Merge #202

202: Add field id word count docids database r=Kerollmops a=LegendreM

This PR introduces a new database, `field_id_word_count_docids`, that maps the number of words in an attribute with a list of document ids. This relation is limited to attributes that contain less than 11 words.
This database is used by the exactness criterion to know if a document has an attribute that contains exactly the query without any additional word.

Fix #165 
Fix #196
Related to [specifications:#36](https://github.com/meilisearch/specifications/pull/36)

Co-authored-by: many <maxime@meilisearch.com>
Co-authored-by: Many <legendre.maxime.isn@gmail.com>

infos/src/main.rs

@@ -23,6 +23,7 @@ const WORD_PAIR_PROXIMITY_DOCIDS_DB_NAME: &str = "word-pair-proximity-docids";
 const WORD_PREFIX_PAIR_PROXIMITY_DOCIDS_DB_NAME: &str = "word-prefix-pair-proximity-docids";
 const WORD_LEVEL_POSITION_DOCIDS_DB_NAME: &str = "word-level-position-docids";
 const WORD_PREFIX_LEVEL_POSITION_DOCIDS_DB_NAME: &str = "word-prefix-level-position-docids";
+const FIELD_ID_WORD_COUNT_DOCIDS_DB_NAME: &str = "field-id-word-count-docids";
 const FACET_ID_F64_DOCIDS_DB_NAME: &str = "facet-id-f64-docids";
 const FACET_ID_STRING_DOCIDS_DB_NAME: &str = "facet-id-string-docids";
 const FIELD_ID_DOCID_FACET_F64S_DB_NAME: &str = "field-id-docid-facet-f64s";
@@ -39,6 +40,7 @@ const ALL_DATABASE_NAMES: &[&str] = &[
     WORD_PREFIX_PAIR_PROXIMITY_DOCIDS_DB_NAME,
     WORD_LEVEL_POSITION_DOCIDS_DB_NAME,
     WORD_PREFIX_LEVEL_POSITION_DOCIDS_DB_NAME,
+    FIELD_ID_WORD_COUNT_DOCIDS_DB_NAME,
     FACET_ID_F64_DOCIDS_DB_NAME,
     FACET_ID_STRING_DOCIDS_DB_NAME,
     FIELD_ID_DOCID_FACET_F64S_DB_NAME,
@@ -155,6 +157,17 @@ enum Command {
         prefixes: Vec<String>,
     },
 
+    /// Outputs a CSV with the documents ids along with
+    /// the field id and the word count where it appears.
+    FieldIdWordCountDocids {
+        /// Display the whole documents ids in details.
+        #[structopt(long)]
+        full_display: bool,
+
+        /// The field name in the document.
+        field_name: String,
+    },
+
     /// Outputs a CSV with the documents ids, words and the positions where this word appears.
     DocidsWordsPositions {
         /// Display the whole positions in detail.
@@ -271,6 +284,9 @@ fn main() -> anyhow::Result<()> {
         WordPrefixesLevelPositionsDocids { full_display, prefixes } => {
             word_prefixes_level_positions_docids(&index, &rtxn, !full_display, prefixes)
         },
+        FieldIdWordCountDocids { full_display, field_name } => {
+            field_id_word_count_docids(&index, &rtxn, !full_display, field_name)
+        },
         DocidsWordsPositions { full_display, internal_documents_ids } => {
             docids_words_positions(&index, &rtxn, !full_display, internal_documents_ids)
         },
@@ -357,6 +373,7 @@ fn biggest_value_sizes(index: &Index, rtxn: &heed::RoTxn, limit: usize) -> anyho
         word_prefix_pair_proximity_docids,
         word_level_position_docids,
         word_prefix_level_position_docids,
+        field_id_word_count_docids,
         facet_id_f64_docids,
         facet_id_string_docids,
         field_id_docid_facet_f64s: _,
@@ -372,6 +389,7 @@ fn biggest_value_sizes(index: &Index, rtxn: &heed::RoTxn, limit: usize) -> anyho
     let word_pair_proximity_docids_name = "word_pair_proximity_docids";
     let word_level_position_docids_name = "word_level_position_docids";
     let word_prefix_level_position_docids_name = "word_prefix_level_position_docids";
+    let field_id_word_count_docids_name = "field_id_word_count_docids";
     let facet_id_f64_docids_name = "facet_id_f64_docids";
     let facet_id_string_docids_name = "facet_id_string_docids";
     let documents_name = "documents";
@@ -443,6 +461,13 @@ fn biggest_value_sizes(index: &Index, rtxn: &heed::RoTxn, limit: usize) -> anyho
             if heap.len() > limit { heap.pop(); }
         }
 
+        for result in field_id_word_count_docids.remap_data_type::<ByteSlice>().iter(rtxn)? {
+            let ((field_id, word_count), docids) = result?;
+            let key = format!("{} {}", field_id, word_count);
+            heap.push(Reverse((docids.len(), key, field_id_word_count_docids_name)));
+            if heap.len() > limit { heap.pop(); }
+        }
+
         let faceted_fields = index.faceted_fields_ids(rtxn)?;
         let fields_ids_map = index.fields_ids_map(rtxn)?;
 
@@ -676,6 +701,39 @@ fn word_prefixes_level_positions_docids(
     Ok(wtr.flush()?)
 }
 
+fn field_id_word_count_docids(
+    index: &Index,
+    rtxn: &heed::RoTxn,
+    debug: bool,
+    field_name: String
+) -> anyhow::Result<()>
+{
+    let stdout = io::stdout();
+    let mut wtr = csv::Writer::from_writer(stdout.lock());
+    wtr.write_record(&["field_name", "word_count", "docids"])?;
+
+    let field_id = index.fields_ids_map(rtxn)?
+        .id(&field_name)
+        .with_context(|| format!("unknown field name: {}", &field_name))?;
+
+    let left = (field_id, 0);
+    let right = (field_id, u8::max_value());
+    let iter = index.field_id_word_count_docids
+        .range(rtxn, &(left..=right))?;
+
+    for result in iter {
+        let ((_, word_count), docids) = result?;
+        let docids = if debug {
+            format!("{:?}", docids)
+        } else {
+            format!("{:?}", docids.iter().collect::<Vec<_>>())
+        };
+        wtr.write_record(&[&field_name, &format!("{}", word_count), &docids])?;
+    }
+
+    Ok(wtr.flush()?)
+}
+
 fn docids_words_positions(
     index: &Index,
     rtxn: &heed::RoTxn,
@@ -870,6 +928,7 @@ fn size_of_databases(index: &Index, rtxn: &heed::RoTxn, names: Vec<String>) -> a
         word_prefix_pair_proximity_docids,
         word_level_position_docids,
         word_prefix_level_position_docids,
+        field_id_word_count_docids,
         facet_id_f64_docids,
         facet_id_string_docids,
         field_id_docid_facet_f64s,
@@ -893,6 +952,7 @@ fn size_of_databases(index: &Index, rtxn: &heed::RoTxn, names: Vec<String>) -> a
             WORD_PREFIX_PAIR_PROXIMITY_DOCIDS_DB_NAME => word_prefix_pair_proximity_docids.as_polymorph(),
             WORD_LEVEL_POSITION_DOCIDS_DB_NAME => word_level_position_docids.as_polymorph(),
             WORD_PREFIX_LEVEL_POSITION_DOCIDS_DB_NAME => word_prefix_level_position_docids.as_polymorph(),
+            FIELD_ID_WORD_COUNT_DOCIDS_DB_NAME => field_id_word_count_docids.as_polymorph(),
             FACET_ID_F64_DOCIDS_DB_NAME => facet_id_f64_docids.as_polymorph(),
             FACET_ID_STRING_DOCIDS_DB_NAME => facet_id_string_docids.as_polymorph(),
             FIELD_ID_DOCID_FACET_F64S_DB_NAME => field_id_docid_facet_f64s.as_polymorph(),
@@ -999,6 +1059,10 @@ fn database_stats(index: &Index, rtxn: &heed::RoTxn, name: &str) -> anyhow::Resu
             let db = index.word_prefix_pair_proximity_docids.as_polymorph();
             compute_stats::<CboRoaringBitmapCodec>(*db, rtxn, name)
         },
+        FIELD_ID_WORD_COUNT_DOCIDS_DB_NAME => {
+            let db = index.field_id_word_count_docids.as_polymorph();
+            compute_stats::<CboRoaringBitmapCodec>(*db, rtxn, name)
+        },
         unknown => anyhow::bail!("unknown database {:?}", unknown),
     }
 }

milli/src/heed_codec/field_id_word_count_codec.rs

@@ -0,0 +1,22 @@
+use std::{borrow::Cow, convert::TryInto};
+
+use crate::FieldId;
+
+pub struct FieldIdWordCountCodec;
+
+impl<'a> heed::BytesDecode<'a> for FieldIdWordCountCodec {
+    type DItem = (FieldId, u8);
+
+    fn bytes_decode(bytes: &'a [u8]) -> Option<Self::DItem> {
+        let [field_id, word_count]: [u8; 2] = bytes.try_into().ok()?;
+        Some((field_id, word_count))
+    }
+}
+
+impl<'a> heed::BytesEncode<'a> for FieldIdWordCountCodec {
+    type EItem = (FieldId, u8);
+
+    fn bytes_encode((field_id, word_count): &Self::EItem) -> Option<Cow<[u8]>> {
+        Some(Cow::Owned(vec![*field_id, *word_count]))
+    }
+}

milli/src/heed_codec/mod.rs

@@ -4,6 +4,7 @@ mod roaring_bitmap;
 mod roaring_bitmap_length;
 mod str_level_position_codec;
 mod str_str_u8_codec;
+mod field_id_word_count_codec;
 pub mod facet;
 
 pub use self::beu32_str_codec::BEU32StrCodec;
@@ -12,3 +13,4 @@ pub use self::roaring_bitmap::{BoRoaringBitmapCodec, CboRoaringBitmapCodec, Roar
 pub use self::roaring_bitmap_length::{BoRoaringBitmapLenCodec, CboRoaringBitmapLenCodec, RoaringBitmapLenCodec};
 pub use self::str_level_position_codec::StrLevelPositionCodec;
 pub use self::str_str_u8_codec::StrStrU8Codec;
+pub use self::field_id_word_count_codec::FieldIdWordCountCodec;

milli/src/index.rs

@@ -13,6 +13,7 @@ use crate::{BEU32, DocumentId, ExternalDocumentsIds, FieldId};
 use crate::{
     BEU32StrCodec, BoRoaringBitmapCodec, CboRoaringBitmapCodec,
     ObkvCodec, RoaringBitmapCodec, RoaringBitmapLenCodec, StrLevelPositionCodec, StrStrU8Codec,
+    FieldIdWordCountCodec,
 };
 use crate::heed_codec::facet::{
     FieldDocIdFacetF64Codec, FieldDocIdFacetStringCodec,
@@ -63,6 +64,8 @@ pub struct Index {
 
     /// Maps the word, level and position range with the docids that corresponds to it.
     pub word_level_position_docids: Database<StrLevelPositionCodec, CboRoaringBitmapCodec>,
+    /// Maps the field id and the word count with the docids that corresponds to it.
+    pub field_id_word_count_docids: Database<FieldIdWordCountCodec, CboRoaringBitmapCodec>,
     /// Maps the level positions of a word prefix with all the docids where this prefix appears.
     pub word_prefix_level_position_docids: Database<StrLevelPositionCodec, CboRoaringBitmapCodec>,
 
@@ -82,7 +85,7 @@ pub struct Index {
 
 impl Index {
     pub fn new<P: AsRef<Path>>(mut options: heed::EnvOpenOptions, path: P) -> anyhow::Result<Index> {
-        options.max_dbs(13);
+        options.max_dbs(14);
 
         let env = options.open(path)?;
         let main = env.create_poly_database(Some("main"))?;
@@ -92,6 +95,7 @@ impl Index {
         let word_pair_proximity_docids = env.create_database(Some("word-pair-proximity-docids"))?;
         let word_prefix_pair_proximity_docids = env.create_database(Some("word-prefix-pair-proximity-docids"))?;
         let word_level_position_docids = env.create_database(Some("word-level-position-docids"))?;
+        let field_id_word_count_docids = env.create_database(Some("field-id-word-count-docids"))?;
         let word_prefix_level_position_docids = env.create_database(Some("word-prefix-level-position-docids"))?;
         let facet_id_f64_docids = env.create_database(Some("facet-id-f64-docids"))?;
         let facet_id_string_docids = env.create_database(Some("facet-id-string-docids"))?;
@@ -111,6 +115,7 @@ impl Index {
             word_prefix_pair_proximity_docids,
             word_level_position_docids,
             word_prefix_level_position_docids,
+            field_id_word_count_docids,
             facet_id_f64_docids,
             facet_id_string_docids,
             field_id_docid_facet_f64s,

milli/src/lib.rs

@@ -23,7 +23,7 @@ use serde_json::{Map, Value};
 pub use self::criterion::{Criterion, default_criteria};
 pub use self::external_documents_ids::ExternalDocumentsIds;
 pub use self::fields_ids_map::FieldsIdsMap;
-pub use self::heed_codec::{BEU32StrCodec, StrStrU8Codec, StrLevelPositionCodec, ObkvCodec};
+pub use self::heed_codec::{BEU32StrCodec, StrStrU8Codec, StrLevelPositionCodec, ObkvCodec, FieldIdWordCountCodec};
 pub use self::heed_codec::{RoaringBitmapCodec, BoRoaringBitmapCodec, CboRoaringBitmapCodec};
 pub use self::heed_codec::{RoaringBitmapLenCodec, BoRoaringBitmapLenCodec, CboRoaringBitmapLenCodec};
 pub use self::index::Index;

milli/src/search/criteria/exactness.rs

@@ -1,9 +1,10 @@
+use std::convert::TryFrom;
 use std::mem::take;
+use std::ops::BitOr;
 
 use log::debug;
 use roaring::RoaringBitmap;
 use itertools::Itertools;
-use std::ops::BitOr;
 
 use crate::search::query_tree::{Operation, PrimitiveQueryPart};
 use crate::search::criteria::{
@@ -162,23 +163,24 @@ fn resolve_state(
     use State::*;
     match state {
         ExactAttribute(mut allowed_candidates) => {
-            let query_len = query.len() as u32;
             let mut candidates = RoaringBitmap::new();
-            let attributes_ids = ctx.searchable_fields_ids()?;
+            if let Ok(query_len) = u8::try_from(query.len()) {
-            for id in attributes_ids {
+                let attributes_ids = ctx.searchable_fields_ids()?;
-                if let Some(attribute_allowed_docids) = ctx.field_id_len_docids(id, query_len)? {
+                for id in attributes_ids {
-                    let mut attribute_candidates_array = attribute_start_with_docids(ctx, id as u32, query)?;
+                    if let Some(attribute_allowed_docids) = ctx.field_id_word_count_docids(id, query_len)? {
-                    attribute_candidates_array.push(attribute_allowed_docids);
+                        let mut attribute_candidates_array = attribute_start_with_docids(ctx, id as u32, query)?;
-                    candidates |= intersection_of(attribute_candidates_array.iter().collect());
+                        attribute_candidates_array.push(attribute_allowed_docids);
+                        candidates |= intersection_of(attribute_candidates_array.iter().collect());
+                    }
                 }
+
+                // only keep allowed candidates
+                candidates &= &allowed_candidates;
+                // remove current candidates from allowed candidates
+                allowed_candidates -= &candidates;
             }
 
-            // only keep allowed candidates
-            candidates &= &allowed_candidates;
-            // remove current candidates from allowed candidates
-            allowed_candidates -= &candidates;
             Ok((candidates, Some(AttributeStartsWith(allowed_candidates))))
-
         },
         AttributeStartsWith(mut allowed_candidates) => {
             let mut candidates = RoaringBitmap::new();

milli/src/search/criteria/mod.rs

@@ -78,7 +78,7 @@ pub trait Context<'c> {
     fn word_position_last_level(&self, word: &str, in_prefix_cache: bool) -> heed::Result<Option<TreeLevel>>;
     fn synonyms(&self, word: &str) -> heed::Result<Option<Vec<Vec<String>>>>;
     fn searchable_fields_ids(&self) ->  heed::Result<Vec<FieldId>>;
-    fn field_id_len_docids(&self, field_id: FieldId, len: u32) -> heed::Result<Option<RoaringBitmap>>;
+    fn field_id_word_count_docids(&self, field_id: FieldId, word_count: u8) -> heed::Result<Option<RoaringBitmap>>;
     fn word_level_position_docids(&self, word: &str, level: TreeLevel, left: u32, right: u32) -> Result<Option<RoaringBitmap>, heed::Error>;
 }
 pub struct CriteriaBuilder<'t> {
@@ -181,8 +181,9 @@ impl<'c> Context<'c> for CriteriaBuilder<'c> {
         }
     }
 
-    fn field_id_len_docids(&self, _field_id: FieldId, _len: u32) -> heed::Result<Option<RoaringBitmap>> {
+    fn field_id_word_count_docids(&self, field_id: FieldId, word_count: u8) -> heed::Result<Option<RoaringBitmap>> {
-        Ok(None)
+        let key = (field_id, word_count);
+        self.index.field_id_word_count_docids.get(self.rtxn, &key)
     }
 
     fn word_level_position_docids(&self, word: &str, level: TreeLevel, left: u32, right: u32) -> Result<Option<RoaringBitmap>, heed::Error> {
@@ -488,7 +489,7 @@ pub mod test {
             todo!()
         }
 
-        fn field_id_len_docids(&self, _field_id: FieldId, _len: u32) -> heed::Result<Option<RoaringBitmap>> {
+        fn field_id_word_count_docids(&self, _field_id: FieldId, _word_count: u8) -> heed::Result<Option<RoaringBitmap>> {
             todo!()
         }
     }

milli/src/update/clear_documents.rs

@@ -29,6 +29,7 @@ impl<'t, 'u, 'i> ClearDocuments<'t, 'u, 'i> {
             word_pair_proximity_docids,
             word_prefix_pair_proximity_docids,
             word_level_position_docids,
+            field_id_word_count_docids,
             word_prefix_level_position_docids,
             facet_id_f64_docids,
             facet_id_string_docids,
@@ -62,6 +63,7 @@ impl<'t, 'u, 'i> ClearDocuments<'t, 'u, 'i> {
         word_pair_proximity_docids.clear(self.wtxn)?;
         word_prefix_pair_proximity_docids.clear(self.wtxn)?;
         word_level_position_docids.clear(self.wtxn)?;
+        field_id_word_count_docids.clear(self.wtxn)?;
         word_prefix_level_position_docids.clear(self.wtxn)?;
         facet_id_f64_docids.clear(self.wtxn)?;
         facet_id_string_docids.clear(self.wtxn)?;
@@ -117,6 +119,7 @@ mod tests {
         assert!(index.word_prefix_docids.is_empty(&rtxn).unwrap());
         assert!(index.docid_word_positions.is_empty(&rtxn).unwrap());
         assert!(index.word_pair_proximity_docids.is_empty(&rtxn).unwrap());
+        assert!(index.field_id_word_count_docids.is_empty(&rtxn).unwrap());
         assert!(index.word_prefix_pair_proximity_docids.is_empty(&rtxn).unwrap());
         assert!(index.facet_id_f64_docids.is_empty(&rtxn).unwrap());
         assert!(index.facet_id_string_docids.is_empty(&rtxn).unwrap());

milli/src/update/delete_documents.rs

@@ -86,6 +86,7 @@ impl<'t, 'u, 'i> DeleteDocuments<'t, 'u, 'i> {
             word_prefix_docids,
             docid_word_positions,
             word_pair_proximity_docids,
+            field_id_word_count_docids,
             word_prefix_pair_proximity_docids,
             word_level_position_docids,
             word_prefix_level_position_docids,
@@ -316,6 +317,20 @@ impl<'t, 'u, 'i> DeleteDocuments<'t, 'u, 'i> {
 
         drop(iter);
 
+        // Remove the documents ids from the field id word count database.
+        let mut iter = field_id_word_count_docids.iter_mut(self.wtxn)?;
+        while let Some((key, mut docids)) = iter.next().transpose()? {
+            let previous_len = docids.len();
+            docids.difference_with(&self.documents_ids);
+            if docids.is_empty() {
+                iter.del_current()?;
+            } else if docids.len() != previous_len {
+                iter.put_current(&key, &docids)?;
+            }
+        }
+
+        drop(iter);
+
         // We delete the documents ids that are under the facet field id values.
         remove_docids_from_facet_field_id_value_docids(
             self.wtxn,

milli/src/update/index_documents/merge_function.rs

@@ -60,6 +60,10 @@ pub fn word_level_position_docids_merge(_key: &[u8], values: &[Cow<[u8]>]) -> an
     cbo_roaring_bitmap_merge(values)
 }
 
+pub fn field_id_word_count_docids_merge(_key: &[u8], values: &[Cow<[u8]>]) -> anyhow::Result<Vec<u8>> {
+    cbo_roaring_bitmap_merge(values)
+}
+
 pub fn facet_field_value_docids_merge(_key: &[u8], values: &[Cow<[u8]>]) -> anyhow::Result<Vec<u8>> {
     cbo_roaring_bitmap_merge(values)
 }

milli/src/update/index_documents/mod.rs

@@ -29,6 +29,7 @@ pub use self::merge_function::{
     docid_word_positions_merge, documents_merge,
     word_level_position_docids_merge, word_prefix_level_positions_docids_merge,
     facet_field_value_docids_merge, field_id_docid_facet_values_merge,
+    field_id_word_count_docids_merge,
 };
 pub use self::transform::{Transform, TransformOutput};
 
@@ -412,6 +413,7 @@ impl<'t, 'u, 'i, 'a> IndexDocuments<'t, 'u, 'i, 'a> {
             Main,
             WordDocids,
             WordLevel0PositionDocids,
+            FieldIdWordCountDocids,
             FacetLevel0NumbersDocids,
         }
 
@@ -476,6 +478,7 @@ impl<'t, 'u, 'i, 'a> IndexDocuments<'t, 'u, 'i, 'a> {
             let mut docid_word_positions_readers = Vec::with_capacity(readers.len());
             let mut words_pairs_proximities_docids_readers = Vec::with_capacity(readers.len());
             let mut word_level_position_docids_readers = Vec::with_capacity(readers.len());
+            let mut field_id_word_count_docids_readers = Vec::with_capacity(readers.len());
             let mut facet_field_numbers_docids_readers = Vec::with_capacity(readers.len());
             let mut facet_field_strings_docids_readers = Vec::with_capacity(readers.len());
             let mut field_id_docid_facet_numbers_readers = Vec::with_capacity(readers.len());
@@ -488,6 +491,7 @@ impl<'t, 'u, 'i, 'a> IndexDocuments<'t, 'u, 'i, 'a> {
                     docid_word_positions,
                     words_pairs_proximities_docids,
                     word_level_position_docids,
+                    field_id_word_count_docids,
                     facet_field_numbers_docids,
                     facet_field_strings_docids,
                     field_id_docid_facet_numbers,
@@ -499,6 +503,7 @@ impl<'t, 'u, 'i, 'a> IndexDocuments<'t, 'u, 'i, 'a> {
                 docid_word_positions_readers.push(docid_word_positions);
                 words_pairs_proximities_docids_readers.push(words_pairs_proximities_docids);
                 word_level_position_docids_readers.push(word_level_position_docids);
+                field_id_word_count_docids_readers.push(field_id_word_count_docids);
                 facet_field_numbers_docids_readers.push(facet_field_numbers_docids);
                 facet_field_strings_docids_readers.push(facet_field_strings_docids);
                 field_id_docid_facet_numbers_readers.push(field_id_docid_facet_numbers);
@@ -536,6 +541,11 @@ impl<'t, 'u, 'i, 'a> IndexDocuments<'t, 'u, 'i, 'a> {
                         word_level_position_docids_readers,
                         word_level_position_docids_merge,
                     ),
+                    (
+                        DatabaseType::FieldIdWordCountDocids,
+                        field_id_word_count_docids_readers,
+                        field_id_word_count_docids_merge,
+                    ),
                 ]
                 .into_par_iter()
                 .for_each(|(dbtype, readers, merge)| {
@@ -595,7 +605,7 @@ impl<'t, 'u, 'i, 'a> IndexDocuments<'t, 'u, 'i, 'a> {
         self.index.put_documents_ids(self.wtxn, &documents_ids)?;
 
         let mut database_count = 0;
-        let total_databases = 10;
+        let total_databases = 11;
 
         progress_callback(UpdateIndexingStep::MergeDataIntoFinalDatabase {
             databases_seen: 0,
@@ -727,6 +737,17 @@ impl<'t, 'u, 'i, 'a> IndexDocuments<'t, 'u, 'i, 'a> {
                         write_method,
                     )?;
                 },
+                DatabaseType::FieldIdWordCountDocids => {
+                    debug!("Writing the field id word count docids into LMDB on disk...");
+                    let db = *self.index.field_id_word_count_docids.as_polymorph();
+                    write_into_lmdb_database(
+                        self.wtxn,
+                        db,
+                        content,
+                        field_id_word_count_docids_merge,
+                        write_method,
+                    )?;
+                },
                 DatabaseType::WordLevel0PositionDocids => {
                     debug!("Writing the word level 0 positions docids into LMDB on disk...");
                     let db = *self.index.word_level_position_docids.as_polymorph();

milli/src/update/index_documents/store.rs

@@ -29,7 +29,7 @@ use super::{MergeFn, create_writer, create_sorter, writer_into_reader};
 use super::merge_function::{
     main_merge, word_docids_merge, words_pairs_proximities_docids_merge,
     word_level_position_docids_merge, facet_field_value_docids_merge,
-    field_id_docid_facet_values_merge,
+    field_id_docid_facet_values_merge, field_id_word_count_docids_merge,
 };
 
 const LMDB_MAX_KEY_LENGTH: usize = 511;
@@ -44,6 +44,7 @@ pub struct Readers {
     pub docid_word_positions: Reader<FileFuse>,
     pub words_pairs_proximities_docids: Reader<FileFuse>,
     pub word_level_position_docids: Reader<FileFuse>,
+    pub field_id_word_count_docids: Reader<FileFuse>,
     pub facet_field_numbers_docids: Reader<FileFuse>,
     pub facet_field_strings_docids: Reader<FileFuse>,
     pub field_id_docid_facet_numbers: Reader<FileFuse>,
@@ -58,6 +59,7 @@ pub struct Store<'s, A> {
     // Caches
     word_docids: LinkedHashMap<SmallVec32<u8>, RoaringBitmap>,
     word_docids_limit: usize,
+    field_id_word_count_docids: HashMap<(FieldId, u8), RoaringBitmap>,
     words_pairs_proximities_docids: LinkedHashMap<(SmallVec32<u8>, SmallVec32<u8>, u8), RoaringBitmap>,
     words_pairs_proximities_docids_limit: usize,
     facet_field_number_docids: LinkedHashMap<(FieldId, OrderedFloat<f64>), RoaringBitmap>,
@@ -72,6 +74,7 @@ pub struct Store<'s, A> {
     word_docids_sorter: Sorter<MergeFn>,
     words_pairs_proximities_docids_sorter: Sorter<MergeFn>,
     word_level_position_docids_sorter: Sorter<MergeFn>,
+    field_id_word_count_docids_sorter: Sorter<MergeFn>,
     facet_field_numbers_docids_sorter: Sorter<MergeFn>,
     facet_field_strings_docids_sorter: Sorter<MergeFn>,
     field_id_docid_facet_numbers_sorter: Sorter<MergeFn>,
@@ -132,6 +135,14 @@ impl<'s, A: AsRef<[u8]>> Store<'s, A> {
             max_nb_chunks,
             max_memory,
         );
+        let field_id_word_count_docids_sorter = create_sorter(
+            field_id_word_count_docids_merge,
+            chunk_compression_type,
+            chunk_compression_level,
+            chunk_fusing_shrink_size,
+            max_nb_chunks,
+            max_memory,
+        );
         let facet_field_numbers_docids_sorter = create_sorter(
             facet_field_value_docids_merge,
             chunk_compression_type,
@@ -184,6 +195,7 @@ impl<'s, A: AsRef<[u8]>> Store<'s, A> {
             faceted_fields,
             // Caches
             word_docids: LinkedHashMap::with_capacity(linked_hash_map_size),
+            field_id_word_count_docids: HashMap::new(),
             word_docids_limit: linked_hash_map_size,
             words_pairs_proximities_docids: LinkedHashMap::with_capacity(linked_hash_map_size),
             words_pairs_proximities_docids_limit: linked_hash_map_size,
@@ -199,6 +211,7 @@ impl<'s, A: AsRef<[u8]>> Store<'s, A> {
             word_docids_sorter,
             words_pairs_proximities_docids_sorter,
             word_level_position_docids_sorter,
+            field_id_word_count_docids_sorter,
             facet_field_numbers_docids_sorter,
             facet_field_strings_docids_sorter,
             field_id_docid_facet_numbers_sorter,
@@ -620,10 +633,17 @@ impl<'s, A: AsRef<[u8]>> Store<'s, A> {
                             let analyzed = self.analyzer.analyze(&content);
                             let tokens = process_tokens(analyzed.tokens());
 
+                            let mut last_pos = None;
                             for (pos, token) in tokens.take_while(|(pos, _)| *pos < MAX_POSITION) {
+                                last_pos = Some(pos);
                                 let position = (attr as usize * MAX_POSITION + pos) as u32;
                                 words_positions.entry(token.text().to_string()).or_insert_with(SmallVec32::new).push(position);
                             }
+
+                            if let Some(last_pos) = last_pos.filter(|p| *p <= 10) {
+                                let key = (attr, last_pos as u8 + 1);
+                                self.field_id_word_count_docids.entry(key).or_insert_with(RoaringBitmap::new).insert(document_id);
+                            }
                         }
                     }
                 }
@@ -683,6 +703,13 @@ impl<'s, A: AsRef<[u8]>> Store<'s, A> {
             word_docids_wtr.insert(word, val)?;
         }
 
+        let mut docids_buffer = Vec::new();
+        for ((fid, count), docids) in self.field_id_word_count_docids {
+            docids_buffer.clear();
+            CboRoaringBitmapCodec::serialize_into(&docids, &mut docids_buffer)?;
+            self.field_id_word_count_docids_sorter.insert([fid, count], &docids_buffer)?;
+        }
+
         let fst = builder.into_set();
         self.main_sorter.insert(WORDS_FST_KEY, fst.as_fst().as_bytes())?;
 
@@ -695,6 +722,9 @@ impl<'s, A: AsRef<[u8]>> Store<'s, A> {
         let mut word_level_position_docids_wtr = tempfile().and_then(|f| create_writer(comp_type, comp_level, f))?;
         self.word_level_position_docids_sorter.write_into(&mut word_level_position_docids_wtr)?;
 
+        let mut field_id_word_count_docids_wtr = tempfile().and_then(|f| create_writer(comp_type, comp_level, f))?;
+        self.field_id_word_count_docids_sorter.write_into(&mut field_id_word_count_docids_wtr)?;
+
         let mut facet_field_numbers_docids_wtr = tempfile().and_then(|f| create_writer(comp_type, comp_level, f))?;
         self.facet_field_numbers_docids_sorter.write_into(&mut facet_field_numbers_docids_wtr)?;
 
@@ -711,6 +741,7 @@ impl<'s, A: AsRef<[u8]>> Store<'s, A> {
         let word_docids = writer_into_reader(word_docids_wtr, shrink_size)?;
         let words_pairs_proximities_docids = writer_into_reader(words_pairs_proximities_docids_wtr, shrink_size)?;
         let word_level_position_docids = writer_into_reader(word_level_position_docids_wtr, shrink_size)?;
+        let field_id_word_count_docids = writer_into_reader(field_id_word_count_docids_wtr, shrink_size)?;
         let facet_field_numbers_docids = writer_into_reader(facet_field_numbers_docids_wtr, shrink_size)?;
         let facet_field_strings_docids = writer_into_reader(facet_field_strings_docids_wtr, shrink_size)?;
         let field_id_docid_facet_numbers = writer_into_reader(field_id_docid_facet_numbers_wtr, shrink_size)?;
@@ -724,6 +755,7 @@ impl<'s, A: AsRef<[u8]>> Store<'s, A> {
             docid_word_positions,
             words_pairs_proximities_docids,
             word_level_position_docids,
+            field_id_word_count_docids,
             facet_field_numbers_docids,
             facet_field_strings_docids,
             field_id_docid_facet_numbers,