Removed redundant check

Closes #997
Merge pull request #996 from lpouget/facet-optional-storage-and-index
2025-12-31 14:32:54 +00:00 · 2021-03-25 14:17:06 +09:00 · 2021-03-25 09:08:36 +09:00 · 2021-03-24 14:56:27 +01:00 · 2021-03-23 18:43:49 +09:00 · 2021-03-23 00:10:46 +09:00
61 changed files with 1353 additions and 515 deletions
--- a/ARCHITECTURE.md
+++ b/ARCHITECTURE.md
@@ -0,0 +1,297 @@
+# Tantivy
+
+## What is tantivy?
+
+Tantivy is a library that is meant to build search engines. Although it is by no mean a port of Lucene, its architecture is strongly inspired by it. If you are familiar with Lucene, you may be struck by the overlapping vocabulary.
+This is not fortuitous.
+
+Tantivy's bread and butter is to address the problem of full-text search :
+
+Given a large set of textual documents, and a text query, return the K-most relevant documents in a very efficient way. In order to execute these queries rapidly, the tantivy need to build an index beforehand. The relevance score implemented in the tantivy is not configurable. Tantivy uses the same score as the default similarity used in Lucene / Elasticsearch, called [BM25](https://en.wikipedia.org/wiki/Okapi_BM25).
+
+But tantivy's scope does not stop there. Numerous features are required to power rich search applications. For instance, one may want to:
+- compute the count of documents matching a query in the different section of an e-commerce website,
+- display an average price per meter square for a real estate search engine,
+- take in account historical user data to rank documents in a specific way,
+- or even use tantivy to power an OLAP database.
+
+A more abstract description of the problem space tantivy is trying to address is the following.
+
+Ingest a large set of documents, create an index that makes it possible to
+rapidly select all documents matching a given predicate (also known as a query) and
+collect some information about them (See collector).
+
+Roughly speaking the design is following these guiding principles:
+- Search should be O(1) in memory.
+- Indexing should be O(1) in memory. (In practise it is just sublinear)
+- Search should be as fast as possible
+
+This comes at the cost of the dynamicity of the index : while it is possible to add, and delete documents from our corpus, the tantivy is designed to handle these updates in large batches.
+
+## [core/](src/core): Index, segments, searchers.
+
+Core contains all of the high level code to make it possible for to create an index, add documents, delete documents and commit.
+
+This is both the most high-level part of tantivy, the least performance sensitive one, the seemingly most mundane code... And paradoxically the most complicated part.
+
+### Index and Segments...
+
+A tantivy index is in fact a collection of smaller independent immutable segments.
+Each segment contains its own independent set of datastructures.
+
+A segment is identified by a segment id that is in fact a UUID.
+The file of a segment has the format
+
+ ```segment-id . ext ```
+
+The extension signals which datastructure (or [`SegmentComponent`](src/core/segment_component.rs)) is stored in the file.
+
+A small `meta.json` file is in charge keeping track of the list of segments, as well as the schema.
+
+On commit, one segment per indexing thread is written to disk, and the `meta.json` is then updated atomically.
+
+For a better idea of how indexing works, you may read the [following blog post](https://fulmicoton.com/posts/behold-tantivy-part2/).
+
+
+### Deletes
+
+Deletes happen by deleting a "term". Tantivy does not offer any notion of primary id, so it is up to the user to use a field in their schema as if it was a primary id, and delete the associated term if they want to delete only one specific document.
+
+On commit, tantivy will find all of the segments with documents matching this existing term and create a [tombstone file](src/fastfield/delete.rs) that represents the bitset of the document that are deleted.
+Like all segment files, this file is immutable. Because it is possible to have more than one tombstone file at a given instant, the tombstone filename has the format ``` segment_id . commit_opstamp . del```.
+
+An opstamp is simply an incremental id that identifies any operation applied to the index. For instance, performing a commit or adding a document.
+
+
+### DocId
+
+Within a segment, all documents are identified by a DocId that ranges within `[0, max_doc)`.
+where max doc is the number of documents in the segment, (deleted or not). Having such a compact `DocId` space is key to the compression of our datastructures.
+
+The DocIds are simply allocated in the order documents are added to the index.
+
+### Merges
+
+In separate threads, tantivy's index writer search for opportunities to merge segments.
+The point of segment merges is to:
+- eventually get rid of tombstoned documents
+- reduce the otherwise evergrowing number of segments.
+
+Indeed, while having several segments instead of one does not hurt search too much, having hundreds can have a measurable impact on the search performance.
+
+### Searcher
+
+The user of the library usually does not need to know about the existence of Segments.
+Searching is done through an object called a [`Searcher`](src/core/searcher.rs), that captures a
+snapshot of the index at one point of time, by holding a list of [SegmentReader](src/core/segment_reader.rs).
+
+In other words, regardless of commits, file garbage collection, or segment merge that might happen, as long as the user holds and reuse the same [Searcher](src/core/searcher.rs), search will happen on an immutable snapshot of the index.
+
+## [directory/](src/directory): Where should the data be stored?
+
+Tantivy, like Lucene, abstracts the place where the data should be stored in a key-trait
+called [`Directory`](src/directory/directory.rs).
+Contrary to Lucene however, "files" are quite different from some kind of `io::Read` object.
+Check out [`src/directory/directory.rs`](src/directory/directory.rs) trait for more details.
+
+Tantivy ships two main directory implementation: the `MMapDirectory` and the `RAMDirectory`,
+but users can extend tantivy with their own implementation.
+
+## [schema/](src/schema): What are documents?
+
+Tantivy's document follow a very strict schema , decided before building any index.
+
+The schema defines all of the fields that the indexes [`Document`](src/schema/document.rs) may and should contain, their types (`text`, `i64`, `u64`, `Date`, ...) as well as how it should be indexed / represented in tantivy.
+
+Depending on the type of the field, you can decide to
+- put it in the docstore
+- store it as a fast field
+- index it
+
+Practically, tantivy will push values associated to this type to up to 3 respective
+datastructures.
+
+*Limitations*
+
+As of today, tantivy's schema impose a 1:1 relationship between a field that is being ingested and a field represented in the search index. In sophisticated search application, it is fairly common to want to index a field twice using different tokenizers, or to index the concatenation of several fields together into one field.
+
+This is not something tantivy supports, and it is up to the user to duplicate field / concatenate fields before feeding them to tantivy.
+
+## General information about these datastructures.
+
+All datastructures in tantivy, have:
+- a writer
+- a serializer
+- a reader
+
+The writer builds a in-memory representation of a batch of documents. This representation is not searchable. It is just meant as intermediary mutable representation, to which we can sequentially add
+the document of a batch. At the end of the batch (or if a memory limit is reached), this representation
+is then converted in an on-disk immutable representation, that is extremely compact.
+This conversion is done by the serializer.
+
+Finally, the reader is in charge of offering an API to read on this on-disk read-only representation.
+In tantivy, readers are designed to require very little anonymous memory. The data is read straight from an mmapped file, and loading an index is as fast as mmapping its files.
+
+## [store/](src/store): Here is my DocId, Gimme my document!
+
+The docstore is a row-oriented storage that, for each documents, stores a subset of the fields
+that are marked as stored in the schema. The docstore is compressed using a general purpose algorithm
+like LZ4.
+
+**Useful for**
+
+In search engines, it is often used to display search results.
+Once the top 10 documents have been identified, we fetch them from the store, and display them or their snippet on the search result page (aka SERP).
+
+**Not useful for**
+
+Fetching a document from the store is typically a "slow" operation. It usually consists in
+- searching into a compact tree-like datastructure to find the position of the right block.
+- decompressing a small block
+- returning the document from this block.
+
+It is NOT meant to be called for every document matching a query.
+
+As a rule of thumb, if you hit the docstore more than 100 times per search query, you are probably misusing tantivy.
+
+
+## [fastfield/](src/fastfield): Here is my DocId, Gimme my value!
+
+Fast fields are stored in a column-oriented storage that allows for random access.
+The only compression applied is bitpacking. The column comes with two meta data.
+The minimum value in the column and the number of bits per doc.
+
+Fetching a value for a `DocId` is then as simple as computing
+
+```
+min_value + fetch_bits(num_bits * doc_id..num_bits * (doc_id+1))
+```
+
+This operation just requires one memory fetch.
+Because, DocSets are scanned through in order (DocId are iterated in a sorted manner) which
+also help locality.
+
+In Lucene's jargon, fast fields are called DocValues.
+
+**Useful for**
+
+They are typically integer values that are useful to either rank or compute aggregate over
+all of the documents matching a query (aka [DocSet](src/docset.rs)).
+
+For instance, one could define a function to combine upvotes with tantivy's internal relevancy score.
+This can be done by fetching a fast field during scoring.
+Once could also compute the mean price of the items matching a query in an e-commerce website.
+This can be done by fetching a fast field in a collector.
+Finally one could decide to post filter a docset to remove docset with a price within a specific range.
+If the ratio of filtered out documents is not too low, an efficient way to do this is to fetch the price, and apply the filter on the collector side.
+
+Aside from integer values, it is also possible to store an actual byte payload.
+For advanced search engine, it is possible to store all of the features required for learning-to-rank in a byte payload, access it during search, and apply the learning-to-rank model.
+
+Finally facets are a specific kind of fast field, and the associated source code is in [`fastfield/facet_reader.rs`](src/fastfield/facet_reader.rs).
+
+# The inverted search index.
+
+The inverted index is the core part of full-text search.
+When presented a new document with the text field "Hello, happy tax payer!", tantivy breaks it into a list of so-called token. In addition to just splitting this strings into tokens, it might also do different kind of operations like dropping the punctuation, converting the character to lowercase, apply stemming etc. Tantivy makes it possible to configure the operations to be applied in the schema
+(tokenizer/ is the place where these operations are implemented).
+
+For instance, the default tokenizer of tantivy would break our text into: `[hello, happy, tax, payer]`.
+The document will therefore be registered in the inverted index as containing the terms
+`[text:hello, text:happy, text:tax, text:payer]`.
+
+The role of the inverted index is, when given a term, supply us with a very fast iterator over
+the sorted doc ids that match the term.
+
+Such an iterator is called a posting list. In addition to giving us `DocId`, they can also give us optionally to the number of occurrence of the term for each document, also called term frequency or TF.
+
+These iterators being sorted by DocId, one can create an iterator over the document containing `text:tax AND text:payer`, `(text:tax AND text:payer) OR (text:contribuable)` or any boolean expression.
+
+In order to represent the function
+```Term ⟶ Posting```
+
+The inverted index actually consists of two datastructures chained together.
+
+- [Term](src/schema/term.rs) ⟶ [TermInfo](src/postings/term_info.rs) is addressed by the term dictionary.
+- [TermInfo](src/postings/term_info.rs) ⟶ [Posting](src/postings/postings.rs) is addressed by the posting lists.
+
+Where [TermInfo](src/postings/term_info.rs) is an object containing some meta data about a term.
+
+
+## [termdict/](src/termdict): Here is a term, give me the [TermInfo](src/postings/term_info.rs)!
+
+Tantivy's term dictionary is mainly in charge of supplying the function
+
+[Term](src/schema/term.rs) ⟶ [TermInfo](src/postings/term_info.rs)
+
+It is itself is broken into two parts.
+- [Term](src/schema/term.rs) ⟶ [TermOrdinal](src/termdict/mod.rs) is addressed by a finite state transducer, implemented by the fst crate.
+- [TermOrdinal](src/termdict/mod.rs) ⟶ [TermInfo](src/postings/term_info.rs) is addressed by the term info store.
+
+
+## [postings/](src/postings): Iterate over documents... very fast!
+
+A posting list makes it possible to store a sorted list of doc ids and for each doc store
+a term frequency as well.
+
+The posting list are stored in a separate file. The [TermInfo](src/postings/term_info.rs) contains an offset into that file and a number of documents for the given posting list. Both are required and sufficient to read the posting list.
+
+The posting list is organized in block of 128 documents.
+One block of doc ids is followed by one block of term frequencies.
+
+The doc ids are delta encoded and bitpacked.
+The term frequencies are bitpacked.
+
+Because the number of docs is rarely a multiple of 128, the last block my contain an arbitrary number of docs between 1 and 127 documents. We then use variable int encoding instead of bitpacking.
+
+## [positions/](src/positions): Where are my terms within the documents?
+
+Phrase queries make it possible to search for documents containing a specific sequence of document.
+For instance, when the phrase query "the art of war" does not match "the war of art".
+To make it possible, it is possible to specify in the schema that a field should store positions in addition to being indexed.
+
+The token positions of all of the terms are then stored in a separate file with the extension `.pos`.
+The [TermInfo](src/postings/term_info.rs) gives an offset (expressed in position this time) in this file. As we iterate throught the docset,
+we advance the position reader by the number of term frequencies of the current document.
+
+## [fieldnorms/](src/fieldnorms): Here is my doc, how many tokens in this field?
+
+The [BM25](https://en.wikipedia.org/wiki/Okapi_BM25) formula also requires to know the number of tokens stored in a specific field for a given document. We store this information on one byte per document in the fieldnorm.
+The fieldnorm is therefore compressed. Values up to 40 are encoded unchanged. There is then a logarithmic mapping that
+
+
+## [tokenizer/](src/tokenizer): How should we process text?
+
+Text processing is key to a good search experience.
+Splits or normalize your text too much, and the search results will have a less precision and a higher recall.
+Do not normalize, or under split your text, you will end up with a higher precision and a lesser recall.
+
+Text processing can be configured by selecting an off-the-shelf [`Tokenizer`](./src/tokenizer/tokenizer.rs) or implementing your own to first split the text into tokens, and then chain different [`TokenFilter`](src/tokenizer/tokenizer.rs)'s to it.
+
+Tantivy's comes with few tokenizers, but external crates are offering advanced tokenizers, such as [Lindera](https://crates.io/crates/lindera) for Japanese.
+
+
+## [query/](src/query): Define and compose queries
+
+The [Query](src/query/query.rs) trait defines what a query is.
+Due to the necessity for some query to compute some statistics over the entire index, and because the
+index is composed of several `SegmentReader`, the path from transforming a `Query` to a iterator over document is slightly convoluted, but fundamentally, this is what a Query is.
+
+The iterator over a document comes with some scoring function. The resulting trait is called a
+[Scorer](src/query/scorer.rs) and is specific to a segment.
+
+Different queries can be combined using the [BooleanQuery](src/query/boolean_query/).
+Tantivy comes with different types of queries, and can be extended by implementing
+the Query`, `Weight` and `Scorer` traits.
+
+## [collector](src/collector): Define what to do with matched documents
+
+Collectors define how to aggregate the documents matching a query, in the broadest sense possible.
+The search will push matched document one by one, calling their
+`fn collect(doc: DocId, score: Score);` method.
+
+Users may implement their own collectors by implementing the [Collector](src/collector/mod.rs) trait.
+
+## [query-grammar](query-grammar): Defines the grammar of the query parser
+
+While the [QueryParser](src/query/query_parser/query_parser.rs) struct is located in the `query/` directory, the actual parser combinator used to convert user queries into an AST is in an external crate called `query-grammar`. This part was externalize to lighten the work of the compiler.
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,11 @@
+Tantivy 0.15.0
+=========================
+- API Changes. Using Range instead of (start, end) in the API and internals (`FileSlice`, `OwnedBytes`, `Snippets`, ...)
+  This change is breaking but migration is trivial.
+- Added an Histogram collector. (@fulmicoton) #994
+- Added support for Option<TCollector>.  (@fulmicoton) 
+
+
 Tantivy 0.14.0
 =========================
 - Remove dependency to atomicwrites #833 .Implemented by @fulmicoton upon suggestion and research from @asafigan).
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -48,6 +48,7 @@ chrono = "0.4"
 smallvec = "1"
 rayon = "1"
 lru = "0.6"
+fastdivide = "0.3"

 [target.'cfg(windows)'.dependencies]
 winapi = "0.3"
@@ -56,7 +57,7 @@ winapi = "0.3"
 rand = "0.8"
 maplit = "1"
 matches = "0.1.8"
-proptest = "0.10"
+proptest = "1.0"
 criterion = "0.3"

 [dev-dependencies.fail]
--- a/examples/faceted_search.rs
+++ b/examples/faceted_search.rs
@@ -23,7 +23,7 @@ fn main() -> tantivy::Result<()> {

    let name = schema_builder.add_text_field("felin_name", TEXT | STORED);
    // this is our faceted field: its scientific classification
-    let classification = schema_builder.add_facet_field("classification");
+    let classification = schema_builder.add_facet_field("classification", INDEXED);

    let schema = schema_builder.build();
    let index = Index::create_in_ram(schema);
--- a/examples/faceted_search_with_tweaked_score.rs
+++ b/examples/faceted_search_with_tweaked_score.rs
@@ -9,7 +9,7 @@ fn main() -> tantivy::Result<()> {
    let mut schema_builder = Schema::builder();

    let title = schema_builder.add_text_field("title", STORED);
-    let ingredient = schema_builder.add_facet_field("ingredient");
+    let ingredient = schema_builder.add_facet_field("ingredient", INDEXED);

    let schema = schema_builder.build();
    let index = Index::create_in_ram(schema.clone());
--- a/examples/iterating_docs_and_positions.rs
+++ b/examples/iterating_docs_and_positions.rs
@@ -1,4 +1,4 @@
-// # Iterating docs and positioms.
+// # Iterating docs and positions.
 //
 // At its core of tantivy, relies on a data structure
 // called an inverted index.
--- a/examples/pre_tokenized_text.rs
+++ b/examples/pre_tokenized_text.rs
@@ -1,6 +1,6 @@
 // # Pre-tokenized text example
 //
-// This example shows how to use pre-tokenized text. Sometimes yout might
+// This example shows how to use pre-tokenized text. Sometimes you might
 // want to index and search through text which is already split into
 // tokens by some external tool.
 //
--- a/examples/snippet.rs
+++ b/examples/snippet.rs
@@ -69,12 +69,12 @@ fn highlight(snippet: Snippet) -> String {
    let mut result = String::new();
    let mut start_from = 0;

-    for (start, end) in snippet.highlighted().iter().map(|h| h.bounds()) {
-        result.push_str(&snippet.fragments()[start_from..start]);
+    for fragment_range in snippet.highlighted() {
+        result.push_str(&snippet.fragments()[start_from..fragment_range.start]);
        result.push_str(" --> ");
-        result.push_str(&snippet.fragments()[start..end]);
+        result.push_str(&snippet.fragments()[fragment_range.clone()]);
        result.push_str(" <-- ");
-        start_from = end;
+        start_from = fragment_range.end;
    }

    result.push_str(&snippet.fragments()[start_from..]);
--- a/src/collector/custom_score_top_collector.rs
+++ b/src/collector/custom_score_top_collector.rs
@@ -58,9 +58,7 @@ where
        segment_local_id: u32,
        segment_reader: &SegmentReader,
    ) -> crate::Result<Self::Child> {
-        let segment_collector = self
-            .collector
-            .for_segment(segment_local_id, segment_reader)?;
+        let segment_collector = self.collector.for_segment(segment_local_id, segment_reader);
        let segment_scorer = self.custom_scorer.segment_scorer(segment_reader)?;
        Ok(CustomScoreTopSegmentCollector {
            segment_collector,
--- a/src/collector/facet_collector.rs
+++ b/src/collector/facet_collector.rs
@@ -12,8 +12,8 @@ use std::collections::btree_map;
 use std::collections::BTreeMap;
 use std::collections::BTreeSet;
 use std::collections::BinaryHeap;
-use std::collections::Bound;
 use std::iter::Peekable;
+use std::ops::Bound;
 use std::{u64, usize};

 struct Hit<'a> {
@@ -80,7 +80,7 @@ fn facet_depth(facet_bytes: &[u8]) -> usize {
 /// ```rust
 /// use tantivy::collector::FacetCollector;
 /// use tantivy::query::AllQuery;
-/// use tantivy::schema::{Facet, Schema, TEXT};
+/// use tantivy::schema::{Facet, Schema, INDEXED, TEXT};
 /// use tantivy::{doc, Index};
 ///
 /// fn example() -> tantivy::Result<()> {
@@ -89,7 +89,7 @@ fn facet_depth(facet_bytes: &[u8]) -> usize {
 ///     // Facet have their own specific type.
 ///     // It is not a bad practise to put all of your
 ///     // facet information in the same field.
-///     let facet = schema_builder.add_facet_field("facet");
+///     let facet = schema_builder.add_facet_field("facet", INDEXED);
 ///     let title = schema_builder.add_text_field("title", TEXT);
 ///     let schema = schema_builder.build();
 ///     let index = Index::create_in_ram(schema);
@@ -461,7 +461,7 @@ mod tests {
    use crate::collector::Count;
    use crate::core::Index;
    use crate::query::{AllQuery, QueryParser, TermQuery};
-    use crate::schema::{Document, Facet, Field, IndexRecordOption, Schema};
+    use crate::schema::{Document, Facet, Field, IndexRecordOption, Schema, INDEXED};
    use crate::Term;
    use rand::distributions::Uniform;
    use rand::prelude::SliceRandom;
@@ -471,7 +471,7 @@ mod tests {
    #[test]
    fn test_facet_collector_drilldown() {
        let mut schema_builder = Schema::builder();
-        let facet_field = schema_builder.add_facet_field("facet");
+        let facet_field = schema_builder.add_facet_field("facet", INDEXED);
        let schema = schema_builder.build();
        let index = Index::create_in_ram(schema);

@@ -531,7 +531,7 @@ mod tests {
    #[test]
    fn test_doc_unsorted_multifacet() {
        let mut schema_builder = Schema::builder();
-        let facet_field = schema_builder.add_facet_field("facets");
+        let facet_field = schema_builder.add_facet_field("facets", INDEXED);
        let schema = schema_builder.build();
        let index = Index::create_in_ram(schema);
        let mut index_writer = index.writer_for_tests().unwrap();
@@ -555,7 +555,7 @@ mod tests {
    #[test]
    fn test_doc_search_by_facet() -> crate::Result<()> {
        let mut schema_builder = Schema::builder();
-        let facet_field = schema_builder.add_facet_field("facet");
+        let facet_field = schema_builder.add_facet_field("facet", INDEXED);
        let schema = schema_builder.build();
        let index = Index::create_in_ram(schema);
        let mut index_writer = index.writer_for_tests()?;
@@ -612,7 +612,7 @@ mod tests {
    #[test]
    fn test_facet_collector_topk() {
        let mut schema_builder = Schema::builder();
-        let facet_field = schema_builder.add_facet_field("facet");
+        let facet_field = schema_builder.add_facet_field("facet", INDEXED);
        let schema = schema_builder.build();
        let index = Index::create_in_ram(schema);

@@ -664,7 +664,7 @@ mod bench {

    use crate::collector::FacetCollector;
    use crate::query::AllQuery;
-    use crate::schema::{Facet, Schema};
+    use crate::schema::{Facet, Schema, INDEXED};
    use crate::Index;
    use rand::seq::SliceRandom;
    use rand::thread_rng;
@@ -673,7 +673,7 @@ mod bench {
    #[bench]
    fn bench_facet_collector(b: &mut Bencher) {
        let mut schema_builder = Schema::builder();
-        let facet_field = schema_builder.add_facet_field("facet");
+        let facet_field = schema_builder.add_facet_field("facet", INDEXED);
        let schema = schema_builder.build();
        let index = Index::create_in_ram(schema);

--- a/src/collector/filter_collector_wrapper.rs
+++ b/src/collector/filter_collector_wrapper.rs
@@ -56,11 +56,11 @@ use crate::{Score, SegmentReader, TantivyError};
 /// ```
 pub struct FilterCollector<TCollector, TPredicate, TPredicateValue: FastValue>
 where
-    TPredicate: 'static,
+    TPredicate: 'static + Clone,
 {
    field: Field,
    collector: TCollector,
-    predicate: &'static TPredicate,
+    predicate: TPredicate,
    t_predicate_value: PhantomData<TPredicateValue>,
 }

@@ -68,12 +68,12 @@ impl<TCollector, TPredicate, TPredicateValue: FastValue>
    FilterCollector<TCollector, TPredicate, TPredicateValue>
 where
    TCollector: Collector + Send + Sync,
-    TPredicate: Fn(TPredicateValue) -> bool + Send + Sync,
+    TPredicate: Fn(TPredicateValue) -> bool + Send + Sync + Clone,
 {
    /// Create a new FilterCollector.
    pub fn new(
        field: Field,
-        predicate: &'static TPredicate,
+        predicate: TPredicate,
        collector: TCollector,
    ) -> FilterCollector<TCollector, TPredicate, TPredicateValue> {
        FilterCollector {
@@ -89,8 +89,8 @@ 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,
+    TPredicate: 'static + Fn(TPredicateValue) -> bool + Send + Sync + Clone,
+    TPredicateValue: FastValue,
 {
    // That's the type of our result.
    // Our standard deviation will be a float.
@@ -133,7 +133,7 @@ where
        Ok(FilterSegmentCollector {
            fast_field_reader,
            segment_collector,
-            predicate: self.predicate,
+            predicate: self.predicate.clone(),
            t_predicate_value: PhantomData,
        })
    }
@@ -153,11 +153,11 @@ where
 pub struct FilterSegmentCollector<TSegmentCollector, TPredicate, TPredicateValue>
 where
    TPredicate: 'static,
-    TPredicateValue: 'static + FastValue,
+    TPredicateValue: FastValue,
 {
    fast_field_reader: FastFieldReader<TPredicateValue>,
    segment_collector: TSegmentCollector,
-    predicate: &'static TPredicate,
+    predicate: TPredicate,
    t_predicate_value: PhantomData<TPredicateValue>,
 }

@@ -166,7 +166,7 @@ impl<TSegmentCollector, TPredicate, TPredicateValue> SegmentCollector
 where
    TSegmentCollector: SegmentCollector,
    TPredicate: 'static + Fn(TPredicateValue) -> bool + Send + Sync,
-    TPredicateValue: 'static + FastValue,
+    TPredicateValue: FastValue,
 {
    type Fruit = TSegmentCollector::Fruit;

--- a/src/collector/histogram_collector.rs
+++ b/src/collector/histogram_collector.rs
@@ -0,0 +1,291 @@
+use crate::collector::{Collector, SegmentCollector};
+use crate::fastfield::{FastFieldReader, FastValue};
+use crate::schema::{Field, Type};
+use crate::{DocId, Score};
+use fastdivide::DividerU64;
+
+/// Histogram builds an histogram of the values of a fastfield for the
+/// collected DocSet.
+///
+/// At construction, it is given parameters that define a partition of an interval
+/// [min_val, max_val) into N buckets with the same width.
+/// The ith bucket is then defined by `[min_val + i * bucket_width, min_val + (i+1) * bucket_width)`
+///
+/// An histogram is then defined as a `Vec<u64>` of length `num_buckets`, that contains a count of
+/// documents for each value bucket.
+///
+/// See also [`HistogramCollector::new()`].
+///
+/// # Warning
+///
+/// f64 field. are not supported.
+#[derive(Clone)]
+pub struct HistogramCollector {
+    min_value: u64,
+    num_buckets: usize,
+    divider: DividerU64,
+    field: Field,
+}
+
+impl HistogramCollector {
+    /// Builds a new HistogramCollector.
+    ///
+    /// The scale/range of the histogram is not dynamic. It is required to
+    /// define it by supplying following parameter:
+    ///  - `min_value`: the minimum value that can be recorded in the histogram.
+    ///  - `bucket_width`: the length of the interval that is associated to each buckets.
+    ///  - `num_buckets`: The overall number of buckets.
+    ///
+    /// Together, this parameters define a partition of `[min_value, min_value + num_buckets * bucket_width)`
+    /// into `num_buckets` intervals of width bucket that we call `bucket`.
+    ///
+    /// # Disclaimer
+    /// This function panics if the field given is of type f64.
+    pub fn new<TFastValue: FastValue>(
+        field: Field,
+        min_value: TFastValue,
+        bucket_width: u64,
+        num_buckets: usize,
+    ) -> HistogramCollector {
+        let fast_type = TFastValue::to_type();
+        assert!(fast_type == Type::U64 || fast_type == Type::I64 || fast_type == Type::Date);
+        HistogramCollector {
+            min_value: min_value.to_u64(),
+            num_buckets,
+            field,
+            divider: DividerU64::divide_by(bucket_width),
+        }
+    }
+}
+
+struct HistogramComputer {
+    counts: Vec<u64>,
+    min_value: u64,
+    divider: DividerU64,
+}
+
+impl HistogramComputer {
+    #[inline]
+    pub(crate) fn add_value(&mut self, value: u64) {
+        if value < self.min_value {
+            return;
+        }
+        let delta = value - self.min_value;
+        let delta_u64 = delta.to_u64();
+        let bucket_id: usize = self.divider.divide(delta_u64) as usize;
+        if bucket_id < self.counts.len() {
+            self.counts[bucket_id] += 1;
+        }
+    }
+
+    fn harvest(self) -> Vec<u64> {
+        self.counts
+    }
+}
+pub struct SegmentHistogramCollector {
+    histogram_computer: HistogramComputer,
+    ff_reader: FastFieldReader<u64>,
+}
+
+impl SegmentCollector for SegmentHistogramCollector {
+    type Fruit = Vec<u64>;
+
+    fn collect(&mut self, doc: DocId, _score: Score) {
+        let value = self.ff_reader.get(doc);
+        self.histogram_computer.add_value(value);
+    }
+
+    fn harvest(self) -> Self::Fruit {
+        self.histogram_computer.harvest()
+    }
+}
+
+impl Collector for HistogramCollector {
+    type Fruit = Vec<u64>;
+    type Child = SegmentHistogramCollector;
+
+    fn for_segment(
+        &self,
+        _segment_local_id: crate::SegmentLocalId,
+        segment: &crate::SegmentReader,
+    ) -> crate::Result<Self::Child> {
+        let ff_reader = segment.fast_fields().u64_lenient(self.field)?;
+        Ok(SegmentHistogramCollector {
+            histogram_computer: HistogramComputer {
+                counts: vec![0; self.num_buckets],
+                min_value: self.min_value,
+                divider: self.divider,
+            },
+            ff_reader,
+        })
+    }
+
+    fn requires_scoring(&self) -> bool {
+        false
+    }
+
+    fn merge_fruits(&self, child_histograms: Vec<Vec<u64>>) -> crate::Result<Vec<u64>> {
+        Ok(add_vecs(child_histograms, self.num_buckets))
+    }
+}
+
+pub fn add_arrays_into(acc: &mut [u64], add: &[u64]) {
+    assert_eq!(acc.len(), add.len());
+    for (dest_bucket, bucket_count) in acc.iter_mut().zip(add) {
+        *dest_bucket += bucket_count;
+    }
+}
+
+fn add_vecs(mut vals_list: Vec<Vec<u64>>, len: usize) -> Vec<u64> {
+    let mut acc = vals_list.pop().unwrap_or_else(|| vec![0u64; len]);
+    assert_eq!(acc.len(), len);
+    for vals in vals_list {
+        add_arrays_into(&mut acc, &vals);
+    }
+    acc
+}
+
+#[cfg(test)]
+mod tests {
+    use super::{add_vecs, HistogramCollector, HistogramComputer};
+    use crate::chrono::{TimeZone, Utc};
+    use crate::schema::{Schema, FAST};
+    use crate::{doc, query, Index};
+    use fastdivide::DividerU64;
+    use query::AllQuery;
+
+    #[test]
+    fn test_add_histograms_simple() {
+        assert_eq!(
+            add_vecs(vec![vec![1, 0, 3], vec![11, 2, 3], vec![0, 0, 1]], 3),
+            vec![12, 2, 7]
+        )
+    }
+
+    #[test]
+    fn test_add_histograms_empty() {
+        assert_eq!(add_vecs(vec![], 3), vec![0, 0, 0])
+    }
+
+    #[test]
+    fn test_histogram_builder_simple() {
+        // [1..3)
+        // [3..5)
+        // ..
+        // [9..11)
+        let mut histogram_computer = HistogramComputer {
+            counts: vec![0; 5],
+            min_value: 1,
+            divider: DividerU64::divide_by(2),
+        };
+        histogram_computer.add_value(1);
+        histogram_computer.add_value(7);
+        assert_eq!(histogram_computer.harvest(), vec![1, 0, 0, 1, 0]);
+    }
+
+    #[test]
+    fn test_histogram_too_low_is_ignored() {
+        let mut histogram_computer = HistogramComputer {
+            counts: vec![0; 5],
+            min_value: 2,
+            divider: DividerU64::divide_by(2),
+        };
+        histogram_computer.add_value(0);
+        assert_eq!(histogram_computer.harvest(), vec![0, 0, 0, 0, 0]);
+    }
+
+    #[test]
+    fn test_histogram_too_high_is_ignored() {
+        let mut histogram_computer = HistogramComputer {
+            counts: vec![0u64; 5],
+            min_value: 0,
+            divider: DividerU64::divide_by(2),
+        };
+        histogram_computer.add_value(10);
+        assert_eq!(histogram_computer.harvest(), vec![0, 0, 0, 0, 0]);
+    }
+    #[test]
+    fn test_no_segments() -> crate::Result<()> {
+        let mut schema_builder = Schema::builder();
+        let val_field = schema_builder.add_u64_field("val_field", FAST);
+        let schema = schema_builder.build();
+        let index = Index::create_in_ram(schema);
+        let reader = index.reader()?;
+        let searcher = reader.searcher();
+        let all_query = AllQuery;
+        let histogram_collector = HistogramCollector::new(val_field, 0u64, 2, 5);
+        let histogram = searcher.search(&all_query, &histogram_collector)?;
+        assert_eq!(histogram, vec![0; 5]);
+        Ok(())
+    }
+
+    #[test]
+    fn test_histogram_i64() -> crate::Result<()> {
+        let mut schema_builder = Schema::builder();
+        let val_field = schema_builder.add_i64_field("val_field", FAST);
+        let schema = schema_builder.build();
+        let index = Index::create_in_ram(schema);
+        let mut writer = index.writer_with_num_threads(1, 4_000_000)?;
+        writer.add_document(doc!(val_field=>12i64));
+        writer.add_document(doc!(val_field=>-30i64));
+        writer.add_document(doc!(val_field=>-12i64));
+        writer.add_document(doc!(val_field=>-10i64));
+        writer.commit()?;
+        let reader = index.reader()?;
+        let searcher = reader.searcher();
+        let all_query = AllQuery;
+        let histogram_collector = HistogramCollector::new(val_field, -20i64, 10u64, 4);
+        let histogram = searcher.search(&all_query, &histogram_collector)?;
+        assert_eq!(histogram, vec![1, 1, 0, 1]);
+        Ok(())
+    }
+
+    #[test]
+    fn test_histogram_merge() -> crate::Result<()> {
+        let mut schema_builder = Schema::builder();
+        let val_field = schema_builder.add_i64_field("val_field", FAST);
+        let schema = schema_builder.build();
+        let index = Index::create_in_ram(schema);
+        let mut writer = index.writer_with_num_threads(1, 4_000_000)?;
+        writer.add_document(doc!(val_field=>12i64));
+        writer.commit()?;
+        writer.add_document(doc!(val_field=>-30i64));
+        writer.commit()?;
+        writer.add_document(doc!(val_field=>-12i64));
+        writer.commit()?;
+        writer.add_document(doc!(val_field=>-10i64));
+        writer.commit()?;
+        let reader = index.reader()?;
+        let searcher = reader.searcher();
+        let all_query = AllQuery;
+        let histogram_collector = HistogramCollector::new(val_field, -20i64, 10u64, 4);
+        let histogram = searcher.search(&all_query, &histogram_collector)?;
+        assert_eq!(histogram, vec![1, 1, 0, 1]);
+        Ok(())
+    }
+
+    #[test]
+    fn test_histogram_dates() -> crate::Result<()> {
+        let mut schema_builder = Schema::builder();
+        let date_field = schema_builder.add_date_field("date_field", FAST);
+        let schema = schema_builder.build();
+        let index = Index::create_in_ram(schema);
+        let mut writer = index.writer_with_num_threads(1, 4_000_000)?;
+        writer.add_document(doc!(date_field=>Utc.ymd(1982, 9, 17).and_hms(0, 0,0)));
+        writer.add_document(doc!(date_field=>Utc.ymd(1986, 3, 9).and_hms(0, 0, 0)));
+        writer.add_document(doc!(date_field=>Utc.ymd(1983, 9, 27).and_hms(0, 0, 0)));
+        writer.commit()?;
+        let reader = index.reader()?;
+        let searcher = reader.searcher();
+        let all_query = AllQuery;
+        let week_histogram_collector = HistogramCollector::new(
+            date_field,
+            Utc.ymd(1980, 1, 1).and_hms(0, 0, 0),
+            3600 * 24 * 365, // it is just for a unit test... sorry leap years.
+            10,
+        );
+        let week_histogram = searcher.search(&all_query, &week_histogram_collector)?;
+        assert_eq!(week_histogram, vec![0, 0, 1, 1, 0, 0, 1, 0, 0, 0]);
+        Ok(())
+    }
+}
--- a/src/collector/mod.rs
+++ b/src/collector/mod.rs
@@ -93,6 +93,9 @@ use downcast_rs::impl_downcast;
 mod count_collector;
 pub use self::count_collector::Count;

+mod histogram_collector;
+pub use histogram_collector::HistogramCollector;
+
 mod multi_collector;
 pub use self::multi_collector::MultiCollector;

@@ -190,6 +193,61 @@ pub trait Collector: Sync + Send {
    }
 }

+impl<TSegmentCollector: SegmentCollector> SegmentCollector for Option<TSegmentCollector> {
+    type Fruit = Option<TSegmentCollector::Fruit>;
+
+    fn collect(&mut self, doc: DocId, score: Score) {
+        if let Some(segment_collector) = self {
+            segment_collector.collect(doc, score);
+        }
+    }
+
+    fn harvest(self) -> Self::Fruit {
+        self.map(|segment_collector| segment_collector.harvest())
+    }
+}
+
+impl<TCollector: Collector> Collector for Option<TCollector> {
+    type Fruit = Option<TCollector::Fruit>;
+
+    type Child = Option<<TCollector as Collector>::Child>;
+
+    fn for_segment(
+        &self,
+        segment_local_id: SegmentLocalId,
+        segment: &SegmentReader,
+    ) -> crate::Result<Self::Child> {
+        Ok(if let Some(inner) = self {
+            let inner_segment_collector = inner.for_segment(segment_local_id, segment)?;
+            Some(inner_segment_collector)
+        } else {
+            None
+        })
+    }
+
+    fn requires_scoring(&self) -> bool {
+        self.as_ref()
+            .map(|inner| inner.requires_scoring())
+            .unwrap_or(false)
+    }
+
+    fn merge_fruits(
+        &self,
+        segment_fruits: Vec<<Self::Child as SegmentCollector>::Fruit>,
+    ) -> crate::Result<Self::Fruit> {
+        if let Some(inner) = self.as_ref() {
+            let inner_segment_fruits: Vec<_> = segment_fruits
+                .into_iter()
+                .flat_map(|fruit_opt| fruit_opt.into_iter())
+                .collect();
+            let fruit = inner.merge_fruits(inner_segment_fruits)?;
+            Ok(Some(fruit))
+        } else {
+            Ok(None)
+        }
+    }
+}
+
 /// The `SegmentCollector` is the trait in charge of defining the
 /// collect operation at the scale of the segment.
 ///
--- a/src/collector/tests.rs
+++ b/src/collector/tests.rs
@@ -3,13 +3,13 @@ use crate::core::SegmentReader;
 use crate::fastfield::BytesFastFieldReader;
 use crate::fastfield::FastFieldReader;
 use crate::schema::Field;
-use crate::DocAddress;
 use crate::DocId;
 use crate::Score;
 use crate::SegmentLocalId;
+use crate::{DocAddress, Document, Searcher};

-use crate::collector::{FilterCollector, TopDocs};
-use crate::query::QueryParser;
+use crate::collector::{Count, FilterCollector, TopDocs};
+use crate::query::{AllQuery, QueryParser};
 use crate::schema::{Schema, FAST, TEXT};
 use crate::DateTime;
 use crate::{doc, Index};
@@ -268,3 +268,30 @@ impl SegmentCollector for BytesFastFieldSegmentCollector {
        self.vals
    }
 }
+
+fn make_test_searcher() -> crate::Result<crate::LeasedItem<Searcher>> {
+    let schema = Schema::builder().build();
+    let index = Index::create_in_ram(schema);
+    let mut index_writer = index.writer_for_tests()?;
+    index_writer.add_document(Document::default());
+    index_writer.add_document(Document::default());
+    index_writer.commit()?;
+    Ok(index.reader()?.searcher())
+}
+
+#[test]
+fn test_option_collector_some() -> crate::Result<()> {
+    let searcher = make_test_searcher()?;
+    let counts = searcher.search(&AllQuery, &Some(Count))?;
+    assert_eq!(counts, Some(2));
+    Ok(())
+}
+
+#[test]
+fn test_option_collector_none() -> crate::Result<()> {
+    let searcher = make_test_searcher()?;
+    let none_collector: Option<Count> = None;
+    let counts = searcher.search(&AllQuery, &none_collector)?;
+    assert_eq!(counts, None);
+    Ok(())
+}
--- a/src/collector/top_collector.rs
+++ b/src/collector/top_collector.rs
@@ -120,11 +120,8 @@ where
        &self,
        segment_id: SegmentLocalId,
        _: &SegmentReader,
-    ) -> crate::Result<TopSegmentCollector<F>> {
-        Ok(TopSegmentCollector::new(
-            segment_id,
-            self.limit + self.offset,
-        ))
+    ) -> TopSegmentCollector<F> {
+        TopSegmentCollector::new(segment_id, self.limit + self.offset)
    }

    /// Create a new TopCollector with the same limit and offset.
--- a/src/collector/top_score_collector.rs
+++ b/src/collector/top_score_collector.rs
@@ -29,7 +29,7 @@ struct FastFieldConvertCollector<
 impl<TCollector, TFastValue> Collector for FastFieldConvertCollector<TCollector, TFastValue>
 where
    TCollector: Collector<Fruit = Vec<(u64, DocAddress)>>,
-    TFastValue: FastValue + 'static,
+    TFastValue: FastValue,
 {
    type Fruit = Vec<(TFastValue, DocAddress)>;

@@ -361,7 +361,7 @@ impl TopDocs {
        fast_field: Field,
    ) -> impl Collector<Fruit = Vec<(TFastValue, DocAddress)>>
    where
-        TFastValue: FastValue + 'static,
+        TFastValue: FastValue,
    {
        let u64_collector = self.order_by_u64_field(fast_field);
        FastFieldConvertCollector {
@@ -603,7 +603,7 @@ impl Collector for TopDocs {
        segment_local_id: SegmentLocalId,
        reader: &SegmentReader,
    ) -> crate::Result<Self::Child> {
-        let collector = self.0.for_segment(segment_local_id, reader)?;
+        let collector = self.0.for_segment(segment_local_id, reader);
        Ok(TopScoreSegmentCollector(collector))
    }

--- a/src/collector/tweak_score_top_collector.rs
+++ b/src/collector/tweak_score_top_collector.rs
@@ -62,9 +62,7 @@ where
        segment_reader: &SegmentReader,
    ) -> Result<Self::Child> {
        let segment_scorer = self.score_tweaker.segment_tweaker(segment_reader)?;
-        let segment_collector = self
-            .collector
-            .for_segment(segment_local_id, segment_reader)?;
+        let segment_collector = self.collector.for_segment(segment_local_id, segment_reader);
        Ok(TopTweakedScoreSegmentCollector {
            segment_collector,
            segment_scorer,
--- a/src/common/composite_file.rs
+++ b/src/common/composite_file.rs
@@ -8,6 +8,8 @@ use crate::space_usage::FieldUsage;
 use crate::space_usage::PerFieldSpaceUsage;
 use std::collections::HashMap;
 use std::io::{self, Read, Write};
+use std::iter::ExactSizeIterator;
+use std::ops::Range;

 use super::HasLen;

@@ -105,7 +107,7 @@ impl<W: TerminatingWrite + Write> CompositeWrite<W> {
 #[derive(Clone)]
 pub struct CompositeFile {
    data: FileSlice,
-    offsets_index: HashMap<FileAddr, (usize, usize)>,
+    offsets_index: HashMap<FileAddr, Range<usize>>,
 }

 impl CompositeFile {
@@ -117,7 +119,7 @@ impl CompositeFile {
        let footer_len = u32::deserialize(&mut footer_len_data.as_slice())? as usize;
        let footer_start = end - 4 - footer_len;
        let footer_data = data
-            .slice(footer_start, footer_start + footer_len)
+            .slice(footer_start..footer_start + footer_len)
            .read_bytes()?;
        let mut footer_buffer = footer_data.as_slice();
        let num_fields = VInt::deserialize(&mut footer_buffer)?.0 as usize;
@@ -138,7 +140,7 @@ impl CompositeFile {
            let file_addr = file_addrs[i];
            let start_offset = offsets[i];
            let end_offset = offsets[i + 1];
-            field_index.insert(file_addr, (start_offset, end_offset));
+            field_index.insert(file_addr, start_offset..end_offset);
        }

        Ok(CompositeFile {
@@ -167,16 +169,16 @@ impl CompositeFile {
    pub fn open_read_with_idx(&self, field: Field, idx: usize) -> Option<FileSlice> {
        self.offsets_index
            .get(&FileAddr { field, idx })
-            .map(|&(from, to)| self.data.slice(from, to))
+            .map(|byte_range| self.data.slice(byte_range.clone()))
    }

    pub fn space_usage(&self) -> PerFieldSpaceUsage {
        let mut fields = HashMap::new();
-        for (&field_addr, &(start, end)) in self.offsets_index.iter() {
+        for (&field_addr, byte_range) in &self.offsets_index {
            fields
                .entry(field_addr.field)
                .or_insert_with(|| FieldUsage::empty(field_addr.field))
-                .add_field_idx(field_addr.idx, end - start);
+                .add_field_idx(field_addr.idx, byte_range.len());
        }
        PerFieldSpaceUsage::new(fields)
    }
--- a/src/core/index.rs
+++ b/src/core/index.rs
@@ -165,7 +165,8 @@ impl Index {
    fn from_directory(directory: ManagedDirectory, schema: Schema) -> crate::Result<Index> {
        save_new_metas(schema.clone(), &directory)?;
        let metas = IndexMeta::with_schema(schema);
-        Index::create_from_metas(directory, &metas, SegmentMetaInventory::default())
+        let index = Index::create_from_metas(directory, &metas, SegmentMetaInventory::default());
+        Ok(index)
    }

    /// Creates a new index given a directory and an `IndexMeta`.
@@ -173,15 +174,15 @@ impl Index {
        directory: ManagedDirectory,
        metas: &IndexMeta,
        inventory: SegmentMetaInventory,
-    ) -> crate::Result<Index> {
+    ) -> Index {
        let schema = metas.schema.clone();
-        Ok(Index {
+        Index {
            directory,
            schema,
            tokenizers: TokenizerManager::default(),
            executor: Arc::new(Executor::single_thread()),
            inventory,
-        })
+        }
    }

    /// Accessor for the tokenizer manager.
@@ -256,7 +257,8 @@ impl Index {
        let directory = ManagedDirectory::wrap(directory)?;
        let inventory = SegmentMetaInventory::default();
        let metas = load_metas(&directory, &inventory)?;
-        Index::create_from_metas(directory, &metas, inventory)
+        let index = Index::create_from_metas(directory, &metas, inventory);
+        Ok(index)
    }

    /// Reads the index meta file from the directory.
--- a/src/core/inverted_index_reader.rs
+++ b/src/core/inverted_index_reader.rs
@@ -90,9 +90,9 @@ impl InvertedIndexReader {
        term_info: &TermInfo,
        block_postings: &mut BlockSegmentPostings,
    ) -> io::Result<()> {
-        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);
+        let postings_slice = self
+            .postings_file_slice
+            .slice(term_info.postings_range.clone());
        block_postings.reset(term_info.doc_freq, postings_slice.read_bytes()?);
        Ok(())
    }
@@ -120,10 +120,9 @@ impl InvertedIndexReader {
        term_info: &TermInfo,
        requested_option: IndexRecordOption,
    ) -> io::Result<BlockSegmentPostings> {
-        let postings_data = self.postings_file_slice.slice(
-            term_info.postings_start_offset as usize,
-            term_info.postings_stop_offset as usize,
-        );
+        let postings_data = self
+            .postings_file_slice
+            .slice(term_info.postings_range.clone());
        BlockSegmentPostings::open(
            term_info.doc_freq,
            postings_data,
--- a/src/core/segment_reader.rs
+++ b/src/core/segment_reader.rs
@@ -108,19 +108,22 @@ impl SegmentReader {
    /// Accessor to the `FacetReader` associated to a given `Field`.
    pub fn facet_reader(&self, field: Field) -> crate::Result<FacetReader> {
        let field_entry = self.schema.get_field_entry(field);
-        if field_entry.field_type() != &FieldType::HierarchicalFacet {
-            return Err(crate::TantivyError::InvalidArgument(format!(
+
+        match field_entry.field_type() {
+            FieldType::HierarchicalFacet(_) => {
+                let term_ords_reader = self.fast_fields().u64s(field)?;
+                let termdict = self
+                    .termdict_composite
+                    .open_read(field)
+                    .map(TermDictionary::open)
+                    .unwrap_or_else(|| Ok(TermDictionary::empty()))?;
+                Ok(FacetReader::new(term_ords_reader, termdict))
+            }
+            _ => Err(crate::TantivyError::InvalidArgument(format!(
                "Field {:?} is not a facet field.",
                field_entry.name()
-            )));
+            ))),
        }
-        let term_ords_reader = self.fast_fields().u64s(field)?;
-        let termdict = self
-            .termdict_composite
-            .open_read(field)
-            .map(TermDictionary::open)
-            .unwrap_or_else(|| Ok(TermDictionary::empty()))?;
-        Ok(FacetReader::new(term_ords_reader, termdict))
    }

    /// Accessor to the segment's `Field norms`'s reader.
@@ -178,10 +181,8 @@ impl SegmentReader {

        let fast_fields_data = segment.open_read(SegmentComponent::FASTFIELDS)?;
        let fast_fields_composite = CompositeFile::open(&fast_fields_data)?;
-        let fast_field_readers = Arc::new(FastFieldReaders::new(
-            schema.clone(),
-            fast_fields_composite,
-        )?);
+        let fast_field_readers =
+            Arc::new(FastFieldReaders::new(schema.clone(), fast_fields_composite));

        let fieldnorm_data = segment.open_read(SegmentComponent::FIELDNORMS)?;
        let fieldnorm_readers = FieldNormReaders::open(fieldnorm_data)?;
--- a/src/directory/file_slice.rs
+++ b/src/directory/file_slice.rs
@@ -2,6 +2,8 @@ use stable_deref_trait::StableDeref;

 use crate::common::HasLen;
 use crate::directory::OwnedBytes;
+use std::fmt;
+use std::ops::Range;
 use std::sync::{Arc, Weak};
 use std::{io, ops::Deref};

@@ -16,23 +18,23 @@ pub type WeakArcBytes = Weak<dyn Deref<Target = [u8]> + Send + Sync + 'static>;
 /// The underlying behavior is therefore specific to the `Directory` that created it.
 /// Despite its name, a `FileSlice` may or may not directly map to an actual file
 /// on the filesystem.
-pub trait FileHandle: 'static + Send + Sync + HasLen {
+pub trait FileHandle: 'static + Send + Sync + HasLen + fmt::Debug {
    /// Reads a slice of bytes.
    ///
    /// This method may panic if the range requested is invalid.
-    fn read_bytes(&self, from: usize, to: usize) -> io::Result<OwnedBytes>;
+    fn read_bytes(&self, range: Range<usize>) -> io::Result<OwnedBytes>;
 }

 impl FileHandle for &'static [u8] {
-    fn read_bytes(&self, from: usize, to: usize) -> io::Result<OwnedBytes> {
-        let bytes = &self[from..to];
+    fn read_bytes(&self, range: Range<usize>) -> io::Result<OwnedBytes> {
+        let bytes = &self[range];
        Ok(OwnedBytes::new(bytes))
    }
 }

 impl<T: Deref<Target = [u8]>> HasLen for T {
    fn len(&self) -> usize {
-        self.as_ref().len()
+        self.deref().len()
    }
 }

@@ -46,14 +48,19 @@ where
 }

 /// Logical slice of read only file in tantivy.
-//
+///
 /// It can be cloned and sliced cheaply.
 ///
 #[derive(Clone)]
 pub struct FileSlice {
    data: Arc<dyn FileHandle>,
-    start: usize,
-    stop: usize,
+    range: Range<usize>,
+}
+
+impl fmt::Debug for FileSlice {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "FileSlice({:?}, {:?})", &self.data, self.range)
+    }
 }

 impl FileSlice {
@@ -68,8 +75,7 @@ impl FileSlice {
    pub fn new_with_num_bytes(file_handle: Box<dyn FileHandle>, num_bytes: usize) -> Self {
        FileSlice {
            data: Arc::from(file_handle),
-            start: 0,
-            stop: num_bytes,
+            range: 0..num_bytes,
        }
    }

@@ -77,14 +83,12 @@ impl FileSlice {
    ///
    /// # Panics
    ///
-    /// Panics if `to < from` or if `to` exceeds the filesize.
-    pub fn slice(&self, from: usize, to: usize) -> FileSlice {
-        assert!(to <= self.len());
-        assert!(to >= from);
+    /// Panics if `byte_range.end` exceeds the filesize.
+    pub fn slice(&self, byte_range: Range<usize>) -> FileSlice {
+        assert!(byte_range.end <= self.len());
        FileSlice {
            data: self.data.clone(),
-            start: self.start + from,
-            stop: self.start + to,
+            range: self.range.start + byte_range.start..self.range.start + byte_range.end,
        }
    }

@@ -101,19 +105,21 @@ impl FileSlice {
    /// In particular, it is  up to the `Directory` implementation
    /// to handle caching if needed.
    pub fn read_bytes(&self) -> io::Result<OwnedBytes> {
-        self.data.read_bytes(self.start, self.stop)
+        self.data.read_bytes(self.range.clone())
    }

    /// Reads a specific slice of data.
    ///
    /// This is equivalent to running `file_slice.slice(from, to).read_bytes()`.
-    pub fn read_bytes_slice(&self, from: usize, to: usize) -> io::Result<OwnedBytes> {
-        assert!(from <= to);
+    pub fn read_bytes_slice(&self, range: Range<usize>) -> io::Result<OwnedBytes> {
        assert!(
-            self.start + to <= self.stop,
-            "`to` exceeds the fileslice length"
+            range.end <= self.len(),
+            "end of requested range exceeds the fileslice length ({} > {})",
+            range.end,
+            self.len()
        );
-        self.data.read_bytes(self.start + from, self.start + to)
+        self.data
+            .read_bytes(self.range.start + range.start..self.range.start + range.end)
    }

    /// Splits the FileSlice at the given offset and return two file slices.
@@ -138,7 +144,7 @@ impl FileSlice {
    ///
    /// Equivalent to `.slice(from_offset, self.len())`
    pub fn slice_from(&self, from_offset: usize) -> FileSlice {
-        self.slice(from_offset, self.len())
+        self.slice(from_offset..self.len())
    }

    /// Like `.slice(...)` but enforcing only the `to`
@@ -146,19 +152,19 @@ impl FileSlice {
    ///
    /// Equivalent to `.slice(0, to_offset)`
    pub fn slice_to(&self, to_offset: usize) -> FileSlice {
-        self.slice(0, to_offset)
+        self.slice(0..to_offset)
    }
 }

 impl FileHandle for FileSlice {
-    fn read_bytes(&self, from: usize, to: usize) -> io::Result<OwnedBytes> {
-        self.read_bytes_slice(from, to)
+    fn read_bytes(&self, range: Range<usize>) -> io::Result<OwnedBytes> {
+        self.read_bytes_slice(range)
    }
 }

 impl HasLen for FileSlice {
    fn len(&self) -> usize {
-        self.stop - self.start
+        self.range.len()
    }
 }

@@ -217,30 +223,23 @@ mod tests {
        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");
+        assert_eq!(slice.slice(1..4).read_bytes()?.as_ref(), b"bcd");
        Ok(())
    }

    #[test]
    fn test_slice_read_slice() -> io::Result<()> {
        let slice_deref = FileSlice::new(Box::new(&b"abcdef"[..]));
-        assert_eq!(slice_deref.read_bytes_slice(1, 4)?.as_ref(), b"bcd");
+        assert_eq!(slice_deref.read_bytes_slice(1..4)?.as_ref(), b"bcd");
        Ok(())
    }

    #[test]
-    #[should_panic(expected = "assertion failed: from <= to")]
-    fn test_slice_read_slice_invalid_range() {
-        let slice_deref = FileSlice::new(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")]
+    #[should_panic(expected = "end of requested range exceeds the fileslice length (10 > 6)")]
    fn test_slice_read_slice_invalid_range_exceeds() {
        let slice_deref = FileSlice::new(Box::new(&b"abcdef"[..]));
        assert_eq!(
-            slice_deref.read_bytes_slice(0, 10).unwrap().as_ref(),
+            slice_deref.read_bytes_slice(0..10).unwrap().as_ref(),
            b"bcd"
        );
    }
--- a/src/directory/file_watcher.rs
+++ b/src/directory/file_watcher.rs
@@ -28,7 +28,11 @@ impl FileWatcher {
    }

    pub fn spawn(&self) {
-        if self.state.compare_and_swap(0, 1, Ordering::SeqCst) > 0 {
+        if self
+            .state
+            .compare_exchange(0, 1, Ordering::SeqCst, Ordering::SeqCst)
+            .is_err()
+        {
            return;
        }

--- a/src/directory/mmap_directory.rs
+++ b/src/directory/mmap_directory.rs
@@ -163,8 +163,8 @@ impl MmapDirectoryInner {
        }
    }

-    fn watch(&self, callback: WatchCallback) -> crate::Result<WatchHandle> {
-        Ok(self.watcher.watch(callback))
+    fn watch(&self, callback: WatchCallback) -> WatchHandle {
+        self.watcher.watch(callback)
    }
 }

@@ -474,7 +474,7 @@ impl Directory for MmapDirectory {
    }

    fn watch(&self, watch_callback: WatchCallback) -> crate::Result<WatchHandle> {
-        self.inner.watch(watch_callback)
+        Ok(self.inner.watch(watch_callback))
    }
 }

--- a/src/directory/owned_bytes.rs
+++ b/src/directory/owned_bytes.rs
@@ -2,7 +2,7 @@ use crate::directory::FileHandle;
 use stable_deref_trait::StableDeref;
 use std::convert::TryInto;
 use std::mem;
-use std::ops::Deref;
+use std::ops::{Deref, Range};
 use std::sync::Arc;
 use std::{fmt, io};

@@ -17,8 +17,8 @@ pub struct OwnedBytes {
 }

 impl FileHandle for OwnedBytes {
-    fn read_bytes(&self, from: usize, to: usize) -> io::Result<OwnedBytes> {
-        Ok(self.slice(from, to))
+    fn read_bytes(&self, range: Range<usize>) -> io::Result<OwnedBytes> {
+        Ok(self.slice(range))
    }
 }

@@ -42,9 +42,9 @@ impl OwnedBytes {
    }

    /// creates a fileslice that is just a view over a slice of the data.
-    pub fn slice(&self, from: usize, to: usize) -> Self {
+    pub fn slice(&self, range: Range<usize>) -> Self {
        OwnedBytes {
-            data: &self.data[from..to],
+            data: &self.data[range],
            box_stable_deref: self.box_stable_deref.clone(),
        }
    }
--- a/src/fastfield/bytes/writer.rs
+++ b/src/fastfield/bytes/writer.rs
@@ -80,7 +80,7 @@ impl BytesFastFieldWriter {
        doc_index_serializer.close_field()?;
        // writing the values themselves
        serializer
-            .new_bytes_fast_field_with_idx(self.field, 1)?
+            .new_bytes_fast_field_with_idx(self.field, 1)
            .write_all(&self.vals)?;
        Ok(())
    }
--- a/src/fastfield/facet_reader.rs
+++ b/src/fastfield/facet_reader.rs
@@ -84,14 +84,106 @@ impl FacetReader {
 mod tests {
    use crate::Index;
    use crate::{
-        schema::{Facet, SchemaBuilder},
-        Document,
+        schema::{Facet, FacetOptions, SchemaBuilder, Value, INDEXED, STORED},
+        DocAddress, Document,
    };

+    #[test]
+    fn test_facet_only_indexed() -> crate::Result<()> {
+        let mut schema_builder = SchemaBuilder::default();
+        let facet_field = schema_builder.add_facet_field("facet", INDEXED);
+        let schema = schema_builder.build();
+        let index = Index::create_in_ram(schema);
+        let mut index_writer = index.writer_for_tests()?;
+        index_writer.add_document(doc!(facet_field=>Facet::from_text("/a/b")));
+        index_writer.commit()?;
+        let searcher = index.reader()?.searcher();
+        let facet_reader = searcher
+            .segment_reader(0u32)
+            .facet_reader(facet_field)
+            .unwrap();
+        let mut facet_ords = Vec::new();
+        facet_reader.facet_ords(0u32, &mut facet_ords);
+        assert_eq!(&facet_ords, &[2u64]);
+        let doc = searcher.doc(DocAddress(0u32, 0u32))?;
+        let value = doc.get_first(facet_field).and_then(Value::path);
+        assert_eq!(value, None);
+        Ok(())
+    }
+
+    #[test]
+    fn test_facet_only_stored() -> crate::Result<()> {
+        let mut schema_builder = SchemaBuilder::default();
+        let facet_field = schema_builder.add_facet_field("facet", STORED);
+        let schema = schema_builder.build();
+        let index = Index::create_in_ram(schema);
+        let mut index_writer = index.writer_for_tests()?;
+        index_writer.add_document(doc!(facet_field=>Facet::from_text("/a/b")));
+        index_writer.commit()?;
+        let searcher = index.reader()?.searcher();
+        let facet_reader = searcher
+            .segment_reader(0u32)
+            .facet_reader(facet_field)
+            .unwrap();
+        let mut facet_ords = Vec::new();
+        facet_reader.facet_ords(0u32, &mut facet_ords);
+        assert!(facet_ords.is_empty());
+        let doc = searcher.doc(DocAddress(0u32, 0u32))?;
+        let value = doc.get_first(facet_field).and_then(Value::path);
+        assert_eq!(value, Some("/a/b".to_string()));
+        Ok(())
+    }
+
+    #[test]
+    fn test_facet_stored_and_indexed() -> crate::Result<()> {
+        let mut schema_builder = SchemaBuilder::default();
+        let facet_field = schema_builder.add_facet_field("facet", STORED | INDEXED);
+        let schema = schema_builder.build();
+        let index = Index::create_in_ram(schema);
+        let mut index_writer = index.writer_for_tests()?;
+        index_writer.add_document(doc!(facet_field=>Facet::from_text("/a/b")));
+        index_writer.commit()?;
+        let searcher = index.reader()?.searcher();
+        let facet_reader = searcher
+            .segment_reader(0u32)
+            .facet_reader(facet_field)
+            .unwrap();
+        let mut facet_ords = Vec::new();
+        facet_reader.facet_ords(0u32, &mut facet_ords);
+        assert_eq!(&facet_ords, &[2u64]);
+        let doc = searcher.doc(DocAddress(0u32, 0u32))?;
+        let value = doc.get_first(facet_field).and_then(Value::path);
+        assert_eq!(value, Some("/a/b".to_string()));
+        Ok(())
+    }
+
+    #[test]
+    fn test_facet_neither_stored_and_indexed() -> crate::Result<()> {
+        let mut schema_builder = SchemaBuilder::default();
+        let facet_field = schema_builder.add_facet_field("facet", FacetOptions::default());
+        let schema = schema_builder.build();
+        let index = Index::create_in_ram(schema);
+        let mut index_writer = index.writer_for_tests()?;
+        index_writer.add_document(doc!(facet_field=>Facet::from_text("/a/b")));
+        index_writer.commit()?;
+        let searcher = index.reader()?.searcher();
+        let facet_reader = searcher
+            .segment_reader(0u32)
+            .facet_reader(facet_field)
+            .unwrap();
+        let mut facet_ords = Vec::new();
+        facet_reader.facet_ords(0u32, &mut facet_ords);
+        assert!(facet_ords.is_empty());
+        let doc = searcher.doc(DocAddress(0u32, 0u32))?;
+        let value = doc.get_first(facet_field).and_then(Value::path);
+        assert_eq!(value, None);
+        Ok(())
+    }
+
    #[test]
    fn test_facet_not_populated_for_all_docs() -> crate::Result<()> {
        let mut schema_builder = SchemaBuilder::default();
-        let facet_field = schema_builder.add_facet_field("facet");
+        let facet_field = schema_builder.add_facet_field("facet", INDEXED);
        let schema = schema_builder.build();
        let index = Index::create_in_ram(schema);
        let mut index_writer = index.writer_for_tests()?;
@@ -110,10 +202,11 @@ mod tests {
        assert!(facet_ords.is_empty());
        Ok(())
    }
+
    #[test]
    fn test_facet_not_populated_for_any_docs() -> crate::Result<()> {
        let mut schema_builder = SchemaBuilder::default();
-        let facet_field = schema_builder.add_facet_field("facet");
+        let facet_field = schema_builder.add_facet_field("facet", INDEXED);
        let schema = schema_builder.build();
        let index = Index::create_in_ram(schema);
        let mut index_writer = index.writer_for_tests()?;
--- a/src/fastfield/mod.rs
+++ b/src/fastfield/mod.rs
@@ -53,7 +53,7 @@ mod serializer;
 mod writer;

 /// Trait for types that are allowed for fast fields: (u64, i64 and f64).
-pub trait FastValue: Clone + Copy + Send + Sync + PartialOrd {
+pub trait FastValue: Clone + Copy + Send + Sync + PartialOrd + 'static {
    /// Converts a value from u64
    ///
    /// Internally all fast field values are encoded as u64.
@@ -96,7 +96,7 @@ impl FastValue for u64 {
    fn fast_field_cardinality(field_type: &FieldType) -> Option<Cardinality> {
        match *field_type {
            FieldType::U64(ref integer_options) => integer_options.get_fastfield_cardinality(),
-            FieldType::HierarchicalFacet => Some(Cardinality::MultiValues),
+            FieldType::HierarchicalFacet(_) => Some(Cardinality::MultiValues),
            _ => None,
        }
    }
--- a/src/fastfield/multivalued/mod.rs
+++ b/src/fastfield/multivalued/mod.rs
@@ -13,6 +13,7 @@ mod tests {
    use crate::schema::Facet;
    use crate::schema::IntOptions;
    use crate::schema::Schema;
+    use crate::schema::INDEXED;
    use crate::Index;
    use chrono::Duration;

@@ -212,7 +213,7 @@ mod tests {
    #[ignore]
    fn test_many_facets() {
        let mut schema_builder = Schema::builder();
-        let field = schema_builder.add_facet_field("facetfield");
+        let field = schema_builder.add_facet_field("facetfield", INDEXED);
        let schema = schema_builder.build();
        let index = Index::create_in_ram(schema);
        let mut index_writer = index.writer_for_tests().unwrap();
--- a/src/fastfield/multivalued/reader.rs
+++ b/src/fastfield/multivalued/reader.rs
@@ -1,3 +1,5 @@
+use std::ops::Range;
+
 use crate::fastfield::{FastFieldReader, FastValue};
 use crate::DocId;

@@ -28,24 +30,24 @@ impl<Item: FastValue> MultiValuedFastFieldReader<Item> {

    /// Returns `(start, stop)`, such that the values associated
    /// to the given document are `start..stop`.
-    fn range(&self, doc: DocId) -> (u64, u64) {
+    fn range(&self, doc: DocId) -> Range<u64> {
        let start = self.idx_reader.get(doc);
        let stop = self.idx_reader.get(doc + 1);
-        (start, stop)
+        start..stop
    }

    /// Returns the array of values associated to the given `doc`.
    pub fn get_vals(&self, doc: DocId, vals: &mut Vec<Item>) {
-        let (start, stop) = self.range(doc);
-        let len = (stop - start) as usize;
+        let range = self.range(doc);
+        let len = (range.end - range.start) as usize;
        vals.resize(len, Item::make_zero());
-        self.vals_reader.get_range_u64(start, &mut vals[..]);
+        self.vals_reader.get_range_u64(range.start, &mut vals[..]);
    }

    /// Returns the number of values associated with the document `DocId`.
    pub fn num_vals(&self, doc: DocId) -> usize {
-        let (start, stop) = self.range(doc);
-        (stop - start) as usize
+        let range = self.range(doc);
+        (range.end - range.start) as usize
    }

    /// Returns the overall number of values in this field  .
@@ -58,12 +60,12 @@ impl<Item: FastValue> MultiValuedFastFieldReader<Item> {
 mod tests {

    use crate::core::Index;
-    use crate::schema::{Facet, Schema};
+    use crate::schema::{Facet, Schema, INDEXED};

    #[test]
    fn test_multifastfield_reader() {
        let mut schema_builder = Schema::builder();
-        let facet_field = schema_builder.add_facet_field("facets");
+        let facet_field = schema_builder.add_facet_field("facets", INDEXED);
        let schema = schema_builder.build();
        let index = Index::create_in_ram(schema);
        let mut index_writer = index
--- a/src/fastfield/multivalued/writer.rs
+++ b/src/fastfield/multivalued/writer.rs
@@ -7,6 +7,7 @@ use crate::termdict::TermOrdinal;
 use crate::DocId;
 use fnv::FnvHashMap;
 use std::io;
+use std::iter::once;

 /// Writer for multi-valued (as in, more than one value per document)
 /// int fast field.
@@ -125,21 +126,18 @@ impl MultiValuedFastFieldWriter {
                        1,
                    )?;

-                    let last_interval = (
-                        self.doc_index.last().cloned().unwrap(),
-                        self.vals.len() as u64,
-                    );
+                    let last_interval =
+                        self.doc_index.last().cloned().unwrap() as usize..self.vals.len();

                    let mut doc_vals: Vec<u64> = Vec::with_capacity(100);
-                    for (start, stop) in self
+                    for range in self
                        .doc_index
                        .windows(2)
-                        .map(|interval| (interval[0], interval[1]))
-                        .chain(Some(last_interval).into_iter())
-                        .map(|(start, stop)| (start as usize, stop as usize))
+                        .map(|interval| interval[0] as usize..interval[1] as usize)
+                        .chain(once(last_interval))
                    {
                        doc_vals.clear();
-                        let remapped_vals = self.vals[start..stop]
+                        let remapped_vals = self.vals[range]
                            .iter()
                            .map(|val| *mapping.get(val).expect("Missing term ordinal"));
                        doc_vals.extend(remapped_vals);
--- a/src/fastfield/readers.rs
+++ b/src/fastfield/readers.rs
@@ -38,20 +38,17 @@ fn type_and_cardinality(field_type: &FieldType) -> Option<(FastType, Cardinality
        FieldType::Date(options) => options
            .get_fastfield_cardinality()
            .map(|cardinality| (FastType::Date, cardinality)),
-        FieldType::HierarchicalFacet => Some((FastType::U64, Cardinality::MultiValues)),
+        FieldType::HierarchicalFacet(_) => Some((FastType::U64, Cardinality::MultiValues)),
        _ => None,
    }
 }

 impl FastFieldReaders {
-    pub(crate) fn new(
-        schema: Schema,
-        fast_fields_composite: CompositeFile,
-    ) -> crate::Result<FastFieldReaders> {
-        Ok(FastFieldReaders {
+    pub(crate) fn new(schema: Schema, fast_fields_composite: CompositeFile) -> FastFieldReaders {
+        FastFieldReaders {
            fast_fields_composite,
            schema,
-        })
+        }
    }

    pub(crate) fn space_usage(&self) -> PerFieldSpaceUsage {
@@ -128,6 +125,14 @@ impl FastFieldReaders {
        self.typed_fast_field_reader(field)
    }

+    /// Returns the `u64` fast field reader reader associated to `field`, regardless of whether the given
+    /// field is effectively of type `u64` or not.
+    ///
+    /// If not, the fastfield reader will returns the u64-value associated to the original FastValue.
+    pub fn u64_lenient(&self, field: Field) -> crate::Result<FastFieldReader<u64>> {
+        self.typed_fast_field_reader(field)
+    }
+
    /// Returns the `i64` fast field reader reader associated to `field`.
    ///
    /// If `field` is not a i64 fast field, this method returns `None`.
--- a/src/fastfield/serializer.rs
+++ b/src/fastfield/serializer.rs
@@ -66,9 +66,9 @@ impl FastFieldSerializer {
        &mut self,
        field: Field,
        idx: usize,
-    ) -> io::Result<FastBytesFieldSerializer<'_, CountingWriter<WritePtr>>> {
+    ) -> FastBytesFieldSerializer<'_, CountingWriter<WritePtr>> {
        let field_write = self.composite_write.for_field_with_idx(field, idx);
-        FastBytesFieldSerializer::open(field_write)
+        FastBytesFieldSerializer { write: field_write }
    }

    /// Closes the serializer
@@ -132,10 +132,6 @@ pub struct FastBytesFieldSerializer<'a, W: Write> {
 }

 impl<'a, W: Write> FastBytesFieldSerializer<'a, W> {
-    fn open(write: &'a mut W) -> io::Result<FastBytesFieldSerializer<'a, W>> {
-        Ok(FastBytesFieldSerializer { write })
-    }
-
    pub fn write_all(&mut self, vals: &[u8]) -> io::Result<()> {
        self.write.write_all(vals)
    }
--- a/src/fastfield/writer.rs
+++ b/src/fastfield/writer.rs
@@ -52,7 +52,7 @@ impl FastFieldsWriter {
                        None => {}
                    }
                }
-                FieldType::HierarchicalFacet => {
+                FieldType::HierarchicalFacet(_) => {
                    let fast_field_writer = MultiValuedFastFieldWriter::new(field, true);
                    multi_values_writers.push(fast_field_writer);
                }
--- a/src/indexer/merger.rs
+++ b/src/indexer/merger.rs
@@ -195,7 +195,7 @@ impl IndexMerger {
        for (field, field_entry) in self.schema.fields() {
            let field_type = field_entry.field_type();
            match field_type {
-                FieldType::HierarchicalFacet => {
+                FieldType::HierarchicalFacet(_) => {
                    let term_ordinal_mapping = term_ord_mappings
                        .remove(&field)
                        .expect("Logic Error in Tantivy (Please report). HierarchicalFact field should have required a\
@@ -476,7 +476,7 @@ impl IndexMerger {
            serialize_idx.close_field()?;
        }

-        let mut serialize_vals = fast_field_serializer.new_bytes_fast_field_with_idx(field, 1)?;
+        let mut serialize_vals = fast_field_serializer.new_bytes_fast_field_with_idx(field, 1);
        for segment_reader in &self.readers {
            let bytes_reader = segment_reader.fast_fields().bytes(field)
                .expect("Failed to find bytes field in fast field reader. This is a bug in tantivy. Please report.");
@@ -515,10 +515,9 @@ impl IndexMerger {
            max_term_ords.push(terms.num_terms() as u64);
        }

-        let mut term_ord_mapping_opt = if *field_type == FieldType::HierarchicalFacet {
-            Some(TermOrdinalMapping::new(max_term_ords))
-        } else {
-            None
+        let mut term_ord_mapping_opt = match field_type {
+            FieldType::HierarchicalFacet(_) => Some(TermOrdinalMapping::new(max_term_ords)),
+            _ => None,
        };

        let mut merged_terms = TermMerger::new(field_term_streams);
@@ -1179,7 +1178,7 @@ mod tests {
    #[test]
    fn test_merge_facets() {
        let mut schema_builder = schema::Schema::builder();
-        let facet_field = schema_builder.add_facet_field("facet");
+        let facet_field = schema_builder.add_facet_field("facet", INDEXED);
        let index = Index::create_in_ram(schema_builder.build());
        let reader = index.reader().unwrap();
        {
--- a/src/indexer/segment_writer.rs
+++ b/src/indexer/segment_writer.rs
@@ -142,7 +142,7 @@ impl SegmentWriter {
            let (term_buffer, multifield_postings) =
                (&mut self.term_buffer, &mut self.multifield_postings);
            match *field_entry.field_type() {
-                FieldType::HierarchicalFacet => {
+                FieldType::HierarchicalFacet(_) => {
                    term_buffer.set_field(field);
                    let facets =
                        field_values
@@ -213,69 +213,59 @@ impl SegmentWriter {

                    self.fieldnorms_writer.record(doc_id, field, num_tokens);
                }
-                FieldType::U64(ref int_option) => {
-                    if int_option.is_indexed() {
-                        for field_value in field_values {
-                            term_buffer.set_field(field_value.field());
-                            let u64_val = field_value
-                                .value()
-                                .u64_value()
-                                .ok_or_else(make_schema_error)?;
-                            term_buffer.set_u64(u64_val);
-                            multifield_postings.subscribe(doc_id, &term_buffer);
-                        }
+                FieldType::U64(_) => {
+                    for field_value in field_values {
+                        term_buffer.set_field(field_value.field());
+                        let u64_val = field_value
+                            .value()
+                            .u64_value()
+                            .ok_or_else(make_schema_error)?;
+                        term_buffer.set_u64(u64_val);
+                        multifield_postings.subscribe(doc_id, &term_buffer);
                    }
                }
-                FieldType::Date(ref int_option) => {
-                    if int_option.is_indexed() {
-                        for field_value in field_values {
-                            term_buffer.set_field(field_value.field());
-                            let date_val = field_value
-                                .value()
-                                .date_value()
-                                .ok_or_else(make_schema_error)?;
-                            term_buffer.set_i64(date_val.timestamp());
-                            multifield_postings.subscribe(doc_id, &term_buffer);
-                        }
+                FieldType::Date(_) => {
+                    for field_value in field_values {
+                        term_buffer.set_field(field_value.field());
+                        let date_val = field_value
+                            .value()
+                            .date_value()
+                            .ok_or_else(make_schema_error)?;
+                        term_buffer.set_i64(date_val.timestamp());
+                        multifield_postings.subscribe(doc_id, &term_buffer);
                    }
                }
-                FieldType::I64(ref int_option) => {
-                    if int_option.is_indexed() {
-                        for field_value in field_values {
-                            term_buffer.set_field(field_value.field());
-                            let i64_val = field_value
-                                .value()
-                                .i64_value()
-                                .ok_or_else(make_schema_error)?;
-                            term_buffer.set_i64(i64_val);
-                            multifield_postings.subscribe(doc_id, &term_buffer);
-                        }
+                FieldType::I64(_) => {
+                    for field_value in field_values {
+                        term_buffer.set_field(field_value.field());
+                        let i64_val = field_value
+                            .value()
+                            .i64_value()
+                            .ok_or_else(make_schema_error)?;
+                        term_buffer.set_i64(i64_val);
+                        multifield_postings.subscribe(doc_id, &term_buffer);
                    }
                }
-                FieldType::F64(ref int_option) => {
-                    if int_option.is_indexed() {
-                        for field_value in field_values {
-                            term_buffer.set_field(field_value.field());
-                            let f64_val = field_value
-                                .value()
-                                .f64_value()
-                                .ok_or_else(make_schema_error)?;
-                            term_buffer.set_f64(f64_val);
-                            multifield_postings.subscribe(doc_id, &term_buffer);
-                        }
+                FieldType::F64(_) => {
+                    for field_value in field_values {
+                        term_buffer.set_field(field_value.field());
+                        let f64_val = field_value
+                            .value()
+                            .f64_value()
+                            .ok_or_else(make_schema_error)?;
+                        term_buffer.set_f64(f64_val);
+                        multifield_postings.subscribe(doc_id, &term_buffer);
                    }
                }
-                FieldType::Bytes(ref option) => {
-                    if option.is_indexed() {
-                        for field_value in field_values {
-                            term_buffer.set_field(field_value.field());
-                            let bytes = field_value
-                                .value()
-                                .bytes_value()
-                                .ok_or_else(make_schema_error)?;
-                            term_buffer.set_bytes(bytes);
-                            self.multifield_postings.subscribe(doc_id, &term_buffer);
-                        }
+                FieldType::Bytes(_) => {
+                    for field_value in field_values {
+                        term_buffer.set_field(field_value.field());
+                        let bytes = field_value
+                            .value()
+                            .bytes_value()
+                            .ok_or_else(make_schema_error)?;
+                        term_buffer.set_bytes(bytes);
+                        self.multifield_postings.subscribe(doc_id, &term_buffer);
                    }
                }
            }
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -234,6 +234,8 @@ pub mod merge_policy {
 /// A `u32` identifying a document within a segment.
 /// Documents have their `DocId` assigned incrementally,
 /// as they are added in the segment.
+///
+/// At most, a segment can contain 2^31 documents.
 pub type DocId = u32;

 /// A u64 assigned to every operation incrementally
--- a/src/postings/block_search.rs
+++ b/src/postings/block_search.rs
@@ -1,3 +1,5 @@
+use std::ops::Range;
+
 use crate::postings::compression::AlignedBuffer;

 /// This modules define the logic used to search for a doc in a given
@@ -72,7 +74,7 @@ fn linear_search(arr: &[u32], target: u32) -> usize {
    arr.iter().map(|&el| if el < target { 1 } else { 0 }).sum()
 }

-fn exponential_search(arr: &[u32], target: u32) -> (usize, usize) {
+fn exponential_search(arr: &[u32], target: u32) -> Range<usize> {
    let end = arr.len();
    let mut begin = 0;
    for &pivot in &[1, 3, 7, 15, 31, 63] {
@@ -80,17 +82,17 @@ fn exponential_search(arr: &[u32], target: u32) -> (usize, usize) {
            break;
        }
        if arr[pivot] > target {
-            return (begin, pivot);
+            return begin..pivot;
        }
        begin = pivot;
    }
-    (begin, end)
+    begin..end
 }

 #[inline(never)]
 fn galloping(block_docs: &[u32], target: u32) -> usize {
-    let (start, end) = exponential_search(&block_docs, target);
-    start + linear_search(&block_docs[start..end], target)
+    let range = exponential_search(&block_docs, target);
+    range.start + linear_search(&block_docs[range], target)
 }

 /// Tantivy may rely on SIMD instructions to search for a specific document within
@@ -182,11 +184,11 @@ mod tests {

    #[test]
    fn test_exponentiel_search() {
-        assert_eq!(exponential_search(&[1, 2], 0), (0, 1));
-        assert_eq!(exponential_search(&[1, 2], 1), (0, 1));
+        assert_eq!(exponential_search(&[1, 2], 0), 0..1);
+        assert_eq!(exponential_search(&[1, 2], 1), 0..1);
        assert_eq!(
            exponential_search(&[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11], 7),
-            (3, 7)
+            3..7
        );
    }

--- a/src/postings/postings_writer.rs
+++ b/src/postings/postings_writer.rs
@@ -16,7 +16,7 @@ use fnv::FnvHashMap;
 use std::collections::HashMap;
 use std::io;
 use std::marker::PhantomData;
-use std::ops::DerefMut;
+use std::ops::{DerefMut, Range};

 fn posting_from_field_entry(field_entry: &FieldEntry) -> Box<dyn PostingsWriter> {
    match *field_entry.field_type() {
@@ -39,7 +39,9 @@ fn posting_from_field_entry(field_entry: &FieldEntry) -> Box<dyn PostingsWriter>
        | FieldType::F64(_)
        | FieldType::Date(_)
        | FieldType::Bytes(_)
-        | FieldType::HierarchicalFacet => SpecializedPostingsWriter::<NothingRecorder>::new_boxed(),
+        | FieldType::HierarchicalFacet(_) => {
+            SpecializedPostingsWriter::<NothingRecorder>::new_boxed()
+        }
    }
 }

@@ -52,7 +54,7 @@ pub struct MultiFieldPostingsWriter {

 fn make_field_partition(
    term_offsets: &[(&[u8], Addr, UnorderedTermId)],
-) -> Vec<(Field, usize, usize)> {
+) -> Vec<(Field, Range<usize>)> {
    let term_offsets_it = term_offsets
        .iter()
        .map(|(key, _, _)| Term::wrap(key).field())
@@ -70,7 +72,7 @@ fn make_field_partition(
    offsets.push(term_offsets.len());
    let mut field_offsets = vec![];
    for i in 0..fields.len() {
-        field_offsets.push((fields[i], offsets[i], offsets[i + 1]));
+        field_offsets.push((fields[i], offsets[i]..offsets[i + 1]));
    }
    field_offsets
 }
@@ -138,14 +140,14 @@ impl MultiFieldPostingsWriter {

        let field_offsets = make_field_partition(&term_offsets);

-        for (field, start, stop) in field_offsets {
+        for (field, byte_offsets) in field_offsets {
            let field_entry = self.schema.get_field_entry(field);

            match *field_entry.field_type() {
-                FieldType::Str(_) | FieldType::HierarchicalFacet => {
+                FieldType::Str(_) | FieldType::HierarchicalFacet(_) => {
                    // populating the (unordered term ord) -> (ordered term ord) mapping
                    // for the field.
-                    let unordered_term_ids = term_offsets[start..stop]
+                    let unordered_term_ids = term_offsets[byte_offsets.clone()]
                        .iter()
                        .map(|&(_, _, bucket)| bucket);
                    let mapping: FnvHashMap<UnorderedTermId, TermOrdinal> = unordered_term_ids
@@ -169,7 +171,7 @@ impl MultiFieldPostingsWriter {
                fieldnorm_reader,
            )?;
            postings_writer.serialize(
-                &term_offsets[start..stop],
+                &term_offsets[byte_offsets],
                &mut field_serializer,
                &self.term_index.heap,
                &self.heap,
--- a/src/postings/segment_postings.rs
+++ b/src/postings/segment_postings.rs
@@ -99,9 +99,9 @@ impl SegmentPostings {
        fieldnorms: Option<&[u32]>,
    ) -> SegmentPostings {
        use crate::directory::FileSlice;
+        use crate::fieldnorm::FieldNormReader;
        use crate::postings::serializer::PostingsSerializer;
        use crate::schema::IndexRecordOption;
-        use crate::fieldnorm::FieldNormReader;
        use crate::Score;
        let mut buffer: Vec<u8> = Vec::new();
        let fieldnorm_reader = fieldnorms.map(FieldNormReader::for_test);
--- a/src/postings/serializer.rs
+++ b/src/postings/serializer.rs
@@ -55,33 +55,17 @@ pub struct InvertedIndexSerializer {
 }

 impl InvertedIndexSerializer {
-    /// Open a new `InvertedIndexSerializer` for the given segment
-    fn create(
-        terms_write: CompositeWrite<WritePtr>,
-        postings_write: CompositeWrite<WritePtr>,
-        positions_write: CompositeWrite<WritePtr>,
-        positionsidx_write: CompositeWrite<WritePtr>,
-        schema: Schema,
-    ) -> crate::Result<InvertedIndexSerializer> {
-        Ok(InvertedIndexSerializer {
-            terms_write,
-            postings_write,
-            positions_write,
-            positionsidx_write,
-            schema,
-        })
-    }
-
    /// Open a new `PostingsSerializer` for the given segment
    pub fn open(segment: &mut Segment) -> crate::Result<InvertedIndexSerializer> {
        use crate::SegmentComponent::{POSITIONS, POSITIONSSKIP, POSTINGS, TERMS};
-        InvertedIndexSerializer::create(
-            CompositeWrite::wrap(segment.open_write(TERMS)?),
-            CompositeWrite::wrap(segment.open_write(POSTINGS)?),
-            CompositeWrite::wrap(segment.open_write(POSITIONS)?),
-            CompositeWrite::wrap(segment.open_write(POSITIONSSKIP)?),
-            segment.schema(),
-        )
+        let inv_index_serializer = InvertedIndexSerializer {
+            terms_write: CompositeWrite::wrap(segment.open_write(TERMS)?),
+            postings_write: CompositeWrite::wrap(segment.open_write(POSTINGS)?),
+            positions_write: CompositeWrite::wrap(segment.open_write(POSITIONS)?),
+            positionsidx_write: CompositeWrite::wrap(segment.open_write(POSITIONSSKIP)?),
+            schema: segment.schema(),
+        };
+        Ok(inv_index_serializer)
    }

    /// Must be called before starting pushing terms of
@@ -183,10 +167,10 @@ impl<'a> FieldSerializer<'a> {
            } else {
                0u64
            };
+        let addr = self.postings_serializer.addr() as usize;
        TermInfo {
            doc_freq: 0,
-            postings_start_offset: self.postings_serializer.addr(),
-            postings_stop_offset: 0u64,
+            postings_range: addr..addr,
            positions_idx,
        }
    }
@@ -242,7 +226,7 @@ impl<'a> FieldSerializer<'a> {
        if self.term_open {
            self.postings_serializer
                .close_term(self.current_term_info.doc_freq)?;
-            self.current_term_info.postings_stop_offset = self.postings_serializer.addr();
+            self.current_term_info.postings_range.end = self.postings_serializer.addr() as usize;
            self.term_dictionary_builder
                .insert_value(&self.current_term_info)?;
            self.term_open = false;
--- a/src/postings/stacker/term_hashmap.rs
+++ b/src/postings/stacker/term_hashmap.rs
@@ -17,10 +17,6 @@ pub fn compute_table_size(num_bits: usize) -> usize {
 /// `KeyValue` is the item stored in the hash table.
 /// The key is actually a `BytesRef` object stored in an external heap.
 /// The `value_addr` also points to an address in the heap.
-///
-/// The key and the value are actually stored contiguously.
-/// For this reason, the (start, stop) information is actually redundant
-/// and can be simplified in the future
 #[derive(Copy, Clone)]
 struct KeyValue {
    key_value_addr: Addr,
--- a/src/postings/term_info.rs
+++ b/src/postings/term_info.rs
@@ -1,25 +1,24 @@
 use crate::common::{BinarySerializable, FixedSize};
 use std::io;
+use std::iter::ExactSizeIterator;
+use std::ops::Range;

 /// `TermInfo` wraps the metadata associated to a Term.
 /// It is segment-local.
-#[derive(Debug, Default, Ord, PartialOrd, Eq, PartialEq, Clone)]
+#[derive(Debug, Default, Eq, PartialEq, Clone)]
 pub struct TermInfo {
    /// Number of documents in the segment containing the term
    pub doc_freq: u32,
-    /// 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,
+    /// Byte range of the posting list within the postings (`.idx`) file.
+    pub postings_range: Range<usize>,
    /// 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);
+        let num_bytes = self.postings_range.len();
+        assert!(num_bytes <= std::u32::MAX as usize);
        num_bytes as u32
    }
 }
@@ -35,7 +34,7 @@ impl FixedSize for TermInfo {
 impl BinarySerializable for TermInfo {
    fn serialize<W: io::Write>(&self, writer: &mut W) -> io::Result<()> {
        self.doc_freq.serialize(writer)?;
-        self.postings_start_offset.serialize(writer)?;
+        (self.postings_range.start as u64).serialize(writer)?;
        self.posting_num_bytes().serialize(writer)?;
        self.positions_idx.serialize(writer)?;
        Ok(())
@@ -43,14 +42,13 @@ impl BinarySerializable for TermInfo {

    fn deserialize<R: io::Read>(reader: &mut R) -> io::Result<Self> {
        let doc_freq = u32::deserialize(reader)?;
-        let postings_start_offset = u64::deserialize(reader)?;
+        let postings_start_offset = u64::deserialize(reader)? as usize;
        let postings_num_bytes = u32::deserialize(reader)?;
-        let postings_stop_offset = postings_start_offset + u64::from(postings_num_bytes);
+        let postings_end_offset = postings_start_offset + u64::from(postings_num_bytes) as usize;
        let positions_idx = u64::deserialize(reader)?;
        Ok(TermInfo {
            doc_freq,
-            postings_start_offset,
-            postings_stop_offset,
+            postings_range: postings_start_offset..postings_end_offset,
            positions_idx,
        })
    }
--- a/src/query/query_parser/query_parser.rs
+++ b/src/query/query_parser/query_parser.rs
@@ -357,7 +357,7 @@ impl QueryParser {
                    ))
                }
            }
-            FieldType::HierarchicalFacet => {
+            FieldType::HierarchicalFacet(_) => {
                let facet = Facet::from_text(phrase);
                Ok(vec![(0, Term::from_field_text(field, facet.encoded_str()))])
            }
@@ -605,7 +605,8 @@ mod test {
        schema_builder.add_text_field("with_stop_words", text_options);
        schema_builder.add_date_field("date", INDEXED);
        schema_builder.add_f64_field("float", INDEXED);
-        schema_builder.add_facet_field("facet");
+        schema_builder.add_facet_field("facet", INDEXED);
+        schema_builder.add_facet_field("facet_not_indexed", STORED);
        schema_builder.add_bytes_field("bytes", INDEXED);
        schema_builder.add_bytes_field("bytes_not_indexed", STORED);
        schema_builder.build()
@@ -658,6 +659,13 @@ mod test {
        );
    }

+    #[test]
+    fn test_parse_query_facet_not_indexed() {
+        let error =
+            parse_query_to_logical_ast("facet_not_indexed:/root/branch/leaf", false).unwrap_err();
+        assert!(matches!(error, QueryParserError::FieldNotIndexed(_)));
+    }
+
    #[test]
    pub fn test_parse_query_with_boost() {
        let mut query_parser = make_query_parser();
@@ -799,7 +807,7 @@ mod test {
    fn test_parse_bytes() {
        test_parse_query_to_logical_ast_helper(
            "bytes:YnVidQ==",
-            "Term(field=12,bytes=[98, 117, 98, 117])",
+            "Term(field=13,bytes=[98, 117, 98, 117])",
            false,
        );
    }
@@ -814,7 +822,7 @@ mod test {
    fn test_parse_bytes_phrase() {
        test_parse_query_to_logical_ast_helper(
            "bytes:\"YnVidQ==\"",
-            "Term(field=12,bytes=[98, 117, 98, 117])",
+            "Term(field=13,bytes=[98, 117, 98, 117])",
            false,
        );
    }
--- a/src/query/range_query.rs
+++ b/src/query/range_query.rs
@@ -10,9 +10,8 @@ use crate::schema::Type;
 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;
+use std::ops::{Bound, Range};

 fn map_bound<TFrom, TTo, Transform: Fn(&TFrom) -> TTo>(
    bound: &Bound<TFrom>,
@@ -276,7 +275,7 @@ pub struct RangeWeight {

 impl RangeWeight {
    fn term_range<'a>(&self, term_dict: &'a TermDictionary) -> io::Result<TermStreamer<'a>> {
-        use std::collections::Bound::*;
+        use std::ops::Bound::*;
        let mut term_stream_builder = term_dict.range();
        term_stream_builder = match self.left_bound {
            Included(ref term_val) => term_stream_builder.ge(term_val),
@@ -336,7 +335,7 @@ mod tests {
    use crate::query::QueryParser;
    use crate::schema::{Document, Field, Schema, INDEXED, TEXT};
    use crate::Index;
-    use std::collections::Bound;
+    use std::ops::Bound;

    #[test]
    fn test_range_query_simple() {
--- a/src/reader/pool.rs
+++ b/src/reader/pool.rs
@@ -100,20 +100,32 @@ impl<T> Pool<T> {

    /// At the exit of this method,
    /// - freshest_generation has a value greater or equal than generation
-    /// - freshest_generation has a value that has been advertised
-    /// - freshest_generation has)
+    /// - freshest_generation has the last value that has been advertised
    fn advertise_generation(&self, generation: usize) {
        // not optimal at all but the easiest to read proof.
+        let mut former_generation = self.freshest_generation.load(Ordering::Acquire);
        loop {
-            let former_generation = self.freshest_generation.load(Ordering::Acquire);
-            if former_generation >= generation {
-                break;
-            }
-            self.freshest_generation.compare_and_swap(
+            match self.freshest_generation.compare_exchange(
                former_generation,
                generation,
                Ordering::SeqCst,
-            );
+                Ordering::SeqCst,
+            ) {
+                Ok(_) => {
+                    // We successfuly updated the value.
+                    return;
+                }
+                Err(current_generation) => {
+                    // The value was updated after we did our load apparently.
+                    // In theory, it is always a value greater than ours, but just to
+                    // simplify the logic, we keep looping until we reach a
+                    // value >= to our target value.
+                    if current_generation >= generation {
+                        return;
+                    }
+                    former_generation = current_generation;
+                }
+            }
        }
    }

--- a/src/schema/facet_options.rs
+++ b/src/schema/facet_options.rs
@@ -0,0 +1,96 @@
+use crate::schema::flags::{IndexedFlag, SchemaFlagList, StoredFlag};
+use serde::{Deserialize, Serialize};
+use std::ops::BitOr;
+
+/// Define how a facet field should be handled by tantivy.
+#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
+pub struct FacetOptions {
+    indexed: bool,
+    stored: bool,
+}
+
+impl FacetOptions {
+    /// Returns true iff the value is stored.
+    pub fn is_stored(&self) -> bool {
+        self.stored
+    }
+
+    /// Returns true iff the value is indexed.
+    pub fn is_indexed(&self) -> bool {
+        self.indexed
+    }
+
+    /// Set the field as stored.
+    ///
+    /// Only the fields that are set as *stored* are
+    /// persisted into the Tantivy's store.
+    pub fn set_stored(mut self) -> FacetOptions {
+        self.stored = true;
+        self
+    }
+
+    /// Set the field as indexed.
+    ///
+    /// Setting a facet as indexed will generate
+    /// a walkable path.
+    pub fn set_indexed(mut self) -> FacetOptions {
+        self.indexed = true;
+        self
+    }
+}
+
+impl Default for FacetOptions {
+    fn default() -> FacetOptions {
+        FacetOptions {
+            indexed: false,
+            stored: false,
+        }
+    }
+}
+
+impl From<()> for FacetOptions {
+    fn from(_: ()) -> FacetOptions {
+        FacetOptions::default()
+    }
+}
+
+impl From<StoredFlag> for FacetOptions {
+    fn from(_: StoredFlag) -> Self {
+        FacetOptions {
+            indexed: false,
+            stored: true,
+        }
+    }
+}
+
+impl From<IndexedFlag> for FacetOptions {
+    fn from(_: IndexedFlag) -> Self {
+        FacetOptions {
+            indexed: true,
+            stored: false,
+        }
+    }
+}
+
+impl<T: Into<FacetOptions>> BitOr<T> for FacetOptions {
+    type Output = FacetOptions;
+
+    fn bitor(self, other: T) -> FacetOptions {
+        let other = other.into();
+        FacetOptions {
+            indexed: self.indexed | other.indexed,
+            stored: self.stored | other.stored,
+        }
+    }
+}
+
+impl<Head, Tail> From<SchemaFlagList<Head, Tail>> for FacetOptions
+where
+    Head: Clone,
+    Tail: Clone,
+    Self: BitOr<Output = Self> + From<Head> + From<Tail>,
+{
+    fn from(head_tail: SchemaFlagList<Head, Tail>) -> Self {
+        Self::from(head_tail.head) | Self::from(head_tail.tail)
+    }
+}
--- a/src/schema/field_entry.rs
+++ b/src/schema/field_entry.rs
@@ -1,3 +1,4 @@
+use crate::schema::FacetOptions;
 use crate::schema::TextOptions;
 use crate::schema::{is_valid_field_name, IntOptions};

@@ -73,11 +74,11 @@ impl FieldEntry {
    }

    /// Creates a field entry for a facet.
-    pub fn new_facet(field_name: String) -> FieldEntry {
+    pub fn new_facet(field_name: String, field_type: FacetOptions) -> FieldEntry {
        assert!(is_valid_field_name(&field_name));
        FieldEntry {
            name: field_name,
-            field_type: FieldType::HierarchicalFacet,
+            field_type: FieldType::HierarchicalFacet(field_type),
        }
    }

@@ -107,7 +108,7 @@ impl FieldEntry {
            | FieldType::I64(ref options)
            | FieldType::F64(ref options)
            | FieldType::Date(ref options) => options.is_indexed(),
-            FieldType::HierarchicalFacet => true,
+            FieldType::HierarchicalFacet(ref options) => options.is_indexed(),
            FieldType::Bytes(ref options) => options.is_indexed(),
        }
    }
@@ -131,8 +132,7 @@ impl FieldEntry {
            | FieldType::F64(ref options)
            | FieldType::Date(ref options) => options.is_stored(),
            FieldType::Str(ref options) => options.is_stored(),
-            // TODO make stored hierarchical facet optional
-            FieldType::HierarchicalFacet => true,
+            FieldType::HierarchicalFacet(ref options) => options.is_stored(),
            FieldType::Bytes(ref options) => options.is_stored(),
        }
    }
@@ -167,8 +167,9 @@ impl Serialize for FieldEntry {
                s.serialize_field("type", "date")?;
                s.serialize_field("options", options)?;
            }
-            FieldType::HierarchicalFacet => {
+            FieldType::HierarchicalFacet(ref options) => {
                s.serialize_field("type", "hierarchical_facet")?;
+                s.serialize_field("options", options)?;
            }
            FieldType::Bytes(ref options) => {
                s.serialize_field("type", "bytes")?;
@@ -225,10 +226,8 @@ impl<'de> Deserialize<'de> for FieldEntry {
                            }
                            let type_string = map.next_value::<String>()?;
                            match type_string.as_str() {
-                                "hierarchical_facet" => {
-                                    field_type = Some(FieldType::HierarchicalFacet);
-                                }
-                                "text" | "u64" | "i64" | "f64" | "date" | "bytes" => {
+                                "text" | "u64" | "i64" | "f64" | "date" | "bytes"
+                                | "hierarchical_facet" => {
                                    // These types require additional options to create a field_type
                                }
                                _ => panic!("unhandled type"),
@@ -248,6 +247,10 @@ impl<'de> Deserialize<'de> for FieldEntry {
                                "f64" => field_type = Some(FieldType::F64(map.next_value()?)),
                                "date" => field_type = Some(FieldType::Date(map.next_value()?)),
                                "bytes" => field_type = Some(FieldType::Bytes(map.next_value()?)),
+                                "hierarchical_facet" => {
+                                    field_type =
+                                        Some(FieldType::HierarchicalFacet(map.next_value()?))
+                                }
                                _ => {
                                    let msg = format!("Unrecognised type {}", ty);
                                    return Err(de::Error::custom(msg));
--- a/src/schema/field_type.rs
+++ b/src/schema/field_type.rs
@@ -1,4 +1,5 @@
 use crate::schema::bytes_options::BytesOptions;
+use crate::schema::facet_options::FacetOptions;
 use crate::schema::Facet;
 use crate::schema::IndexRecordOption;
 use crate::schema::TextFieldIndexing;
@@ -60,7 +61,7 @@ pub enum FieldType {
    /// Signed 64-bits Date 64 field type configuration,
    Date(IntOptions),
    /// Hierachical Facet
-    HierarchicalFacet,
+    HierarchicalFacet(FacetOptions),
    /// Bytes (one per document)
    Bytes(BytesOptions),
 }
@@ -74,7 +75,7 @@ impl FieldType {
            FieldType::I64(_) => Type::I64,
            FieldType::F64(_) => Type::F64,
            FieldType::Date(_) => Type::Date,
-            FieldType::HierarchicalFacet => Type::HierarchicalFacet,
+            FieldType::HierarchicalFacet(_) => Type::HierarchicalFacet,
            FieldType::Bytes(_) => Type::Bytes,
        }
    }
@@ -87,7 +88,7 @@ impl FieldType {
            | FieldType::I64(ref int_options)
            | FieldType::F64(ref int_options) => int_options.is_indexed(),
            FieldType::Date(ref date_options) => date_options.is_indexed(),
-            FieldType::HierarchicalFacet => true,
+            FieldType::HierarchicalFacet(ref facet_options) => facet_options.is_indexed(),
            FieldType::Bytes(ref bytes_options) => bytes_options.is_indexed(),
        }
    }
@@ -111,7 +112,13 @@ impl FieldType {
                    None
                }
            }
-            FieldType::HierarchicalFacet => Some(IndexRecordOption::Basic),
+            FieldType::HierarchicalFacet(ref facet_options) => {
+                if facet_options.is_indexed() {
+                    Some(IndexRecordOption::Basic)
+                } else {
+                    None
+                }
+            }
            FieldType::Bytes(ref bytes_options) => {
                if bytes_options.is_indexed() {
                    Some(IndexRecordOption::Basic)
@@ -144,7 +151,7 @@ impl FieldType {
                FieldType::U64(_) | FieldType::I64(_) | FieldType::F64(_) => Err(
                    ValueParsingError::TypeError(format!("Expected an integer, got {:?}", json)),
                ),
-                FieldType::HierarchicalFacet => Ok(Value::Facet(Facet::from(field_text))),
+                FieldType::HierarchicalFacet(_) => Ok(Value::Facet(Facet::from(field_text))),
                FieldType::Bytes(_) => base64::decode(field_text).map(Value::Bytes).map_err(|_| {
                    ValueParsingError::InvalidBase64(format!(
                        "Expected base64 string, got {:?}",
@@ -177,7 +184,7 @@ impl FieldType {
                        Err(ValueParsingError::OverflowError(msg))
                    }
                }
-                FieldType::Str(_) | FieldType::HierarchicalFacet | FieldType::Bytes(_) => {
+                FieldType::Str(_) | FieldType::HierarchicalFacet(_) | FieldType::Bytes(_) => {
                    let msg = format!("Expected a string, got {:?}", json);
                    Err(ValueParsingError::TypeError(msg))
                }
--- a/src/schema/mod.rs
+++ b/src/schema/mod.rs
@@ -104,6 +104,7 @@ let schema = schema_builder.build();

 mod document;
 mod facet;
+mod facet_options;
 mod schema;
 mod term;

@@ -128,6 +129,7 @@ pub use self::value::Value;

 pub use self::facet::Facet;
 pub(crate) use self::facet::FACET_SEP_BYTE;
+pub use self::facet_options::FacetOptions;

 pub use self::document::Document;
 pub use self::field::Field;
--- a/src/schema/schema.rs
+++ b/src/schema/schema.rs
@@ -146,8 +146,12 @@ impl SchemaBuilder {
    }

    /// Adds a facet field to the schema.
-    pub fn add_facet_field(&mut self, field_name: &str) -> Field {
-        let field_entry = FieldEntry::new_facet(field_name.to_string());
+    pub fn add_facet_field<T: Into<FacetOptions>>(
+        &mut self,
+        field_name: &str,
+        facet_options: T,
+    ) -> Field {
+        let field_entry = FieldEntry::new_facet(field_name.to_string(), facet_options.into());
        self.add_field(field_entry)
    }

@@ -665,7 +669,10 @@ mod tests {
            );
            assert_matches!(
                json_err,
-                Err(DocParsingError::ValueError(_, ValueParsingError::TypeError(_)))
+                Err(DocParsingError::ValueError(
+                    _,
+                    ValueParsingError::TypeError(_)
+                ))
            );
        }
        {
@@ -680,7 +687,10 @@ mod tests {
            );
            assert_matches!(
                json_err,
-                Err(DocParsingError::ValueError(_, ValueParsingError::OverflowError(_)))
+                Err(DocParsingError::ValueError(
+                    _,
+                    ValueParsingError::OverflowError(_)
+                ))
            );
        }
        {
@@ -695,7 +705,10 @@ mod tests {
            );
            assert!(!matches!(
                json_err,
-                Err(DocParsingError::ValueError(_, ValueParsingError::OverflowError(_)))
+                Err(DocParsingError::ValueError(
+                    _,
+                    ValueParsingError::OverflowError(_)
+                ))
            ));
        }
        {
@@ -710,7 +723,10 @@ mod tests {
            );
            assert_matches!(
                json_err,
-                Err(DocParsingError::ValueError(_, ValueParsingError::OverflowError(_)))
+                Err(DocParsingError::ValueError(
+                    _,
+                    ValueParsingError::OverflowError(_)
+                ))
            );
        }
        {
--- a/src/schema/value.rs
+++ b/src/schema/value.rs
@@ -137,6 +137,16 @@ impl Value {
        }
    }

+    /// Returns the path value, provided the value is of the `Facet` type.
+    /// (Returns None if the value is not of the `Facet` type).
+    pub fn path(&self) -> Option<String> {
+        if let Value::Facet(facet) = self {
+            Some(facet.to_path_string())
+        } else {
+            None
+        }
+    }
+
    /// Returns the tokenized text, provided the value is of the `PreTokStr` type.
    ///
    /// Returns None if the value is not of the `PreTokStr` type.
--- a/src/snippet/mod.rs
+++ b/src/snippet/mod.rs
@@ -8,33 +8,17 @@ use htmlescape::encode_minimal;
 use std::cmp::Ordering;
 use std::collections::BTreeMap;
 use std::collections::BTreeSet;
+use std::ops::Range;

 const DEFAULT_MAX_NUM_CHARS: usize = 150;

-#[derive(Debug)]
-pub struct HighlightSection {
-    start: usize,
-    stop: usize,
-}
-
-impl HighlightSection {
-    fn new(start: usize, stop: usize) -> HighlightSection {
-        HighlightSection { start, stop }
-    }
-
-    /// Returns the bounds of the `HighlightSection`.
-    pub fn bounds(&self) -> (usize, usize) {
-        (self.start, self.stop)
-    }
-}
-
 #[derive(Debug)]
 pub struct FragmentCandidate {
    score: Score,
    start_offset: usize,
    stop_offset: usize,
    num_chars: usize,
-    highlighted: Vec<HighlightSection>,
+    highlighted: Vec<Range<usize>>,
 }

 impl FragmentCandidate {
@@ -63,8 +47,7 @@ impl FragmentCandidate {

        if let Some(&score) = terms.get(&token.text.to_lowercase()) {
            self.score += score;
-            self.highlighted
-                .push(HighlightSection::new(token.offset_from, token.offset_to));
+            self.highlighted.push(token.offset_from..token.offset_to);
        }
    }
 }
@@ -74,7 +57,7 @@ impl FragmentCandidate {
 #[derive(Debug)]
 pub struct Snippet {
    fragments: String,
-    highlighted: Vec<HighlightSection>,
+    highlighted: Vec<Range<usize>>,
 }

 const HIGHLIGHTEN_PREFIX: &str = "<b>";
@@ -97,9 +80,9 @@ impl Snippet {
        for item in self.highlighted.iter() {
            html.push_str(&encode_minimal(&self.fragments[start_from..item.start]));
            html.push_str(HIGHLIGHTEN_PREFIX);
-            html.push_str(&encode_minimal(&self.fragments[item.start..item.stop]));
+            html.push_str(&encode_minimal(&self.fragments[item.clone()]));
            html.push_str(HIGHLIGHTEN_POSTFIX);
-            start_from = item.stop;
+            start_from = item.end;
        }
        html.push_str(&encode_minimal(
            &self.fragments[start_from..self.fragments.len()],
@@ -113,7 +96,7 @@ impl Snippet {
    }

    /// Returns a list of higlighted positions from the `Snippet`.
-    pub fn highlighted(&self) -> &[HighlightSection] {
+    pub fn highlighted(&self) -> &[Range<usize>] {
        &self.highlighted
    }
 }
@@ -185,12 +168,7 @@ fn select_best_fragment_combination(fragments: &[FragmentCandidate], text: &str)
        let highlighted = fragment
            .highlighted
            .iter()
-            .map(|item| {
-                HighlightSection::new(
-                    item.start - fragment.start_offset,
-                    item.stop - fragment.start_offset,
-                )
-            })
+            .map(|item| item.start - fragment.start_offset..item.end - fragment.start_offset)
            .collect();
        Snippet {
            fragments: fragment_text.to_string(),
--- a/src/store/index/block.rs
+++ b/src/store/index/block.rs
@@ -2,6 +2,7 @@ use crate::common::VInt;
 use crate::store::index::{Checkpoint, CHECKPOINT_PERIOD};
 use crate::DocId;
 use std::io;
+use std::ops::Range;

 /// Represents a block of checkpoints.
 ///
@@ -24,19 +25,19 @@ impl Default for CheckpointBlock {
 impl CheckpointBlock {
    /// If non-empty returns [start_doc, end_doc)
    /// for the overall block.
-    pub fn doc_interval(&self) -> Option<(DocId, DocId)> {
+    pub fn doc_interval(&self) -> Option<Range<DocId>> {
        let start_doc_opt = self
            .checkpoints
            .first()
            .cloned()
-            .map(|checkpoint| checkpoint.start_doc);
+            .map(|checkpoint| checkpoint.doc_range.start);
        let end_doc_opt = self
            .checkpoints
            .last()
            .cloned()
-            .map(|checkpoint| checkpoint.end_doc);
+            .map(|checkpoint| checkpoint.doc_range.end);
        match (start_doc_opt, end_doc_opt) {
-            (Some(start_doc), Some(end_doc)) => Some((start_doc, end_doc)),
+            (Some(start_doc), Some(end_doc)) => Some(start_doc..end_doc),
            _ => None,
        }
    }
@@ -55,7 +56,7 @@ impl CheckpointBlock {
    }

    pub fn get(&self, idx: usize) -> Checkpoint {
-        self.checkpoints[idx]
+        self.checkpoints[idx].clone()
    }

    pub fn clear(&mut self) {
@@ -67,12 +68,13 @@ impl CheckpointBlock {
        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);
+        VInt(self.checkpoints[0].doc_range.start as u64).serialize_into_vec(buffer);
+        VInt(self.checkpoints[0].byte_range.start as u64).serialize_into_vec(buffer);
        for checkpoint in &self.checkpoints {
-            let delta_doc = checkpoint.end_doc - checkpoint.start_doc;
+            let delta_doc = checkpoint.doc_range.end - checkpoint.doc_range.start;
            VInt(delta_doc as u64).serialize_into_vec(buffer);
-            VInt(checkpoint.end_offset - checkpoint.start_offset).serialize_into_vec(buffer);
+            VInt((checkpoint.byte_range.end - checkpoint.byte_range.start) as u64)
+                .serialize_into_vec(buffer);
        }
    }

@@ -86,15 +88,13 @@ impl CheckpointBlock {
            return Ok(());
        }
        let mut doc = VInt::deserialize_u64(data)? as DocId;
-        let mut start_offset = VInt::deserialize_u64(data)?;
+        let mut start_offset = VInt::deserialize_u64(data)? as usize;
        for _ in 0..len {
            let num_docs = VInt::deserialize_u64(data)? as DocId;
-            let block_num_bytes = VInt::deserialize_u64(data)?;
+            let block_num_bytes = VInt::deserialize_u64(data)? as usize;
            self.checkpoints.push(Checkpoint {
-                start_doc: doc,
-                end_doc: doc + num_docs,
-                start_offset,
-                end_offset: start_offset + block_num_bytes,
+                doc_range: doc..doc + num_docs,
+                byte_range: start_offset..start_offset + block_num_bytes,
            });
            doc += num_docs;
            start_offset += block_num_bytes;
@@ -112,17 +112,15 @@ mod tests {

    fn test_aux_ser_deser(checkpoints: &[Checkpoint]) -> io::Result<()> {
        let mut block = CheckpointBlock::default();
-        for &checkpoint in checkpoints {
-            block.push(checkpoint);
+        for checkpoint in checkpoints {
+            block.push(checkpoint.clone());
        }
        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,
+            doc_range: 0..1,
+            byte_range: 2..3,
        };
        block_deser.push(checkpoint); // < check that value is erased before deser
        let mut data = &buffer[..];
@@ -140,26 +138,22 @@ mod tests {
    #[test]
    fn test_block_serialize_simple() -> io::Result<()> {
        let checkpoints = vec![Checkpoint {
-            start_doc: 10,
-            end_doc: 12,
-            start_offset: 100,
-            end_offset: 120,
+            doc_range: 10..12,
+            byte_range: 100..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 offsets: Vec<usize> = (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],
+                doc_range: start_doc..end_doc,
+                byte_range: offsets[i]..offsets[i + 1],
            });
            start_doc = end_doc;
        }
--- a/src/store/index/mod.rs
+++ b/src/store/index/mod.rs
@@ -1,6 +1,7 @@
 const CHECKPOINT_PERIOD: usize = 8;

 use std::fmt;
+use std::ops::Range;
 mod block;
 mod skip_index;
 mod skip_index_builder;
@@ -15,30 +16,24 @@ pub use self::skip_index_builder::SkipIndexBuilder;
 /// 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)]
+/// The checkpoint describes that the block within the `byte_range`
+/// and spans over the `doc_range`.
+#[derive(Clone, Eq, PartialEq)]
 pub struct Checkpoint {
-    pub start_doc: DocId,
-    pub end_doc: DocId,
-    pub start_offset: u64,
-    pub end_offset: u64,
+    pub doc_range: Range<DocId>,
+    pub byte_range: Range<usize>,
 }

 impl Checkpoint {
    pub(crate) fn follows(&self, other: &Checkpoint) -> bool {
-        (self.start_doc == other.end_doc) && (self.start_offset == other.end_offset)
+        (self.doc_range.start == other.doc_range.end)
+            && (self.byte_range.start == other.byte_range.end)
    }
 }

 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
-        )
+        write!(f, "(doc={:?}, bytes={:?})", self.doc_range, self.byte_range)
    }
 }

@@ -74,12 +69,10 @@ mod tests {
        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,
+            doc_range: 0..2,
+            byte_range: 0..3,
        };
-        skip_index_builder.insert(checkpoint);
+        skip_index_builder.insert(checkpoint.clone());
        skip_index_builder.write(&mut output)?;
        let skip_index: SkipIndex = SkipIndex::open(OwnedBytes::new(output));
        let mut skip_cursor = skip_index.checkpoints();
@@ -93,40 +86,30 @@ mod tests {
        let mut output: Vec<u8> = Vec::new();
        let checkpoints = vec![
            Checkpoint {
-                start_doc: 0,
-                end_doc: 3,
-                start_offset: 0,
-                end_offset: 9,
+                doc_range: 0..3,
+                byte_range: 0..9,
            },
            Checkpoint {
-                start_doc: 3,
-                end_doc: 4,
-                start_offset: 9,
-                end_offset: 25,
+                doc_range: 3..4,
+                byte_range: 9..25,
            },
            Checkpoint {
-                start_doc: 4,
-                end_doc: 6,
-                start_offset: 25,
-                end_offset: 49,
+                doc_range: 4..6,
+                byte_range: 25..49,
            },
            Checkpoint {
-                start_doc: 6,
-                end_doc: 8,
-                start_offset: 49,
-                end_offset: 81,
+                doc_range: 6..8,
+                byte_range: 49..81,
            },
            Checkpoint {
-                start_doc: 8,
-                end_doc: 10,
-                start_offset: 81,
-                end_offset: 100,
+                doc_range: 8..10,
+                byte_range: 81..100,
            },
        ];

        let mut skip_index_builder: SkipIndexBuilder = SkipIndexBuilder::new();
-        for &checkpoint in &checkpoints {
-            skip_index_builder.insert(checkpoint);
+        for checkpoint in &checkpoints {
+            skip_index_builder.insert(checkpoint.clone());
        }
        skip_index_builder.write(&mut output)?;

@@ -138,8 +121,8 @@ mod tests {
        Ok(())
    }

-    fn offset_test(doc: DocId) -> u64 {
-        (doc as u64) * (doc as u64)
+    fn offset_test(doc: DocId) -> usize {
+        (doc as usize) * (doc as usize)
    }

    #[test]
@@ -181,15 +164,13 @@ mod tests {
        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),
+                doc_range: i..(i + 1),
+                byte_range: offset_test(i)..offset_test(i + 1),
            })
            .collect();
        let mut skip_index_builder = SkipIndexBuilder::new();
        for checkpoint in &checkpoints {
-            skip_index_builder.insert(*checkpoint);
+            skip_index_builder.insert(checkpoint.clone());
        }
        skip_index_builder.write(&mut output)?;
        assert_eq!(output.len(), 4035);
@@ -200,10 +181,10 @@ mod tests {
        Ok(())
    }

-    fn integrate_delta(vals: Vec<u64>) -> Vec<u64> {
+    fn integrate_delta(vals: Vec<usize>) -> Vec<usize> {
        let mut output = Vec::with_capacity(vals.len() + 1);
-        output.push(0u64);
-        let mut prev = 0u64;
+        output.push(0);
+        let mut prev = 0;
        for val in vals {
            let new_val = val + prev;
            prev = new_val;
@@ -217,16 +198,14 @@ mod tests {
        (0..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),
+                    proptest::collection::vec(1usize..20, len as usize).prop_map(integrate_delta),
+                    proptest::collection::vec(1usize..26, 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],
+                                doc_range: docs[i] as DocId..docs[i + 1] as DocId,
+                                byte_range: offsets[i]..offsets[i + 1],
                            })
                            .collect::<Vec<Checkpoint>>()
                    })
@@ -240,17 +219,17 @@ mod tests {
    ) -> Option<Checkpoint> {
        checkpoints
            .into_iter()
-            .filter(|checkpoint| checkpoint.end_doc > target)
+            .filter(|checkpoint| checkpoint.doc_range.end > 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 {
+            for doc in 0u32..last_checkpoint.doc_range.end {
                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());
+            assert!(skip_index.seek(last_checkpoint.doc_range.end).is_none());
        }
    }

--- a/src/store/index/skip_index.rs
+++ b/src/store/index/skip_index.rs
@@ -36,21 +36,21 @@ struct Layer {

 impl Layer {
    fn cursor(&self) -> impl Iterator<Item = Checkpoint> + '_ {
-        self.cursor_at_offset(0u64)
+        self.cursor_at_offset(0)
    }

-    fn cursor_at_offset(&self, start_offset: u64) -> impl Iterator<Item = Checkpoint> + '_ {
+    fn cursor_at_offset(&self, start_offset: usize) -> impl Iterator<Item = Checkpoint> + '_ {
        let data = &self.data.as_slice();
        LayerCursor {
-            remaining: &data[start_offset as usize..],
+            remaining: &data[start_offset..],
            block: CheckpointBlock::default(),
            cursor: 0,
        }
    }

-    fn seek_start_at_offset(&self, target: DocId, offset: u64) -> Option<Checkpoint> {
+    fn seek_start_at_offset(&self, target: DocId, offset: usize) -> Option<Checkpoint> {
        self.cursor_at_offset(offset)
-            .find(|checkpoint| checkpoint.end_doc > target)
+            .find(|checkpoint| checkpoint.doc_range.end > target)
    }
 }

@@ -69,7 +69,7 @@ impl SkipIndex {
        let mut layers = Vec::new();
        for end_offset in offsets {
            let layer = Layer {
-                data: data.slice(start_offset as usize, end_offset as usize),
+                data: data.slice(start_offset as usize..end_offset as usize),
            };
            layers.push(layer);
            start_offset = end_offset;
@@ -88,17 +88,15 @@ impl SkipIndex {
        let first_layer_len = self
            .layers
            .first()
-            .map(|layer| layer.data.len() as u64)
-            .unwrap_or(0u64);
+            .map(|layer| layer.data.len())
+            .unwrap_or(0);
        let mut cur_checkpoint = Checkpoint {
-            start_doc: 0u32,
-            end_doc: 1u32,
-            start_offset: 0u64,
-            end_offset: first_layer_len,
+            doc_range: 0u32..1u32,
+            byte_range: 0..first_layer_len,
        };
        for layer in &self.layers {
            if let Some(checkpoint) =
-                layer.seek_start_at_offset(target, cur_checkpoint.start_offset)
+                layer.seek_start_at_offset(target, cur_checkpoint.byte_range.start)
            {
                cur_checkpoint = checkpoint;
            } else {
--- a/src/store/index/skip_index_builder.rs
+++ b/src/store/index/skip_index_builder.rs
@@ -28,16 +28,14 @@ impl LayerBuilder {
    ///
    /// 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;
+        if let Some(doc_range) = self.block.doc_interval() {
+            let start_offset = self.buffer.len();
            self.block.serialize(&mut self.buffer);
-            let end_offset = self.buffer.len() as u64;
+            let end_offset = self.buffer.len();
            self.block.clear();
            Some(Checkpoint {
-                start_doc,
-                end_doc,
-                start_offset,
-                end_offset,
+                doc_range,
+                byte_range: start_offset..end_offset,
            })
        } else {
            None
--- a/src/store/reader.rs
+++ b/src/store/reader.rs
@@ -17,7 +17,7 @@ const LRU_CACHE_CAPACITY: usize = 100;

 type Block = Arc<Vec<u8>>;

-type BlockCache = Arc<Mutex<LruCache<u64, Block>>>;
+type BlockCache = Arc<Mutex<LruCache<usize, Block>>>;

 /// Reads document off tantivy's [`Store`](./index.html)
 pub struct StoreReader {
@@ -59,16 +59,11 @@ impl StoreReader {
    }

    fn compressed_block(&self, checkpoint: &Checkpoint) -> io::Result<OwnedBytes> {
-        self.data
-            .slice(
-                checkpoint.start_offset as usize,
-                checkpoint.end_offset as usize,
-            )
-            .read_bytes()
+        self.data.slice(checkpoint.byte_range.clone()).read_bytes()
    }

    fn read_block(&self, checkpoint: &Checkpoint) -> io::Result<Block> {
-        if let Some(block) = self.cache.lock().unwrap().get(&checkpoint.start_offset) {
+        if let Some(block) = self.cache.lock().unwrap().get(&checkpoint.byte_range.start) {
            self.cache_hits.fetch_add(1, Ordering::SeqCst);
            return Ok(block.clone());
        }
@@ -83,7 +78,7 @@ impl StoreReader {
        self.cache
            .lock()
            .unwrap()
-            .put(checkpoint.start_offset, block.clone());
+            .put(checkpoint.byte_range.start, block.clone());

        Ok(block)
    }
@@ -100,7 +95,7 @@ impl StoreReader {
            crate::TantivyError::InvalidArgument(format!("Failed to lookup Doc #{}.", doc_id))
        })?;
        let mut cursor = &self.read_block(&checkpoint)?[..];
-        for _ in checkpoint.start_doc..doc_id {
+        for _ in checkpoint.doc_range.start..doc_id {
            let doc_length = VInt::deserialize(&mut cursor)?.val() as usize;
            cursor = &cursor[doc_length..];
        }
--- a/src/store/writer.rs
+++ b/src/store/writer.rs
@@ -74,7 +74,7 @@ impl StoreWriter {
        }
        assert_eq!(self.first_doc_in_block, self.doc);
        let doc_shift = self.doc;
-        let start_shift = self.writer.written_bytes() as u64;
+        let start_shift = self.writer.written_bytes() as usize;

        // just bulk write all of the block of the given reader.
        self.writer
@@ -83,34 +83,32 @@ impl StoreWriter {
        // concatenate the index of the `store_reader`, after translating
        // its start doc id and its start file offset.
        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;
+            checkpoint.doc_range.start += doc_shift;
+            checkpoint.doc_range.end += doc_shift;
+            checkpoint.byte_range.start += start_shift;
+            checkpoint.byte_range.end += 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;
+        self.offset_index_writer.insert(checkpoint.clone());
+        self.first_doc_in_block = checkpoint.doc_range.end;
+        self.doc = checkpoint.doc_range.end;
    }

    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)?;
-        let start_offset = self.writer.written_bytes();
+        let start_offset = self.writer.written_bytes() as usize;
        self.writer.write_all(&self.intermediary_buffer)?;
-        let end_offset = self.writer.written_bytes();
+        let end_offset = self.writer.written_bytes() as usize;
        let end_doc = self.doc;
        self.register_checkpoint(Checkpoint {
-            start_doc: self.first_doc_in_block,
-            end_doc,
-            start_offset,
-            end_offset,
+            doc_range: self.first_doc_in_block..end_doc,
+            byte_range: start_offset..end_offset,
        });
        self.current_block.clear();
        Ok(())
--- a/src/termdict/fst_termdict/term_info_store.rs
+++ b/src/termdict/fst_termdict/term_info_store.rs
@@ -68,18 +68,17 @@ impl TermInfoBlockMeta {
        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_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 postings_start_offset = self.ref_term_info.postings_range.start
+            + extract_bits(data, posting_start_addr, self.postings_offset_nbits) as usize;
+        let postings_end_offset = self.ref_term_info.postings_range.start
+            + extract_bits(data, posting_stop_addr, self.postings_offset_nbits) as usize;
        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_start_offset,
-            postings_stop_offset,
+            postings_range: postings_start_offset..postings_end_offset,
            positions_idx,
        }
    }
@@ -163,7 +162,7 @@ fn bitpack_serialize<W: Write>(
    term_info: &TermInfo,
 ) -> io::Result<()> {
    bit_packer.write(
-        term_info.postings_start_offset,
+        term_info.postings_range.start as u64,
        term_info_block_meta.postings_offset_nbits,
        write,
    )?;
@@ -200,15 +199,15 @@ impl TermInfoStoreWriter {
        } else {
            return Ok(());
        };
-        let postings_stop_offset =
-            last_term_info.postings_stop_offset - ref_term_info.postings_start_offset;
+        let postings_end_offset =
+            last_term_info.postings_range.end - ref_term_info.postings_range.start;
        for term_info in &mut self.term_infos[1..] {
-            term_info.postings_start_offset -= ref_term_info.postings_start_offset;
+            term_info.postings_range.start -= ref_term_info.postings_range.start;
            term_info.positions_idx -= ref_term_info.positions_idx;
        }

        let mut max_doc_freq: u32 = 0u32;
-        let max_postings_offset: u64 = postings_stop_offset;
+        let max_postings_offset: usize = postings_end_offset;
        let max_positions_idx: u64 = last_term_info.positions_idx;

        for term_info in &self.term_infos[1..] {
@@ -216,7 +215,7 @@ impl TermInfoStoreWriter {
        }

        let max_doc_freq_nbits: u8 = compute_num_bits(u64::from(max_doc_freq));
-        let max_postings_offset_nbits = compute_num_bits(max_postings_offset);
+        let max_postings_offset_nbits = compute_num_bits(max_postings_offset as u64);
        let max_positions_idx_nbits = compute_num_bits(max_positions_idx);

        let term_info_block_meta = TermInfoBlockMeta {
@@ -238,7 +237,7 @@ impl TermInfoStoreWriter {
        }

        bit_packer.write(
-            postings_stop_offset,
+            postings_end_offset as u64,
            term_info_block_meta.postings_offset_nbits,
            &mut self.buffer_term_infos,
        )?;
@@ -251,7 +250,6 @@ 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 {
@@ -314,8 +312,7 @@ mod tests {
            offset: 2009u64,
            ref_term_info: TermInfo {
                doc_freq: 512,
-                postings_start_offset: 51,
-                postings_stop_offset: 57u64,
+                postings_range: 51..57,
                positions_idx: 3584,
            },
            doc_freq_nbits: 10,
@@ -333,12 +330,11 @@ 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 offset = |i| (i * 13 + i * i);
+        for i in 0usize..1000usize {
            let term_info = TermInfo {
                doc_freq: i as u32,
-                postings_start_offset: offset(i),
-                postings_stop_offset: offset(i + 1),
+                postings_range: offset(i)..offset(i + 1),
                positions_idx: (i * 7) as u64,
            };
            store_writer.write_term_info(&term_info)?;
--- a/src/termdict/tests.rs
+++ b/src/termdict/tests.rs
@@ -9,12 +9,11 @@ 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;
+    let offset = |term_ord: u64| (term_ord * 100 + term_ord * term_ord) as usize;
    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,
+        postings_range: offset(term_ord)..offset(term_ord + 1),
+        positions_idx: offset(term_ord) as u64 * 2u64,
    }
 }
Author	SHA1	Message	Date
Paul Masurel	114fbe2512	Removed redundant check Closes #997	2021-03-25 14:17:06 +09:00
Paul Masurel	155729044b	Merge pull request #996 from lpouget/facet-optional-storage-and-index Make facet indexation and storage optional	2021-03-25 09:08:36 +09:00
Laurent Pouget	4b34231f28	Make facet indexation and storage optional Added a FacetOptions for HierarchicalFacet which add indexed and stored flags to it. Propagate change and update tests accordingly Added a test to ensure that a not indexed flag was taken care of. Added on Value implem the `path()` function to return the stored facet.	2021-03-24 14:56:27 +01:00
Paul Masurel	8e7fe068e9	Fixed Histogram collector comment.	2021-03-23 18:43:49 +09:00
Paul Masurel	4c384272dc	Added debug to FileHandle	2021-03-23 00:10:46 +09:00
Paul Masurel	5de9961cf2	Cargo fmt	2021-03-22 10:38:48 +09:00
Paul Masurel	eab36b5c6a	Using std::iter::once.	2021-03-21 16:55:05 +09:00
Paul Masurel	96e5de2eb9	Merge pull request #995 from bstrie/main Replace deprecated collections::Bound with ops::Bound	2021-03-19 09:06:09 +09:00
bstrie	5f740d9ab4	Replace deprecated collections::Bound with ops::Bound	2021-03-18 17:20:36 -04:00
Paul Masurel	4f32126e35	Allow for non static predicate in the FilterCollector	2021-03-18 21:58:35 +09:00
Paul Masurel	d2d0873fdb	Added support for Option<TCollector>.	2021-03-18 17:28:09 +09:00
Paul Masurel	761298ff00	Added an histogram collector. Closes #994	2021-03-18 16:54:42 +09:00
Paul Masurel	52b1eb2c37	Clippy fix	2021-03-10 14:35:51 +09:00
Paul Masurel	2ab25d994f	Updated Changelog. Closing #991	2021-03-10 14:14:21 +09:00
Paul Masurel	5fac119aa0	Merge pull request #992 from tantivy-search/issue/991 Replacing (start, end) by Range	2021-03-10 14:12:53 +09:00
Paul Masurel	31137beea6	Replacing (start, end) by Range	2021-03-10 14:06:21 +09:00
Paul Masurel	316d65d7c6	removed deprecated compare_and_swap	2021-03-09 10:30:02 +09:00
Paul Masurel	82d7553c63	Merge pull request #988 from lengyijun/patch-9 Update file_slice.rs	2021-03-08 16:17:32 +09:00
lyj	bc0eb813ff	Update file_slice.rs typo fix	2021-03-08 14:12:33 +08:00
Paul Masurel	a259023fd9	Merge pull request #985 from tantivy-search/dependabot/cargo/proptest-1.0 Update proptest requirement from 0.10 to 1.0	2021-02-23 08:48:28 +09:00
dependabot-preview[bot]	25105448e8	Update proptest requirement from 0.10 to 1.0 Updates the requirements on [proptest](https://github.com/altsysrq/proptest) to permit the latest version. - [Release notes](https://github.com/altsysrq/proptest/releases) - [Changelog](https://github.com/AltSysrq/proptest/blob/master/CHANGELOG.md) - [Commits](https://github.com/altsysrq/proptest/compare/0.10.0...1.0.0) Signed-off-by: dependabot-preview[bot] <support@dependabot.com>	2021-02-22 20:13:03 +00:00
Paul Masurel	fe3faf5b3f	Cargo fmt	2021-02-22 14:29:03 +09:00
Paul Masurel	f19dd896cf	Re-added u64_lenient as a public API	2021-02-22 14:07:48 +09:00
Paul Masurel	9fe26c4fdd	Added 'static to FastValue.	2021-02-22 11:02:04 +09:00
Paul Masurel	a369a72cae	Cargo fmt	2021-02-09 15:00:14 +09:00
Paul Masurel	a707967453	Merge pull request #984 from vishalsodani/main Fixed spelling	2021-02-09 09:08:13 +09:00
Vishal Sodani	b2f2097239	Fixed spelling	2021-02-08 20:29:10 +05:30
Vishal Sodani	6ae96038c2	Fixed spelling	2021-02-08 20:18:45 +05:30
Paul Masurel	2c6a0d0a19	Merge pull request #983 from vishalsodani/main Fixed grammar	2021-02-08 23:36:18 +09:00
Vishal Sodani	4bcdca8545	Fixed spelling	2021-02-08 19:51:36 +05:30
Vishal Sodani	67f8e91395	Fixed grammar	2021-02-08 18:26:24 +05:30
Paul Masurel	b209763a55	Added ARCHITECTURE.md	2021-02-08 16:40:20 +09:00
Paul Masurel	5ef96795dc	Added minor comment on DocId	2021-02-08 16:14:05 +09:00