)?;
-        Ok(())
+        atomic_write(&full_path, content)?;
+        self.sync_directory()
     }
 
     fn acquire_lock(&self, lock: &Lock) -> Result<DirectoryLock, LockError> {
@@ -557,8 +489,6 @@ mod tests {
     use crate::Index;
     use crate::ReloadPolicy;
     use crate::{common::HasLen, indexer::LogMergePolicy};
-    use std::fs;
-    use std::sync::atomic::{AtomicUsize, Ordering};
 
     #[test]
     fn test_open_non_existent_path() {
@@ -647,27 +577,6 @@ mod tests {
         assert_eq!(mmap_directory.get_cache_info().mmapped.len(), 0);
     }
 
-    #[test]
-    fn test_watch_wrapper() {
-        let counter: Arc<AtomicUsize> = Default::default();
-        let counter_clone = counter.clone();
-        let tmp_dir = tempfile::TempDir::new().unwrap();
-        let tmp_dirpath = tmp_dir.path().to_owned();
-        let mut watch_wrapper = WatcherWrapper::new(&tmp_dirpath).unwrap();
-        let tmp_file = tmp_dirpath.join(*META_FILEPATH);
-        let _handle = watch_wrapper.watch(Box::new(move || {
-            counter_clone.fetch_add(1, Ordering::SeqCst);
-        }));
-        let (sender, receiver) = crossbeam::channel::unbounded();
-        let _handle2 = watch_wrapper.watch(Box::new(move || {
-            let _ = sender.send(());
-        }));
-        assert_eq!(counter.load(Ordering::SeqCst), 0);
-        fs::write(&tmp_file, b"whateverwilldo").unwrap();
-        assert!(receiver.recv().is_ok());
-        assert!(counter.load(Ordering::SeqCst) >= 1);
-    }
-
     #[test]
     fn test_mmap_released() {
         let mmap_directory = MmapDirectory::create_from_tempdir().unwrap();

src/directory/mod.rs

@@ -10,6 +10,7 @@ mod mmap_directory;
 mod directory;
 mod directory_lock;
 mod file_slice;
+mod file_watcher;
 mod footer;
 mod managed_directory;
 mod owned_bytes;
@@ -22,7 +23,7 @@ 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(crate) use self::file_slice::{ArcBytes, WeakArcBytes};
 pub use self::file_slice::{FileHandle, FileSlice};
 pub use self::owned_bytes::OwnedBytes;
 pub use self::ram_directory::RAMDirectory;

src/directory/owned_bytes.rs

@@ -1,5 +1,6 @@
 use crate::directory::FileHandle;
 use stable_deref_trait::StableDeref;
+use std::convert::TryInto;
 use std::mem;
 use std::ops::Deref;
 use std::sync::Arc;
@@ -95,6 +96,24 @@ impl OwnedBytes {
     pub fn advance(&mut self, advance_len: usize) {
         self.data = &self.data[advance_len..]
     }
+
+    /// Reads an `u8` from the `OwnedBytes` and advance by one byte.
+    pub fn read_u8(&mut self) -> u8 {
+        assert!(!self.is_empty());
+
+        let byte = self.as_slice()[0];
+        self.advance(1);
+        byte
+    }
+
+    /// Reads an `u64` encoded as little-endian from the `OwnedBytes` and advance by 8 bytes.
+    pub fn read_u64(&mut self) -> u64 {
+        assert!(self.len() > 7);
+
+        let octlet: [u8; 8] = self.as_slice()[..8].try_into().unwrap();
+        self.advance(8);
+        u64::from_le_bytes(octlet)
+    }
 }
 
 impl fmt::Debug for OwnedBytes {
@@ -230,6 +249,22 @@ mod tests {
         Ok(())
     }
 
+    #[test]
+    fn test_owned_bytes_read_u8() -> io::Result<()> {
+        let mut bytes = OwnedBytes::new(b"\xFF".as_ref());
+        assert_eq!(bytes.read_u8(), 255);
+        assert_eq!(bytes.len(), 0);
+        Ok(())
+    }
+
+    #[test]
+    fn test_owned_bytes_read_u64() -> io::Result<()> {
+        let mut bytes = OwnedBytes::new(b"\0\xFF\xFF\xFF\xFF\xFF\xFF\xFF".as_ref());
+        assert_eq!(bytes.read_u64(), u64::MAX - 255);
+        assert_eq!(bytes.len(), 0);
+        Ok(())
+    }
+
     #[test]
     fn test_owned_bytes_split() {
         let bytes = OwnedBytes::new(b"abcdefghi".as_ref());

src/directory/ram_directory.rs

@@ -12,6 +12,8 @@ use std::path::{Path, PathBuf};
 use std::result;
 use std::sync::{Arc, RwLock};
 
+use super::FileHandle;
+
 /// Writer associated with the `RAMDirectory`
 ///
 /// The Writer just writes a buffer.
@@ -163,6 +165,11 @@ impl RAMDirectory {
 }
 
 impl Directory for RAMDirectory {
+    fn get_file_handle(&self, path: &Path) -> Result<Box<dyn FileHandle>, OpenReadError> {
+        let file_slice = self.open_read(path)?;
+        Ok(Box::new(file_slice))
+    }
+
     fn open_read(&self, path: &Path) -> result::Result<FileSlice, OpenReadError> {
         self.fs.read().unwrap().open_read(path)
     }
@@ -177,8 +184,15 @@ impl Directory for RAMDirectory {
         self.fs.write().unwrap().delete(path)
     }
 
-    fn exists(&self, path: &Path) -> bool {
-        self.fs.read().unwrap().exists(path)
+    fn exists(&self, path: &Path) -> Result<bool, OpenReadError> {
+        Ok(self
+            .fs
+            .read()
+            .map_err(|e| OpenReadError::IOError {
+                io_error: io::Error::new(io::ErrorKind::Other, e.to_string()),
+                filepath: path.to_path_buf(),
+            })?
+            .exists(path))
     }
 
     fn open_write(&self, path: &Path) -> Result<WritePtr, OpenWriteError> {

src/directory/tests.rs

@@ -130,7 +130,7 @@ fn ram_directory_panics_if_flush_forgotten() {
 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)?;
-    assert!(directory.exists(test_path));
+    assert!(directory.exists(test_path).unwrap());
     write_file.write_all(&[4])?;
     write_file.write_all(&[3])?;
     write_file.write_all(&[7, 3, 5])?;
@@ -139,14 +139,14 @@ fn test_simple(directory: &dyn Directory) -> crate::Result<()> {
     assert_eq!(read_file.as_slice(), &[4u8, 3u8, 7u8, 3u8, 5u8]);
     mem::drop(read_file);
     assert!(directory.delete(test_path).is_ok());
-    assert!(!directory.exists(test_path));
+    assert!(!directory.exists(test_path).unwrap());
     Ok(())
 }
 
 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)?;
-    assert!(directory.exists(test_path));
+    assert!(directory.exists(test_path).unwrap());
     assert!(directory.open_write(test_path).is_err());
     assert!(directory.delete(test_path).is_ok());
     Ok(())
@@ -157,7 +157,7 @@ fn test_write_create_the_file(directory: &dyn Directory) {
     {
         assert!(directory.open_read(test_path).is_err());
         let _w = directory.open_write(test_path).unwrap();
-        assert!(directory.exists(test_path));
+        assert!(directory.exists(test_path).unwrap());
         assert!(directory.open_read(test_path).is_ok());
         assert!(directory.delete(test_path).is_ok());
     }
@@ -190,38 +190,33 @@ fn test_directory_delete(directory: &dyn Directory) -> crate::Result<()> {
 }
 
 fn test_watch(directory: &dyn Directory) {
-    let num_progress: Arc<AtomicUsize> = Default::default();
     let counter: Arc<AtomicUsize> = Default::default();
-    let counter_clone = counter.clone();
-    let (sender, receiver) = crossbeam::channel::unbounded();
-    let watch_callback = Box::new(move || {
-        counter_clone.fetch_add(1, SeqCst);
-    });
-    // This callback is used to synchronize watching in our unit test.
-    // We bind it to a variable because the callback is removed when that
-    // handle is dropped.
-    let watch_handle = directory.watch(watch_callback).unwrap();
-    let _progress_listener = directory
-        .watch(Box::new(move || {
-            let val = num_progress.fetch_add(1, SeqCst);
-            let _ = sender.send(val);
+    let (tx, rx) = crossbeam::channel::unbounded();
+    let timeout = Duration::from_millis(500);
+
+    let handle = directory
+        .watch(WatchCallback::new(move || {
+            let val = counter.fetch_add(1, SeqCst);
+            tx.send(val + 1).unwrap();
         }))
         .unwrap();
 
-    for i in 0..10 {
-        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!(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")
+        .atomic_write(Path::new("meta.json"), b"foo")
         .is_ok());
-    assert!(receiver.recv_timeout(Duration::from_millis(500)).is_ok());
-    assert!(10 <= counter.load(SeqCst));
+    assert_eq!(rx.recv_timeout(timeout), Ok(1));
+
+    assert!(directory
+        .atomic_write(Path::new("meta.json"), b"bar")
+        .is_ok());
+    assert_eq!(rx.recv_timeout(timeout), Ok(2));
+
+    mem::drop(handle);
+
+    assert!(directory
+        .atomic_write(Path::new("meta.json"), b"qux")
+        .is_ok());
+    assert!(rx.recv_timeout(timeout).is_err());
 }
 
 fn test_lock_non_blocking(directory: &dyn Directory) {

src/directory/watch_event_router.rs

@@ -4,8 +4,20 @@ use std::sync::Arc;
 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>;
+/// Cloneable wrapper for callbacks registered when watching files of a `Directory`.
+#[derive(Clone)]
+pub struct WatchCallback(Arc<dyn Fn() + Sync + Send>);
+
+impl WatchCallback {
+    /// Wraps a `Fn()` to create a WatchCallback.
+    pub fn new<F: Fn() + Sync + Send + 'static>(op: F) -> Self {
+        WatchCallback(Arc::new(op))
+    }
+
+    fn call(&self) {
+        self.0()
+    }
+}
 
 /// Helper struct to implement the watch method in `Directory` implementations.
 ///
@@ -34,7 +46,7 @@ impl WatchHandle {
     ///
     /// This function is only useful when implementing a readonly directory.
     pub fn empty() -> WatchHandle {
-        WatchHandle::new(Arc::new(Box::new(|| {})))
+        WatchHandle::new(Arc::new(WatchCallback::new(|| {})))
     }
 }
 
@@ -47,13 +59,13 @@ impl WatchCallbackList {
         WatchHandle::new(watch_callback_arc)
     }
 
-    fn list_callback(&self) -> Vec<Arc<WatchCallback>> {
-        let mut callbacks = vec![];
+    fn list_callback(&self) -> Vec<WatchCallback> {
+        let mut callbacks: Vec<WatchCallback> = vec![];
         let mut router_wlock = self.router.write().unwrap();
         let mut i = 0;
         while i < router_wlock.len() {
             if let Some(watch) = router_wlock[i].upgrade() {
-                callbacks.push(watch);
+                callbacks.push(watch.as_ref().clone());
                 i += 1;
             } else {
                 router_wlock.swap_remove(i);
@@ -75,7 +87,7 @@ impl WatchCallbackList {
             .name("watch-callbacks".to_string())
             .spawn(move || {
                 for callback in callbacks {
-                    callback();
+                    callback.call();
                 }
                 let _ = sender.send(());
             });
@@ -91,7 +103,7 @@ impl WatchCallbackList {
 
 #[cfg(test)]
 mod tests {
-    use crate::directory::WatchCallbackList;
+    use crate::directory::{WatchCallback, WatchCallbackList};
     use futures::executor::block_on;
     use std::mem;
     use std::sync::atomic::{AtomicUsize, Ordering};
@@ -102,7 +114,7 @@ mod tests {
         let watch_event_router = WatchCallbackList::default();
         let counter: Arc<AtomicUsize> = Default::default();
         let counter_clone = counter.clone();
-        let inc_callback = Box::new(move || {
+        let inc_callback = WatchCallback::new(move || {
             counter_clone.fetch_add(1, Ordering::SeqCst);
         });
         block_on(watch_event_router.broadcast());
@@ -130,7 +142,7 @@ mod tests {
         let counter: Arc<AtomicUsize> = Default::default();
         let inc_callback = |inc: usize| {
             let counter_clone = counter.clone();
-            Box::new(move || {
+            WatchCallback::new(move || {
                 counter_clone.fetch_add(inc, Ordering::SeqCst);
             })
         };
@@ -158,7 +170,7 @@ mod tests {
         let watch_event_router = WatchCallbackList::default();
         let counter: Arc<AtomicUsize> = Default::default();
         let counter_clone = counter.clone();
-        let inc_callback = Box::new(move || {
+        let inc_callback = WatchCallback::new(move || {
             counter_clone.fetch_add(1, Ordering::SeqCst);
         });
         let handle_a = watch_event_router.subscribe(inc_callback);

src/docset.rs

@@ -10,7 +10,7 @@ use std::borrow::BorrowMut;
 pub const TERMINATED: DocId = std::i32::MAX as u32;
 
 /// Represents an iterable set of sorted doc ids.
-pub trait DocSet {
+pub trait DocSet: Send {
     /// Goes to the next element.
     ///
     /// The DocId of the next element is returned.
@@ -129,6 +129,14 @@ impl<'a> DocSet for &'a mut dyn DocSet {
     fn size_hint(&self) -> u32 {
         (**self).size_hint()
     }
+
+    fn count(&mut self, delete_bitset: &DeleteBitSet) -> u32 {
+        (**self).count(delete_bitset)
+    }
+
+    fn count_including_deleted(&mut self) -> u32 {
+        (**self).count_including_deleted()
+    }
 }
 
 impl<TDocSet: DocSet + ?Sized> DocSet for Box<TDocSet> {

src/fastfield/bytes/mod.rs

@@ -86,7 +86,7 @@ mod tests {
         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)?;
+        let term_scorer = term_weight.specialized_scorer(searcher.segment_reader(0), 1.0)?;
         assert_eq!(term_scorer.doc(), 0u32);
         Ok(())
     }
@@ -98,10 +98,9 @@ mod tests {
         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, false)?;
-        let term_scorer_err = term_weight.specialized_scorer(searcher.segment_reader(0), 1.0f32);
+        let term_weight_err = term_query.specialized_weight(&searcher, false);
         assert!(matches!(
-            term_scorer_err,
+            term_weight_err,
             Err(crate::TantivyError::SchemaError(_))
         ));
         Ok(())

src/fastfield/facet_reader.rs

@@ -1,4 +1,5 @@
 use super::MultiValueIntFastFieldReader;
+use crate::error::DataCorruption;
 use crate::schema::Facet;
 use crate::termdict::TermDictionary;
 use crate::termdict::TermOrdinal;
@@ -62,12 +63,13 @@ impl FacetReader {
         &mut self,
         facet_ord: TermOrdinal,
         output: &mut Facet,
-    ) -> Result<(), str::Utf8Error> {
+    ) -> crate::Result<()> {
         let found_term = self
             .term_dict
-            .ord_to_term(facet_ord as u64, &mut self.buffer);
+            .ord_to_term(facet_ord as u64, &mut self.buffer)?;
         assert!(found_term, "Term ordinal {} no found.", facet_ord);
-        let facet_str = str::from_utf8(&self.buffer[..])?;
+        let facet_str = str::from_utf8(&self.buffer[..])
+            .map_err(|utf8_err| DataCorruption::comment_only(utf8_err.to_string()))?;
         output.set_facet_str(facet_str);
         Ok(())
     }

src/fastfield/mod.rs

@@ -629,7 +629,7 @@ mod bench {
         {
             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);
+            let fast_field_reader = FastFieldReader::<u64>::open(data).unwrap();
 
             b.iter(|| {
                 let n = test::black_box(7000u32);
@@ -663,7 +663,7 @@ mod bench {
         {
             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);
+            let fast_field_reader = FastFieldReader::<u64>::open(data).unwrap();
 
             b.iter(|| {
                 let n = test::black_box(1000u32);

src/fastfield/reader.rs

@@ -51,6 +51,15 @@ impl<Item: FastValue> FastFieldReader<Item> {
         }
     }
 
+    pub(crate) fn cast<TFastValue: FastValue>(self) -> FastFieldReader<TFastValue> {
+        FastFieldReader {
+            bit_unpacker: self.bit_unpacker,
+            min_value_u64: self.min_value_u64,
+            max_value_u64: self.max_value_u64,
+            _phantom: PhantomData,
+        }
+    }
+
     /// Return the value associated to the given document.
     ///
     /// This accessor should return as fast as possible.

src/fastfield/readers.rs

@@ -1,6 +1,6 @@
 use crate::common::CompositeFile;
-use crate::fastfield::BytesFastFieldReader;
 use crate::fastfield::MultiValueIntFastFieldReader;
+use crate::fastfield::{BytesFastFieldReader, FastValue};
 use crate::fastfield::{FastFieldNotAvailableError, FastFieldReader};
 use crate::schema::{Cardinality, Field, FieldType, Schema};
 use crate::space_usage::PerFieldSpaceUsage;
@@ -201,6 +201,14 @@ impl FastFieldReaders {
         None
     }
 
+    pub(crate) fn typed_fast_field_reader<TFastValue: FastValue>(
+        &self,
+        field: Field,
+    ) -> Option<FastFieldReader<TFastValue>> {
+        self.u64_lenient(field)
+            .map(|fast_field_reader| fast_field_reader.cast())
+    }
+
     /// Returns the `i64` fast field reader reader associated to `field`.
     ///
     /// If `field` is not a i64 fast field, this method returns `None`.

src/fieldnorm/reader.rs

@@ -61,20 +61,56 @@ impl FieldNormReaders {
 /// precompute computationally expensive functions of the fieldnorm
 /// in a very short array.
 #[derive(Clone)]
-pub struct FieldNormReader {
-    data: OwnedBytes,
+pub struct FieldNormReader(ReaderImplEnum);
+
+impl From<ReaderImplEnum> for FieldNormReader {
+    fn from(reader_enum: ReaderImplEnum) -> FieldNormReader {
+        FieldNormReader(reader_enum)
+    }
+}
+
+#[derive(Clone)]
+enum ReaderImplEnum {
+    FromData(OwnedBytes),
+    Const {
+        num_docs: u32,
+        fieldnorm_id: u8,
+        fieldnorm: u32,
+    },
 }
 
 impl FieldNormReader {
+    /// Creates a `FieldNormReader` with a constant fieldnorm.
+    ///
+    /// The fieldnorm will be subjected to compression as if it was coming
+    /// from an array-backed fieldnorm reader.
+    pub fn constant(num_docs: u32, fieldnorm: u32) -> FieldNormReader {
+        let fieldnorm_id = fieldnorm_to_id(fieldnorm);
+        let fieldnorm = id_to_fieldnorm(fieldnorm_id);
+        ReaderImplEnum::Const {
+            num_docs,
+            fieldnorm_id,
+            fieldnorm,
+        }
+        .into()
+    }
+
     /// 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 { data })
+        Ok(FieldNormReader::new(data))
+    }
+
+    fn new(data: OwnedBytes) -> Self {
+        ReaderImplEnum::FromData(data).into()
     }
 
     /// Returns the number of documents in this segment.
     pub fn num_docs(&self) -> u32 {
-        self.data.len() as u32
+        match &self.0 {
+            ReaderImplEnum::FromData(data) => data.len() as u32,
+            ReaderImplEnum::Const { num_docs, .. } => *num_docs,
+        }
     }
 
     /// Returns the `fieldnorm` associated to a doc id.
@@ -87,14 +123,25 @@ impl FieldNormReader {
     /// The fieldnorm is effectively decoded from the
     /// `fieldnorm_id` by doing a simple table lookup.
     pub fn fieldnorm(&self, doc_id: DocId) -> u32 {
-        let fieldnorm_id = self.fieldnorm_id(doc_id);
-        id_to_fieldnorm(fieldnorm_id)
+        match &self.0 {
+            ReaderImplEnum::FromData(data) => {
+                let fieldnorm_id = data.as_slice()[doc_id as usize];
+                id_to_fieldnorm(fieldnorm_id)
+            }
+            ReaderImplEnum::Const { fieldnorm, .. } => *fieldnorm,
+        }
     }
 
     /// Returns the `fieldnorm_id` associated to a document.
     #[inline(always)]
     pub fn fieldnorm_id(&self, doc_id: DocId) -> u8 {
-        self.data.as_slice()[doc_id as usize]
+        match &self.0 {
+            ReaderImplEnum::FromData(data) => {
+                let fieldnorm_id = data.as_slice()[doc_id as usize];
+                fieldnorm_id
+            }
+            ReaderImplEnum::Const { fieldnorm_id, .. } => *fieldnorm_id,
+        }
     }
 
     /// Converts a `fieldnorm_id` into a fieldnorm.
@@ -118,9 +165,7 @@ impl FieldNormReader {
             .map(FieldNormReader::fieldnorm_to_id)
             .collect::<Vec<u8>>();
         let field_norms_data = OwnedBytes::new(field_norms_id);
-        FieldNormReader {
-            data: field_norms_data,
-        }
+        FieldNormReader::new(field_norms_data)
     }
 }
 
@@ -139,4 +184,20 @@ mod tests {
         assert_eq!(fieldnorm_reader.fieldnorm(3), 4);
         assert_eq!(fieldnorm_reader.fieldnorm(4), 983_064);
     }
+
+    #[test]
+    fn test_const_fieldnorm_reader_small_fieldnorm_id() {
+        let fieldnorm_reader = FieldNormReader::constant(1_000_000u32, 10u32);
+        assert_eq!(fieldnorm_reader.num_docs(), 1_000_000u32);
+        assert_eq!(fieldnorm_reader.fieldnorm(0u32), 10u32);
+        assert_eq!(fieldnorm_reader.fieldnorm_id(0u32), 10u8);
+    }
+
+    #[test]
+    fn test_const_fieldnorm_reader_large_fieldnorm_id() {
+        let fieldnorm_reader = FieldNormReader::constant(1_000_000u32, 300u32);
+        assert_eq!(fieldnorm_reader.num_docs(), 1_000_000u32);
+        assert_eq!(fieldnorm_reader.fieldnorm(0u32), 280u32);
+        assert_eq!(fieldnorm_reader.fieldnorm_id(0u32), 72u8);
+    }
 }

src/functional_test.rs

@@ -1,45 +1,94 @@
-use rand::thread_rng;
-use std::collections::HashSet;
-
-use crate::schema::*;
 use crate::Index;
 use crate::Searcher;
+use crate::{doc, schema::*};
+use rand::thread_rng;
 use rand::Rng;
+use std::collections::HashSet;
 
-fn check_index_content(searcher: &Searcher, vals: &HashSet<u64>) {
+fn check_index_content(searcher: &Searcher, vals: &[u64]) -> crate::Result<()> {
     assert!(searcher.segment_readers().len() < 20);
     assert_eq!(searcher.num_docs() as usize, vals.len());
+    for segment_reader in searcher.segment_readers() {
+        let store_reader = segment_reader.get_store_reader()?;
+        for doc_id in 0..segment_reader.max_doc() {
+            let _doc = store_reader.get(doc_id)?;
+        }
+    }
+    Ok(())
 }
 
 #[test]
 #[ignore]
-fn test_indexing() {
+fn test_functional_store() -> crate::Result<()> {
+    env_logger::init();
+    let mut schema_builder = Schema::builder();
+
+    let id_field = schema_builder.add_u64_field("id", INDEXED | STORED);
+    let schema = schema_builder.build();
+
+    let index = Index::create_in_ram(schema);
+    let reader = index.reader()?;
+
+    let mut rng = thread_rng();
+
+    let mut index_writer = index.writer_with_num_threads(3, 12_000_000)?;
+
+    let mut doc_set: Vec<u64> = Vec::new();
+
+    let mut doc_id = 0u64;
+    for iteration in 0.. {
+        let num_docs: usize = rng.gen_range(0..4);
+        if doc_set.len() >= 1 {
+            let doc_to_remove_id = rng.gen_range(0..doc_set.len());
+            let removed_doc_id = doc_set.swap_remove(doc_to_remove_id);
+            index_writer.delete_term(Term::from_field_u64(id_field, removed_doc_id));
+        }
+        for _ in 0..num_docs {
+            doc_set.push(doc_id);
+            index_writer.add_document(doc!(id_field=>doc_id));
+            doc_id += 1;
+        }
+        index_writer.commit()?;
+        reader.reload()?;
+        let searcher = reader.searcher();
+        println!("#{} - {}", iteration, searcher.segment_readers().len());
+        check_index_content(&searcher, &doc_set)?;
+    }
+    Ok(())
+}
+
+#[test]
+#[ignore]
+fn test_functional_indexing() -> crate::Result<()> {
     let mut schema_builder = Schema::builder();
 
     let id_field = schema_builder.add_u64_field("id", INDEXED);
     let multiples_field = schema_builder.add_u64_field("multiples", INDEXED);
     let schema = schema_builder.build();
 
-    let index = Index::create_from_tempdir(schema).unwrap();
-    let reader = index.reader().unwrap();
+    let index = Index::create_from_tempdir(schema)?;
+    let reader = index.reader()?;
 
     let mut rng = thread_rng();
 
-    let mut index_writer = index.writer_with_num_threads(3, 120_000_000).unwrap();
+    let mut index_writer = index.writer_with_num_threads(3, 120_000_000)?;
 
     let mut committed_docs: HashSet<u64> = HashSet::new();
     let mut uncommitted_docs: HashSet<u64> = HashSet::new();
 
     for _ in 0..200 {
-        let random_val = rng.gen_range(0, 20);
+        let random_val = rng.gen_range(0..20);
         if random_val == 0 {
-            index_writer.commit().expect("Commit failed");
+            index_writer.commit()?;
             committed_docs.extend(&uncommitted_docs);
             uncommitted_docs.clear();
-            reader.reload().unwrap();
+            reader.reload()?;
             let searcher = reader.searcher();
             // check that everything is correct.
-            check_index_content(&searcher, &committed_docs);
+            check_index_content(
+                &searcher,
+                &committed_docs.iter().cloned().collect::<Vec<u64>>(),
+            )?;
         } else {
             if committed_docs.remove(&random_val) || uncommitted_docs.remove(&random_val) {
                 let doc_id_term = Term::from_field_u64(id_field, random_val);
@@ -55,4 +104,5 @@ fn test_indexing() {
             }
         }
     }
+    Ok(())
 }

src/indexer/delete_queue.rs

@@ -53,7 +53,7 @@ impl DeleteQueue {
             return block;
         }
         let block = Arc::new(Block {
-            operations: Arc::default(),
+            operations: Arc::new([]),
             next: NextBlock::from(self.clone()),
         });
         wlock.last_block = Arc::downgrade(&block);
@@ -108,7 +108,7 @@ impl DeleteQueue {
         let delete_operations = mem::replace(&mut self_wlock.writer, vec![]);
 
         let new_block = Arc::new(Block {
-            operations: Arc::new(delete_operations.into_boxed_slice()),
+            operations: Arc::from(delete_operations.into_boxed_slice()),
             next: NextBlock::from(self.clone()),
         });
 
@@ -167,7 +167,7 @@ impl NextBlock {
 }
 
 struct Block {
-    operations: Arc<Box<[DeleteOperation]>>,
+    operations: Arc<[DeleteOperation]>,
     next: NextBlock,
 }
 

src/indexer/index_writer.rs

@@ -449,7 +449,7 @@ impl IndexWriter {
     }
 
     /// Accessor to the merge policy.
-    pub fn get_merge_policy(&self) -> Arc<Box<dyn MergePolicy>> {
+    pub fn get_merge_policy(&self) -> Arc<dyn MergePolicy> {
         self.segment_updater.get_merge_policy()
     }
 

src/indexer/log_merge_policy.rs

@@ -8,7 +8,7 @@ const DEFAULT_MIN_LAYER_SIZE: u32 = 10_000;
 const DEFAULT_MIN_MERGE_SIZE: usize = 8;
 const DEFAULT_MAX_MERGE_SIZE: usize = 10_000_000;
 
-/// `LogMergePolicy` tries tries to merge segments that have a similar number of
+/// `LogMergePolicy` tries to merge segments that have a similar number of
 /// documents.
 #[derive(Debug, Clone)]
 pub struct LogMergePolicy {

src/indexer/merger.rs

@@ -503,7 +503,6 @@ impl IndexMerger {
         let mut positions_buffer: Vec<u32> = Vec::with_capacity(1_000);
         let mut delta_computer = DeltaComputer::new();
 
-        let mut field_term_streams = Vec::new();
         let mut max_term_ords: Vec<TermOrdinal> = Vec::new();
 
         let field_readers: Vec<Arc<InvertedIndexReader>> = self
@@ -512,9 +511,10 @@ impl IndexMerger {
             .map(|reader| reader.inverted_index(indexed_field))
             .collect::<crate::Result<Vec<_>>>()?;
 
+        let mut field_term_streams = Vec::new();
         for field_reader in &field_readers {
             let terms = field_reader.terms();
-            field_term_streams.push(terms.stream());
+            field_term_streams.push(terms.stream()?);
             max_term_ords.push(terms.num_terms() as u64);
         }
 

src/indexer/operation.rs

@@ -9,6 +9,15 @@ pub struct DeleteOperation {
     pub term: Term,
 }
 
+impl Default for DeleteOperation {
+    fn default() -> Self {
+        DeleteOperation {
+            opstamp: 0u64,
+            term: Term::new(),
+        }
+    }
+}
+
 /// Timestamped Add operation.
 #[derive(Eq, PartialEq, Debug)]
 pub struct AddOperation {

src/indexer/segment_updater.rs

@@ -154,7 +154,7 @@ pub(crate) struct InnerSegmentUpdater {
 
     index: Index,
     segment_manager: SegmentManager,
-    merge_policy: RwLock<Arc<Box<dyn MergePolicy>>>,
+    merge_policy: RwLock<Arc<dyn MergePolicy>>,
     killed: AtomicBool,
     stamper: Stamper,
     merge_operations: MergeOperationInventory,
@@ -193,19 +193,19 @@ impl SegmentUpdater {
             merge_thread_pool,
             index,
             segment_manager,
-            merge_policy: RwLock::new(Arc::new(Box::new(DefaultMergePolicy::default()))),
+            merge_policy: RwLock::new(Arc::new(DefaultMergePolicy::default())),
             killed: AtomicBool::new(false),
             stamper,
             merge_operations: Default::default(),
         })))
     }
 
-    pub fn get_merge_policy(&self) -> Arc<Box<dyn MergePolicy>> {
+    pub fn get_merge_policy(&self) -> Arc<dyn MergePolicy> {
         self.merge_policy.read().unwrap().clone()
     }
 
     pub fn set_merge_policy(&self, merge_policy: Box<dyn MergePolicy>) {
-        let arc_merge_policy = Arc::new(merge_policy);
+        let arc_merge_policy = Arc::from(merge_policy);
         *self.merge_policy.write().unwrap() = arc_merge_policy;
     }
 

src/lib.rs

@@ -174,7 +174,7 @@ use once_cell::sync::Lazy;
 use serde::{Deserialize, Serialize};
 
 /// Index format version.
-const INDEX_FORMAT_VERSION: u32 = 2;
+const INDEX_FORMAT_VERSION: u32 = 3;
 
 /// Structure version for the index.
 #[derive(Clone, PartialEq, Eq, Serialize, Deserialize)]

src/positions/serializer.rs

@@ -8,7 +8,7 @@ use std::io::{self, Write};
 pub struct PositionSerializer<W: io::Write> {
     bit_packer: BitPacker4x,
     write_stream: CountingWriter<W>,
-    write_skiplist: W,
+    write_skip_index: W,
     block: Vec<u32>,
     buffer: Vec<u8>,
     num_ints: u64,
@@ -16,11 +16,11 @@ pub struct PositionSerializer<W: io::Write> {
 }
 
 impl<W: io::Write> PositionSerializer<W> {
-    pub fn new(write_stream: W, write_skiplist: W) -> PositionSerializer<W> {
+    pub fn new(write_stream: W, write_skip_index: W) -> PositionSerializer<W> {
         PositionSerializer {
             bit_packer: BitPacker4x::new(),
             write_stream: CountingWriter::wrap(write_stream),
-            write_skiplist,
+            write_skip_index,
             block: Vec::with_capacity(128),
             buffer: vec![0u8; 128 * 4],
             num_ints: 0u64,
@@ -52,7 +52,7 @@ impl<W: io::Write> PositionSerializer<W> {
 
     fn flush_block(&mut self) -> io::Result<()> {
         let num_bits = self.bit_packer.num_bits(&self.block[..]);
-        self.write_skiplist.write_all(&[num_bits])?;
+        self.write_skip_index.write_all(&[num_bits])?;
         let written_len = self
             .bit_packer
             .compress(&self.block[..], &mut self.buffer, num_bits);
@@ -70,10 +70,10 @@ impl<W: io::Write> PositionSerializer<W> {
             self.flush_block()?;
         }
         for &long_skip in &self.long_skips {
-            long_skip.serialize(&mut self.write_skiplist)?;
+            long_skip.serialize(&mut self.write_skip_index)?;
         }
-        (self.long_skips.len() as u32).serialize(&mut self.write_skiplist)?;
-        self.write_skiplist.flush()?;
+        (self.long_skips.len() as u32).serialize(&mut self.write_skip_index)?;
+        self.write_skip_index.flush()?;
         self.write_stream.flush()?;
         Ok(())
     }

src/postings/block_segment_postings.rs

@@ -469,7 +469,7 @@ mod tests {
         let segment_reader = searcher.segment_reader(0);
         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();
+        let term_info = inverted_index.get_term_info(&term).unwrap().unwrap();
         inverted_index
             .read_block_postings_from_terminfo(&term_info, IndexRecordOption::Basic)
             .unwrap()
@@ -513,7 +513,7 @@ mod tests {
         {
             let term = Term::from_field_u64(int_field, 0u64);
             let inverted_index = segment_reader.inverted_index(int_field)?;
-            let term_info = inverted_index.get_term_info(&term).unwrap();
+            let term_info = inverted_index.get_term_info(&term)?.unwrap();
             block_segments = inverted_index
                 .read_block_postings_from_terminfo(&term_info, IndexRecordOption::Basic)?;
         }
@@ -521,7 +521,7 @@ mod tests {
         {
             let term = Term::from_field_u64(int_field, 1u64);
             let inverted_index = segment_reader.inverted_index(int_field)?;
-            let term_info = inverted_index.get_term_info(&term).unwrap();
+            let term_info = inverted_index.get_term_info(&term)?.unwrap();
             inverted_index.reset_block_postings_from_terminfo(&term_info, &mut block_segments)?;
         }
         assert_eq!(block_segments.docs(), &[1, 3, 5]);

src/postings/mod.rs

@@ -15,18 +15,14 @@ mod stacker;
 mod term_info;
 
 pub(crate) use self::block_search::BlockSearcher;
-
-pub(crate) use self::postings_writer::MultiFieldPostingsWriter;
-pub use self::serializer::{FieldSerializer, InvertedIndexSerializer};
-
-pub use self::postings::Postings;
-pub(crate) use self::skip::{BlockInfo, SkipReader};
-pub use self::term_info::TermInfo;
-
 pub use self::block_segment_postings::BlockSegmentPostings;
+pub use self::postings::Postings;
+pub(crate) use self::postings_writer::MultiFieldPostingsWriter;
 pub use self::segment_postings::SegmentPostings;
-
+pub use self::serializer::{FieldSerializer, InvertedIndexSerializer};
+pub(crate) use self::skip::{BlockInfo, SkipReader};
 pub(crate) use self::stacker::compute_table_size;
+pub use self::term_info::TermInfo;
 
 pub(crate) type UnorderedTermId = u64;
 
@@ -51,17 +47,14 @@ pub mod tests {
     use crate::indexer::SegmentWriter;
     use crate::merge_policy::NoMergePolicy;
     use crate::query::Scorer;
-    use crate::schema::{Document, Schema, Term, INDEXED, STRING, TEXT};
     use crate::schema::{Field, TextOptions};
     use crate::schema::{IndexRecordOption, TextFieldIndexing};
+    use crate::schema::{Schema, Term, INDEXED, TEXT};
     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;
-    use rand::{Rng, SeedableRng};
-    use std::iter;
+    use std::{iter, mem};
 
     #[test]
     pub fn test_position_write() -> crate::Result<()> {
@@ -78,6 +71,7 @@ pub mod tests {
             field_serializer.write_doc(doc_id, 4, &delta_positions)?;
         }
         field_serializer.close_term()?;
+        mem::drop(field_serializer);
         posting_serializer.close()?;
         let read = segment.open_read(SegmentComponent::POSITIONS)?;
         assert!(read.len() <= 140);
@@ -186,7 +180,7 @@ pub mod tests {
             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!(inverted_index.terms().ord_to_term(0, &mut bytes)?);
             assert_eq!(&bytes, b"hello");
         }
         {
@@ -198,7 +192,7 @@ pub mod tests {
             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!(inverted_index.terms().ord_to_term(0, &mut bytes)?);
             assert_eq!(&bytes[..], ok_token_text.as_bytes());
         }
         Ok(())
@@ -491,53 +485,6 @@ pub mod tests {
         Ok(())
     }
 
-    pub static TERM_A: Lazy<Term> = Lazy::new(|| {
-        let field = Field::from_field_id(0);
-        Term::from_field_text(field, "a")
-    });
-    pub static TERM_B: Lazy<Term> = Lazy::new(|| {
-        let field = Field::from_field_id(0);
-        Term::from_field_text(field, "b")
-    });
-    pub static TERM_C: Lazy<Term> = Lazy::new(|| {
-        let field = Field::from_field_id(0);
-        Term::from_field_text(field, "c")
-    });
-    pub static TERM_D: Lazy<Term> = Lazy::new(|| {
-        let field = Field::from_field_id(0);
-        Term::from_field_text(field, "d")
-    });
-
-    pub static INDEX: Lazy<Index> = Lazy::new(|| {
-        let mut schema_builder = Schema::builder();
-        let text_field = schema_builder.add_text_field("text", STRING);
-        let schema = schema_builder.build();
-
-        let mut rng: StdRng = StdRng::from_seed([1u8; 32]);
-
-        let index = Index::create_in_ram(schema);
-        let posting_list_size = 1_000_000;
-        {
-            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) {
-                    doc.add_text(text_field, "a");
-                }
-                if rng.gen_bool(1f64 / 10f64) {
-                    doc.add_text(text_field, "b");
-                }
-                if rng.gen_bool(1f64 / 5f64) {
-                    doc.add_text(text_field, "c");
-                }
-                doc.add_text(text_field, "d");
-                index_writer.add_document(doc);
-            }
-            assert!(index_writer.commit().is_ok());
-        }
-        index
-    });
-
     /// Wraps a given docset, and forward alls call but the
     /// `.skip_next(...)`. This is useful to test that a specialized
     /// implementation of `.skip_next(...)` is consistent
@@ -602,15 +549,65 @@ pub mod tests {
 
 #[cfg(all(test, feature = "unstable"))]
 mod bench {
-
-    use super::tests::*;
     use crate::docset::TERMINATED;
     use crate::query::Intersection;
     use crate::schema::IndexRecordOption;
+    use crate::schema::{Document, Field, Schema, Term, STRING};
     use crate::tests;
     use crate::DocSet;
+    use crate::Index;
+    use once_cell::sync::Lazy;
+    use rand::rngs::StdRng;
+    use rand::{Rng, SeedableRng};
     use test::{self, Bencher};
 
+    pub static TERM_A: Lazy<Term> = Lazy::new(|| {
+        let field = Field::from_field_id(0);
+        Term::from_field_text(field, "a")
+    });
+    pub static TERM_B: Lazy<Term> = Lazy::new(|| {
+        let field = Field::from_field_id(0);
+        Term::from_field_text(field, "b")
+    });
+    pub static TERM_C: Lazy<Term> = Lazy::new(|| {
+        let field = Field::from_field_id(0);
+        Term::from_field_text(field, "c")
+    });
+    pub static TERM_D: Lazy<Term> = Lazy::new(|| {
+        let field = Field::from_field_id(0);
+        Term::from_field_text(field, "d")
+    });
+
+    pub static INDEX: Lazy<Index> = Lazy::new(|| {
+        let mut schema_builder = Schema::builder();
+        let text_field = schema_builder.add_text_field("text", STRING);
+        let schema = schema_builder.build();
+
+        let mut rng: StdRng = StdRng::from_seed([1u8; 32]);
+
+        let index = Index::create_in_ram(schema);
+        let posting_list_size = 1_000_000;
+        {
+            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) {
+                    doc.add_text(text_field, "a");
+                }
+                if rng.gen_bool(1f64 / 10f64) {
+                    doc.add_text(text_field, "b");
+                }
+                if rng.gen_bool(1f64 / 5f64) {
+                    doc.add_text(text_field, "c");
+                }
+                doc.add_text(text_field, "d");
+                index_writer.add_document(doc);
+            }
+            assert!(index_writer.commit().is_ok());
+        }
+        index
+    });
+
     #[bench]
     fn bench_segment_postings(b: &mut Bencher) {
         let reader = INDEX.reader().unwrap();
@@ -620,7 +617,9 @@ mod bench {
         b.iter(|| {
             let mut segment_postings = segment_reader
                 .inverted_index(TERM_A.field())
-                .read_postings(&*TERM_A, IndexRecordOption::Basic)?
+                .unwrap()
+                .read_postings(&*TERM_A, IndexRecordOption::Basic)
+                .unwrap()
                 .unwrap();
             while segment_postings.advance() != TERMINATED {}
         });
@@ -634,21 +633,25 @@ mod bench {
         b.iter(|| {
             let segment_postings_a = segment_reader
                 .inverted_index(TERM_A.field())
+                .unwrap()
                 .read_postings(&*TERM_A, IndexRecordOption::Basic)
                 .unwrap()
                 .unwrap();
             let segment_postings_b = segment_reader
                 .inverted_index(TERM_B.field())
+                .unwrap()
                 .read_postings(&*TERM_B, IndexRecordOption::Basic)
                 .unwrap()
                 .unwrap();
             let segment_postings_c = segment_reader
                 .inverted_index(TERM_C.field())
+                .unwrap()
                 .read_postings(&*TERM_C, IndexRecordOption::Basic)
                 .unwrap()
                 .unwrap();
             let segment_postings_d = segment_reader
                 .inverted_index(TERM_D.field())
+                .unwrap()
                 .read_postings(&*TERM_D, IndexRecordOption::Basic)
                 .unwrap()
                 .unwrap();
@@ -670,6 +673,7 @@ mod bench {
 
         let mut segment_postings = segment_reader
             .inverted_index(TERM_A.field())
+            .unwrap()
             .read_postings(&*TERM_A, IndexRecordOption::Basic)
             .unwrap()
             .unwrap();
@@ -687,7 +691,9 @@ mod bench {
         b.iter(|| {
             let mut segment_postings = segment_reader
                 .inverted_index(TERM_A.field())
+                .unwrap()
                 .read_postings(&*TERM_A, IndexRecordOption::Basic)
+                .unwrap()
                 .unwrap();
             for doc in &existing_docs {
                 if segment_postings.seek(*doc) == TERMINATED {
@@ -726,7 +732,9 @@ mod bench {
             let n: u32 = test::black_box(17);
             let mut segment_postings = segment_reader
                 .inverted_index(TERM_A.field())
+                .unwrap()
                 .read_postings(&*TERM_A, IndexRecordOption::Basic)
+                .unwrap()
                 .unwrap();
             let mut s = 0u32;
             while segment_postings.doc() != TERMINATED {

src/postings/serializer.rs

@@ -177,14 +177,16 @@ impl<'a> FieldSerializer<'a> {
     }
 
     fn current_term_info(&self) -> TermInfo {
-        let positions_idx = self
-            .positions_serializer_opt
-            .as_ref()
-            .map(PositionSerializer::positions_idx)
-            .unwrap_or(0u64);
+        let positions_idx =
+            if let Some(positions_serializer) = self.positions_serializer_opt.as_ref() {
+                positions_serializer.positions_idx()
+            } else {
+                0u64
+            };
         TermInfo {
             doc_freq: 0,
-            postings_offset: self.postings_serializer.addr(),
+            postings_start_offset: self.postings_serializer.addr(),
+            postings_stop_offset: 0u64,
             positions_idx,
         }
     }
@@ -238,10 +240,11 @@ impl<'a> FieldSerializer<'a> {
     /// using `VInt` encoding.
     pub fn close_term(&mut self) -> io::Result<()> {
         if self.term_open {
-            self.term_dictionary_builder
-                .insert_value(&self.current_term_info)?;
             self.postings_serializer
                 .close_term(self.current_term_info.doc_freq)?;
+            self.current_term_info.postings_stop_offset = self.postings_serializer.addr();
+            self.term_dictionary_builder
+                .insert_value(&self.current_term_info)?;
             self.term_open = false;
         }
         Ok(())

src/postings/skip.rs

@@ -1,32 +1,46 @@
-use crate::common::{read_u32_vint_no_advance, serialize_vint_u32, BinarySerializable};
+use std::convert::TryInto;
+
 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, Score, TERMINATED};
 
+#[inline(always)]
+fn encode_block_wand_max_tf(max_tf: u32) -> u8 {
+    max_tf.min(u8::MAX as u32) as u8
+}
+
+#[inline(always)]
+fn decode_block_wand_max_tf(max_tf_code: u8) -> u32 {
+    if max_tf_code == u8::MAX {
+        u32::MAX
+    } else {
+        max_tf_code as u32
+    }
+}
+
+#[inline(always)]
+fn read_u32(data: &[u8]) -> u32 {
+    u32::from_le_bytes(data[..4].try_into().unwrap())
+}
+
+#[inline(always)]
+fn write_u32(val: u32, buf: &mut Vec<u8>) {
+    buf.extend_from_slice(&val.to_le_bytes());
+}
+
 pub struct SkipSerializer {
     buffer: Vec<u8>,
-    prev_doc: DocId,
 }
 
 impl SkipSerializer {
     pub fn new() -> SkipSerializer {
-        SkipSerializer {
-            buffer: Vec::new(),
-            prev_doc: 0u32,
-        }
+        SkipSerializer { buffer: Vec::new() }
     }
 
     pub fn write_doc(&mut self, last_doc: DocId, doc_num_bits: u8) {
-        assert!(
-            last_doc > self.prev_doc,
-            "write_doc(...) called with non-increasing doc ids. \
-             Did you forget to call clear maybe?"
-        );
-        let delta_doc = last_doc - self.prev_doc;
-        self.prev_doc = last_doc;
-        delta_doc.serialize(&mut self.buffer).unwrap();
+        write_u32(last_doc, &mut self.buffer);
         self.buffer.push(doc_num_bits);
     }
 
@@ -35,16 +49,13 @@ impl SkipSerializer {
     }
 
     pub fn write_total_term_freq(&mut self, tf_sum: u32) {
-        tf_sum
-            .serialize(&mut self.buffer)
-            .expect("Should never fail");
+        write_u32(tf_sum, &mut self.buffer);
     }
 
     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);
+        let block_wand_tf = encode_block_wand_max_tf(term_freq);
+        self.buffer
+            .extend_from_slice(&[fieldnorm_id, block_wand_tf]);
     }
 
     pub fn data(&self) -> &[u8] {
@@ -52,7 +63,6 @@ impl SkipSerializer {
     }
 
     pub fn clear(&mut self) {
-        self.prev_doc = 0u32;
         self.buffer.clear();
     }
 }
@@ -159,18 +169,13 @@ impl SkipReader {
     }
 
     fn read_block_info(&mut self) {
-        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.as_slice()[4];
-
+        let bytes = self.owned_read.as_slice();
+        let advance_len: usize;
+        self.last_doc_in_block = read_u32(bytes);
+        let doc_num_bits = bytes[4];
         match self.skip_info {
             IndexRecordOption::Basic => {
-                self.owned_read.advance(5);
+                advance_len = 5;
                 self.block_info = BlockInfo::BitPacked {
                     doc_num_bits,
                     tf_num_bits: 0,
@@ -180,11 +185,10 @@ impl SkipReader {
                 };
             }
             IndexRecordOption::WithFreqs => {
-                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);
+                let block_wand_term_freq = decode_block_wand_max_tf(bytes[7]);
+                advance_len = 8;
                 self.block_info = BlockInfo::BitPacked {
                     doc_num_bits,
                     tf_num_bits,
@@ -194,16 +198,11 @@ impl SkipReader {
                 };
             }
             IndexRecordOption::WithFreqsAndPositions => {
-                let bytes = self.owned_read.as_slice();
                 let tf_num_bits = bytes[5];
-                let tf_sum = {
-                    let mut buf = [0; 4];
-                    buf.copy_from_slice(&bytes[6..10]);
-                    u32::from_le_bytes(buf)
-                };
+                let tf_sum = read_u32(&bytes[6..10]);
                 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);
+                let block_wand_term_freq = decode_block_wand_max_tf(bytes[11]);
+                advance_len = 12;
                 self.block_info = BlockInfo::BitPacked {
                     doc_num_bits,
                     tf_num_bits,
@@ -213,6 +212,7 @@ impl SkipReader {
                 };
             }
         }
+        self.owned_read.advance(advance_len);
     }
 
     pub fn block_info(&self) -> BlockInfo {
@@ -274,6 +274,24 @@ mod tests {
     use crate::directory::OwnedBytes;
     use crate::postings::compression::COMPRESSION_BLOCK_SIZE;
 
+    #[test]
+    fn test_encode_block_wand_max_tf() {
+        for tf in 0..255 {
+            assert_eq!(super::encode_block_wand_max_tf(tf), tf as u8);
+        }
+        for &tf in &[255, 256, 1_000_000, u32::MAX] {
+            assert_eq!(super::encode_block_wand_max_tf(tf), 255);
+        }
+    }
+
+    #[test]
+    fn test_decode_block_wand_max_tf() {
+        for tf in 0..255 {
+            assert_eq!(super::decode_block_wand_max_tf(tf), tf as u32);
+        }
+        assert_eq!(super::decode_block_wand_max_tf(255), u32::MAX);
+    }
+
     #[test]
     fn test_skip_with_freq() {
         let buf = {

src/postings/term_info.rs

@@ -7,35 +7,50 @@ use std::io;
 pub struct TermInfo {
     /// Number of documents in the segment containing the term
     pub doc_freq: u32,
-    /// Start offset within the postings (`.idx`) file.
-    pub postings_offset: u64,
+    /// Start offset of the posting list within the postings (`.idx`) file.
+    pub postings_start_offset: u64,
+    /// Stop offset of the posting list within the postings (`.idx`) file.
+    /// The byte range is `[start_offset..stop_offset)`.
+    pub postings_stop_offset: u64,
     /// Start offset of the first block within the position (`.pos`) file.
     pub positions_idx: u64,
 }
 
+impl TermInfo {
+    pub(crate) fn posting_num_bytes(&self) -> u32 {
+        let num_bytes = self.postings_stop_offset - self.postings_start_offset;
+        assert!(num_bytes <= std::u32::MAX as u64);
+        num_bytes as u32
+    }
+}
+
 impl FixedSize for TermInfo {
     /// Size required for the binary serialization of a `TermInfo` object.
     /// This is large, but in practise, `TermInfo` are encoded in blocks and
     /// only the first `TermInfo` of a block is serialized uncompressed.
     /// The subsequent `TermInfo` are delta encoded and bitpacked.
-    const SIZE_IN_BYTES: usize = u32::SIZE_IN_BYTES + 2 * u64::SIZE_IN_BYTES;
+    const SIZE_IN_BYTES: usize = 2 * u32::SIZE_IN_BYTES + 2 * u64::SIZE_IN_BYTES;
 }
 
 impl BinarySerializable for TermInfo {
     fn serialize<W: io::Write>(&self, writer: &mut W) -> io::Result<()> {
         self.doc_freq.serialize(writer)?;
-        self.postings_offset.serialize(writer)?;
+        self.postings_start_offset.serialize(writer)?;
+        self.posting_num_bytes().serialize(writer)?;
         self.positions_idx.serialize(writer)?;
         Ok(())
     }
 
     fn deserialize<R: io::Read>(reader: &mut R) -> io::Result<Self> {
         let doc_freq = u32::deserialize(reader)?;
-        let postings_offset = u64::deserialize(reader)?;
+        let postings_start_offset = u64::deserialize(reader)?;
+        let postings_num_bytes = u32::deserialize(reader)?;
+        let postings_stop_offset = postings_start_offset + u64::from(postings_num_bytes);
         let positions_idx = u64::deserialize(reader)?;
         Ok(TermInfo {
             doc_freq,
-            postings_offset,
+            postings_start_offset,
+            postings_stop_offset,
             positions_idx,
         })
     }

src/query/automaton_weight.rs

@@ -7,6 +7,7 @@ use crate::schema::{Field, IndexRecordOption};
 use crate::termdict::{TermDictionary, TermStreamer};
 use crate::TantivyError;
 use crate::{DocId, Score};
+use std::io;
 use std::sync::Arc;
 use tantivy_fst::Automaton;
 
@@ -19,6 +20,7 @@ pub struct AutomatonWeight<A> {
 impl<A> AutomatonWeight<A>
 where
     A: Automaton + Send + Sync + 'static,
+    A::State: Clone,
 {
     /// Create a new AutomationWeight
     pub fn new<IntoArcA: Into<Arc<A>>>(field: Field, automaton: IntoArcA) -> AutomatonWeight<A> {
@@ -28,7 +30,10 @@ where
         }
     }
 
-    fn automaton_stream<'a>(&'a self, term_dict: &'a TermDictionary) -> TermStreamer<'a, &'a A> {
+    fn automaton_stream<'a>(
+        &'a self,
+        term_dict: &'a TermDictionary,
+    ) -> io::Result<TermStreamer<'a, &'a A>> {
         let automaton: &A = &*self.automaton;
         let term_stream_builder = term_dict.search(automaton);
         term_stream_builder.into_stream()
@@ -38,13 +43,14 @@ where
 impl<A> Weight for AutomatonWeight<A>
 where
     A: Automaton + Send + Sync + 'static,
+    A::State: Clone,
 {
     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 term_dict = inverted_index.terms();
-        let mut term_stream = self.automaton_stream(term_dict);
+        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
@@ -98,6 +104,7 @@ mod tests {
         index
     }
 
+    #[derive(Clone, Copy)]
     enum State {
         Start,
         NotMatching,

src/query/bm25.rs

@@ -106,7 +106,7 @@ impl BM25Weight {
         BM25Weight::new(idf_explain, avg_fieldnorm)
     }
 
-    fn new(idf_explain: Explanation, average_fieldnorm: Score) -> BM25Weight {
+    pub(crate) fn new(idf_explain: Explanation, average_fieldnorm: Score) -> BM25Weight {
         let weight = idf_explain.value() * (1.0 + K1);
         BM25Weight {
             idf_explain,

src/query/boolean_query/block_wand.rs

@@ -268,7 +268,7 @@ mod tests {
     }
 
     fn nearly_equals(left: Score, right: Score) -> bool {
-        (left - right).abs() < 0.000001 * (left + right).abs()
+        (left - right).abs() < 0.0001 * (left + right).abs()
     }
 
     fn compute_checkpoints_for_each_pruning(
@@ -424,9 +424,116 @@ mod tests {
         }
     }
 
+    #[test]
+    fn test_fn_reproduce_proptest() {
+        let postings_lists = &[
+            vec![
+                (0, 1),
+                (1, 1),
+                (2, 1),
+                (3, 1),
+                (4, 1),
+                (6, 1),
+                (7, 7),
+                (8, 1),
+                (10, 1),
+                (12, 1),
+                (13, 1),
+                (14, 1),
+                (15, 1),
+                (16, 1),
+                (19, 1),
+                (20, 1),
+                (21, 1),
+                (22, 1),
+                (24, 1),
+                (25, 1),
+                (26, 1),
+                (28, 1),
+                (30, 1),
+                (31, 1),
+                (33, 1),
+                (34, 1),
+                (35, 1),
+                (36, 95),
+                (37, 1),
+                (39, 1),
+                (41, 1),
+                (44, 1),
+                (46, 1),
+            ],
+            vec![
+                (0, 5),
+                (2, 1),
+                (4, 1),
+                (5, 84),
+                (6, 47),
+                (7, 26),
+                (8, 50),
+                (9, 34),
+                (11, 73),
+                (12, 11),
+                (13, 51),
+                (14, 45),
+                (15, 18),
+                (18, 60),
+                (19, 80),
+                (20, 63),
+                (23, 79),
+                (24, 69),
+                (26, 35),
+                (28, 82),
+                (29, 19),
+                (30, 2),
+                (31, 7),
+                (33, 40),
+                (34, 1),
+                (35, 33),
+                (36, 27),
+                (37, 24),
+                (38, 65),
+                (39, 32),
+                (40, 85),
+                (41, 1),
+                (42, 69),
+                (43, 11),
+                (45, 45),
+                (47, 97),
+            ],
+            vec![
+                (2, 1),
+                (4, 1),
+                (7, 94),
+                (8, 1),
+                (9, 1),
+                (10, 1),
+                (12, 1),
+                (15, 1),
+                (22, 1),
+                (23, 1),
+                (26, 1),
+                (27, 1),
+                (32, 1),
+                (33, 1),
+                (34, 1),
+                (36, 96),
+                (39, 1),
+                (41, 1),
+            ],
+        ];
+        let fieldnorms = &[
+            685, 239, 780, 564, 664, 827, 5, 56, 930, 887, 263, 665, 167, 127, 120, 919, 292, 92,
+            489, 734, 814, 724, 700, 304, 128, 779, 311, 877, 774, 15, 866, 368, 894, 371, 982,
+            502, 507, 669, 680, 76, 594, 626, 578, 331, 170, 639, 665, 186,
+        ][..];
+        test_block_wand_aux(postings_lists, fieldnorms);
+    }
+
     proptest! {
         #![proptest_config(ProptestConfig::with_cases(500))]
+        #[ignore]
         #[test]
+        #[ignore]
         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/mod.rs

@@ -310,7 +310,7 @@ mod tests {
         ));
         let query = BooleanQuery::from(vec![(Occur::Should, term_a), (Occur::Should, term_b)]);
         let explanation = query.explain(&searcher, DocAddress(0, 0u32))?;
-        assert_nearly_equals!(explanation.value(), 0.6931472f32);
+        assert_nearly_equals!(explanation.value(), 0.6931472);
         Ok(())
     }
 }

src/query/range_query.rs

@@ -11,6 +11,7 @@ use crate::schema::{Field, IndexRecordOption, Term};
 use crate::termdict::{TermDictionary, TermStreamer};
 use crate::{DocId, Score};
 use std::collections::Bound;
+use std::io;
 use std::ops::Range;
 
 fn map_bound<TFrom, TTo, Transform: Fn(&TFrom) -> TTo>(
@@ -274,7 +275,7 @@ pub struct RangeWeight {
 }
 
 impl RangeWeight {
-    fn term_range<'a>(&self, term_dict: &'a TermDictionary) -> TermStreamer<'a> {
+    fn term_range<'a>(&self, term_dict: &'a TermDictionary) -> io::Result<TermStreamer<'a>> {
         use std::collections::Bound::*;
         let mut term_stream_builder = term_dict.range();
         term_stream_builder = match self.left_bound {
@@ -298,7 +299,7 @@ impl Weight for RangeWeight {
 
         let inverted_index = reader.inverted_index(self.field)?;
         let term_dict = inverted_index.terms();
-        let mut term_range = self.term_range(term_dict);
+        let mut term_range = self.term_range(term_dict)?;
         while term_range.advance() {
             let term_info = term_range.value();
             let mut block_segment_postings = inverted_index

src/query/reqopt_scorer.rs

@@ -12,7 +12,7 @@ use std::marker::PhantomData;
 /// This is useful for queries like `+somethingrequired somethingoptional`.
 ///
 /// Note that `somethingoptional` has no impact on the `DocSet`.
-pub struct RequiredOptionalScorer<TReqScorer, TOptScorer, TScoreCombiner> {
+pub struct RequiredOptionalScorer<TReqScorer, TOptScorer, TScoreCombiner: ScoreCombiner> {
     req_scorer: TReqScorer,
     opt_scorer: TOptScorer,
     score_cache: Option<Score>,
@@ -23,6 +23,7 @@ impl<TReqScorer, TOptScorer, TScoreCombiner>
     RequiredOptionalScorer<TReqScorer, TOptScorer, TScoreCombiner>
 where
     TOptScorer: DocSet,
+    TScoreCombiner: ScoreCombiner,
 {
     /// Creates a new `RequiredOptionalScorer`.
     pub fn new(
@@ -43,6 +44,7 @@ impl<TReqScorer, TOptScorer, TScoreCombiner> DocSet
 where
     TReqScorer: DocSet,
     TOptScorer: DocSet,
+    TScoreCombiner: ScoreCombiner,
 {
     fn advance(&mut self) -> DocId {
         self.score_cache = None;

src/query/score_combiner.rs

@@ -3,7 +3,7 @@ use crate::Score;
 
 /// The `ScoreCombiner` trait defines how to compute
 /// an overall score given a list of scores.
-pub trait ScoreCombiner: Default + Clone + Copy + 'static {
+pub trait ScoreCombiner: Default + Clone + Send + Copy + 'static {
     /// Aggregates the score combiner with the given scorer.
     ///
     /// The `ScoreCombiner` may decide to call `.scorer.score()`

src/query/term_query/mod.rs

@@ -197,7 +197,7 @@ mod tests {
         let searcher = index.reader()?.searcher();
         {
             let explanation = term_query.explain(&searcher, DocAddress(0u32, 1u32))?;
-            assert_nearly_equals!(explanation.value(), 0.6931472f32);
+            assert_nearly_equals!(explanation.value(), 0.6931472);
         }
         {
             let explanation_err = term_query.explain(&searcher, DocAddress(0u32, 0u32));

src/query/term_query/term_query.rs

@@ -1,7 +1,7 @@
 use super::term_weight::TermWeight;
 use crate::query::bm25::BM25Weight;
-use crate::query::Query;
 use crate::query::Weight;
+use crate::query::{Explanation, Query};
 use crate::schema::IndexRecordOption;
 use crate::Searcher;
 use crate::Term;
@@ -93,7 +93,20 @@ impl TermQuery {
         scoring_enabled: bool,
     ) -> crate::Result<TermWeight> {
         let term = self.term.clone();
-        let bm25_weight = BM25Weight::for_terms(searcher, &[term])?;
+        let field_entry = searcher.schema().get_field_entry(term.field());
+        if !field_entry.is_indexed() {
+            return Err(crate::TantivyError::SchemaError(format!(
+                "Field {:?} is not indexed",
+                field_entry.name()
+            )));
+        }
+        let bm25_weight;
+        if scoring_enabled {
+            bm25_weight = BM25Weight::for_terms(searcher, &[term])?;
+        } else {
+            bm25_weight =
+                BM25Weight::new(Explanation::new("<no score>".to_string(), 1.0f32), 1.0f32);
+        }
         let index_record_option = if scoring_enabled {
             self.index_record_option
         } else {
@@ -103,6 +116,7 @@ impl TermQuery {
             self.term.clone(),
             index_record_option,
             bm25_weight,
+            scoring_enabled,
         ))
     }
 }

src/query/term_query/term_scorer.rs

@@ -302,7 +302,7 @@ mod tests {
         let mut rng = rand::thread_rng();
         writer.set_merge_policy(Box::new(NoMergePolicy));
         for _ in 0..3_000 {
-            let term_freq = rng.gen_range(1, 10000);
+            let term_freq = rng.gen_range(1..10000);
             let words: Vec<&str> = std::iter::repeat("bbbb").take(term_freq).collect();
             let text = words.join(" ");
             writer.add_document(doc!(text_field=>text));

src/query/term_query/term_weight.rs

@@ -1,6 +1,7 @@
 use super::term_scorer::TermScorer;
 use crate::core::SegmentReader;
 use crate::docset::DocSet;
+use crate::fieldnorm::FieldNormReader;
 use crate::postings::SegmentPostings;
 use crate::query::bm25::BM25Weight;
 use crate::query::explanation::does_not_match;
@@ -15,6 +16,7 @@ pub struct TermWeight {
     term: Term,
     index_record_option: IndexRecordOption,
     similarity_weight: BM25Weight,
+    scoring_enabled: bool,
 }
 
 impl Weight for TermWeight {
@@ -43,7 +45,7 @@ impl Weight for TermWeight {
         } else {
             let field = self.term.field();
             let inv_index = reader.inverted_index(field)?;
-            let term_info = inv_index.get_term_info(&self.term);
+            let term_info = inv_index.get_term_info(&self.term)?;
             Ok(term_info.map(|term_info| term_info.doc_freq).unwrap_or(0))
         }
     }
@@ -87,11 +89,13 @@ impl TermWeight {
         term: Term,
         index_record_option: IndexRecordOption,
         similarity_weight: BM25Weight,
+        scoring_enabled: bool,
     ) -> TermWeight {
         TermWeight {
             term,
             index_record_option,
             similarity_weight,
+            scoring_enabled,
         }
     }
 
@@ -102,7 +106,11 @@ impl TermWeight {
     ) -> crate::Result<TermScorer> {
         let field = self.term.field();
         let inverted_index = reader.inverted_index(field)?;
-        let fieldnorm_reader = reader.get_fieldnorms_reader(field)?;
+        let fieldnorm_reader = if self.scoring_enabled {
+            reader.get_fieldnorms_reader(field)?
+        } else {
+            FieldNormReader::constant(reader.max_doc(), 1)
+        };
         let similarity_weight = self.similarity_weight.boost_by(boost);
         let postings_opt: Option<SegmentPostings> =
             inverted_index.read_postings(&self.term, self.index_record_option)?;

src/reader/mod.rs

@@ -3,9 +3,9 @@ mod pool;
 pub use self::pool::LeasedItem;
 use self::pool::Pool;
 use crate::core::Segment;
-use crate::directory::Directory;
 use crate::directory::WatchHandle;
 use crate::directory::META_LOCK;
+use crate::directory::{Directory, WatchCallback};
 use crate::Index;
 use crate::Searcher;
 use crate::SegmentReader;
@@ -88,7 +88,7 @@ impl IndexReaderBuilder {
                 let watch_handle = inner_reader_arc
                     .index
                     .directory()
-                    .watch(Box::new(callback))?;
+                    .watch(WatchCallback::new(callback))?;
                 watch_handle_opt = Some(watch_handle);
             }
         }

src/schema/facet.rs

@@ -233,6 +233,7 @@ mod tests {
         assert_eq!(Facet::root(), Facet::from("/"));
         assert_eq!(format!("{}", Facet::root()), "/");
         assert!(Facet::root().is_root());
+        assert_eq!(Facet::root().encoded_str(), "");
     }
 
     #[test]

src/schema/named_field_document.rs

@@ -1,5 +1,5 @@
 use crate::schema::Value;
-use serde::Serialize;
+use serde::{Deserialize, Serialize};
 use std::collections::BTreeMap;
 
 /// Internal representation of a document used for JSON
@@ -8,5 +8,5 @@ use std::collections::BTreeMap;
 /// A `NamedFieldDocument` is a simple representation of a document
 /// as a `BTreeMap<String, Vec<Value>>`.
 ///
-#[derive(Serialize)]
+#[derive(Debug, Deserialize, Serialize)]
 pub struct NamedFieldDocument(pub BTreeMap<String, Vec<Value>>);

src/store/compression_lz4.rs

@@ -3,7 +3,7 @@ use std::io::{self, Read, Write};
 /// Name of the compression scheme used in the doc store.
 ///
 /// This name is appended to the version string of tantivy.
-pub const COMPRESSION: &'static str = "lz4";
+pub const COMPRESSION: &str = "lz4";
 
 pub fn compress(uncompressed: &[u8], compressed: &mut Vec<u8>) -> io::Result<()> {
     compressed.clear();

src/store/index/block.rs

@@ -0,0 +1,168 @@
+use crate::common::VInt;
+use crate::store::index::{Checkpoint, CHECKPOINT_PERIOD};
+use crate::DocId;
+use std::io;
+
+/// Represents a block of checkpoints.
+///
+/// The DocStore index checkpoints are organized into block
+/// for code-readability and compression purpose.
+///
+/// A block can be of any size.
+pub struct CheckpointBlock {
+    pub checkpoints: Vec<Checkpoint>,
+}
+
+impl Default for CheckpointBlock {
+    fn default() -> CheckpointBlock {
+        CheckpointBlock {
+            checkpoints: Vec::with_capacity(2 * CHECKPOINT_PERIOD),
+        }
+    }
+}
+
+impl CheckpointBlock {
+    /// If non-empty returns [start_doc, end_doc)
+    /// for the overall block.
+    pub fn doc_interval(&self) -> Option<(DocId, DocId)> {
+        let start_doc_opt = self
+            .checkpoints
+            .first()
+            .cloned()
+            .map(|checkpoint| checkpoint.start_doc);
+        let end_doc_opt = self
+            .checkpoints
+            .last()
+            .cloned()
+            .map(|checkpoint| checkpoint.end_doc);
+        match (start_doc_opt, end_doc_opt) {
+            (Some(start_doc), Some(end_doc)) => Some((start_doc, end_doc)),
+            _ => None,
+        }
+    }
+
+    /// Adding another checkpoint in the block.
+    pub fn push(&mut self, checkpoint: Checkpoint) {
+        if let Some(prev_checkpoint) = self.checkpoints.last() {
+            assert!(checkpoint.follows(prev_checkpoint));
+        }
+        self.checkpoints.push(checkpoint);
+    }
+
+    /// Returns the number of checkpoints in the block.
+    pub fn len(&self) -> usize {
+        self.checkpoints.len()
+    }
+
+    pub fn get(&self, idx: usize) -> Checkpoint {
+        self.checkpoints[idx]
+    }
+
+    pub fn clear(&mut self) {
+        self.checkpoints.clear();
+    }
+
+    pub fn serialize(&mut self, buffer: &mut Vec<u8>) {
+        VInt(self.checkpoints.len() as u64).serialize_into_vec(buffer);
+        if self.checkpoints.is_empty() {
+            return;
+        }
+        VInt(self.checkpoints[0].start_doc as u64).serialize_into_vec(buffer);
+        VInt(self.checkpoints[0].start_offset as u64).serialize_into_vec(buffer);
+        for checkpoint in &self.checkpoints {
+            let delta_doc = checkpoint.end_doc - checkpoint.start_doc;
+            VInt(delta_doc as u64).serialize_into_vec(buffer);
+            VInt(checkpoint.end_offset - checkpoint.start_offset).serialize_into_vec(buffer);
+        }
+    }
+
+    pub fn deserialize(&mut self, data: &mut &[u8]) -> io::Result<()> {
+        if data.is_empty() {
+            return Err(io::Error::new(io::ErrorKind::UnexpectedEof, ""));
+        }
+        self.checkpoints.clear();
+        let len = VInt::deserialize_u64(data)? as usize;
+        if len == 0 {
+            return Ok(());
+        }
+        let mut doc = VInt::deserialize_u64(data)? as DocId;
+        let mut start_offset = VInt::deserialize_u64(data)?;
+        for _ in 0..len {
+            let num_docs = VInt::deserialize_u64(data)? as DocId;
+            let block_num_bytes = VInt::deserialize_u64(data)?;
+            self.checkpoints.push(Checkpoint {
+                start_doc: doc,
+                end_doc: doc + num_docs,
+                start_offset,
+                end_offset: start_offset + block_num_bytes,
+            });
+            doc += num_docs;
+            start_offset += block_num_bytes;
+        }
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::store::index::block::CheckpointBlock;
+    use crate::store::index::Checkpoint;
+    use crate::DocId;
+    use std::io;
+
+    fn test_aux_ser_deser(checkpoints: &[Checkpoint]) -> io::Result<()> {
+        let mut block = CheckpointBlock::default();
+        for &checkpoint in checkpoints {
+            block.push(checkpoint);
+        }
+        let mut buffer = Vec::new();
+        block.serialize(&mut buffer);
+        let mut block_deser = CheckpointBlock::default();
+        let checkpoint = Checkpoint {
+            start_doc: 0,
+            end_doc: 1,
+            start_offset: 2,
+            end_offset: 3,
+        };
+        block_deser.push(checkpoint); // < check that value is erased before deser
+        let mut data = &buffer[..];
+        block_deser.deserialize(&mut data)?;
+        assert!(data.is_empty());
+        assert_eq!(checkpoints, &block_deser.checkpoints[..]);
+        Ok(())
+    }
+
+    #[test]
+    fn test_block_serialize_empty() -> io::Result<()> {
+        test_aux_ser_deser(&[])
+    }
+
+    #[test]
+    fn test_block_serialize_simple() -> io::Result<()> {
+        let checkpoints = vec![Checkpoint {
+            start_doc: 10,
+            end_doc: 12,
+            start_offset: 100,
+            end_offset: 120,
+        }];
+        test_aux_ser_deser(&checkpoints)
+    }
+
+    #[test]
+    fn test_block_serialize() -> io::Result<()> {
+        let offsets: Vec<u64> = (0..11).map(|i| i * i * i).collect();
+        let mut checkpoints = vec![];
+        let mut start_doc = 0;
+        for i in 0..10 {
+            let end_doc = (i * i) as DocId;
+            checkpoints.push(Checkpoint {
+                start_doc,
+                end_doc,
+                start_offset: offsets[i],
+                end_offset: offsets[i + 1],
+            });
+            start_doc = end_doc;
+        }
+        test_aux_ser_deser(&checkpoints)
+    }
+}

src/store/index/mod.rs

@@ -0,0 +1,274 @@
+const CHECKPOINT_PERIOD: usize = 2;
+
+use std::fmt;
+mod block;
+mod skip_index;
+mod skip_index_builder;
+
+use crate::DocId;
+
+pub use self::skip_index::SkipIndex;
+pub use self::skip_index_builder::SkipIndexBuilder;
+
+/// A checkpoint contains meta-information about
+/// a block. Either a block of documents, or another block
+/// of checkpoints.
+///
+/// All of the intervals here defined are semi-open.
+/// The checkpoint describes that the block within the bytes
+/// `[start_offset..end_offset)` spans over the docs
+/// `[start_doc..end_doc)`.
+#[derive(Clone, Copy, Eq, PartialEq)]
+pub struct Checkpoint {
+    pub start_doc: DocId,
+    pub end_doc: DocId,
+    pub start_offset: u64,
+    pub end_offset: u64,
+}
+
+impl Checkpoint {
+    pub(crate) fn follows(&self, other: &Checkpoint) -> bool {
+        (self.start_doc == other.end_doc) &&
+        (self.start_offset == other.end_offset)
+    }
+}
+
+impl fmt::Debug for Checkpoint {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(
+            f,
+            "(doc=[{}..{}), bytes=[{}..{}))",
+            self.start_doc, self.end_doc, self.start_offset, self.end_offset
+        )
+    }
+}
+
+#[cfg(test)]
+mod tests {
+
+    use std::{io, iter};
+
+    use futures::executor::block_on;
+    use proptest::strategy::{BoxedStrategy, Strategy};
+
+    use crate::directory::OwnedBytes;
+    use crate::indexer::NoMergePolicy;
+    use crate::schema::{SchemaBuilder, STORED, STRING};
+    use crate::store::index::Checkpoint;
+    use crate::{DocAddress, DocId, Index, Term};
+
+    use super::{SkipIndex, SkipIndexBuilder};
+
+    #[test]
+    fn test_skip_index_empty() -> io::Result<()> {
+        let mut output: Vec<u8> = Vec::new();
+        let skip_index_builder: SkipIndexBuilder = SkipIndexBuilder::new();
+        skip_index_builder.write(&mut output)?;
+        let skip_index: SkipIndex = SkipIndex::open(OwnedBytes::new(output));
+        let mut skip_cursor = skip_index.checkpoints();
+        assert!(skip_cursor.next().is_none());
+        Ok(())
+    }
+
+    #[test]
+    fn test_skip_index_single_el() -> io::Result<()> {
+        let mut output: Vec<u8> = Vec::new();
+        let mut skip_index_builder: SkipIndexBuilder = SkipIndexBuilder::new();
+        let checkpoint = Checkpoint {
+            start_doc: 0,
+            end_doc: 2,
+            start_offset: 0,
+            end_offset: 3,
+        };
+        skip_index_builder.insert(checkpoint);
+        skip_index_builder.write(&mut output)?;
+        let skip_index: SkipIndex = SkipIndex::open(OwnedBytes::new(output));
+        let mut skip_cursor = skip_index.checkpoints();
+        assert_eq!(skip_cursor.next(), Some(checkpoint));
+        assert_eq!(skip_cursor.next(), None);
+        Ok(())
+    }
+
+    #[test]
+    fn test_skip_index() -> io::Result<()> {
+        let mut output: Vec<u8> = Vec::new();
+        let checkpoints = vec![
+            Checkpoint {
+                start_doc: 0,
+                end_doc: 3,
+                start_offset: 4,
+                end_offset: 9,
+            },
+            Checkpoint {
+                start_doc: 3,
+                end_doc: 4,
+                start_offset: 9,
+                end_offset: 25,
+            },
+            Checkpoint {
+                start_doc: 4,
+                end_doc: 6,
+                start_offset: 25,
+                end_offset: 49,
+            },
+            Checkpoint {
+                start_doc: 6,
+                end_doc: 8,
+                start_offset: 49,
+                end_offset: 81,
+            },
+            Checkpoint {
+                start_doc: 8,
+                end_doc: 10,
+                start_offset: 81,
+                end_offset: 100,
+            },
+        ];
+
+        let mut skip_index_builder: SkipIndexBuilder = SkipIndexBuilder::new();
+        for &checkpoint in &checkpoints {
+            skip_index_builder.insert(checkpoint);
+        }
+        skip_index_builder.write(&mut output)?;
+
+        let skip_index: SkipIndex = SkipIndex::open(OwnedBytes::new(output));
+        assert_eq!(
+            &skip_index.checkpoints().collect::<Vec<_>>()[..],
+            &checkpoints[..]
+        );
+        Ok(())
+    }
+
+    fn offset_test(doc: DocId) -> u64 {
+        (doc as u64) * (doc as u64)
+    }
+
+    #[test]
+    fn test_merge_store_with_stacking_reproducing_issue969() -> crate::Result<()> {
+        let mut schema_builder = SchemaBuilder::default();
+        let text = schema_builder.add_text_field("text", STORED | STRING);
+        let body = schema_builder.add_text_field("body", STORED);
+        let schema = schema_builder.build();
+        let index = Index::create_in_ram(schema);
+        let mut index_writer = index.writer_for_tests()?;
+        index_writer.set_merge_policy(Box::new(NoMergePolicy));
+        let long_text: String = iter::repeat("abcdefghijklmnopqrstuvwxyz")
+            .take(1_000)
+            .collect();
+        for _ in 0..20 {
+            index_writer.add_document(doc!(body=>long_text.clone()));
+        }
+        index_writer.commit()?;
+        index_writer.add_document(doc!(text=>"testb"));
+        for _ in 0..10 {
+            index_writer.add_document(doc!(text=>"testd", body=>long_text.clone()));
+        }
+        index_writer.commit()?;
+        index_writer.delete_term(Term::from_field_text(text, "testb"));
+        index_writer.commit()?;
+        let segment_ids = index.searchable_segment_ids()?;
+        block_on(index_writer.merge(&segment_ids))?;
+        let reader = index.reader()?;
+        let searcher = reader.searcher();
+        assert_eq!(searcher.num_docs(), 30);
+        for i in 0..searcher.num_docs() as u32 {
+            let _doc = searcher.doc(DocAddress(0u32, i))?;
+        }
+        Ok(())
+    }
+
+    #[test]
+    fn test_skip_index_long() -> io::Result<()> {
+        let mut output: Vec<u8> = Vec::new();
+        let checkpoints: Vec<Checkpoint> = (0..1000)
+            .map(|i| Checkpoint {
+                start_doc: i,
+                end_doc: i + 1,
+                start_offset: offset_test(i),
+                end_offset: offset_test(i + 1),
+            })
+            .collect();
+        let mut skip_index_builder = SkipIndexBuilder::new();
+        for checkpoint in &checkpoints {
+            skip_index_builder.insert(*checkpoint);
+        }
+        skip_index_builder.write(&mut output)?;
+        assert_eq!(output.len(), 4035);
+        let resulting_checkpoints: Vec<Checkpoint> = SkipIndex::open(OwnedBytes::new(output))
+            .checkpoints()
+            .collect();
+        assert_eq!(&resulting_checkpoints, &checkpoints);
+        Ok(())
+    }
+
+    fn integrate_delta(mut vals: Vec<u64>) -> Vec<u64> {
+        let mut prev = 0u64;
+        for val in vals.iter_mut() {
+            let new_val = *val + prev;
+            prev = new_val;
+            *val = new_val;
+        }
+        vals
+    }
+
+    // Generates a sequence of n valid checkpoints, with n < max_len.
+    fn monotonic_checkpoints(max_len: usize) -> BoxedStrategy<Vec<Checkpoint>> {
+        (1..max_len)
+            .prop_flat_map(move |len: usize| {
+                (
+                    proptest::collection::vec(1u64..20u64, len as usize).prop_map(integrate_delta),
+                    proptest::collection::vec(1u64..26u64, len as usize).prop_map(integrate_delta),
+                )
+                    .prop_map(|(docs, offsets)| {
+                        (0..docs.len() - 1)
+                            .map(move |i| Checkpoint {
+                                start_doc: docs[i] as DocId,
+                                end_doc: docs[i + 1] as DocId,
+                                start_offset: offsets[i],
+                                end_offset: offsets[i + 1],
+                            })
+                            .collect::<Vec<Checkpoint>>()
+                    })
+            })
+            .boxed()
+    }
+
+    fn seek_manual<I: Iterator<Item = Checkpoint>>(
+        checkpoints: I,
+        target: DocId,
+    ) -> Option<Checkpoint> {
+        checkpoints
+            .into_iter()
+            .filter(|checkpoint| checkpoint.end_doc > target)
+            .next()
+    }
+
+    fn test_skip_index_aux(skip_index: SkipIndex, checkpoints: &[Checkpoint]) {
+        if let Some(last_checkpoint) = checkpoints.last() {
+            for doc in 0u32..last_checkpoint.end_doc {
+                let expected = seek_manual(skip_index.checkpoints(), doc);
+                assert_eq!(expected, skip_index.seek(doc), "Doc {}", doc);
+            }
+            assert!(skip_index.seek(last_checkpoint.end_doc).is_none());
+        }
+    }
+
+    use proptest::prelude::*;
+
+    proptest! {
+        #![proptest_config(ProptestConfig::with_cases(20))]
+        #[test]
+        fn test_proptest_skip(checkpoints in monotonic_checkpoints(100)) {
+             let mut skip_index_builder = SkipIndexBuilder::new();
+             for checkpoint in checkpoints.iter().cloned() {
+                 skip_index_builder.insert(checkpoint);
+             }
+             let mut buffer = Vec::new();
+             skip_index_builder.write(&mut buffer).unwrap();
+             let skip_index = SkipIndex::open(OwnedBytes::new(buffer));
+             let iter_checkpoints: Vec<Checkpoint> = skip_index.checkpoints().collect();
+             assert_eq!(&checkpoints[..], &iter_checkpoints[..]);
+             test_skip_index_aux(skip_index, &checkpoints[..]);
+         }
+    }
+}

src/store/index/skip_index.rs

@@ -0,0 +1,110 @@
+use crate::common::{BinarySerializable, VInt};
+use crate::directory::OwnedBytes;
+use crate::store::index::block::CheckpointBlock;
+use crate::store::index::Checkpoint;
+use crate::DocId;
+
+pub struct LayerCursor<'a> {
+    remaining: &'a [u8],
+    block: CheckpointBlock,
+    cursor: usize,
+}
+
+impl<'a> Iterator for LayerCursor<'a> {
+    type Item = Checkpoint;
+
+    fn next(&mut self) -> Option<Checkpoint> {
+        if self.cursor == self.block.len() {
+            if self.remaining.is_empty() {
+                return None;
+            }
+            let (block_mut, remaining_mut) = (&mut self.block, &mut self.remaining);
+            if block_mut.deserialize(remaining_mut).is_err() {
+                return None;
+            }
+            self.cursor = 0;
+        }
+        let res = Some(self.block.get(self.cursor));
+        self.cursor += 1;
+        res
+    }
+}
+
+struct Layer {
+    data: OwnedBytes,
+}
+
+impl Layer {
+    fn cursor<'a>(&'a self) -> impl Iterator<Item = Checkpoint> + 'a {
+        self.cursor_at_offset(0u64)
+    }
+
+    fn cursor_at_offset<'a>(&'a self, start_offset: u64) -> impl Iterator<Item = Checkpoint> + 'a {
+        let data = &self.data.as_slice();
+        LayerCursor {
+            remaining: &data[start_offset as usize..],
+            block: CheckpointBlock::default(),
+            cursor: 0,
+        }
+    }
+
+    fn seek_start_at_offset(&self, target: DocId, offset: u64) -> Option<Checkpoint> {
+        self.cursor_at_offset(offset)
+            .find(|checkpoint| checkpoint.end_doc > target)
+    }
+}
+
+pub struct SkipIndex {
+    layers: Vec<Layer>,
+}
+
+impl SkipIndex {
+    pub fn open(mut data: OwnedBytes) -> SkipIndex {
+        let offsets: Vec<u64> = Vec::<VInt>::deserialize(&mut data)
+            .unwrap()
+            .into_iter()
+            .map(|el| el.0)
+            .collect();
+        let mut start_offset = 0;
+        let mut layers = Vec::new();
+        for end_offset in offsets {
+            let layer = Layer {
+                data: data.slice(start_offset as usize, end_offset as usize),
+            };
+            layers.push(layer);
+            start_offset = end_offset;
+        }
+        SkipIndex { layers }
+    }
+
+    pub(crate) fn checkpoints<'a>(&'a self) -> impl Iterator<Item = Checkpoint> + 'a {
+        self.layers
+            .last()
+            .into_iter()
+            .flat_map(|layer| layer.cursor())
+    }
+
+    pub fn seek(&self, target: DocId) -> Option<Checkpoint> {
+        let first_layer_len = self
+            .layers
+            .first()
+            .map(|layer| layer.data.len() as u64)
+            .unwrap_or(0u64);
+        let mut cur_checkpoint = Checkpoint {
+            start_doc: 0u32,
+            end_doc: 1u32,
+            start_offset: 0u64,
+            end_offset: first_layer_len,
+        };
+        for layer in &self.layers {
+            if let Some(checkpoint) =
+                layer.seek_start_at_offset(target, cur_checkpoint.start_offset)
+            {
+                cur_checkpoint = checkpoint;
+            } else {
+                return None;
+            }
+        }
+        Some(cur_checkpoint)
+    }
+}

src/store/index/skip_index_builder.rs

@@ -0,0 +1,117 @@
+use crate::common::{BinarySerializable, VInt};
+use crate::store::index::block::CheckpointBlock;
+use crate::store::index::{Checkpoint, CHECKPOINT_PERIOD};
+use std::io;
+use std::io::Write;
+
+// Each skip contains iterator over pairs (last doc in block, offset to start of block).
+
+struct LayerBuilder {
+    buffer: Vec<u8>,
+    pub block: CheckpointBlock,
+}
+
+impl LayerBuilder {
+    fn finish(self) -> Vec<u8> {
+        self.buffer
+    }
+
+    fn new() -> LayerBuilder {
+        LayerBuilder {
+            buffer: Vec::new(),
+            block: CheckpointBlock::default(),
+        }
+    }
+
+    /// Serializes the block, and return a checkpoint representing
+    /// the entire block.
+    ///
+    /// If the block was empty to begin with, simply return None.
+    fn flush_block(&mut self) -> Option<Checkpoint> {
+        if let Some((start_doc, end_doc)) = self.block.doc_interval() {
+            let start_offset = self.buffer.len() as u64;
+            self.block.serialize(&mut self.buffer);
+            let end_offset = self.buffer.len() as u64;
+            self.block.clear();
+            Some(Checkpoint {
+                start_doc,
+                end_doc,
+                start_offset,
+                end_offset,
+            })
+        } else {
+            None
+        }
+    }
+
+    fn push(&mut self, checkpoint: Checkpoint) {
+        self.block.push(checkpoint);
+    }
+
+    fn insert(&mut self, checkpoint: Checkpoint) -> Option<Checkpoint> {
+        self.push(checkpoint);
+        let emit_skip_info = self.block.len() >= CHECKPOINT_PERIOD;
+        if emit_skip_info {
+            self.flush_block()
+        } else {
+            None
+        }
+    }
+}
+
+pub struct SkipIndexBuilder {
+    layers: Vec<LayerBuilder>,
+}
+
+impl SkipIndexBuilder {
+    pub fn new() -> SkipIndexBuilder {
+        SkipIndexBuilder { layers: Vec::new() }
+    }
+
+    fn get_layer(&mut self, layer_id: usize) -> &mut LayerBuilder {
+        if layer_id == self.layers.len() {
+            let layer_builder = LayerBuilder::new();
+            self.layers.push(layer_builder);
+        }
+        &mut self.layers[layer_id]
+    }
+
+    pub fn insert(&mut self, checkpoint: Checkpoint) {
+        let mut skip_pointer = Some(checkpoint);
+        for layer_id in 0.. {
+            if let Some(checkpoint) = skip_pointer {
+                skip_pointer = self.get_layer(layer_id).insert(checkpoint);
+            } else {
+                break;
+            }
+        }
+    }
+
+    pub fn write<W: Write>(mut self, output: &mut W) -> io::Result<()> {
+        let mut last_pointer = None;
+        for skip_layer in self.layers.iter_mut() {
+            if let Some(checkpoint) = last_pointer {
+                skip_layer.push(checkpoint);
+            }
+            last_pointer = skip_layer.flush_block();
+        }
+        let layer_buffers: Vec<Vec<u8>> = self
+            .layers
+            .into_iter()
+            .rev()
+            .map(|layer| layer.finish())
+            .collect();
+
+        let mut layer_offset = 0;
+        let mut layer_sizes = Vec::new();
+        for layer_buffer in &layer_buffers {
+            layer_offset += layer_buffer.len() as u64;
+            layer_sizes.push(VInt(layer_offset));
+        }
+        layer_sizes.serialize(output)?;
+        for layer_buffer in layer_buffers {
+            output.write_all(&layer_buffer[..])?;
+        }
+        Ok(())
+    }
+}

src/store/mod.rs

@@ -33,8 +33,8 @@ and should rely on either
 
 !*/
 
+mod index;
 mod reader;
-mod skiplist;
 mod writer;
 pub use self::reader::StoreReader;
 pub use self::writer::StoreWriter;

src/store/reader.rs

@@ -1,69 +1,91 @@
 use super::decompress;
-use super::skiplist::SkipList;
+use super::index::SkipIndex;
 use crate::common::VInt;
 use crate::common::{BinarySerializable, HasLen};
 use crate::directory::{FileSlice, OwnedBytes};
 use crate::schema::Document;
 use crate::space_usage::StoreSpaceUsage;
+use crate::store::index::Checkpoint;
 use crate::DocId;
-use std::cell::RefCell;
+use lru::LruCache;
 use std::io;
 use std::mem::size_of;
+use std::sync::atomic::{AtomicUsize, Ordering};
+use std::sync::{Arc, Mutex};
+
+const LRU_CACHE_CAPACITY: usize = 100;
+
+type Block = Arc<Vec<u8>>;
+
+type BlockCache = Arc<Mutex<LruCache<u64, Block>>>;
 
 /// Reads document off tantivy's [`Store`](./index.html)
-#[derive(Clone)]
 pub struct StoreReader {
     data: FileSlice,
-    offset_index_file: OwnedBytes,
-    current_block_offset: RefCell<usize>,
-    current_block: RefCell<Vec<u8>>,
-    max_doc: DocId,
+    cache: BlockCache,
+    cache_hits: Arc<AtomicUsize>,
+    cache_misses: Arc<AtomicUsize>,
+    skip_index: Arc<SkipIndex>,
+    space_usage: StoreSpaceUsage,
 }
 
 impl StoreReader {
     /// Opens a store reader
-    // TODO rename open
     pub fn open(store_file: FileSlice) -> io::Result<StoreReader> {
-        let (data_file, offset_index_file, max_doc) = split_file(store_file)?;
+        let (data_file, offset_index_file) = split_file(store_file)?;
+        let index_data = offset_index_file.read_bytes()?;
+        let space_usage = StoreSpaceUsage::new(data_file.len(), offset_index_file.len());
+        let skip_index = SkipIndex::open(index_data);
         Ok(StoreReader {
             data: data_file,
-            offset_index_file: offset_index_file.read_bytes()?,
-            current_block_offset: RefCell::new(usize::max_value()),
-            current_block: RefCell::new(Vec::new()),
-            max_doc,
+            cache: Arc::new(Mutex::new(LruCache::new(LRU_CACHE_CAPACITY))),
+            cache_hits: Default::default(),
+            cache_misses: Default::default(),
+            skip_index: Arc::new(skip_index),
+            space_usage,
         })
     }
 
-    pub(crate) fn block_index(&self) -> SkipList<'_, u64> {
-        SkipList::from(self.offset_index_file.as_slice())
+    pub(crate) fn block_checkpoints<'a>(&'a self) -> impl Iterator<Item = Checkpoint> + 'a {
+        self.skip_index.checkpoints()
     }
 
-    fn block_offset(&self, doc_id: DocId) -> (DocId, u64) {
-        self.block_index()
-            .seek(u64::from(doc_id) + 1)
-            .map(|(doc, offset)| (doc as DocId, offset))
-            .unwrap_or((0u32, 0u64))
+    fn block_checkpoint(&self, doc_id: DocId) -> Option<Checkpoint> {
+        self.skip_index.seek(doc_id)
     }
 
     pub(crate) fn block_data(&self) -> io::Result<OwnedBytes> {
         self.data.read_bytes()
     }
 
-    fn compressed_block(&self, addr: usize) -> io::Result<OwnedBytes> {
-        let (block_len_bytes, block_body) = self.data.slice_from(addr).split(4);
-        let block_len = u32::deserialize(&mut block_len_bytes.read_bytes()?)?;
-        block_body.slice_to(block_len as usize).read_bytes()
+    fn compressed_block(&self, checkpoint: &Checkpoint) -> io::Result<OwnedBytes> {
+        self.data
+            .slice(
+                checkpoint.start_offset as usize,
+                checkpoint.end_offset as usize,
+            )
+            .read_bytes()
     }
 
-    fn read_block(&self, block_offset: usize) -> io::Result<()> {
-        if block_offset != *self.current_block_offset.borrow() {
-            let mut current_block_mut = self.current_block.borrow_mut();
-            current_block_mut.clear();
-            let compressed_block = self.compressed_block(block_offset)?;
-            decompress(compressed_block.as_slice(), &mut current_block_mut)?;
-            *self.current_block_offset.borrow_mut() = block_offset;
+    fn read_block(&self, checkpoint: &Checkpoint) -> io::Result<Block> {
+        if let Some(block) = self.cache.lock().unwrap().get(&checkpoint.start_offset) {
+            self.cache_hits.fetch_add(1, Ordering::SeqCst);
+            return Ok(block.clone());
         }
-        Ok(())
+
+        self.cache_misses.fetch_add(1, Ordering::SeqCst);
+
+        let compressed_block = self.compressed_block(checkpoint)?;
+        let mut decompressed_block = vec![];
+        decompress(compressed_block.as_slice(), &mut decompressed_block)?;
+
+        let block = Arc::new(decompressed_block);
+        self.cache
+            .lock()
+            .unwrap()
+            .put(checkpoint.start_offset, block.clone());
+
+        Ok(block)
     }
 
     /// Reads a given document.
@@ -74,14 +96,15 @@ impl StoreReader {
     /// It should not be called to score documents
     /// for instance.
     pub fn get(&self, doc_id: DocId) -> crate::Result<Document> {
-        let (first_doc_id, block_offset) = self.block_offset(doc_id);
-        self.read_block(block_offset as usize)?;
-        let current_block_mut = self.current_block.borrow_mut();
-        let mut cursor = &current_block_mut[..];
-        for _ in first_doc_id..doc_id {
+        let checkpoint = self.block_checkpoint(doc_id).ok_or_else(|| {
+            crate::TantivyError::InvalidArgument(format!("Failed to lookup Doc #{}.", doc_id))
+        })?;
+        let mut cursor = &self.read_block(&checkpoint)?[..];
+        for _ in checkpoint.start_doc..doc_id {
             let doc_length = VInt::deserialize(&mut cursor)?.val() as usize;
             cursor = &cursor[doc_length..];
         }
+
         let doc_length = VInt::deserialize(&mut cursor)?.val() as usize;
         cursor = &cursor[..doc_length];
         Ok(Document::deserialize(&mut cursor)?)
@@ -89,21 +112,93 @@ impl StoreReader {
 
     /// Summarize total space usage of this store reader.
     pub fn space_usage(&self) -> StoreSpaceUsage {
-        StoreSpaceUsage::new(self.data.len(), self.offset_index_file.len())
+        self.space_usage.clone()
     }
 }
 
-fn split_file(data: FileSlice) -> io::Result<(FileSlice, FileSlice, DocId)> {
-    let data_len = data.len();
-    let footer_offset = data_len - size_of::<u64>() - size_of::<u32>();
-    let serialized_offset: OwnedBytes = data.slice(footer_offset, data_len).read_bytes()?;
+fn split_file(data: FileSlice) -> io::Result<(FileSlice, FileSlice)> {
+    let (data, footer_len_bytes) = data.split_from_end(size_of::<u64>());
+    let serialized_offset: OwnedBytes = footer_len_bytes.read_bytes()?;
     let mut serialized_offset_buf = serialized_offset.as_slice();
-    let offset = u64::deserialize(&mut serialized_offset_buf)?;
-    let offset = offset as usize;
-    let max_doc = u32::deserialize(&mut serialized_offset_buf)?;
-    Ok((
-        data.slice(0, offset),
-        data.slice(offset, footer_offset),
-        max_doc,
-    ))
+    let offset = u64::deserialize(&mut serialized_offset_buf)? as usize;
+    Ok(data.split(offset))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::schema::Document;
+    use crate::schema::Field;
+    use crate::{directory::RAMDirectory, store::tests::write_lorem_ipsum_store, Directory};
+    use std::path::Path;
+
+    fn get_text_field<'a>(doc: &'a Document, field: &'a Field) -> Option<&'a str> {
+        doc.get_first(*field).and_then(|f| f.text())
+    }
+
+    #[test]
+    fn test_store_lru_cache() -> crate::Result<()> {
+        let directory = RAMDirectory::create();
+        let path = Path::new("store");
+        let writer = directory.open_write(path)?;
+        let schema = write_lorem_ipsum_store(writer, 500);
+        let title = schema.get_field("title").unwrap();
+        let store_file = directory.open_read(path)?;
+        let store = StoreReader::open(store_file)?;
+
+        assert_eq!(store.cache.lock().unwrap().len(), 0);
+        assert_eq!(store.cache_hits.load(Ordering::SeqCst), 0);
+        assert_eq!(store.cache_misses.load(Ordering::SeqCst), 0);
+
+        let doc = store.get(0)?;
+        assert_eq!(get_text_field(&doc, &title), Some("Doc 0"));
+
+        assert_eq!(store.cache.lock().unwrap().len(), 1);
+        assert_eq!(store.cache_hits.load(Ordering::SeqCst), 0);
+        assert_eq!(store.cache_misses.load(Ordering::SeqCst), 1);
+        assert_eq!(
+            store
+                .cache
+                .lock()
+                .unwrap()
+                .peek_lru()
+                .map(|(&k, _)| k as usize),
+            Some(0)
+        );
+
+        let doc = store.get(499)?;
+        assert_eq!(get_text_field(&doc, &title), Some("Doc 499"));
+
+        assert_eq!(store.cache.lock().unwrap().len(), 2);
+        assert_eq!(store.cache_hits.load(Ordering::SeqCst), 0);
+        assert_eq!(store.cache_misses.load(Ordering::SeqCst), 2);
+
+        assert_eq!(
+            store
+                .cache
+                .lock()
+                .unwrap()
+                .peek_lru()
+                .map(|(&k, _)| k as usize),
+            Some(0)
+        );
+
+        let doc = store.get(0)?;
+        assert_eq!(get_text_field(&doc, &title), Some("Doc 0"));
+
+        assert_eq!(store.cache.lock().unwrap().len(), 2);
+        assert_eq!(store.cache_hits.load(Ordering::SeqCst), 1);
+        assert_eq!(store.cache_misses.load(Ordering::SeqCst), 2);
+        assert_eq!(
+            store
+                .cache
+                .lock()
+                .unwrap()
+                .peek_lru()
+                .map(|(&k, _)| k as usize),
+            Some(18806)
+        );
+
+        Ok(())
+    }
 }

src/store/skiplist/mod.rs

@@ -1,168 +0,0 @@
-#![allow(dead_code)]
-
-mod skiplist;
-mod skiplist_builder;
-
-pub use self::skiplist::SkipList;
-pub use self::skiplist_builder::SkipListBuilder;
-
-#[cfg(test)]
-mod tests {
-
-    use super::{SkipList, SkipListBuilder};
-
-    #[test]
-    fn test_skiplist() {
-        let mut output: Vec<u8> = Vec::new();
-        let mut skip_list_builder: SkipListBuilder<u32> = SkipListBuilder::new(8);
-        skip_list_builder.insert(2, &3).unwrap();
-        skip_list_builder.write::<Vec<u8>>(&mut output).unwrap();
-        let mut skip_list: SkipList<'_, u32> = SkipList::from(output.as_slice());
-        assert_eq!(skip_list.next(), Some((2, 3)));
-    }
-
-    #[test]
-    fn test_skiplist2() {
-        let mut output: Vec<u8> = Vec::new();
-        let skip_list_builder: SkipListBuilder<u32> = SkipListBuilder::new(8);
-        skip_list_builder.write::<Vec<u8>>(&mut output).unwrap();
-        let mut skip_list: SkipList<'_, u32> = SkipList::from(output.as_slice());
-        assert_eq!(skip_list.next(), None);
-    }
-
-    #[test]
-    fn test_skiplist3() {
-        let mut output: Vec<u8> = Vec::new();
-        let mut skip_list_builder: SkipListBuilder<()> = SkipListBuilder::new(2);
-        skip_list_builder.insert(2, &()).unwrap();
-        skip_list_builder.insert(3, &()).unwrap();
-        skip_list_builder.insert(5, &()).unwrap();
-        skip_list_builder.insert(7, &()).unwrap();
-        skip_list_builder.insert(9, &()).unwrap();
-        skip_list_builder.write::<Vec<u8>>(&mut output).unwrap();
-        let mut skip_list: SkipList<'_, ()> = SkipList::from(output.as_slice());
-        assert_eq!(skip_list.next().unwrap(), (2, ()));
-        assert_eq!(skip_list.next().unwrap(), (3, ()));
-        assert_eq!(skip_list.next().unwrap(), (5, ()));
-        assert_eq!(skip_list.next().unwrap(), (7, ()));
-        assert_eq!(skip_list.next().unwrap(), (9, ()));
-        assert_eq!(skip_list.next(), None);
-    }
-
-    #[test]
-    fn test_skiplist4() {
-        let mut output: Vec<u8> = Vec::new();
-        let mut skip_list_builder: SkipListBuilder<()> = SkipListBuilder::new(2);
-        skip_list_builder.insert(2, &()).unwrap();
-        skip_list_builder.insert(3, &()).unwrap();
-        skip_list_builder.insert(5, &()).unwrap();
-        skip_list_builder.insert(7, &()).unwrap();
-        skip_list_builder.insert(9, &()).unwrap();
-        skip_list_builder.write::<Vec<u8>>(&mut output).unwrap();
-        let mut skip_list: SkipList<'_, ()> = SkipList::from(output.as_slice());
-        assert_eq!(skip_list.next().unwrap(), (2, ()));
-        skip_list.seek(5);
-        assert_eq!(skip_list.next().unwrap(), (5, ()));
-        assert_eq!(skip_list.next().unwrap(), (7, ()));
-        assert_eq!(skip_list.next().unwrap(), (9, ()));
-        assert_eq!(skip_list.next(), None);
-    }
-
-    #[test]
-    fn test_skiplist5() {
-        let mut output: Vec<u8> = Vec::new();
-        let mut skip_list_builder: SkipListBuilder<()> = SkipListBuilder::new(4);
-        skip_list_builder.insert(2, &()).unwrap();
-        skip_list_builder.insert(3, &()).unwrap();
-        skip_list_builder.insert(5, &()).unwrap();
-        skip_list_builder.insert(6, &()).unwrap();
-        skip_list_builder.write::<Vec<u8>>(&mut output).unwrap();
-        let mut skip_list: SkipList<'_, ()> = SkipList::from(output.as_slice());
-        assert_eq!(skip_list.next().unwrap(), (2, ()));
-        skip_list.seek(6);
-        assert_eq!(skip_list.next().unwrap(), (6, ()));
-        assert_eq!(skip_list.next(), None);
-    }
-
-    #[test]
-    fn test_skiplist6() {
-        let mut output: Vec<u8> = Vec::new();
-        let mut skip_list_builder: SkipListBuilder<()> = SkipListBuilder::new(2);
-        skip_list_builder.insert(2, &()).unwrap();
-        skip_list_builder.insert(3, &()).unwrap();
-        skip_list_builder.insert(5, &()).unwrap();
-        skip_list_builder.insert(7, &()).unwrap();
-        skip_list_builder.insert(9, &()).unwrap();
-        skip_list_builder.write::<Vec<u8>>(&mut output).unwrap();
-        let mut skip_list: SkipList<'_, ()> = SkipList::from(output.as_slice());
-        assert_eq!(skip_list.next().unwrap(), (2, ()));
-        skip_list.seek(10);
-        assert_eq!(skip_list.next(), None);
-    }
-
-    #[test]
-    fn test_skiplist7() {
-        let mut output: Vec<u8> = Vec::new();
-        let mut skip_list_builder: SkipListBuilder<()> = SkipListBuilder::new(4);
-        for i in 0..1000 {
-            skip_list_builder.insert(i, &()).unwrap();
-        }
-        skip_list_builder.insert(1004, &()).unwrap();
-        skip_list_builder.write::<Vec<u8>>(&mut output).unwrap();
-        let mut skip_list: SkipList<'_, ()> = SkipList::from(output.as_slice());
-        assert_eq!(skip_list.next().unwrap(), (0, ()));
-        skip_list.seek(431);
-        assert_eq!(skip_list.next().unwrap(), (431, ()));
-        skip_list.seek(1003);
-        assert_eq!(skip_list.next().unwrap(), (1004, ()));
-        assert_eq!(skip_list.next(), None);
-    }
-
-    #[test]
-    fn test_skiplist8() {
-        let mut output: Vec<u8> = Vec::new();
-        let mut skip_list_builder: SkipListBuilder<u64> = SkipListBuilder::new(8);
-        skip_list_builder.insert(2, &3).unwrap();
-        skip_list_builder.write::<Vec<u8>>(&mut output).unwrap();
-        assert_eq!(output.len(), 11);
-        assert_eq!(output[0], 1u8 + 128u8);
-    }
-
-    #[test]
-    fn test_skiplist9() {
-        let mut output: Vec<u8> = Vec::new();
-        let mut skip_list_builder: SkipListBuilder<u64> = SkipListBuilder::new(4);
-        for i in 0..4 * 4 * 4 {
-            skip_list_builder.insert(i, &i).unwrap();
-        }
-        skip_list_builder.write::<Vec<u8>>(&mut output).unwrap();
-        assert_eq!(output.len(), 774);
-        assert_eq!(output[0], 4u8 + 128u8);
-    }
-
-    #[test]
-    fn test_skiplist10() {
-        // checking that void gets serialized to nothing.
-        let mut output: Vec<u8> = Vec::new();
-        let mut skip_list_builder: SkipListBuilder<()> = SkipListBuilder::new(4);
-        for i in 0..((4 * 4 * 4) - 1) {
-            skip_list_builder.insert(i, &()).unwrap();
-        }
-        skip_list_builder.write::<Vec<u8>>(&mut output).unwrap();
-        assert_eq!(output.len(), 230);
-        assert_eq!(output[0], 128u8 + 3u8);
-    }
-
-    #[test]
-    fn test_skiplist11() {
-        // checking that void gets serialized to nothing.
-        let mut output: Vec<u8> = Vec::new();
-        let mut skip_list_builder: SkipListBuilder<()> = SkipListBuilder::new(4);
-        for i in 0..(4 * 4) {
-            skip_list_builder.insert(i, &()).unwrap();
-        }
-        skip_list_builder.write::<Vec<u8>>(&mut output).unwrap();
-        assert_eq!(output.len(), 65);
-        assert_eq!(output[0], 128u8 + 3u8);
-    }
-}

src/store/skiplist/skiplist.rs

@@ -1,133 +0,0 @@
-use crate::common::{BinarySerializable, VInt};
-use std::cmp::max;
-use std::marker::PhantomData;
-
-static EMPTY: [u8; 0] = [];
-
-struct Layer<'a, T> {
-    data: &'a [u8],
-    cursor: &'a [u8],
-    next_id: Option<u64>,
-    _phantom_: PhantomData<T>,
-}
-
-impl<'a, T: BinarySerializable> Iterator for Layer<'a, T> {
-    type Item = (u64, T);
-
-    fn next(&mut self) -> Option<(u64, T)> {
-        if let Some(cur_id) = self.next_id {
-            let cur_val = T::deserialize(&mut self.cursor).unwrap();
-            self.next_id = VInt::deserialize_u64(&mut self.cursor).ok();
-            Some((cur_id, cur_val))
-        } else {
-            None
-        }
-    }
-}
-
-impl<'a, T: BinarySerializable> From<&'a [u8]> for Layer<'a, T> {
-    fn from(data: &'a [u8]) -> Layer<'a, T> {
-        let mut cursor = data;
-        let next_id = VInt::deserialize_u64(&mut cursor).ok();
-        Layer {
-            data,
-            cursor,
-            next_id,
-            _phantom_: PhantomData,
-        }
-    }
-}
-
-impl<'a, T: BinarySerializable> Layer<'a, T> {
-    fn empty() -> Layer<'a, T> {
-        Layer {
-            data: &EMPTY,
-            cursor: &EMPTY,
-            next_id: None,
-            _phantom_: PhantomData,
-        }
-    }
-
-    fn seek_offset(&mut self, offset: usize) {
-        self.cursor = &self.data[offset..];
-        self.next_id = VInt::deserialize_u64(&mut self.cursor).ok();
-    }
-
-    // Returns the last element (key, val)
-    // such that (key < doc_id)
-    //
-    // If there is no such element anymore,
-    // returns None.
-    //
-    // If the element exists, it will be returned
-    // at the next call to `.next()`.
-    fn seek(&mut self, key: u64) -> Option<(u64, T)> {
-        let mut result: Option<(u64, T)> = None;
-        loop {
-            if let Some(next_id) = self.next_id {
-                if next_id < key {
-                    if let Some(v) = self.next() {
-                        result = Some(v);
-                        continue;
-                    }
-                }
-            }
-            return result;
-        }
-    }
-}
-
-pub struct SkipList<'a, T: BinarySerializable> {
-    data_layer: Layer<'a, T>,
-    skip_layers: Vec<Layer<'a, u64>>,
-}
-
-impl<'a, T: BinarySerializable> Iterator for SkipList<'a, T> {
-    type Item = (u64, T);
-
-    fn next(&mut self) -> Option<(u64, T)> {
-        self.data_layer.next()
-    }
-}
-
-impl<'a, T: BinarySerializable> SkipList<'a, T> {
-    pub fn seek(&mut self, key: u64) -> Option<(u64, T)> {
-        let mut next_layer_skip: Option<(u64, u64)> = None;
-        for skip_layer in &mut self.skip_layers {
-            if let Some((_, offset)) = next_layer_skip {
-                skip_layer.seek_offset(offset as usize);
-            }
-            next_layer_skip = skip_layer.seek(key);
-        }
-        if let Some((_, offset)) = next_layer_skip {
-            self.data_layer.seek_offset(offset as usize);
-        }
-        self.data_layer.seek(key)
-    }
-}
-
-impl<'a, T: BinarySerializable> From<&'a [u8]> for SkipList<'a, T> {
-    fn from(mut data: &'a [u8]) -> SkipList<'a, T> {
-        let offsets: Vec<u64> = Vec::<VInt>::deserialize(&mut data)
-            .unwrap()
-            .into_iter()
-            .map(|el| el.0)
-            .collect();
-        let num_layers = offsets.len();
-        let layers_data: &[u8] = data;
-        let data_layer: Layer<'a, T> = if num_layers == 0 {
-            Layer::empty()
-        } else {
-            let first_layer_data: &[u8] = &layers_data[..offsets[0] as usize];
-            Layer::from(first_layer_data)
-        };
-        let skip_layers = (0..max(1, num_layers) - 1)
-            .map(|i| (offsets[i] as usize, offsets[i + 1] as usize))
-            .map(|(start, stop)| Layer::from(&layers_data[start..stop]))
-            .collect();
-        SkipList {
-            skip_layers,
-            data_layer,
-        }
-    }
-}

src/store/skiplist/skiplist_builder.rs

@@ -1,98 +0,0 @@
-use crate::common::{is_power_of_2, BinarySerializable, VInt};
-use std::io;
-use std::io::Write;
-use std::marker::PhantomData;
-
-struct LayerBuilder<T: BinarySerializable> {
-    period_mask: usize,
-    buffer: Vec<u8>,
-    len: usize,
-    _phantom_: PhantomData<T>,
-}
-
-impl<T: BinarySerializable> LayerBuilder<T> {
-    fn written_size(&self) -> usize {
-        self.buffer.len()
-    }
-
-    fn write(&self, output: &mut dyn Write) -> Result<(), io::Error> {
-        output.write_all(&self.buffer)?;
-        Ok(())
-    }
-
-    fn with_period(period: usize) -> LayerBuilder<T> {
-        assert!(is_power_of_2(period), "The period has to be a power of 2.");
-        LayerBuilder {
-            period_mask: (period - 1),
-            buffer: Vec::new(),
-            len: 0,
-            _phantom_: PhantomData,
-        }
-    }
-
-    fn insert(&mut self, key: u64, value: &T) -> io::Result<Option<(u64, u64)>> {
-        self.len += 1;
-        let offset = self.written_size() as u64;
-        VInt(key).serialize_into_vec(&mut self.buffer);
-        value.serialize(&mut self.buffer)?;
-        let emit_skip_info = (self.period_mask & self.len) == 0;
-        if emit_skip_info {
-            Ok(Some((key, offset)))
-        } else {
-            Ok(None)
-        }
-    }
-}
-
-pub struct SkipListBuilder<T: BinarySerializable> {
-    period: usize,
-    data_layer: LayerBuilder<T>,
-    skip_layers: Vec<LayerBuilder<u64>>,
-}
-
-impl<T: BinarySerializable> SkipListBuilder<T> {
-    pub fn new(period: usize) -> SkipListBuilder<T> {
-        SkipListBuilder {
-            period,
-            data_layer: LayerBuilder::with_period(period),
-            skip_layers: Vec::new(),
-        }
-    }
-
-    fn get_skip_layer(&mut self, layer_id: usize) -> &mut LayerBuilder<u64> {
-        if layer_id == self.skip_layers.len() {
-            let layer_builder = LayerBuilder::with_period(self.period);
-            self.skip_layers.push(layer_builder);
-        }
-        &mut self.skip_layers[layer_id]
-    }
-
-    pub fn insert(&mut self, key: u64, dest: &T) -> io::Result<()> {
-        let mut skip_pointer = self.data_layer.insert(key, dest)?;
-        for layer_id in 0.. {
-            if let Some((skip_doc_id, skip_offset)) = skip_pointer {
-                skip_pointer = self
-                    .get_skip_layer(layer_id)
-                    .insert(skip_doc_id, &skip_offset)?;
-            } else {
-                break;
-            }
-        }
-        Ok(())
-    }
-
-    pub fn write<W: Write>(self, output: &mut W) -> io::Result<()> {
-        let mut size: u64 = self.data_layer.buffer.len() as u64;
-        let mut layer_sizes = vec![VInt(size)];
-        for layer in self.skip_layers.iter().rev() {
-            size += layer.buffer.len() as u64;
-            layer_sizes.push(VInt(size));
-        }
-        layer_sizes.serialize(output)?;
-        self.data_layer.write(output)?;
-        for layer in self.skip_layers.iter().rev() {
-            layer.write(output)?;
-        }
-        Ok(())
-    }
-}

src/store/tests_store.rs

@@ -0,0 +1,50 @@
+use std::path::Path;
+
+use crate::HasLen;
+use crate::directory::{Directory, ManagedDirectory, MmapDirectory, RAMDirectory};
+use crate::fastfield::DeleteBitSet;
+
+use super::{StoreReader, StoreWriter};
+
+#[test]
+fn test_toto2() -> crate::Result<()> {
+    let directory = ManagedDirectory::wrap(MmapDirectory::open("src/store/broken_seg")?)?;
+    let path = Path::new("b6029ade1b954ea1acad15b432eaacb9.store");
+    assert!(directory.validate_checksum(path)?);
+    let store_file = directory.open_read(path)?;
+    let store = StoreReader::open(store_file)?;
+    let documents = store.documents();
+    // for doc in documents {
+    //     println!("{:?}", doc);
+    // }
+    let doc= store.get(15_086)?;
+    Ok(())
+}
+
+#[test]
+fn test_toto() -> crate::Result<()> {
+    let directory = ManagedDirectory::wrap(MmapDirectory::open("src/store/broken_seg")?)?;
+    assert!(directory.validate_checksum(Path::new("e6ece22e5bca4e0dbe7ce3e4dcbd5bbf.store"))?);
+    let store_file = directory.open_read(Path::new("e6ece22e5bca4e0dbe7ce3e4dcbd5bbf.store.patched"))?;
+    let store = StoreReader::open(store_file)?;
+    let doc= store.get(53)?;
+    println!("{:?}", doc);
+    // let documents = store.documents();
+    // let ram_directory = RAMDirectory::create();
+    // let path = Path::new("store");
+
+    // let store_wrt = ram_directory.open_write(path)?;
+    // let mut store_writer = StoreWriter::new(store_wrt);
+    // for doc in &documents {
+    //     store_writer.store(doc)?;
+    // }
+    // store_writer.close()?;
+    // let store_data = ram_directory.open_read(path)?;
+    // let new_store = StoreReader::open(store_data)?;
+    // for doc in 0..59 {
+    //     println!("{}", doc);
+    //     let doc = new_store.get(doc)?;
+    //     println!("{:?}", doc);
+    // }
+    Ok(())
+}

src/store/writer.rs

@@ -1,15 +1,16 @@
 use super::compress;
-use super::skiplist::SkipListBuilder;
+use super::index::SkipIndexBuilder;
 use super::StoreReader;
 use crate::common::CountingWriter;
 use crate::common::{BinarySerializable, VInt};
 use crate::directory::TerminatingWrite;
 use crate::directory::WritePtr;
 use crate::schema::Document;
+use crate::store::index::Checkpoint;
 use crate::DocId;
 use std::io::{self, Write};
 
-const BLOCK_SIZE: usize = 16_384;
+const BLOCK_SIZE: usize = 30;
 
 /// Write tantivy's [`Store`](./index.html)
 ///
@@ -21,7 +22,8 @@ const BLOCK_SIZE: usize = 16_384;
 ///
 pub struct StoreWriter {
     doc: DocId,
-    offset_index_writer: SkipListBuilder<u64>,
+    first_doc_in_block: DocId,
+    offset_index_writer: SkipIndexBuilder,
     writer: CountingWriter<WritePtr>,
     intermediary_buffer: Vec<u8>,
     current_block: Vec<u8>,
@@ -35,7 +37,8 @@ impl StoreWriter {
     pub fn new(writer: WritePtr) -> StoreWriter {
         StoreWriter {
             doc: 0,
-            offset_index_writer: SkipListBuilder::new(4),
+            first_doc_in_block: 0,
+            offset_index_writer: SkipIndexBuilder::new(),
             writer: CountingWriter::wrap(writer),
             intermediary_buffer: Vec::new(),
             current_block: Vec::new(),
@@ -68,11 +71,10 @@ impl StoreWriter {
     pub fn stack(&mut self, store_reader: &StoreReader) -> io::Result<()> {
         if !self.current_block.is_empty() {
             self.write_and_compress_block()?;
-            self.offset_index_writer
-                .insert(u64::from(self.doc), &(self.writer.written_bytes() as u64))?;
         }
-        let doc_offset = self.doc;
-        let start_offset = self.writer.written_bytes() as u64;
+        assert_eq!(self.first_doc_in_block, self.doc);
+        let doc_shift = self.doc;
+        let start_shift = self.writer.written_bytes() as u64;
 
         // just bulk write all of the block of the given reader.
         self.writer
@@ -80,21 +82,36 @@ impl StoreWriter {
 
         // concatenate the index of the `store_reader`, after translating
         // its start doc id and its start file offset.
-        for (next_doc_id, block_addr) in store_reader.block_index() {
-            self.doc = doc_offset + next_doc_id as u32;
-            self.offset_index_writer
-                .insert(u64::from(self.doc), &(start_offset + block_addr))?;
+        for mut checkpoint in store_reader.block_checkpoints() {
+            checkpoint.start_doc += doc_shift;
+            checkpoint.end_doc += doc_shift;
+            checkpoint.start_offset += start_shift;
+            checkpoint.end_offset += start_shift;
+            self.register_checkpoint(checkpoint);
         }
         Ok(())
     }
 
+    fn register_checkpoint(&mut self, checkpoint: Checkpoint) {
+        self.offset_index_writer.insert(checkpoint);
+        self.first_doc_in_block = checkpoint.end_doc;
+        self.doc = checkpoint.end_doc;
+    }
+
     fn write_and_compress_block(&mut self) -> io::Result<()> {
+        assert!(self.doc > 0);
         self.intermediary_buffer.clear();
         compress(&self.current_block[..], &mut self.intermediary_buffer)?;
-        (self.intermediary_buffer.len() as u32).serialize(&mut self.writer)?;
+        let start_offset = self.writer.written_bytes();
         self.writer.write_all(&self.intermediary_buffer)?;
-        self.offset_index_writer
-            .insert(u64::from(self.doc), &(self.writer.written_bytes() as u64))?;
+        let end_offset = self.writer.written_bytes();
+        let end_doc = self.doc;
+        self.register_checkpoint(Checkpoint {
+            start_doc: self.first_doc_in_block,
+            end_doc,
+            start_offset,
+            end_offset,
+        });
         self.current_block.clear();
         Ok(())
     }
@@ -110,7 +127,6 @@ impl StoreWriter {
         let header_offset: u64 = self.writer.written_bytes() as u64;
         self.offset_index_writer.write(&mut self.writer)?;
         header_offset.serialize(&mut self.writer)?;
-        self.doc.serialize(&mut self.writer)?;
         self.writer.terminate()
     }
 }

src/termdict/fst_termdict/mod.rs

@@ -0,0 +1,27 @@
+/*!
+The term dictionary main role is to associate the sorted [`Term`s](../struct.Term.html) to
+a [`TermInfo`](../postings/struct.TermInfo.html) struct that contains some meta-information
+about the term.
+
+Internally, the term dictionary relies on the `fst` crate to store
+a sorted mapping that associate each term to its rank in the lexicographical order.
+For instance, in a dictionary containing the sorted terms "abba", "bjork", "blur" and "donovan",
+the `TermOrdinal` are respectively `0`, `1`, `2`, and `3`.
+
+For `u64`-terms, tantivy explicitely uses a `BigEndian` representation to ensure that the
+lexicographical order matches the natural order of integers.
+
+`i64`-terms are transformed to `u64` using a continuous mapping `val ⟶ val - i64::min_value()`
+and then treated as a `u64`.
+
+`f64`-terms are transformed to `u64` using a mapping that preserve order, and are then treated
+as `u64`.
+
+A second datastructure makes it possible to access a [`TermInfo`](../postings/struct.TermInfo.html).
+*/
+mod streamer;
+mod term_info_store;
+mod termdict;
+
+pub use self::streamer::{TermStreamer, TermStreamerBuilder};
+pub use self::termdict::{TermDictionary, TermDictionaryBuilder};

src/termdict/fst_termdict/streamer.rs

@@ -1,3 +1,5 @@
+use std::io;
+
 use super::TermDictionary;
 use crate::postings::TermInfo;
 use crate::termdict::TermOrdinal;
@@ -59,14 +61,14 @@ where
 
     /// Creates the stream corresponding to the range
     /// of terms defined using the `TermStreamerBuilder`.
-    pub fn into_stream(self) -> TermStreamer<'a, A> {
-        TermStreamer {
+    pub fn into_stream(self) -> io::Result<TermStreamer<'a, A>> {
+        Ok(TermStreamer {
             fst_map: self.fst_map,
             stream: self.stream_builder.into_stream(),
             term_ord: 0u64,
             current_key: Vec::with_capacity(100),
             current_value: TermInfo::default(),
-        }
+        })
     }
 }
 

src/termdict/fst_termdict/term_info_store.rs

@@ -55,22 +55,32 @@ impl TermInfoBlockMeta {
         self.doc_freq_nbits + self.postings_offset_nbits + self.positions_idx_nbits
     }
 
+    // Here inner_offset is the offset within the block, WITHOUT the first term_info.
+    // In other word, term_info #1,#2,#3 gets inner_offset 0,1,2... While term_info #0
+    // is encoded without bitpacking.
     fn deserialize_term_info(&self, data: &[u8], inner_offset: usize) -> TermInfo {
+        assert!(inner_offset < BLOCK_LEN - 1);
         let num_bits = self.num_bits() as usize;
-        let mut cursor = num_bits * inner_offset;
 
-        let doc_freq = extract_bits(data, cursor, self.doc_freq_nbits) as u32;
-        cursor += self.doc_freq_nbits as usize;
+        let posting_start_addr = num_bits * inner_offset;
+        // the stop offset is the start offset of the next term info.
+        let posting_stop_addr = posting_start_addr + num_bits;
+        let doc_freq_addr = posting_start_addr + self.postings_offset_nbits as usize;
+        let positions_idx_addr = doc_freq_addr + self.doc_freq_nbits as usize;
 
-        let postings_offset = extract_bits(data, cursor, self.postings_offset_nbits);
-        cursor += self.postings_offset_nbits as usize;
-
-        let positions_idx = extract_bits(data, cursor, self.positions_idx_nbits);
+        let postings_start_offset = self.ref_term_info.postings_start_offset
+            + extract_bits(data, posting_start_addr, self.postings_offset_nbits);
+        let postings_stop_offset = self.ref_term_info.postings_start_offset
+            + extract_bits(data, posting_stop_addr, self.postings_offset_nbits);
+        let doc_freq = extract_bits(data, doc_freq_addr, self.doc_freq_nbits) as u32;
+        let positions_idx = self.ref_term_info.positions_idx
+            + extract_bits(data, positions_idx_addr, self.positions_idx_nbits);
 
         TermInfo {
             doc_freq,
-            postings_offset: postings_offset + self.ref_term_info.postings_offset,
-            positions_idx: positions_idx + self.ref_term_info.positions_idx,
+            postings_start_offset,
+            postings_stop_offset,
+            positions_idx,
         }
     }
 }
@@ -152,16 +162,17 @@ fn bitpack_serialize<W: Write>(
     term_info_block_meta: &TermInfoBlockMeta,
     term_info: &TermInfo,
 ) -> io::Result<()> {
+    bit_packer.write(
+        term_info.postings_start_offset,
+        term_info_block_meta.postings_offset_nbits,
+        write,
+    )?;
     bit_packer.write(
         u64::from(term_info.doc_freq),
         term_info_block_meta.doc_freq_nbits,
         write,
     )?;
-    bit_packer.write(
-        term_info.postings_offset,
-        term_info_block_meta.postings_offset_nbits,
-        write,
-    )?;
+
     bit_packer.write(
         term_info.positions_idx,
         term_info_block_meta.positions_idx_nbits,
@@ -181,23 +192,27 @@ impl TermInfoStoreWriter {
     }
 
     fn flush_block(&mut self) -> io::Result<()> {
-        if self.term_infos.is_empty() {
-            return Ok(());
-        }
         let mut bit_packer = BitPacker::new();
         let ref_term_info = self.term_infos[0].clone();
+
+        let last_term_info = if let Some(last_term_info) = self.term_infos.last().cloned() {
+            last_term_info
+        } else {
+            return Ok(());
+        };
+        let postings_stop_offset =
+            last_term_info.postings_stop_offset - ref_term_info.postings_start_offset;
         for term_info in &mut self.term_infos[1..] {
-            term_info.postings_offset -= ref_term_info.postings_offset;
+            term_info.postings_start_offset -= ref_term_info.postings_start_offset;
             term_info.positions_idx -= ref_term_info.positions_idx;
         }
 
         let mut max_doc_freq: u32 = 0u32;
-        let mut max_postings_offset: u64 = 0u64;
-        let mut max_positions_idx: u64 = 0u64;
+        let max_postings_offset: u64 = postings_stop_offset;
+        let max_positions_idx: u64 = last_term_info.positions_idx;
+
         for term_info in &self.term_infos[1..] {
             max_doc_freq = cmp::max(max_doc_freq, term_info.doc_freq);
-            max_postings_offset = cmp::max(max_postings_offset, term_info.postings_offset);
-            max_positions_idx = cmp::max(max_positions_idx, term_info.positions_idx);
         }
 
         let max_doc_freq_nbits: u8 = compute_num_bits(u64::from(max_doc_freq));
@@ -222,6 +237,12 @@ impl TermInfoStoreWriter {
             )?;
         }
 
+        bit_packer.write(
+            postings_stop_offset,
+            term_info_block_meta.postings_offset_nbits,
+            &mut self.buffer_term_infos,
+        )?;
+
         // Block need end up at the end of a byte.
         bit_packer.flush(&mut self.buffer_term_infos)?;
         self.term_infos.clear();
@@ -230,6 +251,7 @@ impl TermInfoStoreWriter {
     }
 
     pub fn write_term_info(&mut self, term_info: &TermInfo) -> io::Result<()> {
+        assert!(term_info.postings_stop_offset >= term_info.postings_start_offset);
         self.num_terms += 1u64;
         self.term_infos.push(term_info.clone());
         if self.term_infos.len() >= BLOCK_LEN {
@@ -289,10 +311,11 @@ mod tests {
     #[test]
     fn test_term_info_block_meta_serialization() {
         let term_info_block_meta = TermInfoBlockMeta {
-            offset: 2009,
+            offset: 2009u64,
             ref_term_info: TermInfo {
                 doc_freq: 512,
-                postings_offset: 51,
+                postings_start_offset: 51,
+                postings_stop_offset: 57u64,
                 positions_idx: 3584,
             },
             doc_freq_nbits: 10,
@@ -310,10 +333,12 @@ mod tests {
     fn test_pack() -> crate::Result<()> {
         let mut store_writer = TermInfoStoreWriter::new();
         let mut term_infos = vec![];
+        let offset = |i| (i * 13 + i * i) as u64;
         for i in 0..1000 {
             let term_info = TermInfo {
                 doc_freq: i as u32,
-                postings_offset: (i / 10) as u64,
+                postings_start_offset: offset(i),
+                postings_stop_offset: offset(i + 1),
                 positions_idx: (i * 7) as u64,
             };
             store_writer.write_term_info(&term_info)?;
@@ -323,7 +348,12 @@ mod tests {
         store_writer.serialize(&mut buffer)?;
         let term_info_store = TermInfoStore::open(FileSlice::from(buffer))?;
         for i in 0..1000 {
-            assert_eq!(term_info_store.get(i as u64), term_infos[i]);
+            assert_eq!(
+                term_info_store.get(i as u64),
+                term_infos[i],
+                "term info {}",
+                i
+            );
         }
         Ok(())
     }

src/termdict/fst_termdict/termdict.rs

@@ -80,7 +80,6 @@ where
                 .serialize(&mut counting_writer)?;
             let footer_size = counting_writer.written_bytes();
             (footer_size as u64).serialize(&mut counting_writer)?;
-            counting_writer.flush()?;
         }
         Ok(file)
     }
@@ -139,8 +138,8 @@ impl TermDictionary {
     }
 
     /// Returns the ordinal associated to a given term.
-    pub fn term_ord<K: AsRef<[u8]>>(&self, key: K) -> Option<TermOrdinal> {
-        self.fst_index.get(key)
+    pub fn term_ord<K: AsRef<[u8]>>(&self, key: K) -> io::Result<Option<TermOrdinal>> {
+        Ok(self.fst_index.get(key))
     }
 
     /// Returns the term associated to a given term ordinal.
@@ -152,7 +151,7 @@ impl TermDictionary {
     ///
     /// Regardless of whether the term is found or not,
     /// the buffer may be modified.
-    pub fn ord_to_term(&self, mut ord: TermOrdinal, bytes: &mut Vec<u8>) -> bool {
+    pub fn ord_to_term(&self, mut ord: TermOrdinal, bytes: &mut Vec<u8>) -> io::Result<bool> {
         bytes.clear();
         let fst = self.fst_index.as_fst();
         let mut node = fst.root();
@@ -167,10 +166,10 @@ impl TermDictionary {
                 let new_node_addr = transition.addr;
                 node = fst.node(new_node_addr);
             } else {
-                return false;
+                return Ok(false);
             }
         }
-        true
+        Ok(true)
     }
 
     /// Returns the number of terms in the dictionary.
@@ -179,9 +178,10 @@ impl TermDictionary {
     }
 
     /// Lookups the value corresponding to the key.
-    pub fn get<K: AsRef<[u8]>>(&self, key: K) -> Option<TermInfo> {
-        self.term_ord(key)
-            .map(|term_ord| self.term_info_from_ord(term_ord))
+    pub fn get<K: AsRef<[u8]>>(&self, key: K) -> io::Result<Option<TermInfo>> {
+        Ok(self
+            .term_ord(key)?
+            .map(|term_ord| self.term_info_from_ord(term_ord)))
     }
 
     /// Returns a range builder, to stream all of the terms
@@ -191,7 +191,7 @@ impl TermDictionary {
     }
 
     /// A stream of all the sorted terms. [See also `.stream_field()`](#method.stream_field)
-    pub fn stream(&self) -> TermStreamer<'_> {
+    pub fn stream(&self) -> io::Result<TermStreamer<'_>> {
         self.range().into_stream()
     }
 

src/termdict/merger.rs

@@ -60,12 +60,10 @@ impl<'a> TermMerger<'a> {
 
     pub(crate) fn matching_segments<'b: 'a>(
         &'b self,
-    ) -> Box<dyn 'b + Iterator<Item = (usize, TermOrdinal)>> {
-        Box::new(
-            self.current_streamers
-                .iter()
-                .map(|heap_item| (heap_item.segment_ord, heap_item.streamer.term_ord())),
-        )
+    ) -> impl 'b + Iterator<Item = (usize, TermOrdinal)> {
+        self.current_streamers
+            .iter()
+            .map(|heap_item| (heap_item.segment_ord, heap_item.streamer.term_ord()))
     }
 
     fn advance_segments(&mut self) {

src/termdict/mod.rs

@@ -20,435 +20,37 @@ as `u64`.
 A second datastructure makes it possible to access a [`TermInfo`](../postings/struct.TermInfo.html).
 */
 
+use tantivy_fst::automaton::AlwaysMatch;
+
+mod fst_termdict;
+use fst_termdict as termdict;
+
+mod merger;
+
+#[cfg(test)]
+mod tests;
+
 /// Position of the term in the sorted list of terms.
 pub type TermOrdinal = u64;
 
-mod merger;
-mod streamer;
-mod term_info_store;
-mod termdict;
+/// The term dictionary contains all of the terms in
+/// `tantivy index` in a sorted manner.
+pub type TermDictionary = self::termdict::TermDictionary;
 
-pub use self::merger::TermMerger;
-pub use self::streamer::{TermStreamer, TermStreamerBuilder};
-pub use self::termdict::{TermDictionary, TermDictionaryBuilder};
+/// Builder for the new term dictionary.
+///
+/// Inserting must be done in the order of the `keys`.
+pub type TermDictionaryBuilder<W> = self::termdict::TermDictionaryBuilder<W>;
 
-#[cfg(test)]
-mod tests {
-    use super::{TermDictionary, TermDictionaryBuilder, TermStreamer};
-    use crate::core::Index;
-    use crate::directory::{Directory, FileSlice, RAMDirectory};
-    use crate::postings::TermInfo;
-    use crate::schema::{Schema, TEXT};
-    use std::path::PathBuf;
-    use std::str;
+/// Given a list of sorted term streams,
+/// returns an iterator over sorted unique terms.
+///
+/// The item yield is actually a pair with
+/// - the term
+/// - a slice with the ordinal of the segments containing
+/// the terms.
+pub type TermMerger<'a> = self::merger::TermMerger<'a>;
 
-    const BLOCK_SIZE: usize = 1_500;
-
-    fn make_term_info(val: u64) -> TermInfo {
-        TermInfo {
-            doc_freq: val as u32,
-            positions_idx: val * 2u64,
-            postings_offset: val * 3u64,
-        }
-    }
-
-    #[test]
-    fn test_empty_term_dictionary() {
-        let empty = TermDictionary::empty();
-        assert!(empty.stream().next().is_none());
-    }
-
-    #[test]
-    fn test_term_ordinals() -> crate::Result<()> {
-        const COUNTRIES: [&'static str; 7] = [
-            "San Marino",
-            "Serbia",
-            "Slovakia",
-            "Slovenia",
-            "Spain",
-            "Sweden",
-            "Switzerland",
-        ];
-        let directory = RAMDirectory::create();
-        let path = PathBuf::from("TermDictionary");
-        {
-            let write = directory.open_write(&path)?;
-            let mut term_dictionary_builder = TermDictionaryBuilder::create(write)?;
-            for term in COUNTRIES.iter() {
-                term_dictionary_builder.insert(term.as_bytes(), &make_term_info(0u64))?;
-            }
-            term_dictionary_builder.finish()?;
-        }
-        let term_file = directory.open_read(&path)?;
-        let term_dict: TermDictionary = TermDictionary::open(term_file)?;
-        for (term_ord, term) in COUNTRIES.iter().enumerate() {
-            assert_eq!(term_dict.term_ord(term).unwrap(), term_ord as u64);
-            let mut bytes = vec![];
-            assert!(term_dict.ord_to_term(term_ord as u64, &mut bytes));
-            assert_eq!(bytes, term.as_bytes());
-        }
-        Ok(())
-    }
-
-    #[test]
-    fn test_term_dictionary_simple() -> crate::Result<()> {
-        let directory = RAMDirectory::create();
-        let path = PathBuf::from("TermDictionary");
-        {
-            let write = directory.open_write(&path)?;
-            let mut term_dictionary_builder = TermDictionaryBuilder::create(write)?;
-            term_dictionary_builder.insert("abc".as_bytes(), &make_term_info(34u64))?;
-            term_dictionary_builder.insert("abcd".as_bytes(), &make_term_info(346u64))?;
-            term_dictionary_builder.finish()?;
-        }
-        let file = directory.open_read(&path)?;
-        let term_dict: TermDictionary = TermDictionary::open(file)?;
-        assert_eq!(term_dict.get("abc").unwrap().doc_freq, 34u32);
-        assert_eq!(term_dict.get("abcd").unwrap().doc_freq, 346u32);
-        let mut stream = term_dict.stream();
-        {
-            {
-                let (k, v) = stream.next().unwrap();
-                assert_eq!(k.as_ref(), "abc".as_bytes());
-                assert_eq!(v.doc_freq, 34u32);
-            }
-            assert_eq!(stream.key(), "abc".as_bytes());
-            assert_eq!(stream.value().doc_freq, 34u32);
-        }
-        {
-            {
-                let (k, v) = stream.next().unwrap();
-                assert_eq!(k, "abcd".as_bytes());
-                assert_eq!(v.doc_freq, 346u32);
-            }
-            assert_eq!(stream.key(), "abcd".as_bytes());
-            assert_eq!(stream.value().doc_freq, 346u32);
-        }
-        assert!(!stream.advance());
-        Ok(())
-    }
-
-    #[test]
-    fn test_term_iterator() -> 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()?;
-            index_writer.add_document(doc!(text_field=>"a b d f"));
-            index_writer.commit()?;
-            index_writer.add_document(doc!(text_field=>"a b c d f"));
-            index_writer.commit()?;
-            index_writer.add_document(doc!(text_field => "e f"));
-            index_writer.commit()?;
-        }
-        let searcher = index.reader()?.searcher();
-
-        let field_searcher = searcher.field(text_field)?;
-        let mut term_it = field_searcher.terms();
-        let mut term_string = String::new();
-        while term_it.advance() {
-            //let term = Term::from_bytes(term_it.key());
-            term_string.push_str(str::from_utf8(term_it.key()).expect("test"));
-        }
-        assert_eq!(&*term_string, "abcdef");
-        Ok(())
-    }
-
-    #[test]
-    fn test_term_dictionary_stream() -> crate::Result<()> {
-        let ids: Vec<_> = (0u32..10_000u32)
-            .map(|i| (format!("doc{:0>6}", i), i))
-            .collect();
-        let buffer: Vec<u8> = {
-            let mut term_dictionary_builder = TermDictionaryBuilder::create(vec![]).unwrap();
-            for &(ref id, ref i) in &ids {
-                term_dictionary_builder
-                    .insert(id.as_bytes(), &make_term_info(*i as u64))
-                    .unwrap();
-            }
-            term_dictionary_builder.finish().unwrap()
-        };
-        let term_file = FileSlice::from(buffer);
-        let term_dictionary: TermDictionary = TermDictionary::open(term_file)?;
-        {
-            let mut streamer = term_dictionary.stream();
-            let mut i = 0;
-            while let Some((streamer_k, streamer_v)) = streamer.next() {
-                let &(ref key, ref v) = &ids[i];
-                assert_eq!(streamer_k.as_ref(), key.as_bytes());
-                assert_eq!(streamer_v, &make_term_info(*v as u64));
-                i += 1;
-            }
-        }
-
-        let &(ref key, ref val) = &ids[2047];
-        assert_eq!(
-            term_dictionary.get(key.as_bytes()),
-            Some(make_term_info(*val as u64))
-        );
-        Ok(())
-    }
-
-    #[test]
-    fn test_stream_high_range_prefix_suffix() -> crate::Result<()> {
-        let buffer: Vec<u8> = {
-            let mut term_dictionary_builder = TermDictionaryBuilder::create(vec![]).unwrap();
-            // term requires more than 16bits
-            term_dictionary_builder.insert("abcdefghijklmnopqrstuvwxy", &make_term_info(1))?;
-            term_dictionary_builder.insert("abcdefghijklmnopqrstuvwxyz", &make_term_info(2))?;
-            term_dictionary_builder.insert("abr", &make_term_info(2))?;
-            term_dictionary_builder.finish()?
-        };
-        let term_dict_file = FileSlice::from(buffer);
-        let term_dictionary: TermDictionary = TermDictionary::open(term_dict_file)?;
-        let mut kv_stream = term_dictionary.stream();
-        assert!(kv_stream.advance());
-        assert_eq!(kv_stream.key(), "abcdefghijklmnopqrstuvwxy".as_bytes());
-        assert_eq!(kv_stream.value(), &make_term_info(1));
-        assert!(kv_stream.advance());
-        assert_eq!(kv_stream.key(), "abcdefghijklmnopqrstuvwxyz".as_bytes());
-        assert_eq!(kv_stream.value(), &make_term_info(2));
-        assert!(kv_stream.advance());
-        assert_eq!(kv_stream.key(), "abr".as_bytes());
-        assert!(!kv_stream.advance());
-        Ok(())
-    }
-
-    #[test]
-    fn test_stream_range() -> crate::Result<()> {
-        let ids: Vec<_> = (0u32..10_000u32)
-            .map(|i| (format!("doc{:0>6}", i), i))
-            .collect();
-        let buffer: Vec<u8> = {
-            let mut term_dictionary_builder = TermDictionaryBuilder::create(vec![]).unwrap();
-            for &(ref id, ref i) in &ids {
-                term_dictionary_builder
-                    .insert(id.as_bytes(), &make_term_info(*i as u64))
-                    .unwrap();
-            }
-            term_dictionary_builder.finish().unwrap()
-        };
-
-        let file = FileSlice::from(buffer);
-
-        let term_dictionary: TermDictionary = TermDictionary::open(file)?;
-        {
-            for i in (0..20).chain(6000..8_000) {
-                let &(ref target_key, _) = &ids[i];
-                let mut streamer = term_dictionary
-                    .range()
-                    .ge(target_key.as_bytes())
-                    .into_stream();
-                for j in 0..3 {
-                    let (streamer_k, streamer_v) = streamer.next().unwrap();
-                    let &(ref key, ref v) = &ids[i + j];
-                    assert_eq!(str::from_utf8(streamer_k.as_ref()).unwrap(), key);
-                    assert_eq!(streamer_v.doc_freq, *v);
-                    assert_eq!(streamer_v, &make_term_info(*v as u64));
-                }
-            }
-        }
-
-        {
-            for i in (0..20).chain(BLOCK_SIZE - 10..BLOCK_SIZE + 10) {
-                let &(ref target_key, _) = &ids[i];
-                let mut streamer = term_dictionary
-                    .range()
-                    .gt(target_key.as_bytes())
-                    .into_stream();
-                for j in 0..3 {
-                    let (streamer_k, streamer_v) = streamer.next().unwrap();
-                    let &(ref key, ref v) = &ids[i + j + 1];
-                    assert_eq!(streamer_k.as_ref(), key.as_bytes());
-                    assert_eq!(streamer_v.doc_freq, *v);
-                }
-            }
-        }
-
-        {
-            for i in (0..20).chain(BLOCK_SIZE - 10..BLOCK_SIZE + 10) {
-                for j in 0..3 {
-                    let &(ref fst_key, _) = &ids[i];
-                    let &(ref last_key, _) = &ids[i + j];
-                    let mut streamer = term_dictionary
-                        .range()
-                        .ge(fst_key.as_bytes())
-                        .lt(last_key.as_bytes())
-                        .into_stream();
-                    for _ in 0..j {
-                        assert!(streamer.next().is_some());
-                    }
-                    assert!(streamer.next().is_none());
-                }
-            }
-        }
-        Ok(())
-    }
-
-    #[test]
-    fn test_empty_string() -> crate::Result<()> {
-        let buffer: Vec<u8> = {
-            let mut term_dictionary_builder = TermDictionaryBuilder::create(vec![]).unwrap();
-            term_dictionary_builder
-                .insert(&[], &make_term_info(1 as u64))
-                .unwrap();
-            term_dictionary_builder
-                .insert(&[1u8], &make_term_info(2 as u64))
-                .unwrap();
-            term_dictionary_builder.finish().unwrap()
-        };
-        let file = FileSlice::from(buffer);
-        let term_dictionary: TermDictionary = TermDictionary::open(file)?;
-        let mut stream = term_dictionary.stream();
-        assert!(stream.advance());
-        assert!(stream.key().is_empty());
-        assert!(stream.advance());
-        assert_eq!(stream.key(), &[1u8]);
-        assert!(!stream.advance());
-        Ok(())
-    }
-
-    #[test]
-    fn test_stream_range_boundaries() -> crate::Result<()> {
-        let buffer: Vec<u8> = {
-            let mut term_dictionary_builder = TermDictionaryBuilder::create(Vec::new())?;
-            for i in 0u8..10u8 {
-                let number_arr = [i; 1];
-                term_dictionary_builder.insert(&number_arr, &make_term_info(i as u64))?;
-            }
-            term_dictionary_builder.finish()?
-        };
-        let file = FileSlice::from(buffer);
-        let term_dictionary: TermDictionary = TermDictionary::open(file)?;
-
-        let value_list = |mut streamer: TermStreamer<'_>, backwards: bool| {
-            let mut res: Vec<u32> = vec![];
-            while let Some((_, ref v)) = streamer.next() {
-                res.push(v.doc_freq);
-            }
-            if backwards {
-                res.reverse();
-            }
-            res
-        };
-        {
-            let range = term_dictionary.range().backward().into_stream();
-            assert_eq!(
-                value_list(range, true),
-                vec![0u32, 1u32, 2u32, 3u32, 4u32, 5u32, 6u32, 7u32, 8u32, 9u32]
-            );
-        }
-        {
-            let range = term_dictionary.range().ge([2u8]).into_stream();
-            assert_eq!(
-                value_list(range, false),
-                vec![2u32, 3u32, 4u32, 5u32, 6u32, 7u32, 8u32, 9u32]
-            );
-        }
-        {
-            let range = term_dictionary.range().ge([2u8]).backward().into_stream();
-            assert_eq!(
-                value_list(range, true),
-                vec![2u32, 3u32, 4u32, 5u32, 6u32, 7u32, 8u32, 9u32]
-            );
-        }
-        {
-            let range = term_dictionary.range().gt([2u8]).into_stream();
-            assert_eq!(
-                value_list(range, false),
-                vec![3u32, 4u32, 5u32, 6u32, 7u32, 8u32, 9u32]
-            );
-        }
-        {
-            let range = term_dictionary.range().gt([2u8]).backward().into_stream();
-            assert_eq!(
-                value_list(range, true),
-                vec![3u32, 4u32, 5u32, 6u32, 7u32, 8u32, 9u32]
-            );
-        }
-        {
-            let range = term_dictionary.range().lt([6u8]).into_stream();
-            assert_eq!(
-                value_list(range, false),
-                vec![0u32, 1u32, 2u32, 3u32, 4u32, 5u32]
-            );
-        }
-        {
-            let range = term_dictionary.range().lt([6u8]).backward().into_stream();
-            assert_eq!(
-                value_list(range, true),
-                vec![0u32, 1u32, 2u32, 3u32, 4u32, 5u32]
-            );
-        }
-        {
-            let range = term_dictionary.range().le([6u8]).into_stream();
-            assert_eq!(
-                value_list(range, false),
-                vec![0u32, 1u32, 2u32, 3u32, 4u32, 5u32, 6u32]
-            );
-        }
-        {
-            let range = term_dictionary.range().le([6u8]).backward().into_stream();
-            assert_eq!(
-                value_list(range, true),
-                vec![0u32, 1u32, 2u32, 3u32, 4u32, 5u32, 6u32]
-            );
-        }
-        {
-            let range = term_dictionary.range().ge([0u8]).lt([5u8]).into_stream();
-            assert_eq!(value_list(range, false), vec![0u32, 1u32, 2u32, 3u32, 4u32]);
-        }
-        {
-            let range = term_dictionary
-                .range()
-                .ge([0u8])
-                .lt([5u8])
-                .backward()
-                .into_stream();
-            assert_eq!(value_list(range, true), vec![0u32, 1u32, 2u32, 3u32, 4u32]);
-        }
-        Ok(())
-    }
-
-    #[test]
-    fn test_automaton_search() -> crate::Result<()> {
-        use crate::query::DFAWrapper;
-        use levenshtein_automata::LevenshteinAutomatonBuilder;
-
-        const COUNTRIES: [&'static str; 7] = [
-            "San Marino",
-            "Serbia",
-            "Slovakia",
-            "Slovenia",
-            "Spain",
-            "Sweden",
-            "Switzerland",
-        ];
-
-        let directory = RAMDirectory::create();
-        let path = PathBuf::from("TermDictionary");
-        {
-            let write = directory.open_write(&path)?;
-            let mut term_dictionary_builder = TermDictionaryBuilder::create(write)?;
-            for term in COUNTRIES.iter() {
-                term_dictionary_builder.insert(term.as_bytes(), &make_term_info(0u64))?;
-            }
-            term_dictionary_builder.finish()?;
-        }
-        let file = directory.open_read(&path)?;
-        let term_dict: TermDictionary = TermDictionary::open(file)?;
-
-        // We can now build an entire dfa.
-        let lev_automaton_builder = LevenshteinAutomatonBuilder::new(2, true);
-        let automaton = DFAWrapper(lev_automaton_builder.build_dfa("Spaen"));
-
-        let mut range = term_dict.search(automaton).into_stream();
-
-        // get the first finding
-        assert!(range.advance());
-        assert_eq!("Spain".as_bytes(), range.key());
-        assert!(!range.advance());
-        Ok(())
-    }
-}
+/// `TermStreamer` acts as a cursor over a range of terms of a segment.
+/// Terms are guaranteed to be sorted.
+pub type TermStreamer<'a, A = AlwaysMatch> = self::termdict::TermStreamer<'a, A>;

src/termdict/tests.rs

@@ -0,0 +1,431 @@
+use super::{TermDictionary, TermDictionaryBuilder, TermStreamer};
+
+use crate::directory::{Directory, FileSlice, RAMDirectory, TerminatingWrite};
+use crate::postings::TermInfo;
+
+use std::path::PathBuf;
+use std::str;
+
+const BLOCK_SIZE: usize = 1_500;
+
+fn make_term_info(term_ord: u64) -> TermInfo {
+    let offset = |term_ord: u64| term_ord * 100 + term_ord * term_ord;
+    TermInfo {
+        doc_freq: term_ord as u32,
+        postings_start_offset: offset(term_ord),
+        postings_stop_offset: offset(term_ord + 1),
+        positions_idx: offset(term_ord) * 2u64,
+    }
+}
+
+#[test]
+fn test_empty_term_dictionary() {
+    let empty = TermDictionary::empty();
+    assert!(empty.stream().unwrap().next().is_none());
+}
+
+#[test]
+fn test_term_ordinals() -> crate::Result<()> {
+    const COUNTRIES: [&'static str; 7] = [
+        "San Marino",
+        "Serbia",
+        "Slovakia",
+        "Slovenia",
+        "Spain",
+        "Sweden",
+        "Switzerland",
+    ];
+    let directory = RAMDirectory::create();
+    let path = PathBuf::from("TermDictionary");
+    {
+        let write = directory.open_write(&path)?;
+        let mut term_dictionary_builder = TermDictionaryBuilder::create(write)?;
+        for term in COUNTRIES.iter() {
+            term_dictionary_builder.insert(term.as_bytes(), &make_term_info(0u64))?;
+        }
+        term_dictionary_builder.finish()?.terminate()?;
+    }
+    let term_file = directory.open_read(&path)?;
+    let term_dict: TermDictionary = TermDictionary::open(term_file)?;
+    for (term_ord, term) in COUNTRIES.iter().enumerate() {
+        assert_eq!(term_dict.term_ord(term)?, Some(term_ord as u64));
+        let mut bytes = vec![];
+        assert!(term_dict.ord_to_term(term_ord as u64, &mut bytes)?);
+        assert_eq!(bytes, term.as_bytes());
+    }
+    Ok(())
+}
+
+#[test]
+fn test_term_dictionary_simple() -> crate::Result<()> {
+    let directory = RAMDirectory::create();
+    let path = PathBuf::from("TermDictionary");
+    {
+        let write = directory.open_write(&path)?;
+        let mut term_dictionary_builder = TermDictionaryBuilder::create(write)?;
+        term_dictionary_builder.insert("abc".as_bytes(), &make_term_info(34u64))?;
+        term_dictionary_builder.insert("abcd".as_bytes(), &make_term_info(346u64))?;
+        term_dictionary_builder.finish()?.terminate()?;
+    }
+    let file = directory.open_read(&path)?;
+    let term_dict: TermDictionary = TermDictionary::open(file)?;
+    assert_eq!(term_dict.get("abc")?.unwrap().doc_freq, 34u32);
+    assert_eq!(term_dict.get("abcd")?.unwrap().doc_freq, 346u32);
+    let mut stream = term_dict.stream()?;
+    {
+        {
+            let (k, v) = stream.next().unwrap();
+            assert_eq!(k.as_ref(), "abc".as_bytes());
+            assert_eq!(v.doc_freq, 34u32);
+        }
+        assert_eq!(stream.key(), "abc".as_bytes());
+        assert_eq!(stream.value().doc_freq, 34u32);
+    }
+    {
+        {
+            let (k, v) = stream.next().unwrap();
+            assert_eq!(k, "abcd".as_bytes());
+            assert_eq!(v.doc_freq, 346u32);
+        }
+        assert_eq!(stream.key(), "abcd".as_bytes());
+        assert_eq!(stream.value().doc_freq, 346u32);
+    }
+    assert!(!stream.advance());
+    Ok(())
+}
+
+#[test]
+fn test_term_dictionary_stream() -> crate::Result<()> {
+    let ids: Vec<_> = (0u32..10_000u32)
+        .map(|i| (format!("doc{:0>6}", i), i))
+        .collect();
+    let buffer: Vec<u8> = {
+        let mut term_dictionary_builder = TermDictionaryBuilder::create(vec![]).unwrap();
+        for &(ref id, ref i) in &ids {
+            term_dictionary_builder
+                .insert(id.as_bytes(), &make_term_info(*i as u64))
+                .unwrap();
+        }
+        term_dictionary_builder.finish()?
+    };
+    let term_file = FileSlice::from(buffer);
+    let term_dictionary: TermDictionary = TermDictionary::open(term_file)?;
+    {
+        let mut streamer = term_dictionary.stream()?;
+        let mut i = 0;
+        while let Some((streamer_k, streamer_v)) = streamer.next() {
+            let &(ref key, ref v) = &ids[i];
+            assert_eq!(streamer_k.as_ref(), key.as_bytes());
+            assert_eq!(streamer_v, &make_term_info(*v as u64));
+            i += 1;
+        }
+    }
+
+    let &(ref key, ref val) = &ids[2047];
+    assert_eq!(
+        term_dictionary.get(key.as_bytes())?,
+        Some(make_term_info(*val as u64))
+    );
+    Ok(())
+}
+
+#[test]
+fn test_stream_high_range_prefix_suffix() -> crate::Result<()> {
+    let buffer: Vec<u8> = {
+        let mut term_dictionary_builder = TermDictionaryBuilder::create(vec![]).unwrap();
+        // term requires more than 16bits
+        term_dictionary_builder.insert("abcdefghijklmnopqrstuvwxy", &make_term_info(1))?;
+        term_dictionary_builder.insert("abcdefghijklmnopqrstuvwxyz", &make_term_info(2))?;
+        term_dictionary_builder.insert("abr", &make_term_info(3))?;
+        term_dictionary_builder.finish()?
+    };
+    let term_dict_file = FileSlice::from(buffer);
+    let term_dictionary: TermDictionary = TermDictionary::open(term_dict_file)?;
+    let mut kv_stream = term_dictionary.stream()?;
+    assert!(kv_stream.advance());
+    assert_eq!(kv_stream.key(), "abcdefghijklmnopqrstuvwxy".as_bytes());
+    assert_eq!(kv_stream.value(), &make_term_info(1));
+    assert!(kv_stream.advance());
+    assert_eq!(kv_stream.key(), "abcdefghijklmnopqrstuvwxyz".as_bytes());
+    assert_eq!(kv_stream.value(), &make_term_info(2));
+    assert!(kv_stream.advance());
+    assert_eq!(kv_stream.key(), "abr".as_bytes());
+    assert_eq!(kv_stream.value(), &make_term_info(3));
+    assert!(!kv_stream.advance());
+    Ok(())
+}
+
+#[test]
+fn test_stream_range() -> crate::Result<()> {
+    let ids: Vec<_> = (0u32..10_000u32)
+        .map(|i| (format!("doc{:0>6}", i), i))
+        .collect();
+    let buffer: Vec<u8> = {
+        let mut term_dictionary_builder = TermDictionaryBuilder::create(vec![]).unwrap();
+        for &(ref id, ref i) in &ids {
+            term_dictionary_builder
+                .insert(id.as_bytes(), &make_term_info(*i as u64))
+                .unwrap();
+        }
+        term_dictionary_builder.finish()?
+    };
+
+    let file = FileSlice::from(buffer);
+
+    let term_dictionary: TermDictionary = TermDictionary::open(file)?;
+    {
+        for i in (0..20).chain(6000..8_000) {
+            let &(ref target_key, _) = &ids[i];
+            let mut streamer = term_dictionary
+                .range()
+                .ge(target_key.as_bytes())
+                .into_stream()?;
+            for j in 0..3 {
+                let (streamer_k, streamer_v) = streamer.next().unwrap();
+                let &(ref key, ref v) = &ids[i + j];
+                assert_eq!(str::from_utf8(streamer_k.as_ref()).unwrap(), key);
+                assert_eq!(streamer_v.doc_freq, *v);
+                assert_eq!(streamer_v, &make_term_info(*v as u64));
+            }
+        }
+    }
+
+    {
+        for i in (0..20).chain(BLOCK_SIZE - 10..BLOCK_SIZE + 10) {
+            let &(ref target_key, _) = &ids[i];
+            let mut streamer = term_dictionary
+                .range()
+                .gt(target_key.as_bytes())
+                .into_stream()?;
+            for j in 0..3 {
+                let (streamer_k, streamer_v) = streamer.next().unwrap();
+                let &(ref key, ref v) = &ids[i + j + 1];
+                assert_eq!(streamer_k.as_ref(), key.as_bytes());
+                assert_eq!(streamer_v.doc_freq, *v);
+            }
+        }
+    }
+
+    {
+        for i in (0..20).chain(BLOCK_SIZE - 10..BLOCK_SIZE + 10) {
+            for j in 0..3 {
+                let &(ref fst_key, _) = &ids[i];
+                let &(ref last_key, _) = &ids[i + j];
+                let mut streamer = term_dictionary
+                    .range()
+                    .ge(fst_key.as_bytes())
+                    .lt(last_key.as_bytes())
+                    .into_stream()?;
+                for _ in 0..j {
+                    assert!(streamer.next().is_some());
+                }
+                assert!(streamer.next().is_none());
+            }
+        }
+    }
+    Ok(())
+}
+
+#[test]
+fn test_empty_string() -> crate::Result<()> {
+    let buffer: Vec<u8> = {
+        let mut term_dictionary_builder = TermDictionaryBuilder::create(vec![]).unwrap();
+        term_dictionary_builder
+            .insert(&[], &make_term_info(1 as u64))
+            .unwrap();
+        term_dictionary_builder
+            .insert(&[1u8], &make_term_info(2 as u64))
+            .unwrap();
+        term_dictionary_builder.finish()?
+    };
+    let file = FileSlice::from(buffer);
+    let term_dictionary: TermDictionary = TermDictionary::open(file)?;
+    let mut stream = term_dictionary.stream()?;
+    assert!(stream.advance());
+    assert!(stream.key().is_empty());
+    assert!(stream.advance());
+    assert_eq!(stream.key(), &[1u8]);
+    assert!(!stream.advance());
+    Ok(())
+}
+
+fn stream_range_test_dict() -> crate::Result<TermDictionary> {
+    let buffer: Vec<u8> = {
+        let mut term_dictionary_builder = TermDictionaryBuilder::create(Vec::new())?;
+        for i in 0u8..10u8 {
+            let number_arr = [i; 1];
+            term_dictionary_builder.insert(&number_arr, &make_term_info(i as u64))?;
+        }
+        term_dictionary_builder.finish()?
+    };
+    let file = FileSlice::from(buffer);
+    TermDictionary::open(file)
+}
+
+#[test]
+fn test_stream_range_boundaries_forward() -> crate::Result<()> {
+    let term_dictionary = stream_range_test_dict()?;
+    let value_list = |mut streamer: TermStreamer<'_>| {
+        let mut res: Vec<u32> = vec![];
+        while let Some((_, ref v)) = streamer.next() {
+            res.push(v.doc_freq);
+        }
+        res
+    };
+    {
+        let range = term_dictionary.range().ge([2u8]).into_stream()?;
+        assert_eq!(
+            value_list(range),
+            vec![2u32, 3u32, 4u32, 5u32, 6u32, 7u32, 8u32, 9u32]
+        );
+    }
+    {
+        let range = term_dictionary.range().gt([2u8]).into_stream()?;
+        assert_eq!(
+            value_list(range),
+            vec![3u32, 4u32, 5u32, 6u32, 7u32, 8u32, 9u32]
+        );
+    }
+    {
+        let range = term_dictionary.range().lt([6u8]).into_stream()?;
+        assert_eq!(value_list(range), vec![0u32, 1u32, 2u32, 3u32, 4u32, 5u32]);
+    }
+    {
+        let range = term_dictionary.range().le([6u8]).into_stream()?;
+        assert_eq!(
+            value_list(range),
+            vec![0u32, 1u32, 2u32, 3u32, 4u32, 5u32, 6u32]
+        );
+    }
+    {
+        let range = term_dictionary.range().ge([0u8]).lt([5u8]).into_stream()?;
+        assert_eq!(value_list(range), vec![0u32, 1u32, 2u32, 3u32, 4u32]);
+    }
+    Ok(())
+}
+
+#[test]
+fn test_stream_range_boundaries_backward() -> crate::Result<()> {
+    let term_dictionary = stream_range_test_dict()?;
+    let value_list_backward = |mut streamer: TermStreamer<'_>| {
+        let mut res: Vec<u32> = vec![];
+        while let Some((_, ref v)) = streamer.next() {
+            res.push(v.doc_freq);
+        }
+        res.reverse();
+        res
+    };
+    {
+        let range = term_dictionary.range().backward().into_stream()?;
+        assert_eq!(
+            value_list_backward(range),
+            vec![0u32, 1u32, 2u32, 3u32, 4u32, 5u32, 6u32, 7u32, 8u32, 9u32]
+        );
+    }
+    {
+        let range = term_dictionary.range().ge([2u8]).backward().into_stream()?;
+        assert_eq!(
+            value_list_backward(range),
+            vec![2u32, 3u32, 4u32, 5u32, 6u32, 7u32, 8u32, 9u32]
+        );
+    }
+    {
+        let range = term_dictionary.range().gt([2u8]).backward().into_stream()?;
+        assert_eq!(
+            value_list_backward(range),
+            vec![3u32, 4u32, 5u32, 6u32, 7u32, 8u32, 9u32]
+        );
+    }
+    {
+        let range = term_dictionary.range().lt([6u8]).backward().into_stream()?;
+        assert_eq!(
+            value_list_backward(range),
+            vec![0u32, 1u32, 2u32, 3u32, 4u32, 5u32]
+        );
+    }
+    {
+        let range = term_dictionary.range().le([6u8]).backward().into_stream()?;
+        assert_eq!(
+            value_list_backward(range),
+            vec![0u32, 1u32, 2u32, 3u32, 4u32, 5u32, 6u32]
+        );
+    }
+    {
+        let range = term_dictionary
+            .range()
+            .ge([0u8])
+            .lt([5u8])
+            .backward()
+            .into_stream()?;
+        assert_eq!(
+            value_list_backward(range),
+            vec![0u32, 1u32, 2u32, 3u32, 4u32]
+        );
+    }
+    Ok(())
+}
+
+#[test]
+fn test_ord_to_term() -> crate::Result<()> {
+    let termdict = stream_range_test_dict()?;
+    let mut bytes = vec![];
+    for b in 0u8..10u8 {
+        termdict.ord_to_term(b as u64, &mut bytes)?;
+        assert_eq!(&bytes, &[b]);
+    }
+    Ok(())
+}
+
+#[test]
+fn test_stream_term_ord() -> crate::Result<()> {
+    let termdict = stream_range_test_dict()?;
+    let mut stream = termdict.stream()?;
+    for b in 0u8..10u8 {
+        assert!(stream.advance(), true);
+        assert_eq!(stream.term_ord(), b as u64);
+        assert_eq!(stream.key(), &[b]);
+    }
+    assert!(!stream.advance());
+    Ok(())
+}
+
+#[test]
+fn test_automaton_search() -> crate::Result<()> {
+    use crate::query::DFAWrapper;
+    use levenshtein_automata::LevenshteinAutomatonBuilder;
+
+    const COUNTRIES: [&'static str; 7] = [
+        "San Marino",
+        "Serbia",
+        "Slovakia",
+        "Slovenia",
+        "Spain",
+        "Sweden",
+        "Switzerland",
+    ];
+
+    let directory = RAMDirectory::create();
+    let path = PathBuf::from("TermDictionary");
+    {
+        let write = directory.open_write(&path)?;
+        let mut term_dictionary_builder = TermDictionaryBuilder::create(write)?;
+        for term in COUNTRIES.iter() {
+            term_dictionary_builder.insert(term.as_bytes(), &make_term_info(0u64))?;
+        }
+        term_dictionary_builder.finish()?.terminate()?;
+    }
+    let file = directory.open_read(&path)?;
+    let term_dict: TermDictionary = TermDictionary::open(file)?;
+
+    // We can now build an entire dfa.
+    let lev_automaton_builder = LevenshteinAutomatonBuilder::new(2, true);
+    let automaton = DFAWrapper(lev_automaton_builder.build_dfa("Spaen"));
+
+    let mut range = term_dict.search(automaton).into_stream()?;
+
+    // get the first finding
+    assert!(range.advance());
+    assert_eq!("Spain".as_bytes(), range.key());
+    assert!(!range.advance());
+    Ok(())
+}

tests/failpoints/mod.rs

@@ -18,7 +18,7 @@ fn test_failpoints_managed_directory_gc_if_delete_fails() {
         .unwrap()
         .terminate()
         .unwrap();
-    assert!(managed_directory.exists(test_path));
+    assert!(managed_directory.exists(test_path).unwrap());
     // triggering gc and setting the delete operation to fail.
     //
     // We are checking that the gc operation is not removing the
@@ -29,12 +29,12 @@ fn test_failpoints_managed_directory_gc_if_delete_fails() {
     // lock file.
     fail::cfg("RAMDirectory::delete", "1*off->1*return").unwrap();
     assert!(managed_directory.garbage_collect(Default::default).is_ok());
-    assert!(managed_directory.exists(test_path));
+    assert!(managed_directory.exists(test_path).unwrap());
 
     // running the gc a second time should remove the file.
     assert!(managed_directory.garbage_collect(Default::default).is_ok());
     assert!(
-        !managed_directory.exists(test_path),
+        !managed_directory.exists(test_path).unwrap(),
         "The file should have been deleted"
     );
 }