Merge #308

308: Implement a better parallel indexer r=Kerollmops a=ManyTheFish

Rewrite the indexer:
- enhance memory consumption control
- optimize parallelism using rayon and crossbeam channel
- factorize the different parts and make new DB implementation easier
- optimize and fix prefix databases


Co-authored-by: many <maxime@meilisearch.com>

http-ui/src/main.rs

@@ -343,10 +343,7 @@ async fn main() -> anyhow::Result<()> {
             update_builder.thread_pool(GLOBAL_THREAD_POOL.get().unwrap());
             update_builder.log_every_n(indexer_opt_cloned.log_every_n);
             update_builder.max_memory(indexer_opt_cloned.max_memory.get_bytes() as usize);
-            update_builder.linked_hash_map_size(indexer_opt_cloned.linked_hash_map_size);
             update_builder.chunk_compression_type(indexer_opt_cloned.chunk_compression_type);
-            update_builder
-                .chunk_fusing_shrink_size(indexer_opt_cloned.chunk_fusing_shrink_size.get_bytes());
 
             let before_update = Instant::now();
             // we extract the update type and execute the update itself.

infos/src/main.rs

@@ -207,6 +207,24 @@ enum Command {
         word2: String,
     },
 
+    /// Outputs a CSV with the proximities for the two specified words and
+    /// the documents ids where these relations appears.
+    ///
+    /// `word1`, `prefix` defines the word pair specified *in this specific order*.
+    /// `proximity` defines the proximity between the two specified words.
+    /// `documents_ids` defines the documents ids where the relation appears.
+    WordPrefixPairProximitiesDocids {
+        /// Display the whole documents ids in details.
+        #[structopt(long)]
+        full_display: bool,
+
+        /// First word of the word pair.
+        word1: String,
+
+        /// Second word of the word pair.
+        prefix: String,
+    },
+
     /// Outputs the words FST to standard output.
     ///
     /// One can use the FST binary helper to dissect and analyze it,
@@ -282,6 +300,9 @@ fn main() -> anyhow::Result<()> {
         WordPairProximitiesDocids { full_display, word1, word2 } => {
             word_pair_proximities_docids(&index, &rtxn, !full_display, word1, word2)
         }
+        WordPrefixPairProximitiesDocids { full_display, word1, prefix } => {
+            word_prefix_pair_proximities_docids(&index, &rtxn, !full_display, word1, prefix)
+        }
         ExportWordsFst => export_words_fst(&index, &rtxn),
         ExportWordsPrefixFst => export_words_prefix_fst(&index, &rtxn),
         ExportDocuments { internal_documents_ids } => {
@@ -1131,3 +1152,46 @@ fn word_pair_proximities_docids(
 
     Ok(wtr.flush()?)
 }
+
+fn word_prefix_pair_proximities_docids(
+    index: &Index,
+    rtxn: &heed::RoTxn,
+    debug: bool,
+    word1: String,
+    word_prefix: String,
+) -> anyhow::Result<()> {
+    use heed::types::ByteSlice;
+    use milli::RoaringBitmapCodec;
+
+    let stdout = io::stdout();
+    let mut wtr = csv::Writer::from_writer(stdout.lock());
+    wtr.write_record(&["word1", "word_prefix", "proximity", "documents_ids"])?;
+
+    // Create the prefix key with only the pair of words.
+    let mut prefix = Vec::with_capacity(word1.len() + word_prefix.len() + 1);
+    prefix.extend_from_slice(word1.as_bytes());
+    prefix.push(0);
+    prefix.extend_from_slice(word_prefix.as_bytes());
+
+    let db = index.word_prefix_pair_proximity_docids.as_polymorph();
+    let iter = db.prefix_iter::<_, ByteSlice, RoaringBitmapCodec>(rtxn, &prefix)?;
+    for result in iter {
+        let (key, docids) = result?;
+
+        // Skip keys that are longer than the requested one,
+        // a longer key means that the second word is a prefix of the request word.
+        if key.len() != prefix.len() + 1 {
+            continue;
+        }
+
+        let proximity = key.last().unwrap();
+        let docids = if debug {
+            format!("{:?}", docids)
+        } else {
+            format!("{:?}", docids.iter().collect::<Vec<_>>())
+        };
+        wtr.write_record(&[&word1, &word_prefix, &proximity.to_string(), &docids])?;
+    }
+
+    Ok(wtr.flush()?)
+}

milli/Cargo.toml

@@ -9,12 +9,13 @@ bstr = "0.2.15"
 byteorder = "1.4.2"
 chrono = { version = "0.4.19", features = ["serde"] }
 concat-arrays = "0.1.2"
+crossbeam-channel = "0.5.1"
 csv = "1.1.5"
 either = "1.6.1"
 flate2 = "1.0.20"
 fst = "0.4.5"
 fxhash = "0.2.1"
-grenad = { git = "https://github.com/Kerollmops/grenad.git", rev = "3adcb26" }
+grenad = "0.3.0"
 heed = { git = "https://github.com/Kerollmops/heed", tag = "v0.12.1", default-features = false, features = ["lmdb", "sync-read-txn"] }
 human_format = "1.0.3"
 levenshtein_automata = { version = "0.2.0", features = ["fst_automaton"] }

milli/src/heed_codec/facet/facet_string_level_zero_value_codec.rs

@@ -2,51 +2,64 @@ use std::borrow::Cow;
 use std::convert::TryInto;
 use std::{marker, str};
 
-use super::try_split_at;
+use crate::error::SerializationError;
+use crate::heed_codec::RoaringBitmapCodec;
+use crate::{try_split_array_at, try_split_at, Result};
 
-/// A codec that encodes a string in front of the value.
+pub type FacetStringLevelZeroValueCodec = StringValueCodec<RoaringBitmapCodec>;
+
+/// A codec that encodes a string in front of a value.
 ///
 /// The usecase is for the facet string levels algorithm where we must know the
 /// original string of a normalized facet value, the original values are stored
 /// in the value to not break the lexicographical ordering of the LMDB keys.
-pub struct FacetStringLevelZeroValueCodec<C>(marker::PhantomData<C>);
+pub struct StringValueCodec<C>(marker::PhantomData<C>);
 
-impl<'a, C> heed::BytesDecode<'a> for FacetStringLevelZeroValueCodec<C>
+impl<'a, C> heed::BytesDecode<'a> for StringValueCodec<C>
 where
     C: heed::BytesDecode<'a>,
 {
     type DItem = (&'a str, C::DItem);
 
     fn bytes_decode(bytes: &'a [u8]) -> Option<Self::DItem> {
-        let (string_len, bytes) = try_split_at(bytes, 2)?;
+        let (string, bytes) = decode_prefix_string(bytes)?;
-        let string_len = string_len.try_into().ok().map(u16::from_be_bytes)?;
-
-        let (string, bytes) = try_split_at(bytes, string_len as usize)?;
-        let string = str::from_utf8(string).ok()?;
-
         C::bytes_decode(bytes).map(|item| (string, item))
     }
 }
 
-impl<'a, C> heed::BytesEncode<'a> for FacetStringLevelZeroValueCodec<C>
+impl<'a, C> heed::BytesEncode<'a> for StringValueCodec<C>
 where
     C: heed::BytesEncode<'a>,
 {
     type EItem = (&'a str, C::EItem);
 
     fn bytes_encode((string, value): &'a Self::EItem) -> Option<Cow<[u8]>> {
-        let string_len: u16 = string.len().try_into().ok()?;
         let value_bytes = C::bytes_encode(&value)?;
 
         let mut bytes = Vec::with_capacity(2 + string.len() + value_bytes.len());
-        bytes.extend_from_slice(&string_len.to_be_bytes());
+        encode_prefix_string(string, &mut bytes).ok()?;
-        bytes.extend_from_slice(string.as_bytes());
         bytes.extend_from_slice(&value_bytes[..]);
 
         Some(Cow::Owned(bytes))
     }
 }
 
+pub fn decode_prefix_string(value: &[u8]) -> Option<(&str, &[u8])> {
+    let (original_length_bytes, bytes) = try_split_array_at(value)?;
+    let original_length = u16::from_be_bytes(original_length_bytes) as usize;
+    let (string, bytes) = try_split_at(bytes, original_length)?;
+    let string = str::from_utf8(string).ok()?;
+    Some((string, bytes))
+}
+
+pub fn encode_prefix_string(string: &str, buffer: &mut Vec<u8>) -> Result<()> {
+    let string_len: u16 =
+        string.len().try_into().map_err(|_| SerializationError::InvalidNumberSerialization)?;
+    buffer.extend_from_slice(&string_len.to_be_bytes());
+    buffer.extend_from_slice(string.as_bytes());
+    Ok(())
+}
+
 #[cfg(test)]
 mod tests {
     use heed::types::Unit;
@@ -54,17 +67,15 @@ mod tests {
     use roaring::RoaringBitmap;
 
     use super::*;
-    use crate::CboRoaringBitmapCodec;
 
     #[test]
     fn deserialize_roaring_bitmaps() {
         let string = "abc";
         let docids: RoaringBitmap = (0..100).chain(3500..4398).collect();
         let key = (string, docids.clone());
-        let bytes =
+        let bytes = StringValueCodec::<RoaringBitmapCodec>::bytes_encode(&key).unwrap();
-            FacetStringLevelZeroValueCodec::<CboRoaringBitmapCodec>::bytes_encode(&key).unwrap();
         let (out_string, out_docids) =
-            FacetStringLevelZeroValueCodec::<CboRoaringBitmapCodec>::bytes_decode(&bytes).unwrap();
+            StringValueCodec::<RoaringBitmapCodec>::bytes_decode(&bytes).unwrap();
         assert_eq!((out_string, out_docids), (string, docids));
     }
 
@@ -72,9 +83,8 @@ mod tests {
     fn deserialize_unit() {
         let string = "def";
         let key = (string, ());
-        let bytes = FacetStringLevelZeroValueCodec::<Unit>::bytes_encode(&key).unwrap();
+        let bytes = StringValueCodec::<Unit>::bytes_encode(&key).unwrap();
-        let (out_string, out_unit) =
+        let (out_string, out_unit) = StringValueCodec::<Unit>::bytes_decode(&bytes).unwrap();
-            FacetStringLevelZeroValueCodec::<Unit>::bytes_decode(&bytes).unwrap();
         assert_eq!((out_string, out_unit), (string, ()));
     }
 }

milli/src/heed_codec/facet/mod.rs

@@ -9,7 +9,9 @@ mod field_doc_id_facet_string_codec;
 pub use self::facet_level_value_f64_codec::FacetLevelValueF64Codec;
 pub use self::facet_level_value_u32_codec::FacetLevelValueU32Codec;
 pub use self::facet_string_level_zero_codec::FacetStringLevelZeroCodec;
-pub use self::facet_string_level_zero_value_codec::FacetStringLevelZeroValueCodec;
+pub use self::facet_string_level_zero_value_codec::{
+    decode_prefix_string, encode_prefix_string, FacetStringLevelZeroValueCodec,
+};
 pub use self::facet_string_zero_bounds_value_codec::FacetStringZeroBoundsValueCodec;
 pub use self::field_doc_id_facet_f64_codec::FieldDocIdFacetF64Codec;
 pub use self::field_doc_id_facet_string_codec::FieldDocIdFacetStringCodec;

milli/src/heed_codec/roaring_bitmap/cbo_roaring_bitmap_codec.rs

@@ -52,6 +52,46 @@ impl CboRoaringBitmapCodec {
             RoaringBitmap::deserialize_from(bytes)
         }
     }
+
+    /// Merge serialized CboRoaringBitmaps in a buffer.
+    ///
+    /// if the merged values length is under the threshold, values are directly
+    /// serialized in the buffer else a RoaringBitmap is created from the
+    /// values and is serialized in the buffer.
+    pub fn merge_into(slices: &[Cow<[u8]>], buffer: &mut Vec<u8>) -> io::Result<()> {
+        let mut roaring = RoaringBitmap::new();
+        let mut vec = Vec::new();
+
+        for bytes in slices {
+            if bytes.len() <= THRESHOLD * size_of::<u32>() {
+                let mut reader = bytes.as_ref();
+                while let Ok(integer) = reader.read_u32::<NativeEndian>() {
+                    vec.push(integer);
+                }
+            } else {
+                roaring |= RoaringBitmap::deserialize_from(bytes.as_ref())?;
+            }
+        }
+
+        if roaring.is_empty() {
+            vec.sort_unstable();
+            vec.dedup();
+
+            if vec.len() <= THRESHOLD {
+                for integer in vec {
+                    buffer.extend_from_slice(&integer.to_ne_bytes());
+                }
+            } else {
+                let roaring = RoaringBitmap::from_sorted_iter(vec.into_iter());
+                roaring.serialize_into(buffer)?;
+            }
+        } else {
+            roaring.extend(vec);
+            roaring.serialize_into(buffer)?;
+        }
+
+        Ok(())
+    }
 }
 
 impl heed::BytesDecode<'_> for CboRoaringBitmapCodec {
@@ -106,4 +146,40 @@ mod tests {
 
         assert!(roaring_size > bo_size);
     }
+
+    #[test]
+    fn merge_cbo_roaring_bitmaps() {
+        let mut buffer = Vec::new();
+
+        let small_data = vec![
+            RoaringBitmap::from_sorted_iter(1..4),
+            RoaringBitmap::from_sorted_iter(2..5),
+            RoaringBitmap::from_sorted_iter(4..6),
+            RoaringBitmap::from_sorted_iter(1..3),
+        ];
+
+        let small_data: Vec<_> =
+            small_data.iter().map(|b| CboRoaringBitmapCodec::bytes_encode(b).unwrap()).collect();
+        CboRoaringBitmapCodec::merge_into(small_data.as_slice(), &mut buffer).unwrap();
+        let bitmap = CboRoaringBitmapCodec::deserialize_from(&buffer).unwrap();
+        let expected = RoaringBitmap::from_sorted_iter(1..6);
+        assert_eq!(bitmap, expected);
+
+        let medium_data = vec![
+            RoaringBitmap::from_sorted_iter(1..4),
+            RoaringBitmap::from_sorted_iter(2..5),
+            RoaringBitmap::from_sorted_iter(4..8),
+            RoaringBitmap::from_sorted_iter(0..3),
+            RoaringBitmap::from_sorted_iter(7..23),
+        ];
+
+        let medium_data: Vec<_> =
+            medium_data.iter().map(|b| CboRoaringBitmapCodec::bytes_encode(b).unwrap()).collect();
+        buffer.clear();
+        CboRoaringBitmapCodec::merge_into(medium_data.as_slice(), &mut buffer).unwrap();
+
+        let bitmap = CboRoaringBitmapCodec::deserialize_from(&buffer).unwrap();
+        let expected = RoaringBitmap::from_sorted_iter(0..23);
+        assert_eq!(bitmap, expected);
+    }
 }

milli/src/index.rs

@@ -93,8 +93,7 @@ pub struct Index {
     /// Maps the facet field id, level and the number with the docids that corresponds to it.
     pub facet_id_f64_docids: Database<FacetLevelValueF64Codec, CboRoaringBitmapCodec>,
     /// Maps the facet field id and the string with the original string and docids that corresponds to it.
-    pub facet_id_string_docids:
+    pub facet_id_string_docids: Database<FacetStringLevelZeroCodec, FacetStringLevelZeroValueCodec>,
-        Database<FacetStringLevelZeroCodec, FacetStringLevelZeroValueCodec<CboRoaringBitmapCodec>>,
 
     /// Maps the document id, the facet field id and the numbers.
     pub field_id_docid_facet_f64s: Database<FieldDocIdFacetF64Codec, Unit>,

milli/src/lib.rs

@@ -13,11 +13,9 @@ mod search;
 pub mod tree_level;
 pub mod update;
 
-use std::borrow::Cow;
 use std::collections::{BTreeMap, HashMap};
 use std::convert::{TryFrom, TryInto};
 use std::hash::BuildHasherDefault;
-use std::result::Result as StdResult;
 
 use fxhash::{FxHasher32, FxHasher64};
 pub use grenad::CompressionType;
@@ -54,8 +52,6 @@ pub type FieldId = u16;
 pub type Position = u32;
 pub type FieldDistribution = BTreeMap<String, u64>;
 
-type MergeFn<E> = for<'a> fn(&[u8], &[Cow<'a, [u8]>]) -> StdResult<Vec<u8>, E>;
-
 /// Transform a raw obkv store into a JSON Object.
 pub fn obkv_to_json(
     displayed_fields: &[FieldId],

milli/src/proximity.rs

@@ -2,8 +2,8 @@ use std::cmp;
 
 use crate::{Attribute, Position};
 
-const ONE_ATTRIBUTE: u32 = 1000;
+pub const ONE_ATTRIBUTE: u32 = 1000;
-const MAX_DISTANCE: u32 = 8;
+pub const MAX_DISTANCE: u32 = 8;
 
 pub fn index_proximity(lhs: u32, rhs: u32) -> u32 {
     if lhs <= rhs {

milli/src/search/criteria/mod.rs

@@ -461,13 +461,18 @@ fn query_pair_proximity_docids(
     let prefix = right.prefix;
     match (&left.kind, &right.kind) {
         (QueryKind::Exact { word: left, .. }, QueryKind::Exact { word: right, .. }) => {
-            if prefix && ctx.in_prefix_cache(&right) {
+            if prefix {
-                Ok(ctx
+                match ctx.word_prefix_pair_proximity_docids(
-                    .word_prefix_pair_proximity_docids(left.as_str(), right.as_str(), proximity)?
+                    left.as_str(),
-                    .unwrap_or_default())
+                    right.as_str(),
-            } else if prefix {
+                    proximity,
+                )? {
+                    Some(docids) => Ok(docids),
+                    None => {
                         let r_words = word_derivations(&right, true, 0, ctx.words_fst(), wdcache)?;
                         all_word_pair_proximity_docids(ctx, &[(left, 0)], &r_words, proximity)
+                    }
+                }
             } else {
                 Ok(ctx
                     .word_pair_proximity_docids(left.as_str(), right.as_str(), proximity)?
@@ -477,22 +482,24 @@ fn query_pair_proximity_docids(
         (QueryKind::Tolerant { typo, word: left }, QueryKind::Exact { word: right, .. }) => {
             let l_words =
                 word_derivations(&left, false, *typo, ctx.words_fst(), wdcache)?.to_owned();
-            if prefix && ctx.in_prefix_cache(&right) {
+            if prefix {
                 let mut docids = RoaringBitmap::new();
                 for (left, _) in l_words {
-                    let current_docids = ctx
+                    let current_docids = match ctx.word_prefix_pair_proximity_docids(
-                        .word_prefix_pair_proximity_docids(
+                        left.as_str(),
-                            left.as_ref(),
+                        right.as_str(),
-                            right.as_ref(),
                         proximity,
-                        )?
+                    )? {
-                        .unwrap_or_default();
+                        Some(docids) => Ok(docids),
+                        None => {
+                            let r_words =
+                                word_derivations(&right, true, 0, ctx.words_fst(), wdcache)?;
+                            all_word_pair_proximity_docids(ctx, &[(left, 0)], &r_words, proximity)
+                        }
+                    }?;
                     docids |= current_docids;
                 }
                 Ok(docids)
-            } else if prefix {
-                let r_words = word_derivations(&right, true, 0, ctx.words_fst(), wdcache)?;
-                all_word_pair_proximity_docids(ctx, &l_words, &r_words, proximity)
             } else {
                 all_word_pair_proximity_docids(ctx, &l_words, &[(right, 0)], proximity)
             }

milli/src/search/facet/facet_string.rs

@@ -269,11 +269,7 @@ impl<'t> Iterator for FacetStringGroupRevRange<'t> {
 ///
 /// It yields the facet string and the roaring bitmap associated with it.
 pub struct FacetStringLevelZeroRange<'t> {
-    iter: RoRange<
+    iter: RoRange<'t, FacetStringLevelZeroCodec, FacetStringLevelZeroValueCodec>,
-        't,
-        FacetStringLevelZeroCodec,
-        FacetStringLevelZeroValueCodec<CboRoaringBitmapCodec>,
-    >,
 }
 
 impl<'t> FacetStringLevelZeroRange<'t> {
@@ -316,10 +312,7 @@ impl<'t> FacetStringLevelZeroRange<'t> {
         let iter = db
             .remap_key_type::<ByteSlice>()
             .range(rtxn, &(left_bound, right_bound))?
-            .remap_types::<
+            .remap_types::<FacetStringLevelZeroCodec, FacetStringLevelZeroValueCodec>();
-                FacetStringLevelZeroCodec,
-                FacetStringLevelZeroValueCodec<CboRoaringBitmapCodec>
-            >();
 
         Ok(FacetStringLevelZeroRange { iter })
     }
@@ -340,11 +333,7 @@ impl<'t> Iterator for FacetStringLevelZeroRange<'t> {
 }
 
 pub struct FacetStringLevelZeroRevRange<'t> {
-    iter: RoRevRange<
+    iter: RoRevRange<'t, FacetStringLevelZeroCodec, FacetStringLevelZeroValueCodec>,
-        't,
-        FacetStringLevelZeroCodec,
-        FacetStringLevelZeroValueCodec<CboRoaringBitmapCodec>,
-    >,
 }
 
 impl<'t> FacetStringLevelZeroRevRange<'t> {
@@ -387,10 +376,7 @@ impl<'t> FacetStringLevelZeroRevRange<'t> {
         let iter = db
             .remap_key_type::<ByteSlice>()
             .rev_range(rtxn, &(left_bound, right_bound))?
-            .remap_types::<
+            .remap_types::<FacetStringLevelZeroCodec, FacetStringLevelZeroValueCodec>();
-                FacetStringLevelZeroCodec,
-                FacetStringLevelZeroValueCodec<CboRoaringBitmapCodec>
-            >();
 
         Ok(FacetStringLevelZeroRevRange { iter })
     }

milli/src/search/facet/filter_condition.rs

@@ -392,10 +392,7 @@ impl FilterCondition {
         rtxn: &heed::RoTxn,
         index: &Index,
         numbers_db: heed::Database<FacetLevelValueF64Codec, CboRoaringBitmapCodec>,
-        strings_db: heed::Database<
+        strings_db: heed::Database<FacetStringLevelZeroCodec, FacetStringLevelZeroValueCodec>,
-            FacetStringLevelZeroCodec,
-            FacetStringLevelZeroValueCodec<CboRoaringBitmapCodec>,
-        >,
         field_id: FieldId,
         operator: &Operator,
     ) -> Result<RoaringBitmap> {

milli/src/update/delete_documents.rs

@@ -490,7 +490,7 @@ fn remove_docids_from_facet_field_id_string_docids<'a, C, D>(
             None => {
                 // The key corresponds to a level zero facet string.
                 let (original_value, mut docids) =
-                    FacetStringLevelZeroValueCodec::<CboRoaringBitmapCodec>::bytes_decode(val)
+                    FacetStringLevelZeroValueCodec::bytes_decode(val)
                         .ok_or_else(|| SerializationError::Decoding { db_name })?;
 
                 let previous_len = docids.len();
@@ -501,8 +501,7 @@ fn remove_docids_from_facet_field_id_string_docids<'a, C, D>(
                 } else if docids.len() != previous_len {
                     let key = key.to_owned();
                     let val = &(original_value, docids);
-                    let value_bytes =
+                    let value_bytes = FacetStringLevelZeroValueCodec::bytes_encode(val)
-                        FacetStringLevelZeroValueCodec::<CboRoaringBitmapCodec>::bytes_encode(val)
                         .ok_or_else(|| SerializationError::Encoding { db_name })?;
 
                     // safety: we don't keep references from inside the LMDB database.

milli/src/update/facets.rs

@@ -3,7 +3,7 @@ use std::num::{NonZeroU8, NonZeroUsize};
 use std::{cmp, mem};
 
 use chrono::Utc;
-use grenad::{CompressionType, FileFuse, Reader, Writer};
+use grenad::{CompressionType, Reader, Writer};
 use heed::types::{ByteSlice, DecodeIgnore};
 use heed::{BytesEncode, Error};
 use log::debug;
@@ -25,7 +25,6 @@ pub struct Facets<'t, 'u, 'i> {
     index: &'i Index,
     pub(crate) chunk_compression_type: CompressionType,
     pub(crate) chunk_compression_level: Option<u32>,
-    pub(crate) chunk_fusing_shrink_size: Option<u64>,
     level_group_size: NonZeroUsize,
     min_level_size: NonZeroUsize,
     _update_id: u64,
@@ -42,7 +41,6 @@ impl<'t, 'u, 'i> Facets<'t, 'u, 'i> {
             index,
             chunk_compression_type: CompressionType::None,
             chunk_compression_level: None,
-            chunk_fusing_shrink_size: None,
             level_group_size: NonZeroUsize::new(4).unwrap(),
             min_level_size: NonZeroUsize::new(5).unwrap(),
             _update_id: update_id,
@@ -59,6 +57,7 @@ impl<'t, 'u, 'i> Facets<'t, 'u, 'i> {
         self
     }
 
+    #[logging_timer::time("Facets::{}")]
     pub fn execute(self) -> Result<()> {
         self.index.set_updated_at(self.wtxn, &Utc::now())?;
         // We get the faceted fields to be able to create the facet levels.
@@ -86,7 +85,6 @@ impl<'t, 'u, 'i> Facets<'t, 'u, 'i> {
                 self.index.facet_id_string_docids,
                 self.chunk_compression_type,
                 self.chunk_compression_level,
-                self.chunk_fusing_shrink_size,
                 self.level_group_size,
                 self.min_level_size,
                 field_id,
@@ -107,7 +105,6 @@ impl<'t, 'u, 'i> Facets<'t, 'u, 'i> {
                 self.index.facet_id_f64_docids,
                 self.chunk_compression_type,
                 self.chunk_compression_level,
-                self.chunk_fusing_shrink_size,
                 self.level_group_size,
                 self.min_level_size,
                 field_id,
@@ -128,7 +125,7 @@ impl<'t, 'u, 'i> Facets<'t, 'u, 'i> {
                 self.wtxn,
                 *self.index.facet_id_f64_docids.as_polymorph(),
                 facet_number_levels,
-                |_, _| Err(InternalError::IndexingMergingKeys { process: "facet number levels" }),
+                |_, _| Err(InternalError::IndexingMergingKeys { process: "facet number levels" })?,
                 WriteMethod::GetMergePut,
             )?;
 
@@ -136,7 +133,7 @@ impl<'t, 'u, 'i> Facets<'t, 'u, 'i> {
                 self.wtxn,
                 *self.index.facet_id_string_docids.as_polymorph(),
                 facet_string_levels,
-                |_, _| Err(InternalError::IndexingMergingKeys { process: "facet string levels" }),
+                |_, _| Err(InternalError::IndexingMergingKeys { process: "facet string levels" })?,
                 WriteMethod::GetMergePut,
             )?;
         }
@@ -161,11 +158,10 @@ fn compute_facet_number_levels<'t>(
     db: heed::Database<FacetLevelValueF64Codec, CboRoaringBitmapCodec>,
     compression_type: CompressionType,
     compression_level: Option<u32>,
-    shrink_size: Option<u64>,
     level_group_size: NonZeroUsize,
     min_level_size: NonZeroUsize,
     field_id: FieldId,
-) -> Result<Reader<FileFuse>> {
+) -> Result<Reader<File>> {
     let first_level_size = db
         .remap_key_type::<ByteSlice>()
         .prefix_iter(rtxn, &field_id.to_be_bytes())?
@@ -219,7 +215,7 @@ fn compute_facet_number_levels<'t>(
         }
     }
 
-    writer_into_reader(writer, shrink_size)
+    writer_into_reader(writer)
 }
 
 fn write_number_entry(
@@ -239,7 +235,7 @@ fn write_number_entry(
 
 fn compute_faceted_strings_documents_ids(
     rtxn: &heed::RoTxn,
-    db: heed::Database<ByteSlice, FacetStringLevelZeroValueCodec<CboRoaringBitmapCodec>>,
+    db: heed::Database<ByteSlice, FacetStringLevelZeroValueCodec>,
     field_id: FieldId,
 ) -> Result<RoaringBitmap> {
     let mut documents_ids = RoaringBitmap::new();
@@ -278,17 +274,13 @@ fn clear_field_string_levels<'t>(
 
 fn compute_facet_string_levels<'t>(
     rtxn: &'t heed::RoTxn,
-    db: heed::Database<
+    db: heed::Database<FacetStringLevelZeroCodec, FacetStringLevelZeroValueCodec>,
-        FacetStringLevelZeroCodec,
-        FacetStringLevelZeroValueCodec<CboRoaringBitmapCodec>,
-    >,
     compression_type: CompressionType,
     compression_level: Option<u32>,
-    shrink_size: Option<u64>,
     level_group_size: NonZeroUsize,
     min_level_size: NonZeroUsize,
     field_id: FieldId,
-) -> Result<Reader<FileFuse>> {
+) -> Result<Reader<File>> {
     let first_level_size = db
         .remap_key_type::<ByteSlice>()
         .prefix_iter(rtxn, &field_id.to_be_bytes())?
@@ -340,7 +332,7 @@ fn compute_facet_string_levels<'t>(
         }
     }
 
-    writer_into_reader(writer, shrink_size)
+    writer_into_reader(writer)
 }
 
 fn write_string_entry(

milli/src/update/index_documents/extract/extract_docid_word_positions.rs

@@ -0,0 +1,167 @@
+use std::collections::HashSet;
+use std::convert::TryInto;
+use std::fs::File;
+use std::{io, mem, str};
+
+use meilisearch_tokenizer::token::SeparatorKind;
+use meilisearch_tokenizer::{Analyzer, AnalyzerConfig, Token, TokenKind};
+use roaring::RoaringBitmap;
+use serde_json::Value;
+
+use super::helpers::{concat_u32s_array, create_sorter, sorter_into_reader, GrenadParameters};
+use crate::error::{InternalError, SerializationError};
+use crate::proximity::ONE_ATTRIBUTE;
+use crate::{FieldId, Result};
+
+/// Extracts the word and positions where this word appear and
+/// prefixes it by the document id.
+///
+/// Returns the generated internal documents ids and a grenad reader
+/// with the list of extracted words from the given chunk of documents.
+#[logging_timer::time]
+pub fn extract_docid_word_positions<R: io::Read>(
+    mut obkv_documents: grenad::Reader<R>,
+    indexer: GrenadParameters,
+    searchable_fields: &Option<HashSet<FieldId>>,
+    stop_words: Option<&fst::Set<&[u8]>>,
+) -> Result<(RoaringBitmap, grenad::Reader<File>)> {
+    let max_memory = indexer.max_memory_by_thread();
+
+    let mut documents_ids = RoaringBitmap::new();
+    let mut docid_word_positions_sorter = create_sorter(
+        concat_u32s_array,
+        indexer.chunk_compression_type,
+        indexer.chunk_compression_level,
+        indexer.max_nb_chunks,
+        max_memory,
+    );
+
+    let mut key_buffer = Vec::new();
+    let mut field_buffer = String::new();
+    let mut config = AnalyzerConfig::default();
+    if let Some(stop_words) = stop_words {
+        config.stop_words(stop_words);
+    }
+    let analyzer = Analyzer::<Vec<u8>>::new(AnalyzerConfig::default());
+
+    while let Some((key, value)) = obkv_documents.next()? {
+        let document_id = key
+            .try_into()
+            .map(u32::from_be_bytes)
+            .map_err(|_| SerializationError::InvalidNumberSerialization)?;
+        let obkv = obkv::KvReader::<FieldId>::new(value);
+
+        documents_ids.push(document_id);
+        key_buffer.clear();
+        key_buffer.extend_from_slice(&document_id.to_be_bytes());
+
+        for (field_id, field_bytes) in obkv.iter() {
+            if searchable_fields.as_ref().map_or(true, |sf| sf.contains(&field_id)) {
+                let value =
+                    serde_json::from_slice(field_bytes).map_err(InternalError::SerdeJson)?;
+                field_buffer.clear();
+                if let Some(field) = json_to_string(&value, &mut field_buffer) {
+                    let analyzed = analyzer.analyze(field);
+                    let tokens = process_tokens(analyzed.tokens())
+                        .take_while(|(p, _)| (*p as u32) < ONE_ATTRIBUTE);
+
+                    for (index, token) in tokens {
+                        let token = token.text().trim();
+                        key_buffer.truncate(mem::size_of::<u32>());
+                        key_buffer.extend_from_slice(token.as_bytes());
+
+                        let position: u32 = index
+                            .try_into()
+                            .map_err(|_| SerializationError::InvalidNumberSerialization)?;
+                        let position = field_id as u32 * ONE_ATTRIBUTE + position;
+                        docid_word_positions_sorter.insert(&key_buffer, &position.to_ne_bytes())?;
+                    }
+                }
+            }
+        }
+    }
+
+    sorter_into_reader(docid_word_positions_sorter, indexer).map(|reader| (documents_ids, reader))
+}
+
+/// Transform a JSON value into a string that can be indexed.
+fn json_to_string<'a>(value: &'a Value, buffer: &'a mut String) -> Option<&'a str> {
+    fn inner(value: &Value, output: &mut String) -> bool {
+        use std::fmt::Write;
+        match value {
+            Value::Null => false,
+            Value::Bool(boolean) => write!(output, "{}", boolean).is_ok(),
+            Value::Number(number) => write!(output, "{}", number).is_ok(),
+            Value::String(string) => write!(output, "{}", string).is_ok(),
+            Value::Array(array) => {
+                let mut count = 0;
+                for value in array {
+                    if inner(value, output) {
+                        output.push_str(". ");
+                        count += 1;
+                    }
+                }
+                // check that at least one value was written
+                count != 0
+            }
+            Value::Object(object) => {
+                let mut buffer = String::new();
+                let mut count = 0;
+                for (key, value) in object {
+                    buffer.clear();
+                    let _ = write!(&mut buffer, "{}: ", key);
+                    if inner(value, &mut buffer) {
+                        buffer.push_str(". ");
+                        // We write the "key: value. " pair only when
+                        // we are sure that the value can be written.
+                        output.push_str(&buffer);
+                        count += 1;
+                    }
+                }
+                // check that at least one value was written
+                count != 0
+            }
+        }
+    }
+
+    if let Value::String(string) = value {
+        Some(&string)
+    } else if inner(value, buffer) {
+        Some(buffer)
+    } else {
+        None
+    }
+}
+
+/// take an iterator on tokens and compute their relative position depending on separator kinds
+/// if it's an `Hard` separator we add an additional relative proximity of 8 between words,
+/// else we keep the standart proximity of 1 between words.
+fn process_tokens<'a>(
+    tokens: impl Iterator<Item = Token<'a>>,
+) -> impl Iterator<Item = (usize, Token<'a>)> {
+    tokens
+        .skip_while(|token| token.is_separator().is_some())
+        .scan((0, None), |(offset, prev_kind), token| {
+            match token.kind {
+                TokenKind::Word | TokenKind::StopWord | TokenKind::Unknown => {
+                    *offset += match *prev_kind {
+                        Some(TokenKind::Separator(SeparatorKind::Hard)) => 8,
+                        Some(_) => 1,
+                        None => 0,
+                    };
+                    *prev_kind = Some(token.kind)
+                }
+                TokenKind::Separator(SeparatorKind::Hard) => {
+                    *prev_kind = Some(token.kind);
+                }
+                TokenKind::Separator(SeparatorKind::Soft)
+                    if *prev_kind != Some(TokenKind::Separator(SeparatorKind::Hard)) =>
+                {
+                    *prev_kind = Some(token.kind);
+                }
+                _ => (),
+            }
+            Some((*offset, token))
+        })
+        .filter(|(_, t)| t.is_word())
+}

milli/src/update/index_documents/extract/extract_facet_number_docids.rs

@@ -0,0 +1,42 @@
+use std::fs::File;
+use std::io;
+
+use heed::{BytesDecode, BytesEncode};
+
+use super::helpers::{
+    create_sorter, merge_cbo_roaring_bitmaps, sorter_into_reader, GrenadParameters,
+};
+use crate::heed_codec::facet::{FacetLevelValueF64Codec, FieldDocIdFacetF64Codec};
+use crate::Result;
+
+/// Extracts the facet number and the documents ids where this facet number appear.
+///
+/// Returns a grenad reader with the list of extracted facet numbers and
+/// documents ids from the given chunk of docid facet number positions.
+#[logging_timer::time]
+pub fn extract_facet_number_docids<R: io::Read>(
+    mut docid_fid_facet_number: grenad::Reader<R>,
+    indexer: GrenadParameters,
+) -> Result<grenad::Reader<File>> {
+    let max_memory = indexer.max_memory_by_thread();
+
+    let mut facet_number_docids_sorter = create_sorter(
+        merge_cbo_roaring_bitmaps,
+        indexer.chunk_compression_type,
+        indexer.chunk_compression_level,
+        indexer.max_nb_chunks,
+        max_memory,
+    );
+
+    while let Some((key_bytes, _)) = docid_fid_facet_number.next()? {
+        let (field_id, document_id, number) =
+            FieldDocIdFacetF64Codec::bytes_decode(key_bytes).unwrap();
+
+        let key = (field_id, 0, number, number);
+        let key_bytes = FacetLevelValueF64Codec::bytes_encode(&key).unwrap();
+
+        facet_number_docids_sorter.insert(key_bytes, document_id.to_ne_bytes())?;
+    }
+
+    sorter_into_reader(facet_number_docids_sorter, indexer)
+}

milli/src/update/index_documents/extract/extract_facet_string_docids.rs

@@ -0,0 +1,58 @@
+use std::fs::File;
+use std::iter::FromIterator;
+use std::{io, str};
+
+use roaring::RoaringBitmap;
+
+use super::helpers::{
+    create_sorter, keep_first_prefix_value_merge_roaring_bitmaps, sorter_into_reader,
+    try_split_array_at, GrenadParameters,
+};
+use crate::heed_codec::facet::{encode_prefix_string, FacetStringLevelZeroCodec};
+use crate::{FieldId, Result};
+
+/// Extracts the facet string and the documents ids where this facet string appear.
+///
+/// Returns a grenad reader with the list of extracted facet strings and
+/// documents ids from the given chunk of docid facet string positions.
+#[logging_timer::time]
+pub fn extract_facet_string_docids<R: io::Read>(
+    mut docid_fid_facet_string: grenad::Reader<R>,
+    indexer: GrenadParameters,
+) -> Result<grenad::Reader<File>> {
+    let max_memory = indexer.max_memory_by_thread();
+
+    let mut facet_string_docids_sorter = create_sorter(
+        keep_first_prefix_value_merge_roaring_bitmaps,
+        indexer.chunk_compression_type,
+        indexer.chunk_compression_level,
+        indexer.max_nb_chunks,
+        max_memory,
+    );
+
+    let mut key_buffer = Vec::new();
+    let mut value_buffer = Vec::new();
+    while let Some((key, original_value_bytes)) = docid_fid_facet_string.next()? {
+        let (field_id_bytes, bytes) = try_split_array_at(key).unwrap();
+        let field_id = FieldId::from_be_bytes(field_id_bytes);
+        let (document_id_bytes, normalized_value_bytes) = try_split_array_at(bytes).unwrap();
+        let document_id = u32::from_be_bytes(document_id_bytes);
+        let original_value = str::from_utf8(original_value_bytes)?;
+
+        key_buffer.clear();
+        FacetStringLevelZeroCodec::serialize_into(
+            field_id,
+            str::from_utf8(normalized_value_bytes)?,
+            &mut key_buffer,
+        );
+
+        value_buffer.clear();
+        encode_prefix_string(original_value, &mut value_buffer)?;
+        let bitmap = RoaringBitmap::from_iter(Some(document_id));
+        bitmap.serialize_into(&mut value_buffer)?;
+
+        facet_string_docids_sorter.insert(&key_buffer, &value_buffer)?;
+    }
+
+    sorter_into_reader(facet_string_docids_sorter, indexer)
+}

milli/src/update/index_documents/extract/extract_fid_docid_facet_values.rs

@@ -0,0 +1,120 @@
+use std::collections::HashSet;
+use std::fs::File;
+use std::io;
+use std::mem::size_of;
+
+use heed::zerocopy::AsBytes;
+use serde_json::Value;
+
+use super::helpers::{create_sorter, keep_first, sorter_into_reader, GrenadParameters};
+use crate::error::InternalError;
+use crate::facet::value_encoding::f64_into_bytes;
+use crate::{DocumentId, FieldId, Result};
+
+/// Extracts the facet values of each faceted field of each document.
+///
+/// Returns the generated grenad reader containing the docid the fid and the orginal value as key
+/// and the normalized value as value extracted from the given chunk of documents.
+#[logging_timer::time]
+pub fn extract_fid_docid_facet_values<R: io::Read>(
+    mut obkv_documents: grenad::Reader<R>,
+    indexer: GrenadParameters,
+    faceted_fields: &HashSet<FieldId>,
+) -> Result<(grenad::Reader<File>, grenad::Reader<File>)> {
+    let max_memory = indexer.max_memory_by_thread();
+
+    let mut fid_docid_facet_numbers_sorter = create_sorter(
+        keep_first,
+        indexer.chunk_compression_type,
+        indexer.chunk_compression_level,
+        indexer.max_nb_chunks,
+        max_memory.map(|m| m / 2),
+    );
+
+    let mut fid_docid_facet_strings_sorter = create_sorter(
+        keep_first,
+        indexer.chunk_compression_type,
+        indexer.chunk_compression_level,
+        indexer.max_nb_chunks,
+        max_memory.map(|m| m / 2),
+    );
+
+    let mut key_buffer = Vec::new();
+    while let Some((docid_bytes, value)) = obkv_documents.next()? {
+        let obkv = obkv::KvReader::new(value);
+
+        for (field_id, field_bytes) in obkv.iter() {
+            if faceted_fields.contains(&field_id) {
+                let value =
+                    serde_json::from_slice(field_bytes).map_err(InternalError::SerdeJson)?;
+                let (numbers, strings) = extract_facet_values(&value);
+
+                key_buffer.clear();
+
+                // prefix key with the field_id and the document_id
+                key_buffer.extend_from_slice(&field_id.to_be_bytes());
+                key_buffer.extend_from_slice(&docid_bytes);
+
+                // insert facet numbers in sorter
+                for number in numbers {
+                    key_buffer.truncate(size_of::<FieldId>() + size_of::<DocumentId>());
+                    if let Some(value_bytes) = f64_into_bytes(number) {
+                        key_buffer.extend_from_slice(&value_bytes);
+                        key_buffer.extend_from_slice(&number.to_be_bytes());
+
+                        fid_docid_facet_numbers_sorter.insert(&key_buffer, ().as_bytes())?;
+                    }
+                }
+
+                // insert  normalized and original facet string in sorter
+                for (normalized, original) in strings.into_iter().filter(|(n, _)| !n.is_empty()) {
+                    key_buffer.truncate(size_of::<FieldId>() + size_of::<DocumentId>());
+                    key_buffer.extend_from_slice(normalized.as_bytes());
+                    fid_docid_facet_strings_sorter.insert(&key_buffer, original.as_bytes())?;
+                }
+            }
+        }
+    }
+
+    Ok((
+        sorter_into_reader(fid_docid_facet_numbers_sorter, indexer.clone())?,
+        sorter_into_reader(fid_docid_facet_strings_sorter, indexer)?,
+    ))
+}
+
+fn extract_facet_values(value: &Value) -> (Vec<f64>, Vec<(String, String)>) {
+    fn inner_extract_facet_values(
+        value: &Value,
+        can_recurse: bool,
+        output_numbers: &mut Vec<f64>,
+        output_strings: &mut Vec<(String, String)>,
+    ) {
+        match value {
+            Value::Null => (),
+            Value::Bool(b) => output_strings.push((b.to_string(), b.to_string())),
+            Value::Number(number) => {
+                if let Some(float) = number.as_f64() {
+                    output_numbers.push(float);
+                }
+            }
+            Value::String(original) => {
+                let normalized = original.trim().to_lowercase();
+                output_strings.push((normalized, original.clone()));
+            }
+            Value::Array(values) => {
+                if can_recurse {
+                    for value in values {
+                        inner_extract_facet_values(value, false, output_numbers, output_strings);
+                    }
+                }
+            }
+            Value::Object(_) => (),
+        }
+    }
+
+    let mut facet_number_values = Vec::new();
+    let mut facet_string_values = Vec::new();
+    inner_extract_facet_values(value, true, &mut facet_number_values, &mut facet_string_values);
+
+    (facet_number_values, facet_string_values)
+}

milli/src/update/index_documents/extract/extract_fid_word_count_docids.rs

@@ -0,0 +1,95 @@
+use std::collections::HashMap;
+use std::fs::File;
+use std::{cmp, io};
+
+use grenad::Sorter;
+
+use super::helpers::{
+    create_sorter, merge_cbo_roaring_bitmaps, read_u32_ne_bytes, sorter_into_reader,
+    try_split_array_at, GrenadParameters, MergeFn,
+};
+use crate::error::SerializationError;
+use crate::index::db_name::DOCID_WORD_POSITIONS;
+use crate::proximity::extract_position;
+use crate::{DocumentId, FieldId, Result};
+
+/// Extracts the field id word count and the documents ids where
+/// this field id with this amount of words appear.
+///
+/// Returns a grenad reader with the list of extracted field id word counts
+/// and documents ids from the given chunk of docid word positions.
+#[logging_timer::time]
+pub fn extract_fid_word_count_docids<R: io::Read>(
+    mut docid_word_positions: grenad::Reader<R>,
+    indexer: GrenadParameters,
+) -> Result<grenad::Reader<File>> {
+    let max_memory = indexer.max_memory_by_thread();
+
+    let mut fid_word_count_docids_sorter = create_sorter(
+        merge_cbo_roaring_bitmaps,
+        indexer.chunk_compression_type,
+        indexer.chunk_compression_level,
+        indexer.max_nb_chunks,
+        max_memory,
+    );
+
+    // This map is assumed to not consume a lot of memory.
+    let mut document_fid_wordcount = HashMap::new();
+    let mut current_document_id = None;
+
+    while let Some((key, value)) = docid_word_positions.next()? {
+        let (document_id_bytes, _word_bytes) = try_split_array_at(key)
+            .ok_or_else(|| SerializationError::Decoding { db_name: Some(DOCID_WORD_POSITIONS) })?;
+        let document_id = u32::from_be_bytes(document_id_bytes);
+
+        let curr_document_id = *current_document_id.get_or_insert(document_id);
+        if curr_document_id != document_id {
+            drain_document_fid_wordcount_into_sorter(
+                &mut fid_word_count_docids_sorter,
+                &mut document_fid_wordcount,
+                curr_document_id,
+            )?;
+            current_document_id = Some(document_id);
+        }
+
+        for position in read_u32_ne_bytes(value) {
+            let (field_id, position) = extract_position(position);
+            let word_count = position + 1;
+
+            let value = document_fid_wordcount.entry(field_id as FieldId).or_insert(0);
+            *value = cmp::max(*value, word_count);
+        }
+    }
+
+    if let Some(document_id) = current_document_id {
+        // We must make sure that don't lose the current document field id
+        // word count map if we break because we reached the end of the chunk.
+        drain_document_fid_wordcount_into_sorter(
+            &mut fid_word_count_docids_sorter,
+            &mut document_fid_wordcount,
+            document_id,
+        )?;
+    }
+
+    sorter_into_reader(fid_word_count_docids_sorter, indexer)
+}
+
+fn drain_document_fid_wordcount_into_sorter(
+    fid_word_count_docids_sorter: &mut Sorter<MergeFn>,
+    document_fid_wordcount: &mut HashMap<FieldId, u32>,
+    document_id: DocumentId,
+) -> Result<()> {
+    let mut key_buffer = Vec::new();
+
+    for (fid, count) in document_fid_wordcount.drain() {
+        if count <= 10 {
+            key_buffer.clear();
+            key_buffer.extend_from_slice(&fid.to_be_bytes());
+            key_buffer.push(count as u8);
+
+            fid_word_count_docids_sorter.insert(&key_buffer, document_id.to_ne_bytes())?;
+        }
+    }
+
+    Ok(())
+}

milli/src/update/index_documents/extract/extract_word_docids.rs

@@ -0,0 +1,46 @@
+use std::fs::File;
+use std::io;
+use std::iter::FromIterator;
+
+use roaring::RoaringBitmap;
+
+use super::helpers::{
+    create_sorter, merge_roaring_bitmaps, serialize_roaring_bitmap, sorter_into_reader,
+    try_split_array_at, GrenadParameters,
+};
+use crate::error::SerializationError;
+use crate::index::db_name::DOCID_WORD_POSITIONS;
+use crate::Result;
+
+/// Extracts the word and the documents ids where this word appear.
+///
+/// Returns a grenad reader with the list of extracted words and
+/// documents ids from the given chunk of docid word positions.
+#[logging_timer::time]
+pub fn extract_word_docids<R: io::Read>(
+    mut docid_word_positions: grenad::Reader<R>,
+    indexer: GrenadParameters,
+) -> Result<grenad::Reader<File>> {
+    let max_memory = indexer.max_memory_by_thread();
+
+    let mut word_docids_sorter = create_sorter(
+        merge_roaring_bitmaps,
+        indexer.chunk_compression_type,
+        indexer.chunk_compression_level,
+        indexer.max_nb_chunks,
+        max_memory,
+    );
+
+    let mut value_buffer = Vec::new();
+    while let Some((key, _value)) = docid_word_positions.next()? {
+        let (document_id_bytes, word_bytes) = try_split_array_at(key)
+            .ok_or_else(|| SerializationError::Decoding { db_name: Some(DOCID_WORD_POSITIONS) })?;
+        let document_id = u32::from_be_bytes(document_id_bytes);
+
+        let bitmap = RoaringBitmap::from_iter(Some(document_id));
+        serialize_roaring_bitmap(&bitmap, &mut value_buffer)?;
+        word_docids_sorter.insert(word_bytes, &value_buffer)?;
+    }
+
+    sorter_into_reader(word_docids_sorter, indexer)
+}

milli/src/update/index_documents/extract/extract_word_level_position_docids.rs

@@ -0,0 +1,51 @@
+use std::fs::File;
+use std::io;
+
+use super::helpers::{
+    create_sorter, merge_cbo_roaring_bitmaps, read_u32_ne_bytes, sorter_into_reader,
+    try_split_array_at, GrenadParameters,
+};
+use crate::error::SerializationError;
+use crate::index::db_name::DOCID_WORD_POSITIONS;
+use crate::{DocumentId, Result};
+
+/// Extracts the word positions and the documents ids where this word appear.
+///
+/// Returns a grenad reader with the list of extracted words at positions and
+/// documents ids from the given chunk of docid word positions.
+#[logging_timer::time]
+pub fn extract_word_level_position_docids<R: io::Read>(
+    mut docid_word_positions: grenad::Reader<R>,
+    indexer: GrenadParameters,
+) -> Result<grenad::Reader<File>> {
+    let max_memory = indexer.max_memory_by_thread();
+
+    let mut word_level_position_docids_sorter = create_sorter(
+        merge_cbo_roaring_bitmaps,
+        indexer.chunk_compression_type,
+        indexer.chunk_compression_level,
+        indexer.max_nb_chunks,
+        max_memory,
+    );
+
+    let mut key_buffer = Vec::new();
+    while let Some((key, value)) = docid_word_positions.next()? {
+        let (document_id_bytes, word_bytes) = try_split_array_at(key)
+            .ok_or_else(|| SerializationError::Decoding { db_name: Some(DOCID_WORD_POSITIONS) })?;
+        let document_id = DocumentId::from_be_bytes(document_id_bytes);
+
+        for position in read_u32_ne_bytes(value) {
+            key_buffer.clear();
+            key_buffer.extend_from_slice(word_bytes);
+            key_buffer.push(0); // tree level
+
+            // Levels are composed of left and right bounds.
+            key_buffer.extend_from_slice(&position.to_be_bytes());
+            key_buffer.extend_from_slice(&position.to_be_bytes());
+
+            word_level_position_docids_sorter.insert(&key_buffer, &document_id.to_ne_bytes())?;
+        }
+    }
+
+    sorter_into_reader(word_level_position_docids_sorter, indexer)
+}

milli/src/update/index_documents/extract/extract_word_pair_proximity_docids.rs

@@ -0,0 +1,174 @@
+use std::cmp::Ordering;
+use std::collections::{BinaryHeap, HashMap};
+use std::fs::File;
+use std::{cmp, io, mem, str, vec};
+
+use super::helpers::{
+    create_sorter, merge_cbo_roaring_bitmaps, read_u32_ne_bytes, sorter_into_reader,
+    try_split_array_at, GrenadParameters, MergeFn,
+};
+use crate::error::SerializationError;
+use crate::index::db_name::DOCID_WORD_POSITIONS;
+use crate::proximity::{positions_proximity, MAX_DISTANCE};
+use crate::{DocumentId, Result};
+
+/// Extracts the best proximity between pairs of words and the documents ids where this pair appear.
+///
+/// Returns a grenad reader with the list of extracted word pairs proximities and
+/// documents ids from the given chunk of docid word positions.
+#[logging_timer::time]
+pub fn extract_word_pair_proximity_docids<R: io::Read>(
+    mut docid_word_positions: grenad::Reader<R>,
+    indexer: GrenadParameters,
+) -> Result<grenad::Reader<File>> {
+    let max_memory = indexer.max_memory_by_thread();
+
+    let mut word_pair_proximity_docids_sorter = create_sorter(
+        merge_cbo_roaring_bitmaps,
+        indexer.chunk_compression_type,
+        indexer.chunk_compression_level,
+        indexer.max_nb_chunks,
+        max_memory.map(|m| m / 2),
+    );
+
+    // This map is assumed to not consume a lot of memory.
+    let mut document_word_positions_heap = BinaryHeap::new();
+    let mut current_document_id = None;
+
+    while let Some((key, value)) = docid_word_positions.next()? {
+        let (document_id_bytes, word_bytes) = try_split_array_at(key)
+            .ok_or_else(|| SerializationError::Decoding { db_name: Some(DOCID_WORD_POSITIONS) })?;
+        let document_id = u32::from_be_bytes(document_id_bytes);
+        let word = str::from_utf8(word_bytes)?;
+
+        let curr_document_id = *current_document_id.get_or_insert(document_id);
+        if curr_document_id != document_id {
+            let document_word_positions_heap = mem::take(&mut document_word_positions_heap);
+            document_word_positions_into_sorter(
+                curr_document_id,
+                document_word_positions_heap,
+                &mut word_pair_proximity_docids_sorter,
+            )?;
+            current_document_id = Some(document_id);
+        }
+
+        let word = word.to_string();
+        let mut iter = read_u32_ne_bytes(value).collect::<Vec<_>>().into_iter();
+        if let Some(position) = iter.next() {
+            document_word_positions_heap.push(PeekedWordPosition { word, position, iter });
+        }
+    }
+
+    if let Some(document_id) = current_document_id {
+        // We must make sure that don't lose the current document field id
+        // word count map if we break because we reached the end of the chunk.
+        let document_word_positions_heap = mem::take(&mut document_word_positions_heap);
+        document_word_positions_into_sorter(
+            document_id,
+            document_word_positions_heap,
+            &mut word_pair_proximity_docids_sorter,
+        )?;
+    }
+
+    sorter_into_reader(word_pair_proximity_docids_sorter, indexer)
+}
+
+/// Fills the list of all pairs of words with the shortest proximity between 1 and 7 inclusive.
+///
+/// This list is used by the engine to calculate the documents containing words that are
+/// close to each other.
+fn document_word_positions_into_sorter<'b>(
+    document_id: DocumentId,
+    mut word_positions_heap: BinaryHeap<PeekedWordPosition<vec::IntoIter<u32>>>,
+    word_pair_proximity_docids_sorter: &mut grenad::Sorter<MergeFn>,
+) -> Result<()> {
+    let mut word_pair_proximity = HashMap::new();
+    let mut ordered_peeked_word_positions = Vec::new();
+    while !word_positions_heap.is_empty() {
+        while let Some(peeked_word_position) = word_positions_heap.pop() {
+            ordered_peeked_word_positions.push(peeked_word_position);
+            if ordered_peeked_word_positions.len() == 7 {
+                break;
+            }
+        }
+
+        if let Some((head, tail)) = ordered_peeked_word_positions.split_first() {
+            for PeekedWordPosition { word, position, .. } in tail {
+                let prox = positions_proximity(head.position, *position);
+                if prox > 0 && prox < MAX_DISTANCE {
+                    word_pair_proximity
+                        .entry((head.word.clone(), word.clone()))
+                        .and_modify(|p| {
+                            *p = cmp::min(*p, prox);
+                        })
+                        .or_insert(prox);
+
+                    // We also compute the inverse proximity.
+                    let prox = prox + 1;
+                    if prox < MAX_DISTANCE {
+                        word_pair_proximity
+                            .entry((word.clone(), head.word.clone()))
+                            .and_modify(|p| {
+                                *p = cmp::min(*p, prox);
+                            })
+                            .or_insert(prox);
+                    }
+                }
+            }
+
+            // Push the tail in the heap.
+            let tail_iter = ordered_peeked_word_positions.drain(1..);
+            word_positions_heap.extend(tail_iter);
+
+            // Advance the head and push it in the heap.
+            if let Some(mut head) = ordered_peeked_word_positions.pop() {
+                if let Some(next_position) = head.iter.next() {
+                    word_positions_heap.push(PeekedWordPosition {
+                        word: head.word,
+                        position: next_position,
+                        iter: head.iter,
+                    });
+                }
+            }
+        }
+    }
+
+    let mut key_buffer = Vec::new();
+    for ((w1, w2), prox) in word_pair_proximity {
+        key_buffer.clear();
+        key_buffer.extend_from_slice(w1.as_bytes());
+        key_buffer.push(0);
+        key_buffer.extend_from_slice(w2.as_bytes());
+        key_buffer.push(prox as u8);
+
+        word_pair_proximity_docids_sorter.insert(&key_buffer, &document_id.to_ne_bytes())?;
+    }
+
+    Ok(())
+}
+
+struct PeekedWordPosition<I> {
+    word: String,
+    position: u32,
+    iter: I,
+}
+
+impl<I> Ord for PeekedWordPosition<I> {
+    fn cmp(&self, other: &Self) -> Ordering {
+        self.position.cmp(&other.position).reverse()
+    }
+}
+
+impl<I> PartialOrd for PeekedWordPosition<I> {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+impl<I> Eq for PeekedWordPosition<I> {}
+
+impl<I> PartialEq for PeekedWordPosition<I> {
+    fn eq(&self, other: &Self) -> bool {
+        self.position == other.position
+    }
+}

milli/src/update/index_documents/extract/mod.rs

@@ -0,0 +1,230 @@
+mod extract_docid_word_positions;
+mod extract_facet_number_docids;
+mod extract_facet_string_docids;
+mod extract_fid_docid_facet_values;
+mod extract_fid_word_count_docids;
+mod extract_word_docids;
+mod extract_word_level_position_docids;
+mod extract_word_pair_proximity_docids;
+
+use std::collections::HashSet;
+use std::fs::File;
+
+use crossbeam_channel::Sender;
+use log::debug;
+use rayon::prelude::*;
+
+use self::extract_docid_word_positions::extract_docid_word_positions;
+use self::extract_facet_number_docids::extract_facet_number_docids;
+use self::extract_facet_string_docids::extract_facet_string_docids;
+use self::extract_fid_docid_facet_values::extract_fid_docid_facet_values;
+use self::extract_fid_word_count_docids::extract_fid_word_count_docids;
+use self::extract_word_docids::extract_word_docids;
+use self::extract_word_level_position_docids::extract_word_level_position_docids;
+use self::extract_word_pair_proximity_docids::extract_word_pair_proximity_docids;
+use super::helpers::{
+    into_clonable_grenad, keep_first_prefix_value_merge_roaring_bitmaps, merge_cbo_roaring_bitmaps,
+    merge_readers, merge_roaring_bitmaps, CursorClonableMmap, GrenadParameters, MergeFn,
+};
+use super::{helpers, TypedChunk};
+use crate::{FieldId, Result};
+
+/// Extract data for each databases from obkv documents in parallel.
+/// Send data in grenad file over provided Sender.
+pub(crate) fn data_from_obkv_documents(
+    obkv_chunks: impl Iterator<Item = Result<grenad::Reader<File>>> + Send,
+    indexer: GrenadParameters,
+    lmdb_writer_sx: Sender<Result<TypedChunk>>,
+    searchable_fields: Option<HashSet<FieldId>>,
+    faceted_fields: HashSet<FieldId>,
+    stop_words: Option<fst::Set<&[u8]>>,
+) -> Result<()> {
+    let result: Result<(Vec<_>, (Vec<_>, Vec<_>))> = obkv_chunks
+        .par_bridge()
+        .map(|result| {
+            extract_documents_data(
+                result,
+                indexer,
+                lmdb_writer_sx.clone(),
+                &searchable_fields,
+                &faceted_fields,
+                &stop_words,
+            )
+        })
+        .collect();
+
+    let (
+        docid_word_positions_chunks,
+        (docid_fid_facet_numbers_chunks, docid_fid_facet_strings_chunks),
+    ) = result?;
+
+    spawn_extraction_task(
+        docid_word_positions_chunks.clone(),
+        indexer.clone(),
+        lmdb_writer_sx.clone(),
+        extract_word_pair_proximity_docids,
+        merge_cbo_roaring_bitmaps,
+        TypedChunk::WordPairProximityDocids,
+        "word-pair-proximity-docids",
+    );
+
+    spawn_extraction_task(
+        docid_word_positions_chunks.clone(),
+        indexer.clone(),
+        lmdb_writer_sx.clone(),
+        extract_fid_word_count_docids,
+        merge_cbo_roaring_bitmaps,
+        TypedChunk::FieldIdWordcountDocids,
+        "field-id-wordcount-docids",
+    );
+
+    spawn_extraction_task(
+        docid_word_positions_chunks.clone(),
+        indexer.clone(),
+        lmdb_writer_sx.clone(),
+        extract_word_docids,
+        merge_roaring_bitmaps,
+        TypedChunk::WordDocids,
+        "word-docids",
+    );
+
+    spawn_extraction_task(
+        docid_word_positions_chunks.clone(),
+        indexer.clone(),
+        lmdb_writer_sx.clone(),
+        extract_word_level_position_docids,
+        merge_cbo_roaring_bitmaps,
+        TypedChunk::WordLevelPositionDocids,
+        "word-level-position-docids",
+    );
+
+    spawn_extraction_task(
+        docid_fid_facet_strings_chunks.clone(),
+        indexer.clone(),
+        lmdb_writer_sx.clone(),
+        extract_facet_string_docids,
+        keep_first_prefix_value_merge_roaring_bitmaps,
+        TypedChunk::FieldIdFacetStringDocids,
+        "field-id-facet-string-docids",
+    );
+
+    spawn_extraction_task(
+        docid_fid_facet_numbers_chunks.clone(),
+        indexer.clone(),
+        lmdb_writer_sx.clone(),
+        extract_facet_number_docids,
+        merge_cbo_roaring_bitmaps,
+        TypedChunk::FieldIdFacetNumberDocids,
+        "field-id-facet-number-docids",
+    );
+
+    Ok(())
+}
+
+/// Spawn a new task to extract data for a specific DB using extract_fn.
+/// Generated grenad chunks are merged using the merge_fn.
+/// The result of merged chunks is serialized as TypedChunk using the serialize_fn
+/// and sent into lmdb_writer_sx.
+fn spawn_extraction_task<FE, FS>(
+    chunks: Vec<grenad::Reader<CursorClonableMmap>>,
+    indexer: GrenadParameters,
+    lmdb_writer_sx: Sender<Result<TypedChunk>>,
+    extract_fn: FE,
+    merge_fn: MergeFn,
+    serialize_fn: FS,
+    name: &'static str,
+) where
+    FE: Fn(grenad::Reader<CursorClonableMmap>, GrenadParameters) -> Result<grenad::Reader<File>>
+        + Sync
+        + Send
+        + 'static,
+    FS: Fn(grenad::Reader<File>) -> TypedChunk + Sync + Send + 'static,
+{
+    rayon::spawn(move || {
+        let chunks: Result<Vec<_>> =
+            chunks.into_par_iter().map(|chunk| extract_fn(chunk, indexer.clone())).collect();
+        rayon::spawn(move || match chunks {
+            Ok(chunks) => {
+                debug!("merge {} database", name);
+                let reader = merge_readers(chunks, merge_fn, indexer);
+                let _ = lmdb_writer_sx.send(reader.map(|r| serialize_fn(r)));
+            }
+            Err(e) => {
+                let _ = lmdb_writer_sx.send(Err(e));
+            }
+        })
+    });
+}
+
+/// Extract chuncked data and send it into lmdb_writer_sx sender:
+/// - documents
+/// - documents_ids
+/// - docid_word_positions
+/// - docid_fid_facet_numbers
+/// - docid_fid_facet_strings
+fn extract_documents_data(
+    documents_chunk: Result<grenad::Reader<File>>,
+    indexer: GrenadParameters,
+    lmdb_writer_sx: Sender<Result<TypedChunk>>,
+    searchable_fields: &Option<HashSet<FieldId>>,
+    faceted_fields: &HashSet<FieldId>,
+    stop_words: &Option<fst::Set<&[u8]>>,
+) -> Result<(
+    grenad::Reader<CursorClonableMmap>,
+    (grenad::Reader<CursorClonableMmap>, grenad::Reader<CursorClonableMmap>),
+)> {
+    let documents_chunk = documents_chunk.and_then(|c| unsafe { into_clonable_grenad(c) })?;
+
+    let _ = lmdb_writer_sx.send(Ok(TypedChunk::Documents(documents_chunk.clone())));
+
+    let (docid_word_positions_chunk, docid_fid_facet_values_chunks): (Result<_>, Result<_>) =
+        rayon::join(
+            || {
+                let (documents_ids, docid_word_positions_chunk) = extract_docid_word_positions(
+                    documents_chunk.clone(),
+                    indexer.clone(),
+                    searchable_fields,
+                    stop_words.as_ref(),
+                )?;
+
+                // send documents_ids to DB writer
+                let _ = lmdb_writer_sx.send(Ok(TypedChunk::NewDocumentsIds(documents_ids)));
+
+                // send docid_word_positions_chunk to DB writer
+                let docid_word_positions_chunk =
+                    unsafe { into_clonable_grenad(docid_word_positions_chunk)? };
+                let _ = lmdb_writer_sx
+                    .send(Ok(TypedChunk::DocidWordPositions(docid_word_positions_chunk.clone())));
+
+                Ok(docid_word_positions_chunk)
+            },
+            || {
+                let (docid_fid_facet_numbers_chunk, docid_fid_facet_strings_chunk) =
+                    extract_fid_docid_facet_values(
+                        documents_chunk.clone(),
+                        indexer.clone(),
+                        faceted_fields,
+                    )?;
+
+                // send docid_fid_facet_numbers_chunk to DB writer
+                let docid_fid_facet_numbers_chunk =
+                    unsafe { into_clonable_grenad(docid_fid_facet_numbers_chunk)? };
+
+                let _ = lmdb_writer_sx.send(Ok(TypedChunk::FieldIdDocidFacetNumbers(
+                    docid_fid_facet_numbers_chunk.clone(),
+                )));
+
+                // send docid_fid_facet_strings_chunk to DB writer
+                let docid_fid_facet_strings_chunk =
+                    unsafe { into_clonable_grenad(docid_fid_facet_strings_chunk)? };
+
+                let _ = lmdb_writer_sx.send(Ok(TypedChunk::FieldIdDocidFacetStrings(
+                    docid_fid_facet_strings_chunk.clone(),
+                )));
+
+                Ok((docid_fid_facet_numbers_chunk, docid_fid_facet_strings_chunk))
+            },
+        );
+
+    Ok((docid_word_positions_chunk?, docid_fid_facet_values_chunks?))
+}

milli/src/update/index_documents/helpers/clonable_mmap.rs

@@ -0,0 +1,24 @@
+use std::sync::Arc;
+
+use memmap::Mmap;
+
+/// Wrapper around Mmap allowing to virtualy clone grenad-chunks
+/// in a parallel process like the indexing.
+#[derive(Debug, Clone)]
+pub struct ClonableMmap {
+    inner: Arc<Mmap>,
+}
+
+impl AsRef<[u8]> for ClonableMmap {
+    fn as_ref(&self) -> &[u8] {
+        self.inner.as_ref()
+    }
+}
+
+impl From<Mmap> for ClonableMmap {
+    fn from(inner: Mmap) -> ClonableMmap {
+        ClonableMmap { inner: Arc::new(inner) }
+    }
+}
+
+pub type CursorClonableMmap = std::io::Cursor<ClonableMmap>;

milli/src/update/index_documents/helpers/grenad_helpers.rs

@@ -0,0 +1,262 @@
+use std::borrow::Cow;
+use std::fs::File;
+use std::io::{self, Seek, SeekFrom};
+use std::time::Instant;
+
+use grenad::{CompressionType, MergerIter, Reader, Sorter};
+use heed::types::ByteSlice;
+use log::debug;
+
+use super::{ClonableMmap, MergeFn};
+use crate::error::InternalError;
+use crate::update::index_documents::WriteMethod;
+use crate::Result;
+
+pub type CursorClonableMmap = io::Cursor<ClonableMmap>;
+
+pub fn create_writer<R: io::Write>(
+    typ: grenad::CompressionType,
+    level: Option<u32>,
+    file: R,
+) -> io::Result<grenad::Writer<R>> {
+    let mut builder = grenad::Writer::builder();
+    builder.compression_type(typ);
+    if let Some(level) = level {
+        builder.compression_level(level);
+    }
+    builder.build(file)
+}
+
+pub fn create_sorter(
+    merge: MergeFn,
+    chunk_compression_type: grenad::CompressionType,
+    chunk_compression_level: Option<u32>,
+    max_nb_chunks: Option<usize>,
+    max_memory: Option<usize>,
+) -> grenad::Sorter<MergeFn> {
+    let mut builder = grenad::Sorter::builder(merge);
+    builder.chunk_compression_type(chunk_compression_type);
+    if let Some(level) = chunk_compression_level {
+        builder.chunk_compression_level(level);
+    }
+    if let Some(nb_chunks) = max_nb_chunks {
+        builder.max_nb_chunks(nb_chunks);
+    }
+    if let Some(memory) = max_memory {
+        builder.dump_threshold(memory);
+        builder.allow_realloc(false);
+    }
+    builder.build()
+}
+
+pub fn sorter_into_reader(
+    sorter: grenad::Sorter<MergeFn>,
+    indexer: GrenadParameters,
+) -> Result<grenad::Reader<File>> {
+    let mut writer = tempfile::tempfile().and_then(|file| {
+        create_writer(indexer.chunk_compression_type, indexer.chunk_compression_level, file)
+    })?;
+    sorter.write_into(&mut writer)?;
+    Ok(writer_into_reader(writer)?)
+}
+
+pub fn writer_into_reader(writer: grenad::Writer<File>) -> Result<grenad::Reader<File>> {
+    let mut file = writer.into_inner()?;
+    file.seek(SeekFrom::Start(0))?;
+    grenad::Reader::new(file).map_err(Into::into)
+}
+
+pub unsafe fn into_clonable_grenad(
+    reader: grenad::Reader<File>,
+) -> Result<grenad::Reader<CursorClonableMmap>> {
+    let file = reader.into_inner();
+    let mmap = memmap::Mmap::map(&file)?;
+    let cursor = io::Cursor::new(ClonableMmap::from(mmap));
+    let reader = grenad::Reader::new(cursor)?;
+    Ok(reader)
+}
+
+pub fn merge_readers<R: io::Read>(
+    readers: Vec<grenad::Reader<R>>,
+    merge_fn: MergeFn,
+    indexer: GrenadParameters,
+) -> Result<grenad::Reader<File>> {
+    let mut merger_builder = grenad::MergerBuilder::new(merge_fn);
+    merger_builder.extend(readers);
+    let merger = merger_builder.build();
+    let mut writer = tempfile::tempfile().and_then(|file| {
+        create_writer(indexer.chunk_compression_type, indexer.chunk_compression_level, file)
+    })?;
+    merger.write_into(&mut writer)?;
+    let reader = writer_into_reader(writer)?;
+    Ok(reader)
+}
+
+#[derive(Debug, Clone, Copy)]
+pub struct GrenadParameters {
+    pub chunk_compression_type: CompressionType,
+    pub chunk_compression_level: Option<u32>,
+    pub max_memory: Option<usize>,
+    pub max_nb_chunks: Option<usize>,
+}
+
+impl Default for GrenadParameters {
+    fn default() -> Self {
+        Self {
+            chunk_compression_type: CompressionType::None,
+            chunk_compression_level: None,
+            max_memory: None,
+            max_nb_chunks: None,
+        }
+    }
+}
+
+impl GrenadParameters {
+    /// This function use the number of threads in the current threadpool to compute the value.
+    /// This should be called inside of a rayon thread pool,
+    /// Otherwise, it will take the global number of threads.
+    pub fn max_memory_by_thread(&self) -> Option<usize> {
+        self.max_memory.map(|max_memory| max_memory / rayon::current_num_threads())
+    }
+}
+
+/// Returns an iterator that outputs grenad readers of obkv documents
+/// with a maximum size of approximately `documents_chunks_size`.
+///
+/// The grenad obkv entries are composed of an incremental document id big-endian
+/// encoded as the key and an obkv object with an `u8` for the field as the key
+/// and a simple UTF-8 encoded string as the value.
+pub fn grenad_obkv_into_chunks<R: io::Read>(
+    mut reader: grenad::Reader<R>,
+    indexer: GrenadParameters,
+    documents_chunk_size: usize,
+) -> Result<impl Iterator<Item = Result<grenad::Reader<File>>>> {
+    let mut continue_reading = true;
+
+    let indexer_clone = indexer.clone();
+    let mut transposer = move || {
+        if !continue_reading {
+            return Ok(None);
+        }
+
+        let mut current_chunk_size = 0u64;
+        let mut obkv_documents = tempfile::tempfile().and_then(|file| {
+            create_writer(
+                indexer_clone.chunk_compression_type,
+                indexer_clone.chunk_compression_level,
+                file,
+            )
+        })?;
+
+        while let Some((document_id, obkv)) = reader.next()? {
+            obkv_documents.insert(document_id, obkv)?;
+            current_chunk_size += document_id.len() as u64 + obkv.len() as u64;
+
+            if current_chunk_size >= documents_chunk_size as u64 {
+                return writer_into_reader(obkv_documents).map(Some);
+            }
+        }
+
+        continue_reading = false;
+        writer_into_reader(obkv_documents).map(Some)
+    };
+
+    Ok(std::iter::from_fn(move || transposer().transpose()))
+}
+
+pub fn write_into_lmdb_database(
+    wtxn: &mut heed::RwTxn,
+    database: heed::PolyDatabase,
+    mut reader: Reader<File>,
+    merge: MergeFn,
+    method: WriteMethod,
+) -> Result<()> {
+    debug!("Writing MTBL stores...");
+    let before = Instant::now();
+
+    match method {
+        WriteMethod::Append => {
+            let mut out_iter = database.iter_mut::<_, ByteSlice, ByteSlice>(wtxn)?;
+            while let Some((k, v)) = reader.next()? {
+                // safety: we don't keep references from inside the LMDB database.
+                unsafe { out_iter.append(k, v)? };
+            }
+        }
+        WriteMethod::GetMergePut => {
+            while let Some((k, v)) = reader.next()? {
+                let mut iter = database.prefix_iter_mut::<_, ByteSlice, ByteSlice>(wtxn, k)?;
+                match iter.next().transpose()? {
+                    Some((key, old_val)) if key == k => {
+                        let vals = &[Cow::Borrowed(old_val), Cow::Borrowed(v)][..];
+                        let val = merge(k, &vals)?;
+                        // safety: we don't keep references from inside the LMDB database.
+                        unsafe { iter.put_current(k, &val)? };
+                    }
+                    _ => {
+                        drop(iter);
+                        database.put::<_, ByteSlice, ByteSlice>(wtxn, k, v)?;
+                    }
+                }
+            }
+        }
+    }
+
+    debug!("MTBL stores merged in {:.02?}!", before.elapsed());
+    Ok(())
+}
+
+pub fn sorter_into_lmdb_database(
+    wtxn: &mut heed::RwTxn,
+    database: heed::PolyDatabase,
+    sorter: Sorter<MergeFn>,
+    merge: MergeFn,
+    method: WriteMethod,
+) -> Result<()> {
+    debug!("Writing MTBL sorter...");
+    let before = Instant::now();
+
+    merger_iter_into_lmdb_database(wtxn, database, sorter.into_merger_iter()?, merge, method)?;
+
+    debug!("MTBL sorter writen in {:.02?}!", before.elapsed());
+    Ok(())
+}
+
+fn merger_iter_into_lmdb_database<R: io::Read>(
+    wtxn: &mut heed::RwTxn,
+    database: heed::PolyDatabase,
+    mut sorter: MergerIter<R, MergeFn>,
+    merge: MergeFn,
+    method: WriteMethod,
+) -> Result<()> {
+    match method {
+        WriteMethod::Append => {
+            let mut out_iter = database.iter_mut::<_, ByteSlice, ByteSlice>(wtxn)?;
+            while let Some((k, v)) = sorter.next()? {
+                // safety: we don't keep references from inside the LMDB database.
+                unsafe { out_iter.append(k, v)? };
+            }
+        }
+        WriteMethod::GetMergePut => {
+            while let Some((k, v)) = sorter.next()? {
+                let mut iter = database.prefix_iter_mut::<_, ByteSlice, ByteSlice>(wtxn, k)?;
+                match iter.next().transpose()? {
+                    Some((key, old_val)) if key == k => {
+                        let vals = vec![Cow::Borrowed(old_val), Cow::Borrowed(v)];
+                        let val = merge(k, &vals).map_err(|_| {
+                            // TODO just wrap this error?
+                            InternalError::IndexingMergingKeys { process: "get-put-merge" }
+                        })?;
+                        // safety: we don't keep references from inside the LMDB database.
+                        unsafe { iter.put_current(k, &val)? };
+                    }
+                    _ => {
+                        drop(iter);
+                        database.put::<_, ByteSlice, ByteSlice>(wtxn, k, v)?;
+                    }
+                }
+            }
+        }
+    }
+
+    Ok(())
+}

milli/src/update/index_documents/helpers/merge_functions.rs

@@ -0,0 +1,130 @@
+use std::borrow::Cow;
+use std::io;
+use std::result::Result as StdResult;
+
+use roaring::RoaringBitmap;
+
+use super::read_u32_ne_bytes;
+use crate::heed_codec::facet::{decode_prefix_string, encode_prefix_string};
+use crate::heed_codec::CboRoaringBitmapCodec;
+use crate::Result;
+
+pub type MergeFn = for<'a> fn(&[u8], &[Cow<'a, [u8]>]) -> Result<Cow<'a, [u8]>>;
+
+pub fn concat_u32s_array<'a>(_key: &[u8], values: &[Cow<'a, [u8]>]) -> Result<Cow<'a, [u8]>> {
+    if values.len() == 1 {
+        Ok(values[0].clone())
+    } else {
+        let capacity = values.iter().map(|v| v.len()).sum::<usize>();
+        let mut output = Vec::with_capacity(capacity);
+        values.iter().for_each(|integers| output.extend_from_slice(integers));
+        Ok(Cow::Owned(output))
+    }
+}
+
+pub fn roaring_bitmap_from_u32s_array(slice: &[u8]) -> RoaringBitmap {
+    read_u32_ne_bytes(slice).collect()
+}
+
+pub fn serialize_roaring_bitmap(bitmap: &RoaringBitmap, buffer: &mut Vec<u8>) -> io::Result<()> {
+    buffer.clear();
+    buffer.reserve(bitmap.serialized_size());
+    bitmap.serialize_into(buffer)
+}
+
+pub fn merge_roaring_bitmaps<'a>(_key: &[u8], values: &[Cow<'a, [u8]>]) -> Result<Cow<'a, [u8]>> {
+    if values.len() == 1 {
+        Ok(values[0].clone())
+    } else {
+        let merged = values
+            .iter()
+            .map(AsRef::as_ref)
+            .map(RoaringBitmap::deserialize_from)
+            .map(StdResult::unwrap)
+            .reduce(|a, b| a | b)
+            .unwrap();
+        let mut buffer = Vec::new();
+        serialize_roaring_bitmap(&merged, &mut buffer)?;
+        Ok(Cow::Owned(buffer))
+    }
+}
+
+pub fn keep_first_prefix_value_merge_roaring_bitmaps<'a>(
+    _key: &[u8],
+    values: &[Cow<'a, [u8]>],
+) -> Result<Cow<'a, [u8]>> {
+    if values.len() == 1 {
+        Ok(values[0].clone())
+    } else {
+        let original = decode_prefix_string(&values[0]).unwrap().0;
+        let merged_bitmaps = values
+            .iter()
+            .map(AsRef::as_ref)
+            .map(decode_prefix_string)
+            .map(Option::unwrap)
+            .map(|(_, bitmap_bytes)| bitmap_bytes)
+            .map(RoaringBitmap::deserialize_from)
+            .map(StdResult::unwrap)
+            .reduce(|a, b| a | b)
+            .unwrap();
+
+        let cap = std::mem::size_of::<u16>() + original.len() + merged_bitmaps.serialized_size();
+        let mut buffer = Vec::with_capacity(cap);
+        encode_prefix_string(original, &mut buffer)?;
+        merged_bitmaps.serialize_into(&mut buffer)?;
+        Ok(Cow::Owned(buffer))
+    }
+}
+
+pub fn keep_first<'a>(_key: &[u8], values: &[Cow<'a, [u8]>]) -> Result<Cow<'a, [u8]>> {
+    Ok(values[0].clone())
+}
+
+/// Only the last value associated with an id is kept.
+pub fn keep_latest_obkv<'a>(_key: &[u8], obkvs: &[Cow<'a, [u8]>]) -> Result<Cow<'a, [u8]>> {
+    Ok(obkvs.last().unwrap().clone())
+}
+
+/// Merge all the obks in the order we see them.
+pub fn merge_obkvs<'a>(_key: &[u8], obkvs: &[Cow<'a, [u8]>]) -> Result<Cow<'a, [u8]>> {
+    Ok(obkvs
+        .into_iter()
+        .cloned()
+        .reduce(|acc, current| {
+            let first = obkv::KvReader::new(&acc);
+            let second = obkv::KvReader::new(&current);
+            let mut buffer = Vec::new();
+            merge_two_obkvs(first, second, &mut buffer);
+            Cow::from(buffer)
+        })
+        .unwrap())
+}
+
+pub fn merge_two_obkvs(base: obkv::KvReaderU16, update: obkv::KvReaderU16, buffer: &mut Vec<u8>) {
+    use itertools::merge_join_by;
+    use itertools::EitherOrBoth::{Both, Left, Right};
+
+    buffer.clear();
+
+    let mut writer = obkv::KvWriter::new(buffer);
+    for eob in merge_join_by(base.iter(), update.iter(), |(b, _), (u, _)| b.cmp(u)) {
+        match eob {
+            Both(_, (k, v)) | Left((k, v)) | Right((k, v)) => writer.insert(k, v).unwrap(),
+        }
+    }
+
+    writer.finish().unwrap();
+}
+
+pub fn merge_cbo_roaring_bitmaps<'a>(
+    _key: &[u8],
+    values: &[Cow<'a, [u8]>],
+) -> Result<Cow<'a, [u8]>> {
+    if values.len() == 1 {
+        Ok(values[0].clone())
+    } else {
+        let mut vec = Vec::new();
+        CboRoaringBitmapCodec::merge_into(values, &mut vec)?;
+        Ok(Cow::from(vec))
+    }
+}

milli/src/update/index_documents/helpers/mod.rs

@@ -0,0 +1,45 @@
+mod clonable_mmap;
+mod grenad_helpers;
+mod merge_functions;
+
+use std::convert::{TryFrom, TryInto};
+
+pub use clonable_mmap::{ClonableMmap, CursorClonableMmap};
+pub use grenad_helpers::{
+    create_sorter, create_writer, grenad_obkv_into_chunks, into_clonable_grenad, merge_readers,
+    sorter_into_lmdb_database, sorter_into_reader, write_into_lmdb_database, writer_into_reader,
+    GrenadParameters,
+};
+pub use merge_functions::{
+    concat_u32s_array, keep_first, keep_first_prefix_value_merge_roaring_bitmaps, keep_latest_obkv,
+    merge_cbo_roaring_bitmaps, merge_obkvs, merge_roaring_bitmaps, merge_two_obkvs,
+    roaring_bitmap_from_u32s_array, serialize_roaring_bitmap, MergeFn,
+};
+
+pub fn valid_lmdb_key(key: impl AsRef<[u8]>) -> bool {
+    key.as_ref().len() <= 511
+}
+
+/// Divides one slice into two at an index, returns `None` if mid is out of bounds.
+pub fn try_split_at<T>(slice: &[T], mid: usize) -> Option<(&[T], &[T])> {
+    if mid <= slice.len() {
+        Some(slice.split_at(mid))
+    } else {
+        None
+    }
+}
+
+/// Divides one slice into an array and the tail at an index,
+/// returns `None` if `N` is out of bounds.
+pub fn try_split_array_at<T, const N: usize>(slice: &[T]) -> Option<([T; N], &[T])>
+where
+    [T; N]: for<'a> TryFrom<&'a [T]>,
+{
+    let (head, tail) = try_split_at(slice, N)?;
+    let head = head.try_into().ok()?;
+    Some((head, tail))
+}
+
+pub fn read_u32_ne_bytes(bytes: &[u8]) -> impl Iterator<Item = u32> + '_ {
+    bytes.chunks_exact(4).flat_map(TryInto::try_into).map(u32::from_ne_bytes)
+}

milli/src/update/index_documents/merge_function.rs

@@ -1,106 +0,0 @@
-use std::borrow::Cow;
-use std::result::Result as StdResult;
-
-use fst::IntoStreamer;
-use heed::{BytesDecode, BytesEncode};
-use roaring::RoaringBitmap;
-
-use crate::error::SerializationError;
-use crate::heed_codec::facet::FacetStringLevelZeroValueCodec;
-use crate::heed_codec::CboRoaringBitmapCodec;
-use crate::Result;
-
-/// Only the last value associated with an id is kept.
-pub fn keep_latest_obkv(_key: &[u8], obkvs: &[Cow<[u8]>]) -> Result<Vec<u8>> {
-    Ok(obkvs.last().unwrap().clone().into_owned())
-}
-
-/// Merge all the obks in the order we see them.
-pub fn merge_obkvs(_key: &[u8], obkvs: &[Cow<[u8]>]) -> Result<Vec<u8>> {
-    let mut iter = obkvs.iter();
-    let first = iter.next().map(|b| b.clone().into_owned()).unwrap();
-    Ok(iter.fold(first, |acc, current| {
-        let first = obkv::KvReader::new(&acc);
-        let second = obkv::KvReader::new(current);
-        let mut buffer = Vec::new();
-        merge_two_obkvs(first, second, &mut buffer);
-        buffer
-    }))
-}
-
-// Union of multiple FSTs
-pub fn fst_merge(_key: &[u8], values: &[Cow<[u8]>]) -> Result<Vec<u8>> {
-    let fsts = values.iter().map(fst::Set::new).collect::<StdResult<Vec<_>, _>>()?;
-    let op_builder: fst::set::OpBuilder = fsts.iter().map(|fst| fst.into_stream()).collect();
-    let op = op_builder.r#union();
-
-    let mut build = fst::SetBuilder::memory();
-    build.extend_stream(op.into_stream()).unwrap();
-    Ok(build.into_inner().unwrap())
-}
-
-pub fn keep_first(_key: &[u8], values: &[Cow<[u8]>]) -> Result<Vec<u8>> {
-    Ok(values.first().unwrap().to_vec())
-}
-
-pub fn merge_two_obkvs(base: obkv::KvReaderU16, update: obkv::KvReaderU16, buffer: &mut Vec<u8>) {
-    use itertools::merge_join_by;
-    use itertools::EitherOrBoth::{Both, Left, Right};
-
-    buffer.clear();
-
-    let mut writer = obkv::KvWriter::new(buffer);
-    for eob in merge_join_by(base.iter(), update.iter(), |(b, _), (u, _)| b.cmp(u)) {
-        match eob {
-            Both(_, (k, v)) | Left((k, v)) | Right((k, v)) => writer.insert(k, v).unwrap(),
-        }
-    }
-
-    writer.finish().unwrap();
-}
-
-pub fn roaring_bitmap_merge(_key: &[u8], values: &[Cow<[u8]>]) -> Result<Vec<u8>> {
-    let (head, tail) = values.split_first().unwrap();
-    let mut head = RoaringBitmap::deserialize_from(&head[..])?;
-
-    for value in tail {
-        head |= RoaringBitmap::deserialize_from(&value[..])?;
-    }
-
-    let mut vec = Vec::with_capacity(head.serialized_size());
-    head.serialize_into(&mut vec)?;
-    Ok(vec)
-}
-
-/// Uses the FacetStringLevelZeroValueCodec to merge the values.
-pub fn tuple_string_cbo_roaring_bitmap_merge(_key: &[u8], values: &[Cow<[u8]>]) -> Result<Vec<u8>> {
-    let (head, tail) = values.split_first().unwrap();
-    let (head_string, mut head_rb) =
-        FacetStringLevelZeroValueCodec::<CboRoaringBitmapCodec>::bytes_decode(&head[..])
-            .ok_or(SerializationError::Decoding { db_name: None })?;
-
-    for value in tail {
-        let (_string, rb) =
-            FacetStringLevelZeroValueCodec::<CboRoaringBitmapCodec>::bytes_decode(&value[..])
-                .ok_or(SerializationError::Decoding { db_name: None })?;
-        head_rb |= rb;
-    }
-
-    FacetStringLevelZeroValueCodec::<CboRoaringBitmapCodec>::bytes_encode(&(head_string, head_rb))
-        .map(|cow| cow.into_owned())
-        .ok_or(SerializationError::Encoding { db_name: None })
-        .map_err(Into::into)
-}
-
-pub fn cbo_roaring_bitmap_merge(_key: &[u8], values: &[Cow<[u8]>]) -> Result<Vec<u8>> {
-    let (head, tail) = values.split_first().unwrap();
-    let mut head = CboRoaringBitmapCodec::deserialize_from(&head[..])?;
-
-    for value in tail {
-        head |= CboRoaringBitmapCodec::deserialize_from(&value[..])?;
-    }
-
-    let mut vec = Vec::new();
-    CboRoaringBitmapCodec::serialize_into(&head, &mut vec);
-    Ok(vec)
-}

milli/src/update/index_documents/mod.rs

@@ -1,240 +1,44 @@
-use std::borrow::Cow;
+mod extract;
+mod helpers;
+mod transform;
+mod typed_chunk;
+
 use std::collections::HashSet;
-use std::fs::File;
+use std::io::{self, BufRead, BufReader};
-use std::io::{self, BufRead, BufReader, Seek, SeekFrom};
+use std::iter::FromIterator;
 use std::num::{NonZeroU32, NonZeroUsize};
-use std::result::Result as StdResult;
-use std::str;
-use std::sync::mpsc::sync_channel;
 use std::time::Instant;
 
-use bstr::ByteSlice as _;
 use chrono::Utc;
-use grenad::{CompressionType, FileFuse, Merger, MergerIter, Reader, Sorter, Writer};
+use crossbeam_channel::{Receiver, Sender};
-use heed::types::ByteSlice;
+use grenad::{self, CompressionType};
-use log::{debug, error, info};
+use log::{debug, info};
-use memmap::Mmap;
-use rayon::prelude::*;
 use rayon::ThreadPool;
+use roaring::RoaringBitmap;
 use serde::{Deserialize, Serialize};
+use typed_chunk::{write_typed_chunk_into_index, TypedChunk};
 
-pub use self::merge_function::{
+pub use self::helpers::{
-    cbo_roaring_bitmap_merge, fst_merge, keep_first, roaring_bitmap_merge,
+    create_sorter, create_writer, merge_cbo_roaring_bitmaps, merge_roaring_bitmaps,
-    tuple_string_cbo_roaring_bitmap_merge,
+    sorter_into_lmdb_database, write_into_lmdb_database, writer_into_reader, MergeFn,
 };
-use self::store::{Readers, Store};
+use self::helpers::{grenad_obkv_into_chunks, GrenadParameters};
 pub use self::transform::{Transform, TransformOutput};
-use super::UpdateBuilder;
-use crate::error::{Error, InternalError};
 use crate::update::{
-    Facets, UpdateIndexingStep, WordPrefixDocids, WordPrefixPairProximityDocids,
+    Facets, UpdateBuilder, UpdateIndexingStep, WordPrefixDocids, WordPrefixPairProximityDocids,
     WordsLevelPositions, WordsPrefixesFst,
 };
-use crate::{Index, MergeFn, Result};
+use crate::{Index, Result};
 
-mod merge_function;
+static MERGED_DATABASE_COUNT: usize = 7;
-mod store;
+static PREFIX_DATABASE_COUNT: usize = 5;
-mod transform;
+static TOTAL_POSTING_DATABASE_COUNT: usize = MERGED_DATABASE_COUNT + PREFIX_DATABASE_COUNT;
 
 #[derive(Debug, Serialize, Deserialize, Clone)]
 pub struct DocumentAdditionResult {
     pub nb_documents: usize,
 }
 
-#[derive(Debug, Copy, Clone)]
-pub enum WriteMethod {
-    Append,
-    GetMergePut,
-}
-
-pub fn create_writer(
-    typ: CompressionType,
-    level: Option<u32>,
-    file: File,
-) -> io::Result<Writer<File>> {
-    let mut builder = Writer::builder();
-    builder.compression_type(typ);
-    if let Some(level) = level {
-        builder.compression_level(level);
-    }
-    builder.build(file)
-}
-
-pub fn create_sorter<E>(
-    merge: MergeFn<E>,
-    chunk_compression_type: CompressionType,
-    chunk_compression_level: Option<u32>,
-    chunk_fusing_shrink_size: Option<u64>,
-    max_nb_chunks: Option<usize>,
-    max_memory: Option<usize>,
-) -> Sorter<MergeFn<E>> {
-    let mut builder = Sorter::builder(merge);
-    if let Some(shrink_size) = chunk_fusing_shrink_size {
-        builder.file_fusing_shrink_size(shrink_size);
-    }
-    builder.chunk_compression_type(chunk_compression_type);
-    if let Some(level) = chunk_compression_level {
-        builder.chunk_compression_level(level);
-    }
-    if let Some(nb_chunks) = max_nb_chunks {
-        builder.max_nb_chunks(nb_chunks);
-    }
-    if let Some(memory) = max_memory {
-        builder.max_memory(memory);
-    }
-    builder.build()
-}
-
-pub fn writer_into_reader(
-    writer: Writer<File>,
-    shrink_size: Option<u64>,
-) -> Result<Reader<FileFuse>> {
-    let mut file = writer.into_inner()?;
-    file.seek(SeekFrom::Start(0))?;
-    let file = if let Some(shrink_size) = shrink_size {
-        FileFuse::builder().shrink_size(shrink_size).build(file)
-    } else {
-        FileFuse::new(file)
-    };
-    Reader::new(file).map_err(Into::into)
-}
-
-pub fn merge_readers<E>(
-    sources: Vec<Reader<FileFuse>>,
-    merge: MergeFn<E>,
-) -> Merger<FileFuse, MergeFn<E>> {
-    let mut builder = Merger::builder(merge);
-    builder.extend(sources);
-    builder.build()
-}
-
-pub fn merge_into_lmdb_database<E>(
-    wtxn: &mut heed::RwTxn,
-    database: heed::PolyDatabase,
-    sources: Vec<Reader<FileFuse>>,
-    merge: MergeFn<E>,
-    method: WriteMethod,
-) -> Result<()>
-where
-    Error: From<E>,
-{
-    debug!("Merging {} MTBL stores...", sources.len());
-    let before = Instant::now();
-
-    let merger = merge_readers(sources, merge);
-    merger_iter_into_lmdb_database(wtxn, database, merger.into_merge_iter()?, merge, method)?;
-
-    debug!("MTBL stores merged in {:.02?}!", before.elapsed());
-    Ok(())
-}
-
-pub fn write_into_lmdb_database<E>(
-    wtxn: &mut heed::RwTxn,
-    database: heed::PolyDatabase,
-    mut reader: Reader<FileFuse>,
-    merge: MergeFn<E>,
-    method: WriteMethod,
-) -> Result<()>
-where
-    Error: From<E>,
-{
-    debug!("Writing MTBL stores...");
-    let before = Instant::now();
-
-    match method {
-        WriteMethod::Append => {
-            let mut out_iter = database.iter_mut::<_, ByteSlice, ByteSlice>(wtxn)?;
-            while let Some((k, v)) = reader.next()? {
-                // safety: we don't keep references from inside the LMDB database.
-                unsafe { out_iter.append(k, v)? };
-            }
-        }
-        WriteMethod::GetMergePut => {
-            while let Some((k, v)) = reader.next()? {
-                let mut iter = database.prefix_iter_mut::<_, ByteSlice, ByteSlice>(wtxn, k)?;
-                match iter.next().transpose()? {
-                    Some((key, old_val)) if key == k => {
-                        let vals = &[Cow::Borrowed(old_val), Cow::Borrowed(v)][..];
-                        let val = merge(k, &vals)?;
-                        // safety: we don't keep references from inside the LMDB database.
-                        unsafe { iter.put_current(k, &val)? };
-                    }
-                    _ => {
-                        drop(iter);
-                        database.put::<_, ByteSlice, ByteSlice>(wtxn, k, v)?;
-                    }
-                }
-            }
-        }
-    }
-
-    debug!("MTBL stores merged in {:.02?}!", before.elapsed());
-    Ok(())
-}
-
-pub fn sorter_into_lmdb_database<E>(
-    wtxn: &mut heed::RwTxn,
-    database: heed::PolyDatabase,
-    sorter: Sorter<MergeFn<E>>,
-    merge: MergeFn<E>,
-    method: WriteMethod,
-) -> Result<()>
-where
-    Error: From<E>,
-    Error: From<grenad::Error<E>>,
-{
-    debug!("Writing MTBL sorter...");
-    let before = Instant::now();
-
-    merger_iter_into_lmdb_database(wtxn, database, sorter.into_iter()?, merge, method)?;
-
-    debug!("MTBL sorter writen in {:.02?}!", before.elapsed());
-    Ok(())
-}
-
-fn merger_iter_into_lmdb_database<R: io::Read, E>(
-    wtxn: &mut heed::RwTxn,
-    database: heed::PolyDatabase,
-    mut sorter: MergerIter<R, MergeFn<E>>,
-    merge: MergeFn<E>,
-    method: WriteMethod,
-) -> Result<()>
-where
-    Error: From<E>,
-{
-    match method {
-        WriteMethod::Append => {
-            let mut out_iter = database.iter_mut::<_, ByteSlice, ByteSlice>(wtxn)?;
-            while let Some((k, v)) = sorter.next()? {
-                // safety: we don't keep references from inside the LMDB database.
-                unsafe { out_iter.append(k, v)? };
-            }
-        }
-        WriteMethod::GetMergePut => {
-            while let Some((k, v)) = sorter.next()? {
-                let mut iter = database.prefix_iter_mut::<_, ByteSlice, ByteSlice>(wtxn, k)?;
-                match iter.next().transpose()? {
-                    Some((key, old_val)) if key == k => {
-                        let vals = vec![Cow::Borrowed(old_val), Cow::Borrowed(v)];
-                        let val = merge(k, &vals).map_err(|_| {
-                            // TODO just wrap this error?
-                            InternalError::IndexingMergingKeys { process: "get-put-merge" }
-                        })?;
-                        // safety: we don't keep references from inside the LMDB database.
-                        unsafe { iter.put_current(k, &val)? };
-                    }
-                    _ => {
-                        drop(iter);
-                        database.put::<_, ByteSlice, ByteSlice>(wtxn, k, v)?;
-                    }
-                }
-            }
-        }
-    }
-
-    Ok(())
-}
-
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize, Deserialize)]
 #[non_exhaustive]
 pub enum IndexDocumentsMethod {
@@ -247,6 +51,12 @@ pub enum IndexDocumentsMethod {
     UpdateDocuments,
 }
 
+#[derive(Debug, Copy, Clone)]
+pub enum WriteMethod {
+    Append,
+    GetMergePut,
+}
+
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize, Deserialize)]
 #[non_exhaustive]
 pub enum UpdateFormat {
@@ -262,16 +72,15 @@ pub struct IndexDocuments<'t, 'u, 'i, 'a> {
     wtxn: &'t mut heed::RwTxn<'i, 'u>,
     index: &'i Index,
     pub(crate) log_every_n: Option<usize>,
+    pub(crate) documents_chunk_size: Option<usize>,
     pub(crate) max_nb_chunks: Option<usize>,
     pub(crate) max_memory: Option<usize>,
-    pub(crate) linked_hash_map_size: Option<usize>,
     pub(crate) chunk_compression_type: CompressionType,
     pub(crate) chunk_compression_level: Option<u32>,
-    pub(crate) chunk_fusing_shrink_size: Option<u64>,
     pub(crate) thread_pool: Option<&'a ThreadPool>,
     facet_level_group_size: Option<NonZeroUsize>,
     facet_min_level_size: Option<NonZeroUsize>,
-    words_prefix_threshold: Option<f64>,
+    words_prefix_threshold: Option<u32>,
     max_prefix_length: Option<usize>,
     words_positions_level_group_size: Option<NonZeroU32>,
     words_positions_min_level_size: Option<NonZeroU32>,
@@ -291,12 +100,11 @@ impl<'t, 'u, 'i, 'a> IndexDocuments<'t, 'u, 'i, 'a> {
             wtxn,
             index,
             log_every_n: None,
+            documents_chunk_size: None,
             max_nb_chunks: None,
             max_memory: None,
-            linked_hash_map_size: None,
             chunk_compression_type: CompressionType::None,
             chunk_compression_level: None,
-            chunk_fusing_shrink_size: None,
             thread_pool: None,
             facet_level_group_size: None,
             facet_min_level_size: None,
@@ -327,6 +135,7 @@ impl<'t, 'u, 'i, 'a> IndexDocuments<'t, 'u, 'i, 'a> {
         self.autogenerate_docids = false;
     }
 
+    #[logging_timer::time("IndexDocuments::{}")]
     pub fn execute<R, F>(self, reader: R, progress_callback: F) -> Result<DocumentAdditionResult>
     where
         R: io::Read,
@@ -344,14 +153,12 @@ impl<'t, 'u, 'i, 'a> IndexDocuments<'t, 'u, 'i, 'a> {
         let before_transform = Instant::now();
         let update_id = self.update_id;
         let progress_callback = |step| progress_callback(step, update_id);
-
         let transform = Transform {
             rtxn: &self.wtxn,
             index: self.index,
             log_every_n: self.log_every_n,
             chunk_compression_type: self.chunk_compression_type,
             chunk_compression_level: self.chunk_compression_level,
-            chunk_fusing_shrink_size: self.chunk_fusing_shrink_size,
             max_nb_chunks: self.max_nb_chunks,
             max_memory: self.max_memory,
             index_documents_method: self.update_method,
@@ -374,12 +181,11 @@ impl<'t, 'u, 'i, 'a> IndexDocuments<'t, 'u, 'i, 'a> {
         Ok(DocumentAdditionResult { nb_documents })
     }
 
+    #[logging_timer::time("IndexDocuments::{}")]
     pub fn execute_raw<F>(self, output: TransformOutput, progress_callback: F) -> Result<()>
     where
         F: Fn(UpdateIndexingStep) + Sync,
     {
-        let before_indexing = Instant::now();
-
         let TransformOutput {
             primary_key,
             fields_ids_map,
@@ -395,6 +201,78 @@ impl<'t, 'u, 'i, 'a> IndexDocuments<'t, 'u, 'i, 'a> {
         // up to date field map.
         self.index.put_fields_ids_map(self.wtxn, &fields_ids_map)?;
 
+        let backup_pool;
+        let pool = match self.thread_pool {
+            Some(pool) => pool,
+            #[cfg(not(test))]
+            None => {
+                // We initialize a bakcup pool with the default
+                // settings if none have already been set.
+                backup_pool = rayon::ThreadPoolBuilder::new().build()?;
+                &backup_pool
+            }
+            #[cfg(test)]
+            None => {
+                // We initialize a bakcup pool with the default
+                // settings if none have already been set.
+                backup_pool = rayon::ThreadPoolBuilder::new().num_threads(1).build()?;
+                &backup_pool
+            }
+        };
+
+        let documents_file = grenad::Reader::new(documents_file)?;
+
+        // create LMDB writer channel
+        let (lmdb_writer_sx, lmdb_writer_rx): (
+            Sender<Result<TypedChunk>>,
+            Receiver<Result<TypedChunk>>,
+        ) = crossbeam_channel::unbounded();
+
+        // get searchable fields for word databases
+        let searchable_fields =
+            self.index.searchable_fields_ids(self.wtxn)?.map(HashSet::from_iter);
+        // get filterable fields for facet databases
+        let faceted_fields = self.index.faceted_fields_ids(self.wtxn)?;
+
+        let stop_words = self.index.stop_words(self.wtxn)?;
+        // let stop_words = stop_words.as_ref();
+
+        // Run extraction pipeline in parallel.
+        pool.install(|| {
+            let params = GrenadParameters {
+                chunk_compression_type: self.chunk_compression_type,
+                chunk_compression_level: self.chunk_compression_level,
+                max_memory: self.max_memory,
+                max_nb_chunks: self.max_nb_chunks, // default value, may be chosen.
+            };
+
+            // split obkv file into several chuncks
+            let chunk_iter = grenad_obkv_into_chunks(
+                documents_file,
+                params.clone(),
+                self.documents_chunk_size.unwrap_or(1024 * 1024 * 128), // 128MiB
+            );
+
+            let result = chunk_iter.map(|chunk_iter| {
+                // extract all databases from the chunked obkv douments
+                extract::data_from_obkv_documents(
+                    chunk_iter,
+                    params,
+                    lmdb_writer_sx.clone(),
+                    searchable_fields,
+                    faceted_fields,
+                    stop_words,
+                )
+            });
+
+            if let Err(e) = result {
+                let _ = lmdb_writer_sx.send(Err(e));
+            }
+
+            // needs to be droped to avoid channel waiting lock.
+            drop(lmdb_writer_sx)
+        });
+
         // We delete the documents that this document addition replaces. This way we are
         // able to simply insert all the documents even if they already exist in the database.
         if !replaced_documents_ids.is_empty() {
@@ -402,10 +280,9 @@ impl<'t, 'u, 'i, 'a> IndexDocuments<'t, 'u, 'i, 'a> {
                 log_every_n: self.log_every_n,
                 max_nb_chunks: self.max_nb_chunks,
                 max_memory: self.max_memory,
-                linked_hash_map_size: self.linked_hash_map_size,
+                documents_chunk_size: self.documents_chunk_size,
                 chunk_compression_type: self.chunk_compression_type,
                 chunk_compression_level: self.chunk_compression_level,
-                chunk_fusing_shrink_size: self.chunk_fusing_shrink_size,
                 thread_pool: self.thread_pool,
                 update_id: self.update_id,
             };
@@ -416,189 +293,39 @@ impl<'t, 'u, 'i, 'a> IndexDocuments<'t, 'u, 'i, 'a> {
             debug!("{} documents actually deleted", deleted_documents_count);
         }
 
-        if documents_count == 0 {
+        let index_documents_ids = self.index.documents_ids(self.wtxn)?;
-            return Ok(());
+        let index_is_empty = index_documents_ids.len() == 0;
-        }
+        let mut final_documents_ids = RoaringBitmap::new();
 
-        let bytes = unsafe { Mmap::map(&documents_file)? };
+        let mut databases_seen = 0;
-        let documents = grenad::Reader::new(bytes.as_bytes()).unwrap();
+        progress_callback(UpdateIndexingStep::MergeDataIntoFinalDatabase {
-
+            databases_seen,
-        // The enum which indicates the type of the readers
+            total_databases: TOTAL_POSTING_DATABASE_COUNT,
-        // merges that are potentially done on different threads.
-        enum DatabaseType {
-            Main,
-            WordDocids,
-            WordLevel0PositionDocids,
-            FieldIdWordCountDocids,
-            FacetLevel0NumbersDocids,
-        }
-
-        let faceted_fields = self.index.faceted_fields_ids(self.wtxn)?;
-        let searchable_fields: HashSet<_> = match self.index.searchable_fields_ids(self.wtxn)? {
-            Some(fields) => fields.iter().copied().collect(),
-            None => fields_ids_map.iter().map(|(id, _name)| id).collect(),
-        };
-
-        let stop_words = self.index.stop_words(self.wtxn)?;
-        let stop_words = stop_words.as_ref();
-        let linked_hash_map_size = self.linked_hash_map_size;
-        let max_nb_chunks = self.max_nb_chunks;
-        let max_memory = self.max_memory;
-        let chunk_compression_type = self.chunk_compression_type;
-        let chunk_compression_level = self.chunk_compression_level;
-        let log_every_n = self.log_every_n;
-        let chunk_fusing_shrink_size = self.chunk_fusing_shrink_size;
-
-        let backup_pool;
-        let pool = match self.thread_pool {
-            Some(pool) => pool,
-            None => {
-                // We initialize a bakcup pool with the default
-                // settings if none have already been set.
-                backup_pool = rayon::ThreadPoolBuilder::new().build()?;
-                &backup_pool
-            }
-        };
-
-        let readers = pool.install(|| {
-            let num_threads = rayon::current_num_threads();
-            let max_memory_by_job = max_memory.map(|mm| mm / num_threads);
-
-            let readers = rayon::iter::repeatn(documents, num_threads)
-                .enumerate()
-                .map(|(i, documents)| {
-                    let store = Store::new(
-                        searchable_fields.clone(),
-                        faceted_fields.clone(),
-                        linked_hash_map_size,
-                        max_nb_chunks,
-                        max_memory_by_job,
-                        chunk_compression_type,
-                        chunk_compression_level,
-                        chunk_fusing_shrink_size,
-                        stop_words,
-                    )?;
-                    store.index(
-                        documents,
-                        documents_count,
-                        i,
-                        num_threads,
-                        log_every_n,
-                        &progress_callback,
-                    )
-                })
-                .collect::<StdResult<Vec<_>, _>>()?;
-
-            let mut main_readers = Vec::with_capacity(readers.len());
-            let mut word_docids_readers = Vec::with_capacity(readers.len());
-            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());
-            let mut field_id_docid_facet_strings_readers = Vec::with_capacity(readers.len());
-            let mut documents_readers = Vec::with_capacity(readers.len());
-            readers.into_iter().for_each(|readers| {
-                let Readers {
-                    main,
-                    word_docids,
-                    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,
-                    field_id_docid_facet_strings,
-                    documents,
-                } = readers;
-                main_readers.push(main);
-                word_docids_readers.push(word_docids);
-                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);
-                field_id_docid_facet_strings_readers.push(field_id_docid_facet_strings);
-                documents_readers.push(documents);
         });
 
-            // This is the function that merge the readers
+        for typed_chunk in lmdb_writer_rx {
-            // by using the given merge function.
+            let (docids, is_merged_database) =
-            let merge_readers = move |readers, merge| {
+                write_typed_chunk_into_index(typed_chunk?, &self.index, self.wtxn, index_is_empty)?;
-                let mut writer = tempfile::tempfile().and_then(|f| {
+            if !docids.is_empty() {
-                    create_writer(chunk_compression_type, chunk_compression_level, f)
+                final_documents_ids |= docids;
-                })?;
+                let documents_seen_count = final_documents_ids.len();
-                let merger = merge_readers(readers, merge);
+                progress_callback(UpdateIndexingStep::IndexDocuments {
-                merger.write_into(&mut writer)?;
+                    documents_seen: documents_seen_count as usize,
-                writer_into_reader(writer, chunk_fusing_shrink_size)
+                    total_documents: documents_count,
-            };
+                });
-
+                debug!(
-            // The enum and the channel which is used to transfert
+                    "We have seen {} documents on {} total document so far",
-            // the readers merges potentially done on another thread.
+                    documents_seen_count, documents_count
-            let (sender, receiver) = sync_channel(2);
+                );
-
-            debug!("Merging the main, word docids and words pairs proximity docids in parallel...");
-            rayon::spawn(move || {
-                vec![
-                    (DatabaseType::Main, main_readers, fst_merge as MergeFn<_>),
-                    (DatabaseType::WordDocids, word_docids_readers, roaring_bitmap_merge),
-                    (
-                        DatabaseType::FacetLevel0NumbersDocids,
-                        facet_field_numbers_docids_readers,
-                        cbo_roaring_bitmap_merge,
-                    ),
-                    (
-                        DatabaseType::WordLevel0PositionDocids,
-                        word_level_position_docids_readers,
-                        cbo_roaring_bitmap_merge,
-                    ),
-                    (
-                        DatabaseType::FieldIdWordCountDocids,
-                        field_id_word_count_docids_readers,
-                        cbo_roaring_bitmap_merge,
-                    ),
-                ]
-                .into_par_iter()
-                .for_each(|(dbtype, readers, merge)| {
-                    let result = merge_readers(readers, merge);
-                    if let Err(e) = sender.send((dbtype, result)) {
-                        error!("sender error: {}", e);
             }
+            if is_merged_database {
+                databases_seen += 1;
+                progress_callback(UpdateIndexingStep::MergeDataIntoFinalDatabase {
+                    databases_seen: databases_seen,
+                    total_databases: TOTAL_POSTING_DATABASE_COUNT,
                 });
-            });
+            }
-
+        }
-            Ok((
-                receiver,
-                docid_word_positions_readers,
-                documents_readers,
-                words_pairs_proximities_docids_readers,
-                facet_field_strings_docids_readers,
-                field_id_docid_facet_numbers_readers,
-                field_id_docid_facet_strings_readers,
-            )) as Result<_>
-        })?;
-
-        let (
-            receiver,
-            docid_word_positions_readers,
-            documents_readers,
-            words_pairs_proximities_docids_readers,
-            facet_field_strings_docids_readers,
-            field_id_docid_facet_numbers_readers,
-            field_id_docid_facet_strings_readers,
-        ) = readers;
-
-        let mut documents_ids = self.index.documents_ids(self.wtxn)?;
-        let contains_documents = !documents_ids.is_empty();
-        let write_method =
-            if contains_documents { WriteMethod::GetMergePut } else { WriteMethod::Append };
-
-        debug!("Writing using the write method: {:?}", write_method);
 
         // We write the field distribution into the main database
         self.index.put_field_distribution(self.wtxn, &field_distribution)?;
@@ -609,180 +336,24 @@ impl<'t, 'u, 'i, 'a> IndexDocuments<'t, 'u, 'i, 'a> {
         // We write the external documents ids into the main database.
         self.index.put_external_documents_ids(self.wtxn, &external_documents_ids)?;
 
-        // We merge the new documents ids with the existing ones.
+        let all_documents_ids = index_documents_ids | new_documents_ids | replaced_documents_ids;
-        documents_ids |= new_documents_ids;
+        self.index.put_documents_ids(self.wtxn, &all_documents_ids)?;
-        documents_ids |= replaced_documents_ids;
-        self.index.put_documents_ids(self.wtxn, &documents_ids)?;
 
-        let mut database_count = 0;
+        self.execute_prefix_databases(progress_callback)
-        let total_databases = 11;
-
-        progress_callback(UpdateIndexingStep::MergeDataIntoFinalDatabase {
-            databases_seen: 0,
-            total_databases,
-        });
-
-        debug!("Inserting the docid word positions into LMDB on disk...");
-        merge_into_lmdb_database(
-            self.wtxn,
-            *self.index.docid_word_positions.as_polymorph(),
-            docid_word_positions_readers,
-            keep_first,
-            write_method,
-        )?;
-
-        database_count += 1;
-        progress_callback(UpdateIndexingStep::MergeDataIntoFinalDatabase {
-            databases_seen: database_count,
-            total_databases,
-        });
-
-        debug!("Inserting the documents into LMDB on disk...");
-        merge_into_lmdb_database(
-            self.wtxn,
-            *self.index.documents.as_polymorph(),
-            documents_readers,
-            keep_first,
-            write_method,
-        )?;
-
-        database_count += 1;
-        progress_callback(UpdateIndexingStep::MergeDataIntoFinalDatabase {
-            databases_seen: database_count,
-            total_databases,
-        });
-
-        debug!("Writing the facet id string docids into LMDB on disk...");
-        merge_into_lmdb_database(
-            self.wtxn,
-            *self.index.facet_id_string_docids.as_polymorph(),
-            facet_field_strings_docids_readers,
-            tuple_string_cbo_roaring_bitmap_merge,
-            write_method,
-        )?;
-
-        database_count += 1;
-        progress_callback(UpdateIndexingStep::MergeDataIntoFinalDatabase {
-            databases_seen: database_count,
-            total_databases,
-        });
-
-        debug!("Writing the field id docid facet numbers into LMDB on disk...");
-        merge_into_lmdb_database(
-            self.wtxn,
-            *self.index.field_id_docid_facet_f64s.as_polymorph(),
-            field_id_docid_facet_numbers_readers,
-            keep_first,
-            write_method,
-        )?;
-
-        database_count += 1;
-        progress_callback(UpdateIndexingStep::MergeDataIntoFinalDatabase {
-            databases_seen: database_count,
-            total_databases,
-        });
-
-        debug!("Writing the field id docid facet strings into LMDB on disk...");
-        merge_into_lmdb_database(
-            self.wtxn,
-            *self.index.field_id_docid_facet_strings.as_polymorph(),
-            field_id_docid_facet_strings_readers,
-            keep_first,
-            write_method,
-        )?;
-
-        database_count += 1;
-        progress_callback(UpdateIndexingStep::MergeDataIntoFinalDatabase {
-            databases_seen: database_count,
-            total_databases,
-        });
-
-        debug!("Writing the words pairs proximities docids into LMDB on disk...");
-        merge_into_lmdb_database(
-            self.wtxn,
-            *self.index.word_pair_proximity_docids.as_polymorph(),
-            words_pairs_proximities_docids_readers,
-            cbo_roaring_bitmap_merge,
-            write_method,
-        )?;
-
-        database_count += 1;
-        progress_callback(UpdateIndexingStep::MergeDataIntoFinalDatabase {
-            databases_seen: database_count,
-            total_databases,
-        });
-
-        for (db_type, result) in receiver {
-            let content = result?;
-            match db_type {
-                DatabaseType::Main => {
-                    debug!("Writing the main elements into LMDB on disk...");
-                    write_into_lmdb_database(
-                        self.wtxn,
-                        self.index.main,
-                        content,
-                        fst_merge,
-                        WriteMethod::GetMergePut,
-                    )?;
-                }
-                DatabaseType::WordDocids => {
-                    debug!("Writing the words docids into LMDB on disk...");
-                    let db = *self.index.word_docids.as_polymorph();
-                    write_into_lmdb_database(
-                        self.wtxn,
-                        db,
-                        content,
-                        roaring_bitmap_merge,
-                        write_method,
-                    )?;
-                }
-                DatabaseType::FacetLevel0NumbersDocids => {
-                    debug!("Writing the facet numbers docids into LMDB on disk...");
-                    let db = *self.index.facet_id_f64_docids.as_polymorph();
-                    write_into_lmdb_database(
-                        self.wtxn,
-                        db,
-                        content,
-                        cbo_roaring_bitmap_merge,
-                        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,
-                        cbo_roaring_bitmap_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();
-                    write_into_lmdb_database(
-                        self.wtxn,
-                        db,
-                        content,
-                        cbo_roaring_bitmap_merge,
-                        write_method,
-                    )?;
-                }
     }
 
-            database_count += 1;
+    #[logging_timer::time("IndexDocuments::{}")]
-            progress_callback(UpdateIndexingStep::MergeDataIntoFinalDatabase {
+    pub fn execute_prefix_databases<F>(self, progress_callback: F) -> Result<()>
-                databases_seen: database_count,
+    where
-                total_databases,
+        F: Fn(UpdateIndexingStep) + Sync,
-            });
+    {
-        }
+        // Merged databases are already been indexed, we start from this count;
+        let mut databases_seen = MERGED_DATABASE_COUNT;
 
         // Run the facets update operation.
         let mut builder = Facets::new(self.wtxn, self.index, self.update_id);
         builder.chunk_compression_type = self.chunk_compression_type;
         builder.chunk_compression_level = self.chunk_compression_level;
-        builder.chunk_fusing_shrink_size = self.chunk_fusing_shrink_size;
         if let Some(value) = self.facet_level_group_size {
             builder.level_group_size(value);
         }
@@ -791,6 +362,12 @@ impl<'t, 'u, 'i, 'a> IndexDocuments<'t, 'u, 'i, 'a> {
         }
         builder.execute()?;
 
+        databases_seen += 1;
+        progress_callback(UpdateIndexingStep::MergeDataIntoFinalDatabase {
+            databases_seen: databases_seen,
+            total_databases: TOTAL_POSTING_DATABASE_COUNT,
+        });
+
         // Run the words prefixes update operation.
         let mut builder = WordsPrefixesFst::new(self.wtxn, self.index, self.update_id);
         if let Some(value) = self.words_prefix_threshold {
@@ -801,29 +378,44 @@ impl<'t, 'u, 'i, 'a> IndexDocuments<'t, 'u, 'i, 'a> {
         }
         builder.execute()?;
 
+        databases_seen += 1;
+        progress_callback(UpdateIndexingStep::MergeDataIntoFinalDatabase {
+            databases_seen: databases_seen,
+            total_databases: TOTAL_POSTING_DATABASE_COUNT,
+        });
+
         // Run the word prefix docids update operation.
         let mut builder = WordPrefixDocids::new(self.wtxn, self.index);
         builder.chunk_compression_type = self.chunk_compression_type;
         builder.chunk_compression_level = self.chunk_compression_level;
-        builder.chunk_fusing_shrink_size = self.chunk_fusing_shrink_size;
         builder.max_nb_chunks = self.max_nb_chunks;
         builder.max_memory = self.max_memory;
         builder.execute()?;
 
+        databases_seen += 1;
+        progress_callback(UpdateIndexingStep::MergeDataIntoFinalDatabase {
+            databases_seen: databases_seen,
+            total_databases: TOTAL_POSTING_DATABASE_COUNT,
+        });
+
         // Run the word prefix pair proximity docids update operation.
         let mut builder = WordPrefixPairProximityDocids::new(self.wtxn, self.index);
         builder.chunk_compression_type = self.chunk_compression_type;
         builder.chunk_compression_level = self.chunk_compression_level;
-        builder.chunk_fusing_shrink_size = self.chunk_fusing_shrink_size;
         builder.max_nb_chunks = self.max_nb_chunks;
         builder.max_memory = self.max_memory;
         builder.execute()?;
 
+        databases_seen += 1;
+        progress_callback(UpdateIndexingStep::MergeDataIntoFinalDatabase {
+            databases_seen: databases_seen,
+            total_databases: TOTAL_POSTING_DATABASE_COUNT,
+        });
+
         // Run the words level positions update operation.
         let mut builder = WordsLevelPositions::new(self.wtxn, self.index);
         builder.chunk_compression_type = self.chunk_compression_type;
         builder.chunk_compression_level = self.chunk_compression_level;
-        builder.chunk_fusing_shrink_size = self.chunk_fusing_shrink_size;
         if let Some(value) = self.words_positions_level_group_size {
             builder.level_group_size(value);
         }
@@ -832,9 +424,11 @@ impl<'t, 'u, 'i, 'a> IndexDocuments<'t, 'u, 'i, 'a> {
         }
         builder.execute()?;
 
-        debug_assert_eq!(database_count, total_databases);
+        databases_seen += 1;
-
+        progress_callback(UpdateIndexingStep::MergeDataIntoFinalDatabase {
-        info!("Transform output indexed in {:.02?}", before_indexing.elapsed());
+            databases_seen: databases_seen,
+            total_databases: TOTAL_POSTING_DATABASE_COUNT,
+        });
 
         Ok(())
     }

milli/src/update/index_documents/store.rs

@@ -1,985 +0,0 @@
-use std::borrow::Cow;
-use std::collections::{BTreeMap, HashMap, HashSet};
-use std::convert::{TryFrom, TryInto};
-use std::fs::File;
-use std::iter::FromIterator;
-use std::time::Instant;
-use std::{cmp, iter};
-
-use bstr::ByteSlice as _;
-use concat_arrays::concat_arrays;
-use fst::Set;
-use grenad::{CompressionType, FileFuse, Reader, Sorter, Writer};
-use heed::BytesEncode;
-use linked_hash_map::LinkedHashMap;
-use log::{debug, info, warn};
-use meilisearch_tokenizer::token::SeparatorKind;
-use meilisearch_tokenizer::{Analyzer, AnalyzerConfig, Token, TokenKind};
-use ordered_float::OrderedFloat;
-use roaring::RoaringBitmap;
-use serde_json::Value;
-use tempfile::tempfile;
-
-use super::merge_function::{
-    cbo_roaring_bitmap_merge, fst_merge, keep_first, roaring_bitmap_merge,
-    tuple_string_cbo_roaring_bitmap_merge,
-};
-use super::{create_sorter, create_writer, writer_into_reader, MergeFn};
-use crate::error::{Error, InternalError, SerializationError};
-use crate::heed_codec::facet::{
-    FacetLevelValueF64Codec, FacetStringLevelZeroCodec, FacetStringLevelZeroValueCodec,
-    FieldDocIdFacetF64Codec, FieldDocIdFacetStringCodec,
-};
-use crate::heed_codec::{BoRoaringBitmapCodec, CboRoaringBitmapCodec};
-use crate::update::UpdateIndexingStep;
-use crate::{json_to_string, DocumentId, FieldId, Position, Result, SmallVec32};
-
-const LMDB_MAX_KEY_LENGTH: usize = 511;
-const ONE_KILOBYTE: usize = 1024 * 1024;
-
-const MAX_POSITION: usize = 1000;
-const WORDS_FST_KEY: &[u8] = crate::index::main_key::WORDS_FST_KEY.as_bytes();
-
-pub struct Readers {
-    pub main: Reader<FileFuse>,
-    pub word_docids: Reader<FileFuse>,
-    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>,
-    pub field_id_docid_facet_strings: Reader<FileFuse>,
-    pub documents: Reader<FileFuse>,
-}
-
-pub struct Store<'s, A> {
-    // Indexing parameters
-    searchable_fields: HashSet<FieldId>,
-    filterable_fields: HashSet<FieldId>,
-    // 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>,
-    facet_field_string_docids: LinkedHashMap<(FieldId, String), (String, RoaringBitmap)>,
-    facet_field_value_docids_limit: usize,
-    // MTBL parameters
-    chunk_compression_type: CompressionType,
-    chunk_compression_level: Option<u32>,
-    chunk_fusing_shrink_size: Option<u64>,
-    // MTBL sorters
-    main_sorter: Sorter<MergeFn<Error>>,
-    word_docids_sorter: Sorter<MergeFn<Error>>,
-    words_pairs_proximities_docids_sorter: Sorter<MergeFn<Error>>,
-    word_level_position_docids_sorter: Sorter<MergeFn<Error>>,
-    field_id_word_count_docids_sorter: Sorter<MergeFn<Error>>,
-    facet_field_numbers_docids_sorter: Sorter<MergeFn<Error>>,
-    facet_field_strings_docids_sorter: Sorter<MergeFn<Error>>,
-    field_id_docid_facet_numbers_sorter: Sorter<MergeFn<Error>>,
-    field_id_docid_facet_strings_sorter: Sorter<MergeFn<Error>>,
-    // MTBL writers
-    docid_word_positions_writer: Writer<File>,
-    documents_writer: Writer<File>,
-    // tokenizer
-    analyzer: Analyzer<'s, A>,
-}
-
-impl<'s, A: AsRef<[u8]>> Store<'s, A> {
-    pub fn new(
-        searchable_fields: HashSet<FieldId>,
-        filterable_fields: HashSet<FieldId>,
-        linked_hash_map_size: Option<usize>,
-        max_nb_chunks: Option<usize>,
-        max_memory: Option<usize>,
-        chunk_compression_type: CompressionType,
-        chunk_compression_level: Option<u32>,
-        chunk_fusing_shrink_size: Option<u64>,
-        stop_words: Option<&'s Set<A>>,
-    ) -> Result<Self> {
-        // We divide the max memory by the number of sorter the Store have.
-        let max_memory = max_memory.map(|mm| cmp::max(ONE_KILOBYTE, mm / 5));
-        let linked_hash_map_size = linked_hash_map_size.unwrap_or(500);
-
-        let main_sorter = create_sorter(
-            fst_merge,
-            chunk_compression_type,
-            chunk_compression_level,
-            chunk_fusing_shrink_size,
-            max_nb_chunks,
-            max_memory,
-        );
-        let word_docids_sorter = create_sorter(
-            roaring_bitmap_merge,
-            chunk_compression_type,
-            chunk_compression_level,
-            chunk_fusing_shrink_size,
-            max_nb_chunks,
-            max_memory,
-        );
-        let words_pairs_proximities_docids_sorter = create_sorter(
-            cbo_roaring_bitmap_merge,
-            chunk_compression_type,
-            chunk_compression_level,
-            chunk_fusing_shrink_size,
-            max_nb_chunks,
-            max_memory,
-        );
-        let word_level_position_docids_sorter = create_sorter(
-            cbo_roaring_bitmap_merge,
-            chunk_compression_type,
-            chunk_compression_level,
-            chunk_fusing_shrink_size,
-            max_nb_chunks,
-            max_memory,
-        );
-        let field_id_word_count_docids_sorter = create_sorter(
-            cbo_roaring_bitmap_merge,
-            chunk_compression_type,
-            chunk_compression_level,
-            chunk_fusing_shrink_size,
-            max_nb_chunks,
-            max_memory,
-        );
-        let facet_field_numbers_docids_sorter = create_sorter(
-            cbo_roaring_bitmap_merge,
-            chunk_compression_type,
-            chunk_compression_level,
-            chunk_fusing_shrink_size,
-            max_nb_chunks,
-            max_memory,
-        );
-        let facet_field_strings_docids_sorter = create_sorter(
-            tuple_string_cbo_roaring_bitmap_merge,
-            chunk_compression_type,
-            chunk_compression_level,
-            chunk_fusing_shrink_size,
-            max_nb_chunks,
-            max_memory,
-        );
-        let field_id_docid_facet_numbers_sorter = create_sorter(
-            keep_first,
-            chunk_compression_type,
-            chunk_compression_level,
-            chunk_fusing_shrink_size,
-            max_nb_chunks,
-            Some(1024 * 1024 * 1024), // 1MB
-        );
-        let field_id_docid_facet_strings_sorter = create_sorter(
-            keep_first,
-            chunk_compression_type,
-            chunk_compression_level,
-            chunk_fusing_shrink_size,
-            max_nb_chunks,
-            Some(1024 * 1024 * 1024), // 1MB
-        );
-
-        let documents_writer = tempfile()
-            .and_then(|f| create_writer(chunk_compression_type, chunk_compression_level, f))?;
-        let docid_word_positions_writer = tempfile()
-            .and_then(|f| create_writer(chunk_compression_type, chunk_compression_level, f))?;
-
-        let mut config = AnalyzerConfig::default();
-        if let Some(stop_words) = stop_words {
-            config.stop_words(stop_words);
-        }
-        let analyzer = Analyzer::new(config);
-
-        Ok(Store {
-            // Indexing parameters.
-            searchable_fields,
-            filterable_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,
-            facet_field_number_docids: LinkedHashMap::with_capacity(linked_hash_map_size),
-            facet_field_string_docids: LinkedHashMap::with_capacity(linked_hash_map_size),
-            facet_field_value_docids_limit: linked_hash_map_size,
-            // MTBL parameters
-            chunk_compression_type,
-            chunk_compression_level,
-            chunk_fusing_shrink_size,
-            // MTBL sorters
-            main_sorter,
-            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,
-            field_id_docid_facet_strings_sorter,
-            // MTBL writers
-            docid_word_positions_writer,
-            documents_writer,
-            // tokenizer
-            analyzer,
-        })
-    }
-
-    // Save the documents ids under the position and word we have seen it.
-    fn insert_word_docid(&mut self, word: &str, id: DocumentId) -> Result<()> {
-        // if get_refresh finds the element it is assured to be at the end of the linked hash map.
-        match self.word_docids.get_refresh(word.as_bytes()) {
-            Some(old) => {
-                old.insert(id);
-            }
-            None => {
-                let word_vec = SmallVec32::from(word.as_bytes());
-                // A newly inserted element is append at the end of the linked hash map.
-                self.word_docids.insert(word_vec, RoaringBitmap::from_iter(Some(id)));
-                // If the word docids just reached it's capacity we must make sure to remove
-                // one element, this way next time we insert we doesn't grow the capacity.
-                if self.word_docids.len() == self.word_docids_limit {
-                    // Removing the front element is equivalent to removing the LRU element.
-                    let lru = self.word_docids.pop_front();
-                    Self::write_word_docids(&mut self.word_docids_sorter, lru)?;
-                }
-            }
-        }
-        Ok(())
-    }
-
-    fn insert_facet_number_values_docid(
-        &mut self,
-        field_id: FieldId,
-        value: OrderedFloat<f64>,
-        id: DocumentId,
-    ) -> Result<()> {
-        let sorter = &mut self.field_id_docid_facet_numbers_sorter;
-        Self::write_field_id_docid_facet_number_value(sorter, field_id, id, value)?;
-
-        let key = (field_id, value);
-        // if get_refresh finds the element it is assured to be at the end of the linked hash map.
-        match self.facet_field_number_docids.get_refresh(&key) {
-            Some(old) => {
-                old.insert(id);
-            }
-            None => {
-                // A newly inserted element is append at the end of the linked hash map.
-                self.facet_field_number_docids.insert(key, RoaringBitmap::from_iter(Some(id)));
-                // If the word docids just reached it's capacity we must make sure to remove
-                // one element, this way next time we insert we doesn't grow the capacity.
-                if self.facet_field_number_docids.len() == self.facet_field_value_docids_limit {
-                    // Removing the front element is equivalent to removing the LRU element.
-                    Self::write_facet_field_number_docids(
-                        &mut self.facet_field_numbers_docids_sorter,
-                        self.facet_field_number_docids.pop_front(),
-                    )?;
-                }
-            }
-        }
-
-        Ok(())
-    }
-
-    // Save the documents ids under the facet field id and value we have seen it.
-    fn insert_facet_string_values_docid(
-        &mut self,
-        field_id: FieldId,
-        normalized_value: String,
-        original_value: String,
-        id: DocumentId,
-    ) -> Result<()> {
-        if normalized_value.is_empty() {
-            return Ok(());
-        }
-
-        let sorter = &mut self.field_id_docid_facet_strings_sorter;
-        Self::write_field_id_docid_facet_string_value(
-            sorter,
-            field_id,
-            id,
-            &normalized_value,
-            &original_value,
-        )?;
-
-        let key = (field_id, normalized_value);
-        // if get_refresh finds the element it is assured to be at the end of the linked hash map.
-        match self.facet_field_string_docids.get_refresh(&key) {
-            Some((_original_value, old)) => {
-                old.insert(id);
-            }
-            None => {
-                // A newly inserted element is append at the end of the linked hash map.
-                self.facet_field_string_docids
-                    .insert(key, (original_value, RoaringBitmap::from_iter(Some(id))));
-                // If the word docids just reached it's capacity we must make sure to remove
-                // one element, this way next time we insert we doesn't grow the capacity.
-                if self.facet_field_string_docids.len() == self.facet_field_value_docids_limit {
-                    // Removing the front element is equivalent to removing the LRU element.
-                    Self::write_facet_field_string_docids(
-                        &mut self.facet_field_strings_docids_sorter,
-                        self.facet_field_string_docids.pop_front(),
-                    )?;
-                }
-            }
-        }
-
-        Ok(())
-    }
-
-    // Save the documents ids under the words pairs proximities that it contains.
-    fn insert_words_pairs_proximities_docids<'a>(
-        &mut self,
-        words_pairs_proximities: impl IntoIterator<Item = ((&'a str, &'a str), u8)>,
-        id: DocumentId,
-    ) -> Result<()> {
-        for ((w1, w2), prox) in words_pairs_proximities {
-            let w1 = SmallVec32::from(w1.as_bytes());
-            let w2 = SmallVec32::from(w2.as_bytes());
-            let key = (w1, w2, prox);
-            // if get_refresh finds the element it is assured
-            // to be at the end of the linked hash map.
-            match self.words_pairs_proximities_docids.get_refresh(&key) {
-                Some(old) => {
-                    old.insert(id);
-                }
-                None => {
-                    // A newly inserted element is append at the end of the linked hash map.
-                    let ids = RoaringBitmap::from_iter(Some(id));
-                    self.words_pairs_proximities_docids.insert(key, ids);
-                }
-            }
-        }
-
-        // If the linked hashmap is over capacity we must remove the overflowing elements.
-        let len = self.words_pairs_proximities_docids.len();
-        let overflow = len.checked_sub(self.words_pairs_proximities_docids_limit);
-        if let Some(overflow) = overflow {
-            let mut lrus = Vec::with_capacity(overflow);
-            // Removing front elements is equivalent to removing the LRUs.
-            let iter = iter::from_fn(|| self.words_pairs_proximities_docids.pop_front());
-            iter.take(overflow).for_each(|x| lrus.push(x));
-            Self::write_words_pairs_proximities(
-                &mut self.words_pairs_proximities_docids_sorter,
-                lrus,
-            )?;
-        }
-
-        Ok(())
-    }
-
-    fn write_document(
-        &mut self,
-        document_id: DocumentId,
-        words_positions: &mut HashMap<String, SmallVec32<Position>>,
-        facet_numbers_values: &mut HashMap<FieldId, Vec<f64>>,
-        facet_strings_values: &mut HashMap<FieldId, Vec<(String, String)>>,
-        record: &[u8],
-    ) -> Result<()> {
-        // We compute the list of words pairs proximities (self-join) and write it directly to disk.
-        let words_pair_proximities = compute_words_pair_proximities(&words_positions);
-        self.insert_words_pairs_proximities_docids(words_pair_proximities, document_id)?;
-
-        // We store document_id associated with all the words the record contains.
-        for (word, _) in words_positions.iter() {
-            self.insert_word_docid(word, document_id)?;
-        }
-
-        self.documents_writer.insert(document_id.to_be_bytes(), record)?;
-        Self::write_docid_word_positions(
-            &mut self.docid_word_positions_writer,
-            document_id,
-            words_positions,
-        )?;
-        Self::write_word_position_docids(
-            &mut self.word_level_position_docids_sorter,
-            document_id,
-            words_positions,
-        )?;
-
-        words_positions.clear();
-
-        // We store document_id associated with all the facet numbers fields ids and values.
-        for (field, values) in facet_numbers_values.drain() {
-            for value in values {
-                let value = OrderedFloat::from(value);
-                self.insert_facet_number_values_docid(field, value, document_id)?;
-            }
-        }
-
-        // We store document_id associated with all the facet strings fields ids and values.
-        for (field, values) in facet_strings_values.drain() {
-            for (normalized, original) in values {
-                self.insert_facet_string_values_docid(field, normalized, original, document_id)?;
-            }
-        }
-
-        Ok(())
-    }
-
-    fn write_words_pairs_proximities<E>(
-        sorter: &mut Sorter<MergeFn<E>>,
-        iter: impl IntoIterator<Item = ((SmallVec32<u8>, SmallVec32<u8>, u8), RoaringBitmap)>,
-    ) -> Result<()>
-    where
-        Error: From<E>,
-    {
-        let mut key = Vec::new();
-        let mut buffer = Vec::new();
-
-        for ((w1, w2, min_prox), docids) in iter {
-            key.clear();
-            key.extend_from_slice(w1.as_bytes());
-            key.push(0);
-            key.extend_from_slice(w2.as_bytes());
-            // Storing the minimun proximity found between those words
-            key.push(min_prox);
-            // We serialize the document ids into a buffer
-            buffer.clear();
-            buffer.reserve(CboRoaringBitmapCodec::serialized_size(&docids));
-            CboRoaringBitmapCodec::serialize_into(&docids, &mut buffer);
-            // that we write under the generated key into MTBL
-            if lmdb_key_valid_size(&key) {
-                sorter.insert(&key, &buffer)?;
-            } else {
-                warn!(
-                    "words pairs proximity ({:?} - {:?}, {:?}) is too large to be saved",
-                    w1, w2, min_prox
-                );
-            }
-        }
-
-        Ok(())
-    }
-
-    fn write_docid_word_positions(
-        writer: &mut Writer<File>,
-        id: DocumentId,
-        words_positions: &HashMap<String, SmallVec32<Position>>,
-    ) -> Result<()> {
-        // We prefix the words by the document id.
-        let mut key = id.to_be_bytes().to_vec();
-        let mut buffer = Vec::new();
-        let base_size = key.len();
-
-        // We order the words lexicographically, this way we avoid passing by a sorter.
-        let words_positions = BTreeMap::from_iter(words_positions);
-
-        for (word, positions) in words_positions {
-            key.truncate(base_size);
-            key.extend_from_slice(word.as_bytes());
-            buffer.clear();
-
-            // We serialize the positions into a buffer.
-            let positions = RoaringBitmap::from_iter(positions.iter().cloned());
-            BoRoaringBitmapCodec::serialize_into(&positions, &mut buffer);
-
-            // that we write under the generated key into MTBL
-            if lmdb_key_valid_size(&key) {
-                writer.insert(&key, &buffer)?;
-            } else {
-                warn!("word {:?} is too large to be saved", word.as_bytes().as_bstr());
-            }
-        }
-
-        Ok(())
-    }
-
-    fn write_word_position_docids<E>(
-        writer: &mut Sorter<MergeFn<E>>,
-        document_id: DocumentId,
-        words_positions: &HashMap<String, SmallVec32<Position>>,
-    ) -> Result<()>
-    where
-        Error: From<E>,
-    {
-        let mut key_buffer = Vec::new();
-        let mut data_buffer = Vec::new();
-
-        for (word, positions) in words_positions {
-            key_buffer.clear();
-            key_buffer.extend_from_slice(word.as_bytes());
-            key_buffer.push(0); // level 0
-
-            for position in positions {
-                key_buffer.truncate(word.len() + 1);
-                let position_bytes = position.to_be_bytes();
-                key_buffer.extend_from_slice(position_bytes.as_bytes());
-                key_buffer.extend_from_slice(position_bytes.as_bytes());
-
-                data_buffer.clear();
-                let positions = RoaringBitmap::from_iter(Some(document_id));
-                // We serialize the positions into a buffer.
-                CboRoaringBitmapCodec::serialize_into(&positions, &mut data_buffer);
-
-                // that we write under the generated key into MTBL
-                if lmdb_key_valid_size(&key_buffer) {
-                    writer.insert(&key_buffer, &data_buffer)?;
-                } else {
-                    warn!("word {:?} is too large to be saved", word.as_bytes().as_bstr());
-                }
-            }
-        }
-
-        Ok(())
-    }
-
-    fn write_facet_field_string_docids<I, E>(sorter: &mut Sorter<MergeFn<E>>, iter: I) -> Result<()>
-    where
-        I: IntoIterator<Item = ((FieldId, String), (String, RoaringBitmap))>,
-        Error: From<E>,
-    {
-        let mut key_buffer = Vec::new();
-
-        for ((field_id, normalized_value), (original_value, docids)) in iter {
-            key_buffer.clear();
-
-            FacetStringLevelZeroCodec::serialize_into(field_id, &normalized_value, &mut key_buffer);
-
-            let data = (original_value.as_str(), docids);
-            let data = FacetStringLevelZeroValueCodec::<CboRoaringBitmapCodec>::bytes_encode(&data)
-                .ok_or(SerializationError::Encoding { db_name: Some("facet-id-string-docids") })?;
-
-            if lmdb_key_valid_size(&key_buffer) {
-                sorter.insert(&key_buffer, &data)?;
-            } else {
-                warn!(
-                    "facet value {:?} is too large to be saved",
-                    original_value.as_bytes().as_bstr()
-                );
-            }
-        }
-
-        Ok(())
-    }
-
-    fn write_facet_field_number_docids<I, E>(sorter: &mut Sorter<MergeFn<E>>, iter: I) -> Result<()>
-    where
-        I: IntoIterator<Item = ((FieldId, OrderedFloat<f64>), RoaringBitmap)>,
-        Error: From<E>,
-    {
-        let mut data_buffer = Vec::new();
-
-        for ((field_id, value), docids) in iter {
-            data_buffer.clear();
-
-            let key = FacetLevelValueF64Codec::bytes_encode(&(field_id, 0, *value, *value))
-                .map(Cow::into_owned)
-                .ok_or(SerializationError::Encoding { db_name: Some("facet level value") })?;
-
-            CboRoaringBitmapCodec::serialize_into(&docids, &mut data_buffer);
-
-            if lmdb_key_valid_size(&key) {
-                sorter.insert(&key, &data_buffer)?;
-            }
-        }
-
-        Ok(())
-    }
-
-    fn write_field_id_docid_facet_number_value<E>(
-        sorter: &mut Sorter<MergeFn<E>>,
-        field_id: FieldId,
-        document_id: DocumentId,
-        value: OrderedFloat<f64>,
-    ) -> Result<()>
-    where
-        Error: From<E>,
-    {
-        let key = FieldDocIdFacetF64Codec::bytes_encode(&(field_id, document_id, *value))
-            .map(Cow::into_owned)
-            .ok_or(SerializationError::Encoding { db_name: Some("facet level value") })?;
-
-        if lmdb_key_valid_size(&key) {
-            sorter.insert(&key, &[])?;
-        }
-
-        Ok(())
-    }
-
-    fn write_field_id_docid_facet_string_value<E>(
-        sorter: &mut Sorter<MergeFn<E>>,
-        field_id: FieldId,
-        document_id: DocumentId,
-        normalized_value: &str,
-        original_value: &str,
-    ) -> Result<()>
-    where
-        Error: From<E>,
-    {
-        let mut buffer = Vec::new();
-        FieldDocIdFacetStringCodec::serialize_into(
-            field_id,
-            document_id,
-            normalized_value,
-            &mut buffer,
-        );
-
-        if lmdb_key_valid_size(&buffer) {
-            sorter.insert(&buffer, original_value.as_bytes())?;
-        } else {
-            warn!("facet value {:?} is too large to be saved", original_value.as_bytes().as_bstr());
-        }
-
-        Ok(())
-    }
-
-    fn write_word_docids<I, E>(sorter: &mut Sorter<MergeFn<E>>, iter: I) -> Result<()>
-    where
-        I: IntoIterator<Item = (SmallVec32<u8>, RoaringBitmap)>,
-        Error: From<E>,
-    {
-        let mut key = Vec::new();
-        let mut buffer = Vec::new();
-
-        for (word, ids) in iter {
-            key.clear();
-            key.extend_from_slice(&word);
-            // We serialize the document ids into a buffer
-            buffer.clear();
-            let ids = RoaringBitmap::from_iter(ids);
-            buffer.reserve(ids.serialized_size());
-            ids.serialize_into(&mut buffer)?;
-            // that we write under the generated key into MTBL
-            if lmdb_key_valid_size(&key) {
-                sorter.insert(&key, &buffer)?;
-            } else {
-                warn!("word {:?} is too large to be saved", word.as_bytes().as_bstr());
-            }
-        }
-
-        Ok(())
-    }
-
-    pub fn index<F>(
-        mut self,
-        mut documents: grenad::Reader<&[u8]>,
-        documents_count: usize,
-        thread_index: usize,
-        num_threads: usize,
-        log_every_n: Option<usize>,
-        mut progress_callback: F,
-    ) -> Result<Readers>
-    where
-        F: FnMut(UpdateIndexingStep),
-    {
-        debug!("{:?}: Indexing in a Store...", thread_index);
-
-        let mut before = Instant::now();
-        let mut words_positions = HashMap::new();
-        let mut facet_numbers_values = HashMap::new();
-        let mut facet_strings_values = HashMap::new();
-
-        let mut count: usize = 0;
-        while let Some((key, value)) = documents.next()? {
-            let document_id = key.try_into().map(u32::from_be_bytes).unwrap();
-            let document = obkv::KvReader::new(value);
-
-            // We skip documents that must not be indexed by this thread.
-            if count % num_threads == thread_index {
-                // This is a log routine that we do every `log_every_n` documents.
-                if thread_index == 0 && log_every_n.map_or(false, |len| count % len == 0) {
-                    info!(
-                        "We have seen {} documents so far ({:.02?}).",
-                        format_count(count),
-                        before.elapsed()
-                    );
-                    progress_callback(UpdateIndexingStep::IndexDocuments {
-                        documents_seen: count,
-                        total_documents: documents_count,
-                    });
-                    before = Instant::now();
-                }
-
-                for (attr, content) in document.iter() {
-                    if self.filterable_fields.contains(&attr)
-                        || self.searchable_fields.contains(&attr)
-                    {
-                        let value =
-                            serde_json::from_slice(content).map_err(InternalError::SerdeJson)?;
-
-                        if self.filterable_fields.contains(&attr) {
-                            let (facet_numbers, facet_strings) = extract_facet_values(&value);
-                            facet_numbers_values
-                                .entry(attr)
-                                .or_insert_with(Vec::new)
-                                .extend(facet_numbers);
-                            facet_strings_values
-                                .entry(attr)
-                                .or_insert_with(Vec::new)
-                                .extend(facet_strings);
-                        }
-
-                        if self.searchable_fields.contains(&attr) {
-                            let content = match json_to_string(&value) {
-                                Some(content) => content,
-                                None => continue,
-                            };
-
-                            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);
-                            }
-                        }
-                    }
-                }
-
-                // We write the document in the documents store.
-                self.write_document(
-                    document_id,
-                    &mut words_positions,
-                    &mut facet_numbers_values,
-                    &mut facet_strings_values,
-                    value,
-                )?;
-            }
-
-            // Compute the document id of the next document.
-            count += 1;
-        }
-
-        progress_callback(UpdateIndexingStep::IndexDocuments {
-            documents_seen: count,
-            total_documents: documents_count,
-        });
-
-        let readers = self.finish()?;
-        debug!("{:?}: Store created!", thread_index);
-        Ok(readers)
-    }
-
-    fn finish(mut self) -> Result<Readers> {
-        let comp_type = self.chunk_compression_type;
-        let comp_level = self.chunk_compression_level;
-        let shrink_size = self.chunk_fusing_shrink_size;
-
-        Self::write_word_docids(&mut self.word_docids_sorter, self.word_docids)?;
-        Self::write_words_pairs_proximities(
-            &mut self.words_pairs_proximities_docids_sorter,
-            self.words_pairs_proximities_docids,
-        )?;
-        Self::write_facet_field_number_docids(
-            &mut self.facet_field_numbers_docids_sorter,
-            self.facet_field_number_docids,
-        )?;
-
-        Self::write_facet_field_string_docids(
-            &mut self.facet_field_strings_docids_sorter,
-            self.facet_field_string_docids,
-        )?;
-
-        let mut word_docids_wtr =
-            tempfile().and_then(|f| create_writer(comp_type, comp_level, f))?;
-        let mut builder = fst::SetBuilder::memory();
-
-        let mut iter = self.word_docids_sorter.into_iter()?;
-        while let Some((word, val)) = iter.next()? {
-            // This is a lexicographically ordered word position
-            // we use the key to construct the words fst.
-            builder.insert(word)?;
-            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);
-            let key: [u8; 3] = concat_arrays!(fid.to_be_bytes(), [count]);
-            self.field_id_word_count_docids_sorter.insert(key, &docids_buffer)?;
-        }
-
-        let fst = builder.into_set();
-        self.main_sorter.insert(WORDS_FST_KEY, fst.as_fst().as_bytes())?;
-
-        let mut main_wtr = tempfile().and_then(|f| create_writer(comp_type, comp_level, f))?;
-        self.main_sorter.write_into(&mut main_wtr)?;
-
-        let mut words_pairs_proximities_docids_wtr =
-            tempfile().and_then(|f| create_writer(comp_type, comp_level, f))?;
-        self.words_pairs_proximities_docids_sorter
-            .write_into(&mut words_pairs_proximities_docids_wtr)?;
-
-        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)?;
-
-        let mut facet_field_strings_docids_wtr =
-            tempfile().and_then(|f| create_writer(comp_type, comp_level, f))?;
-        self.facet_field_strings_docids_sorter.write_into(&mut facet_field_strings_docids_wtr)?;
-
-        let mut field_id_docid_facet_numbers_wtr =
-            tempfile().and_then(|f| create_writer(comp_type, comp_level, f))?;
-        self.field_id_docid_facet_numbers_sorter
-            .write_into(&mut field_id_docid_facet_numbers_wtr)?;
-
-        let mut field_id_docid_facet_strings_wtr =
-            tempfile().and_then(|f| create_writer(comp_type, comp_level, f))?;
-        self.field_id_docid_facet_strings_sorter
-            .write_into(&mut field_id_docid_facet_strings_wtr)?;
-
-        let main = writer_into_reader(main_wtr, shrink_size)?;
-        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)?;
-        let field_id_docid_facet_strings =
-            writer_into_reader(field_id_docid_facet_strings_wtr, shrink_size)?;
-        let docid_word_positions =
-            writer_into_reader(self.docid_word_positions_writer, shrink_size)?;
-        let documents = writer_into_reader(self.documents_writer, shrink_size)?;
-
-        Ok(Readers {
-            main,
-            word_docids,
-            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,
-            field_id_docid_facet_strings,
-            documents,
-        })
-    }
-}
-
-/// Outputs a list of all pairs of words with the shortest proximity between 1 and 7 inclusive.
-///
-/// This list is used by the engine to calculate the documents containing words that are
-/// close to each other.
-fn compute_words_pair_proximities(
-    word_positions: &HashMap<String, SmallVec32<Position>>,
-) -> HashMap<(&str, &str), u8> {
-    use itertools::Itertools;
-
-    let mut words_pair_proximities = HashMap::new();
-    for ((w1, ps1), (w2, ps2)) in word_positions.iter().cartesian_product(word_positions) {
-        let mut min_prox = None;
-        for (ps1, ps2) in ps1.iter().cartesian_product(ps2) {
-            let prox = crate::proximity::positions_proximity(*ps1, *ps2);
-            let prox = u8::try_from(prox).unwrap();
-            // We don't care about a word that appear at the
-            // same position or too far from the other.
-            if prox >= 1 && prox <= 7 && min_prox.map_or(true, |mp| prox < mp) {
-                min_prox = Some(prox)
-            }
-        }
-
-        if let Some(min_prox) = min_prox {
-            words_pair_proximities.insert((w1.as_str(), w2.as_str()), min_prox);
-        }
-    }
-
-    words_pair_proximities
-}
-
-fn format_count(n: usize) -> String {
-    human_format::Formatter::new().with_decimals(1).with_separator("").format(n as f64)
-}
-
-fn lmdb_key_valid_size(key: &[u8]) -> bool {
-    !key.is_empty() && key.len() <= LMDB_MAX_KEY_LENGTH
-}
-
-/// take an iterator on tokens and compute their relative position depending on separator kinds
-/// if it's an `Hard` separator we add an additional relative proximity of 8 between words,
-/// else we keep the standart proximity of 1 between words.
-fn process_tokens<'a>(
-    tokens: impl Iterator<Item = Token<'a>>,
-) -> impl Iterator<Item = (usize, Token<'a>)> {
-    tokens
-        .skip_while(|token| token.is_separator().is_some())
-        .scan((0, None), |(offset, prev_kind), token| {
-            match token.kind {
-                TokenKind::Word | TokenKind::StopWord | TokenKind::Unknown => {
-                    *offset += match *prev_kind {
-                        Some(TokenKind::Separator(SeparatorKind::Hard)) => 8,
-                        Some(_) => 1,
-                        None => 0,
-                    };
-                    *prev_kind = Some(token.kind)
-                }
-                TokenKind::Separator(SeparatorKind::Hard) => {
-                    *prev_kind = Some(token.kind);
-                }
-                TokenKind::Separator(SeparatorKind::Soft)
-                    if *prev_kind != Some(TokenKind::Separator(SeparatorKind::Hard)) =>
-                {
-                    *prev_kind = Some(token.kind);
-                }
-                _ => (),
-            }
-            Some((*offset, token))
-        })
-        .filter(|(_, t)| t.is_word())
-}
-
-fn extract_facet_values(value: &Value) -> (Vec<f64>, Vec<(String, String)>) {
-    fn inner_extract_facet_values(
-        value: &Value,
-        can_recurse: bool,
-        output_numbers: &mut Vec<f64>,
-        output_strings: &mut Vec<(String, String)>,
-    ) {
-        match value {
-            Value::Null => (),
-            Value::Bool(b) => output_strings.push((b.to_string(), b.to_string())),
-            Value::Number(number) => {
-                if let Some(float) = number.as_f64() {
-                    output_numbers.push(float);
-                }
-            }
-            Value::String(original) => {
-                let normalized = original.trim().to_lowercase();
-                output_strings.push((normalized, original.clone()));
-            }
-            Value::Array(values) => {
-                if can_recurse {
-                    for value in values {
-                        inner_extract_facet_values(value, false, output_numbers, output_strings);
-                    }
-                }
-            }
-            Value::Object(_) => (),
-        }
-    }
-
-    let mut facet_number_values = Vec::new();
-    let mut facet_string_values = Vec::new();
-    inner_extract_facet_values(value, true, &mut facet_number_values, &mut facet_string_values);
-
-    (facet_number_values, facet_string_values)
-}

milli/src/update/index_documents/transform.rs

@@ -11,15 +11,14 @@ use log::info;
 use roaring::RoaringBitmap;
 use serde_json::{Map, Value};
 
-use super::merge_function::merge_two_obkvs;
+use super::helpers::{
-use super::{create_sorter, create_writer, IndexDocumentsMethod};
+    create_sorter, create_writer, keep_latest_obkv, merge_obkvs, merge_two_obkvs, MergeFn,
-use crate::error::{Error, InternalError, UserError};
-use crate::index::db_name;
-use crate::update::index_documents::merge_function::{keep_latest_obkv, merge_obkvs};
-use crate::update::{AvailableDocumentsIds, UpdateIndexingStep};
-use crate::{
-    ExternalDocumentsIds, FieldDistribution, FieldId, FieldsIdsMap, Index, MergeFn, Result, BEU32,
 };
+use super::IndexDocumentsMethod;
+use crate::error::{InternalError, UserError};
+use crate::index::db_name;
+use crate::update::{AvailableDocumentsIds, UpdateIndexingStep};
+use crate::{ExternalDocumentsIds, FieldDistribution, FieldId, FieldsIdsMap, Index, Result, BEU32};
 
 const DEFAULT_PRIMARY_KEY_NAME: &str = "id";
 
@@ -46,7 +45,6 @@ pub struct Transform<'t, 'i> {
     pub log_every_n: Option<usize>,
     pub chunk_compression_type: CompressionType,
     pub chunk_compression_level: Option<u32>,
-    pub chunk_fusing_shrink_size: Option<u64>,
     pub max_nb_chunks: Option<usize>,
     pub max_memory: Option<usize>,
     pub index_documents_method: IndexDocumentsMethod,
@@ -149,7 +147,6 @@ impl Transform<'_, '_> {
             merge_function,
             self.chunk_compression_type,
             self.chunk_compression_level,
-            self.chunk_fusing_shrink_size,
             self.max_nb_chunks,
             self.max_memory,
         );
@@ -169,7 +166,7 @@ impl Transform<'_, '_> {
             }
 
             obkv_buffer.clear();
-            let mut writer = obkv::KvWriter::new(&mut obkv_buffer);
+            let mut writer = obkv::KvWriter::<_, FieldId>::new(&mut obkv_buffer);
 
             // We prepare the fields ids map with the documents keys.
             for (key, _value) in &document {
@@ -209,7 +206,6 @@ impl Transform<'_, '_> {
                         .map_err(InternalError::SerdeJson)?;
                     writer.insert(field_id, &json_buffer)?;
                 }
-
                 // We validate the document id [a-zA-Z0-9\-_].
                 if field_id == primary_key_id && validate_document_id(&external_id).is_none() {
                     return Err(UserError::InvalidDocumentId {
@@ -291,7 +287,6 @@ impl Transform<'_, '_> {
             keep_latest_obkv,
             self.chunk_compression_type,
             self.chunk_compression_level,
-            self.chunk_fusing_shrink_size,
             self.max_nb_chunks,
             self.max_memory,
         );
@@ -306,7 +301,7 @@ impl Transform<'_, '_> {
         let mut record = csv::StringRecord::new();
         while csv.read_record(&mut record).map_err(UserError::Csv)? {
             obkv_buffer.clear();
-            let mut writer = obkv::KvWriter::new(&mut obkv_buffer);
+            let mut writer = obkv::KvWriter::<_, FieldId>::new(&mut obkv_buffer);
 
             if self.log_every_n.map_or(false, |len| documents_count % len == 0) {
                 progress_callback(UpdateIndexingStep::TransformFromUserIntoGenericFormat {
@@ -372,9 +367,9 @@ impl Transform<'_, '_> {
     /// Generate the `TransformOutput` based on the given sorter that can be generated from any
     /// format like CSV, JSON or JSON stream. This sorter must contain a key that is the document
     /// id for the user side and the value must be an obkv where keys are valid fields ids.
-    fn output_from_sorter<F, E>(
+    fn output_from_sorter<F>(
         self,
-        sorter: grenad::Sorter<MergeFn<E>>,
+        sorter: grenad::Sorter<MergeFn>,
         primary_key: String,
         fields_ids_map: FieldsIdsMap,
         approximate_number_of_documents: usize,
@@ -383,7 +378,6 @@ impl Transform<'_, '_> {
     ) -> Result<TransformOutput>
     where
         F: Fn(UpdateIndexingStep) + Sync,
-        Error: From<E>,
     {
         let documents_ids = self.index.documents_ids(self.rtxn)?;
         let mut field_distribution = self.index.field_distribution(self.rtxn)?;
@@ -391,10 +385,15 @@ impl Transform<'_, '_> {
 
         // Once we have sort and deduplicated the documents we write them into a final file.
         let mut final_sorter = create_sorter(
-            |_id, _obkvs| Err(InternalError::IndexingMergingKeys { process: "documents" }),
+            |_id, obkvs| {
+                if obkvs.len() == 1 {
+                    Ok(obkvs[0].clone())
+                } else {
+                    Err(InternalError::IndexingMergingKeys { process: "documents" }.into())
+                }
+            },
             self.chunk_compression_type,
             self.chunk_compression_level,
-            self.chunk_fusing_shrink_size,
             self.max_nb_chunks,
             self.max_memory,
         );
@@ -405,7 +404,7 @@ impl Transform<'_, '_> {
 
         // While we write into final file we get or generate the internal documents ids.
         let mut documents_count = 0;
-        let mut iter = sorter.into_iter()?;
+        let mut iter = sorter.into_merger_iter()?;
         while let Some((external_id, update_obkv)) = iter.next()? {
             if self.log_every_n.map_or(false, |len| documents_count % len == 0) {
                 progress_callback(UpdateIndexingStep::ComputeIdsAndMergeDocuments {
@@ -534,7 +533,7 @@ impl Transform<'_, '_> {
             let docid = docid.get();
 
             obkv_buffer.clear();
-            let mut obkv_writer = obkv::KvWriter::new(&mut obkv_buffer);
+            let mut obkv_writer = obkv::KvWriter::<_, FieldId>::new(&mut obkv_buffer);
 
             // We iterate over the new `FieldsIdsMap` ids in order and construct the new obkv.
             for (id, name) in new_fields_ids_map.iter() {

milli/src/update/index_documents/typed_chunk.rs

@@ -0,0 +1,282 @@
+use std::borrow::Cow;
+use std::fs::File;
+
+use heed::types::ByteSlice;
+use heed::{BytesDecode, RwTxn};
+use roaring::RoaringBitmap;
+
+use super::helpers::{
+    roaring_bitmap_from_u32s_array, serialize_roaring_bitmap, valid_lmdb_key, CursorClonableMmap,
+};
+use crate::heed_codec::facet::{decode_prefix_string, encode_prefix_string};
+use crate::update::index_documents::helpers::into_clonable_grenad;
+use crate::{BoRoaringBitmapCodec, CboRoaringBitmapCodec, Index, Result};
+
+pub(crate) enum TypedChunk {
+    DocidWordPositions(grenad::Reader<CursorClonableMmap>),
+    FieldIdDocidFacetStrings(grenad::Reader<CursorClonableMmap>),
+    FieldIdDocidFacetNumbers(grenad::Reader<CursorClonableMmap>),
+    Documents(grenad::Reader<CursorClonableMmap>),
+    FieldIdWordcountDocids(grenad::Reader<File>),
+    NewDocumentsIds(RoaringBitmap),
+    WordDocids(grenad::Reader<File>),
+    WordLevelPositionDocids(grenad::Reader<File>),
+    WordPairProximityDocids(grenad::Reader<File>),
+    FieldIdFacetStringDocids(grenad::Reader<File>),
+    FieldIdFacetNumberDocids(grenad::Reader<File>),
+}
+
+/// Write typed chunk in the corresponding LMDB database of the provided index.
+/// Return new documents seen.
+pub(crate) fn write_typed_chunk_into_index(
+    typed_chunk: TypedChunk,
+    index: &Index,
+    wtxn: &mut RwTxn,
+    index_is_empty: bool,
+) -> Result<(RoaringBitmap, bool)> {
+    let mut is_merged_database = false;
+    match typed_chunk {
+        TypedChunk::DocidWordPositions(docid_word_positions_iter) => {
+            write_entries_into_database(
+                docid_word_positions_iter,
+                &index.docid_word_positions,
+                wtxn,
+                index_is_empty,
+                |value, buffer| {
+                    // ensure that values are unique and ordered
+                    let positions = roaring_bitmap_from_u32s_array(value);
+                    BoRoaringBitmapCodec::serialize_into(&positions, buffer);
+                    Ok(buffer)
+                },
+                |new_values, db_values, buffer| {
+                    let new_values = roaring_bitmap_from_u32s_array(new_values);
+                    let positions = match BoRoaringBitmapCodec::bytes_decode(db_values) {
+                        Some(db_values) => new_values | db_values,
+                        None => new_values, // should not happen
+                    };
+                    BoRoaringBitmapCodec::serialize_into(&positions, buffer);
+                    Ok(())
+                },
+            )?;
+        }
+        TypedChunk::Documents(mut obkv_documents_iter) => {
+            while let Some((key, value)) = obkv_documents_iter.next()? {
+                index.documents.remap_types::<ByteSlice, ByteSlice>().put(wtxn, key, value)?;
+            }
+        }
+        TypedChunk::FieldIdWordcountDocids(fid_word_count_docids_iter) => {
+            append_entries_into_database(
+                fid_word_count_docids_iter,
+                &index.field_id_word_count_docids,
+                wtxn,
+                index_is_empty,
+                |value, _buffer| Ok(value),
+                merge_cbo_roaring_bitmaps,
+            )?;
+            is_merged_database = true;
+        }
+        TypedChunk::NewDocumentsIds(documents_ids) => {
+            return Ok((documents_ids, is_merged_database))
+        }
+        TypedChunk::WordDocids(word_docids_iter) => {
+            let mut word_docids_iter = unsafe { into_clonable_grenad(word_docids_iter) }?;
+            append_entries_into_database(
+                word_docids_iter.clone(),
+                &index.word_docids,
+                wtxn,
+                index_is_empty,
+                |value, _buffer| Ok(value),
+                merge_roaring_bitmaps,
+            )?;
+
+            // create fst from word docids
+            let mut builder = fst::SetBuilder::memory();
+            while let Some((word, _value)) = word_docids_iter.next()? {
+                // This is a lexicographically ordered word position
+                // we use the key to construct the words fst.
+                builder.insert(word)?;
+            }
+            let fst = builder.into_set().map_data(std::borrow::Cow::Owned)?;
+            let db_fst = index.words_fst(wtxn)?;
+
+            // merge new fst with database fst
+            let union_stream = fst.op().add(db_fst.stream()).union();
+            let mut builder = fst::SetBuilder::memory();
+            builder.extend_stream(union_stream)?;
+            let fst = builder.into_set();
+            index.put_words_fst(wtxn, &fst)?;
+            is_merged_database = true;
+        }
+        TypedChunk::WordLevelPositionDocids(word_level_position_docids_iter) => {
+            append_entries_into_database(
+                word_level_position_docids_iter,
+                &index.word_level_position_docids,
+                wtxn,
+                index_is_empty,
+                |value, _buffer| Ok(value),
+                merge_cbo_roaring_bitmaps,
+            )?;
+            is_merged_database = true;
+        }
+        TypedChunk::FieldIdFacetNumberDocids(facet_id_f64_docids_iter) => {
+            append_entries_into_database(
+                facet_id_f64_docids_iter,
+                &index.facet_id_f64_docids,
+                wtxn,
+                index_is_empty,
+                |value, _buffer| Ok(value),
+                merge_cbo_roaring_bitmaps,
+            )?;
+            is_merged_database = true;
+        }
+        TypedChunk::WordPairProximityDocids(word_pair_proximity_docids_iter) => {
+            append_entries_into_database(
+                word_pair_proximity_docids_iter,
+                &index.word_pair_proximity_docids,
+                wtxn,
+                index_is_empty,
+                |value, _buffer| Ok(value),
+                merge_cbo_roaring_bitmaps,
+            )?;
+            is_merged_database = true;
+        }
+        TypedChunk::FieldIdDocidFacetNumbers(mut fid_docid_facet_number) => {
+            let index_fid_docid_facet_numbers =
+                index.field_id_docid_facet_f64s.remap_types::<ByteSlice, ByteSlice>();
+            while let Some((key, value)) = fid_docid_facet_number.next()? {
+                if valid_lmdb_key(key) {
+                    index_fid_docid_facet_numbers.put(wtxn, key, &value)?;
+                }
+            }
+        }
+        TypedChunk::FieldIdDocidFacetStrings(mut fid_docid_facet_string) => {
+            let index_fid_docid_facet_strings =
+                index.field_id_docid_facet_strings.remap_types::<ByteSlice, ByteSlice>();
+            while let Some((key, value)) = fid_docid_facet_string.next()? {
+                if valid_lmdb_key(key) {
+                    index_fid_docid_facet_strings.put(wtxn, key, &value)?;
+                }
+            }
+        }
+        TypedChunk::FieldIdFacetStringDocids(facet_id_string_docids) => {
+            append_entries_into_database(
+                facet_id_string_docids,
+                &index.facet_id_string_docids,
+                wtxn,
+                index_is_empty,
+                |value, _buffer| Ok(value),
+                |new_values, db_values, buffer| {
+                    let (_, new_values) = decode_prefix_string(new_values).unwrap();
+                    let new_values = RoaringBitmap::deserialize_from(new_values)?;
+                    let (db_original, db_values) = decode_prefix_string(db_values).unwrap();
+                    let db_values = RoaringBitmap::deserialize_from(db_values)?;
+                    let values = new_values | db_values;
+                    encode_prefix_string(db_original, buffer)?;
+                    Ok(values.serialize_into(buffer)?)
+                },
+            )?;
+            is_merged_database = true;
+        }
+    }
+
+    Ok((RoaringBitmap::new(), is_merged_database))
+}
+
+fn merge_roaring_bitmaps(new_value: &[u8], db_value: &[u8], buffer: &mut Vec<u8>) -> Result<()> {
+    let new_value = RoaringBitmap::deserialize_from(new_value)?;
+    let db_value = RoaringBitmap::deserialize_from(db_value)?;
+    let value = new_value | db_value;
+    Ok(serialize_roaring_bitmap(&value, buffer)?)
+}
+
+fn merge_cbo_roaring_bitmaps(
+    new_value: &[u8],
+    db_value: &[u8],
+    buffer: &mut Vec<u8>,
+) -> Result<()> {
+    Ok(CboRoaringBitmapCodec::merge_into(
+        &[Cow::Borrowed(db_value), Cow::Borrowed(new_value)],
+        buffer,
+    )?)
+}
+
+/// Write provided entries in database using serialize_value function.
+/// merge_values function is used if an entry already exist in the database.
+fn write_entries_into_database<R, K, V, FS, FM>(
+    mut data: grenad::Reader<R>,
+    database: &heed::Database<K, V>,
+    wtxn: &mut RwTxn,
+    index_is_empty: bool,
+    serialize_value: FS,
+    merge_values: FM,
+) -> Result<()>
+where
+    R: std::io::Read,
+    FS: for<'a> Fn(&'a [u8], &'a mut Vec<u8>) -> Result<&'a [u8]>,
+    FM: Fn(&[u8], &[u8], &mut Vec<u8>) -> Result<()>,
+{
+    let mut buffer = Vec::new();
+    let database = database.remap_types::<ByteSlice, ByteSlice>();
+
+    while let Some((key, value)) = data.next()? {
+        if valid_lmdb_key(key) {
+            buffer.clear();
+            let value = if index_is_empty {
+                serialize_value(value, &mut buffer)?
+            } else {
+                match database.get(wtxn, key)? {
+                    Some(prev_value) => {
+                        merge_values(value, prev_value, &mut buffer)?;
+                        &buffer[..]
+                    }
+                    None => serialize_value(value, &mut buffer)?,
+                }
+            };
+            database.put(wtxn, key, value)?;
+        }
+    }
+
+    Ok(())
+}
+
+/// Write provided entries in database using serialize_value function.
+/// merge_values function is used if an entry already exist in the database.
+/// All provided entries must be ordered.
+/// If the index is not empty, write_entries_into_database is called instead.
+fn append_entries_into_database<R, K, V, FS, FM>(
+    mut data: grenad::Reader<R>,
+    database: &heed::Database<K, V>,
+    wtxn: &mut RwTxn,
+    index_is_empty: bool,
+    serialize_value: FS,
+    merge_values: FM,
+) -> Result<()>
+where
+    R: std::io::Read,
+    FS: for<'a> Fn(&'a [u8], &'a mut Vec<u8>) -> Result<&'a [u8]>,
+    FM: Fn(&[u8], &[u8], &mut Vec<u8>) -> Result<()>,
+{
+    if !index_is_empty {
+        return write_entries_into_database(
+            data,
+            database,
+            wtxn,
+            false,
+            serialize_value,
+            merge_values,
+        );
+    }
+
+    let mut buffer = Vec::new();
+    let mut database = database.iter_mut(wtxn)?.remap_types::<ByteSlice, ByteSlice>();
+
+    while let Some((key, value)) = data.next()? {
+        if valid_lmdb_key(key) {
+            buffer.clear();
+            let value = serialize_value(value, &mut buffer)?;
+            unsafe { database.append(key, value)? };
+        }
+    }
+
+    Ok(())
+}

milli/src/update/settings.rs

@@ -65,10 +65,9 @@ pub struct Settings<'a, 't, 'u, 'i> {
     pub(crate) log_every_n: Option<usize>,
     pub(crate) max_nb_chunks: Option<usize>,
     pub(crate) max_memory: Option<usize>,
-    pub(crate) linked_hash_map_size: Option<usize>,
+    pub(crate) documents_chunk_size: Option<usize>,
     pub(crate) chunk_compression_type: CompressionType,
     pub(crate) chunk_compression_level: Option<u32>,
-    pub(crate) chunk_fusing_shrink_size: Option<u64>,
     pub(crate) thread_pool: Option<&'a ThreadPool>,
     update_id: u64,
 
@@ -95,10 +94,9 @@ impl<'a, 't, 'u, 'i> Settings<'a, 't, 'u, 'i> {
             log_every_n: None,
             max_nb_chunks: None,
             max_memory: None,
-            linked_hash_map_size: None,
+            documents_chunk_size: None,
             chunk_compression_type: CompressionType::None,
             chunk_compression_level: None,
-            chunk_fusing_shrink_size: None,
             thread_pool: None,
             searchable_fields: Setting::NotSet,
             displayed_fields: Setting::NotSet,
@@ -205,7 +203,6 @@ impl<'a, 't, 'u, 'i> Settings<'a, 't, 'u, 'i> {
             log_every_n: self.log_every_n,
             chunk_compression_type: self.chunk_compression_type,
             chunk_compression_level: self.chunk_compression_level,
-            chunk_fusing_shrink_size: self.chunk_fusing_shrink_size,
             max_nb_chunks: self.max_nb_chunks,
             max_memory: self.max_memory,
             index_documents_method: IndexDocumentsMethod::ReplaceDocuments,
@@ -232,10 +229,9 @@ impl<'a, 't, 'u, 'i> Settings<'a, 't, 'u, 'i> {
         indexing_builder.log_every_n = self.log_every_n;
         indexing_builder.max_nb_chunks = self.max_nb_chunks;
         indexing_builder.max_memory = self.max_memory;
-        indexing_builder.linked_hash_map_size = self.linked_hash_map_size;
+        indexing_builder.documents_chunk_size = self.documents_chunk_size;
         indexing_builder.chunk_compression_type = self.chunk_compression_type;
         indexing_builder.chunk_compression_level = self.chunk_compression_level;
-        indexing_builder.chunk_fusing_shrink_size = self.chunk_fusing_shrink_size;
         indexing_builder.thread_pool = self.thread_pool;
         indexing_builder.execute_raw(output, &cb)?;
 

milli/src/update/update_builder.rs

@@ -7,11 +7,10 @@ use crate::{Index, Result};
 pub struct UpdateBuilder<'a> {
     pub(crate) log_every_n: Option<usize>,
     pub(crate) max_nb_chunks: Option<usize>,
+    pub(crate) documents_chunk_size: Option<usize>,
     pub(crate) max_memory: Option<usize>,
-    pub(crate) linked_hash_map_size: Option<usize>,
     pub(crate) chunk_compression_type: CompressionType,
     pub(crate) chunk_compression_level: Option<u32>,
-    pub(crate) chunk_fusing_shrink_size: Option<u64>,
     pub(crate) thread_pool: Option<&'a ThreadPool>,
     pub(crate) update_id: u64,
 }
@@ -21,11 +20,10 @@ impl<'a> UpdateBuilder<'a> {
         UpdateBuilder {
             log_every_n: None,
             max_nb_chunks: None,
+            documents_chunk_size: None,
             max_memory: None,
-            linked_hash_map_size: None,
             chunk_compression_type: CompressionType::None,
             chunk_compression_level: None,
-            chunk_fusing_shrink_size: None,
             thread_pool: None,
             update_id,
         }
@@ -43,8 +41,8 @@ impl<'a> UpdateBuilder<'a> {
         self.max_memory = Some(max_memory);
     }
 
-    pub fn linked_hash_map_size(&mut self, linked_hash_map_size: usize) {
+    pub fn documents_chunk_size(&mut self, documents_chunk_size: usize) {
-        self.linked_hash_map_size = Some(linked_hash_map_size);
+        self.documents_chunk_size = Some(documents_chunk_size);
     }
 
     pub fn chunk_compression_type(&mut self, chunk_compression_type: CompressionType) {
@@ -55,10 +53,6 @@ impl<'a> UpdateBuilder<'a> {
         self.chunk_compression_level = Some(chunk_compression_level);
     }
 
-    pub fn chunk_fusing_shrink_size(&mut self, chunk_fusing_shrink_size: u64) {
-        self.chunk_fusing_shrink_size = Some(chunk_fusing_shrink_size);
-    }
-
     pub fn thread_pool(&mut self, thread_pool: &'a ThreadPool) {
         self.thread_pool = Some(thread_pool);
     }
@@ -89,10 +83,9 @@ impl<'a> UpdateBuilder<'a> {
         builder.log_every_n = self.log_every_n;
         builder.max_nb_chunks = self.max_nb_chunks;
         builder.max_memory = self.max_memory;
-        builder.linked_hash_map_size = self.linked_hash_map_size;
+        builder.documents_chunk_size = self.documents_chunk_size;
         builder.chunk_compression_type = self.chunk_compression_type;
         builder.chunk_compression_level = self.chunk_compression_level;
-        builder.chunk_fusing_shrink_size = self.chunk_fusing_shrink_size;
         builder.thread_pool = self.thread_pool;
 
         builder
@@ -108,10 +101,9 @@ impl<'a> UpdateBuilder<'a> {
         builder.log_every_n = self.log_every_n;
         builder.max_nb_chunks = self.max_nb_chunks;
         builder.max_memory = self.max_memory;
-        builder.linked_hash_map_size = self.linked_hash_map_size;
+        builder.documents_chunk_size = self.documents_chunk_size;
         builder.chunk_compression_type = self.chunk_compression_type;
         builder.chunk_compression_level = self.chunk_compression_level;
-        builder.chunk_fusing_shrink_size = self.chunk_fusing_shrink_size;
         builder.thread_pool = self.thread_pool;
 
         builder
@@ -126,7 +118,6 @@ impl<'a> UpdateBuilder<'a> {
 
         builder.chunk_compression_type = self.chunk_compression_type;
         builder.chunk_compression_level = self.chunk_compression_level;
-        builder.chunk_fusing_shrink_size = self.chunk_fusing_shrink_size;
 
         builder
     }

milli/src/update/word_prefix_docids.rs

@@ -5,7 +5,7 @@ use grenad::CompressionType;
 use heed::types::ByteSlice;
 
 use crate::update::index_documents::{
-    create_sorter, roaring_bitmap_merge, sorter_into_lmdb_database, WriteMethod,
+    create_sorter, merge_roaring_bitmaps, sorter_into_lmdb_database, WriteMethod,
 };
 use crate::{Index, Result};
 
@@ -14,7 +14,6 @@ pub struct WordPrefixDocids<'t, 'u, 'i> {
     index: &'i Index,
     pub(crate) chunk_compression_type: CompressionType,
     pub(crate) chunk_compression_level: Option<u32>,
-    pub(crate) chunk_fusing_shrink_size: Option<u64>,
     pub(crate) max_nb_chunks: Option<usize>,
     pub(crate) max_memory: Option<usize>,
 }
@@ -29,12 +28,12 @@ impl<'t, 'u, 'i> WordPrefixDocids<'t, 'u, 'i> {
             index,
             chunk_compression_type: CompressionType::None,
             chunk_compression_level: None,
-            chunk_fusing_shrink_size: None,
             max_nb_chunks: None,
             max_memory: None,
         }
     }
 
+    #[logging_timer::time("WordPrefixDocids::{}")]
     pub fn execute(self) -> Result<()> {
         // Clear the word prefix docids database.
         self.index.word_prefix_docids.clear(self.wtxn)?;
@@ -44,10 +43,9 @@ impl<'t, 'u, 'i> WordPrefixDocids<'t, 'u, 'i> {
         // It is forbidden to keep a mutable reference into the database
         // and write into it at the same time, therefore we write into another file.
         let mut prefix_docids_sorter = create_sorter(
-            roaring_bitmap_merge,
+            merge_roaring_bitmaps,
             self.chunk_compression_type,
             self.chunk_compression_level,
-            self.chunk_fusing_shrink_size,
             self.max_nb_chunks,
             self.max_memory,
         );
@@ -70,7 +68,7 @@ impl<'t, 'u, 'i> WordPrefixDocids<'t, 'u, 'i> {
             self.wtxn,
             *self.index.word_prefix_docids.as_polymorph(),
             prefix_docids_sorter,
-            roaring_bitmap_merge,
+            merge_roaring_bitmaps,
             WriteMethod::Append,
         )?;
 

milli/src/update/word_prefix_pair_proximity_docids.rs

@@ -1,15 +1,13 @@
-use std::str;
+use std::collections::HashMap;
 
-use fst::automaton::{Automaton, Str};
+use fst::IntoStreamer;
-use fst::{IntoStreamer, Streamer};
 use grenad::CompressionType;
 use heed::types::ByteSlice;
-use heed::BytesEncode;
 use log::debug;
+use slice_group_by::GroupBy;
 
-use crate::heed_codec::StrStrU8Codec;
 use crate::update::index_documents::{
-    cbo_roaring_bitmap_merge, create_sorter, sorter_into_lmdb_database, WriteMethod,
+    create_sorter, merge_cbo_roaring_bitmaps, sorter_into_lmdb_database, MergeFn, WriteMethod,
 };
 use crate::{Index, Result};
 
@@ -18,9 +16,9 @@ pub struct WordPrefixPairProximityDocids<'t, 'u, 'i> {
     index: &'i Index,
     pub(crate) chunk_compression_type: CompressionType,
     pub(crate) chunk_compression_level: Option<u32>,
-    pub(crate) chunk_fusing_shrink_size: Option<u64>,
     pub(crate) max_nb_chunks: Option<usize>,
     pub(crate) max_memory: Option<usize>,
+    threshold: u32,
 }
 
 impl<'t, 'u, 'i> WordPrefixPairProximityDocids<'t, 'u, 'i> {
@@ -33,55 +31,123 @@ impl<'t, 'u, 'i> WordPrefixPairProximityDocids<'t, 'u, 'i> {
             index,
             chunk_compression_type: CompressionType::None,
             chunk_compression_level: None,
-            chunk_fusing_shrink_size: None,
             max_nb_chunks: None,
             max_memory: None,
+            threshold: 100,
         }
     }
 
+    /// Set the number of words required to make a prefix be part of the words prefixes
+    /// database. If a word prefix is supposed to match more than this number of words in the
+    /// dictionnary, therefore this prefix is added to the words prefixes datastructures.
+    ///
+    /// Default value is 100. This value must be higher than 50 and will be clamped
+    /// to these bound otherwise.
+    pub fn threshold(&mut self, value: u32) -> &mut Self {
+        self.threshold = value.max(50);
+        self
+    }
+
+    #[logging_timer::time("WordPrefixPairProximityDocids::{}")]
     pub fn execute(self) -> Result<()> {
         debug!("Computing and writing the word prefix pair proximity docids into LMDB on disk...");
 
         self.index.word_prefix_pair_proximity_docids.clear(self.wtxn)?;
 
-        let prefix_fst = self.index.words_prefixes_fst(self.wtxn)?;
-
         // Here we create a sorter akin to the previous one.
         let mut word_prefix_pair_proximity_docids_sorter = create_sorter(
-            cbo_roaring_bitmap_merge,
+            merge_cbo_roaring_bitmaps,
             self.chunk_compression_type,
             self.chunk_compression_level,
-            self.chunk_fusing_shrink_size,
             self.max_nb_chunks,
             self.max_memory,
         );
 
-        // We insert all the word pairs corresponding to the word-prefix pairs
+        let prefix_fst = self.index.words_prefixes_fst(self.wtxn)?;
-        // where the prefixes appears in the prefix FST previously constructed.
+        let prefix_fst_keys = prefix_fst.into_stream().into_bytes();
-        let db = self.index.word_pair_proximity_docids.remap_data_type::<ByteSlice>();
+        let prefix_fst_keys: Vec<_> = prefix_fst_keys
-        for result in db.iter(self.wtxn)? {
+            .as_slice()
-            let ((word1, word2, prox), data) = result?;
+            .linear_group_by_key(|x| std::str::from_utf8(&x).unwrap().chars().nth(0).unwrap())
-            let automaton = Str::new(word2).starts_with();
+            .collect();
-            let mut matching_prefixes = prefix_fst.search(automaton).into_stream();
+
-            while let Some(prefix) = matching_prefixes.next() {
+        let mut db =
-                let prefix = str::from_utf8(prefix)?;
+            self.index.word_pair_proximity_docids.remap_data_type::<ByteSlice>().iter(self.wtxn)?;
-                let pair = (word1, prefix, prox);
+
-                let bytes = StrStrU8Codec::bytes_encode(&pair).unwrap();
+        let mut buffer = Vec::new();
-                word_prefix_pair_proximity_docids_sorter.insert(bytes, data)?;
+        let mut current_prefixes: Option<&&[Vec<u8>]> = None;
+        let mut prefixes_cache = HashMap::new();
+        while let Some(((w1, w2, prox), data)) = db.next().transpose()? {
+            current_prefixes = match current_prefixes.take() {
+                Some(prefixes) if w2.as_bytes().starts_with(&prefixes[0]) => Some(prefixes),
+                _otherwise => {
+                    write_prefixes_in_sorter(
+                        &mut prefixes_cache,
+                        &mut word_prefix_pair_proximity_docids_sorter,
+                        self.threshold,
+                    )?;
+                    prefix_fst_keys.iter().find(|prefixes| w2.as_bytes().starts_with(&prefixes[0]))
+                }
+            };
+
+            if let Some(prefixes) = current_prefixes {
+                buffer.clear();
+                buffer.extend_from_slice(w1.as_bytes());
+                buffer.push(0);
+                for prefix in prefixes.iter().filter(|prefix| w2.as_bytes().starts_with(prefix)) {
+                    buffer.truncate(w1.len() + 1);
+                    buffer.extend_from_slice(prefix);
+                    buffer.push(prox);
+
+                    match prefixes_cache.get_mut(&buffer) {
+                        Some(value) => value.push(data),
+                        None => {
+                            prefixes_cache.insert(buffer.clone(), vec![data]);
+                        }
+                    }
+                }
             }
         }
 
+        write_prefixes_in_sorter(
+            &mut prefixes_cache,
+            &mut word_prefix_pair_proximity_docids_sorter,
+            self.threshold,
+        )?;
+
         drop(prefix_fst);
+        drop(db);
 
         // We finally write the word prefix pair proximity docids into the LMDB database.
         sorter_into_lmdb_database(
             self.wtxn,
             *self.index.word_prefix_pair_proximity_docids.as_polymorph(),
             word_prefix_pair_proximity_docids_sorter,
-            cbo_roaring_bitmap_merge,
+            merge_cbo_roaring_bitmaps,
             WriteMethod::Append,
         )?;
 
         Ok(())
     }
 }
+
+fn write_prefixes_in_sorter(
+    prefixes: &mut HashMap<Vec<u8>, Vec<&[u8]>>,
+    sorter: &mut grenad::Sorter<MergeFn>,
+    min_word_per_prefix: u32,
+) -> Result<()> {
+    for (i, (key, data_slices)) in prefixes.drain().enumerate() {
+        // if the number of words prefixed by the prefix is higher than the threshold,
+        // we insert it in the sorter.
+        if data_slices.len() > min_word_per_prefix as usize {
+            for data in data_slices {
+                sorter.insert(&key, data)?;
+            }
+        // if the first prefix isn't elligible for insertion,
+        // then the other prefixes can't be elligible.
+        } else if i == 0 {
+            break;
+        }
+    }
+
+    Ok(())
+}

milli/src/update/words_level_positions.rs

@@ -4,7 +4,7 @@ use std::num::NonZeroU32;
 use std::{cmp, str};
 
 use fst::Streamer;
-use grenad::{CompressionType, FileFuse, Reader, Writer};
+use grenad::{CompressionType, Reader, Writer};
 use heed::types::{ByteSlice, DecodeIgnore, Str};
 use heed::{BytesEncode, Error};
 use log::debug;
@@ -14,7 +14,7 @@ use crate::error::{InternalError, SerializationError};
 use crate::heed_codec::{CboRoaringBitmapCodec, StrLevelPositionCodec};
 use crate::index::main_key::WORDS_PREFIXES_FST_KEY;
 use crate::update::index_documents::{
-    cbo_roaring_bitmap_merge, create_sorter, create_writer, sorter_into_lmdb_database,
+    create_sorter, create_writer, merge_cbo_roaring_bitmaps, sorter_into_lmdb_database,
     write_into_lmdb_database, writer_into_reader, WriteMethod,
 };
 use crate::{Index, Result, TreeLevel};
@@ -24,7 +24,6 @@ pub struct WordsLevelPositions<'t, 'u, 'i> {
     index: &'i Index,
     pub(crate) chunk_compression_type: CompressionType,
     pub(crate) chunk_compression_level: Option<u32>,
-    pub(crate) chunk_fusing_shrink_size: Option<u64>,
     pub(crate) max_nb_chunks: Option<usize>,
     pub(crate) max_memory: Option<usize>,
     level_group_size: NonZeroU32,
@@ -41,7 +40,6 @@ impl<'t, 'u, 'i> WordsLevelPositions<'t, 'u, 'i> {
             index,
             chunk_compression_type: CompressionType::None,
             chunk_compression_level: None,
-            chunk_fusing_shrink_size: None,
             max_nb_chunks: None,
             max_memory: None,
             level_group_size: NonZeroU32::new(4).unwrap(),
@@ -59,6 +57,7 @@ impl<'t, 'u, 'i> WordsLevelPositions<'t, 'u, 'i> {
         self
     }
 
+    #[logging_timer::time("WordsLevelPositions::{}")]
     pub fn execute(self) -> Result<()> {
         debug!("Computing and writing the word levels positions docids into LMDB on disk...");
 
@@ -68,7 +67,6 @@ impl<'t, 'u, 'i> WordsLevelPositions<'t, 'u, 'i> {
             self.index.word_level_position_docids,
             self.chunk_compression_type,
             self.chunk_compression_level,
-            self.chunk_fusing_shrink_size,
             self.level_group_size,
             self.min_level_size,
         )?;
@@ -81,7 +79,7 @@ impl<'t, 'u, 'i> WordsLevelPositions<'t, 'u, 'i> {
             self.wtxn,
             *self.index.word_level_position_docids.as_polymorph(),
             entries,
-            |_, _| Err(InternalError::IndexingMergingKeys { process: "word level position" }),
+            |_, _| Err(InternalError::IndexingMergingKeys { process: "word level position" })?,
             WriteMethod::Append,
         )?;
 
@@ -89,10 +87,9 @@ impl<'t, 'u, 'i> WordsLevelPositions<'t, 'u, 'i> {
         self.index.word_prefix_level_position_docids.clear(self.wtxn)?;
 
         let mut word_prefix_level_positions_docids_sorter = create_sorter(
-            cbo_roaring_bitmap_merge,
+            merge_cbo_roaring_bitmaps,
             self.chunk_compression_type,
             self.chunk_compression_level,
-            self.chunk_fusing_shrink_size,
             self.max_nb_chunks,
             self.max_memory,
         );
@@ -131,7 +128,7 @@ impl<'t, 'u, 'i> WordsLevelPositions<'t, 'u, 'i> {
             self.wtxn,
             *self.index.word_prefix_level_position_docids.as_polymorph(),
             word_prefix_level_positions_docids_sorter,
-            cbo_roaring_bitmap_merge,
+            merge_cbo_roaring_bitmaps,
             WriteMethod::Append,
         )?;
 
@@ -141,7 +138,6 @@ impl<'t, 'u, 'i> WordsLevelPositions<'t, 'u, 'i> {
             self.index.word_prefix_level_position_docids,
             self.chunk_compression_type,
             self.chunk_compression_level,
-            self.chunk_fusing_shrink_size,
             self.level_group_size,
             self.min_level_size,
         )?;
@@ -155,7 +151,7 @@ impl<'t, 'u, 'i> WordsLevelPositions<'t, 'u, 'i> {
             *self.index.word_prefix_level_position_docids.as_polymorph(),
             entries,
             |_, _| {
-                Err(InternalError::IndexingMergingKeys { process: "word prefix level position" })
+                Err(InternalError::IndexingMergingKeys { process: "word prefix level position" })?
             },
             WriteMethod::Append,
         )?;
@@ -185,10 +181,9 @@ fn compute_positions_levels(
     words_positions_db: heed::Database<StrLevelPositionCodec, CboRoaringBitmapCodec>,
     compression_type: CompressionType,
     compression_level: Option<u32>,
-    shrink_size: Option<u64>,
     level_group_size: NonZeroU32,
     min_level_size: NonZeroU32,
-) -> Result<Reader<FileFuse>> {
+) -> Result<Reader<File>> {
     // It is forbidden to keep a cursor and write in a database at the same time with LMDB
     // therefore we write the facet levels entries into a grenad file before transfering them.
     let mut writer = tempfile::tempfile()
@@ -254,7 +249,7 @@ fn compute_positions_levels(
         }
     }
 
-    writer_into_reader(writer, shrink_size)
+    writer_into_reader(writer)
 }
 
 fn write_level_entry(

milli/src/update/words_prefixes_fst.rs

@@ -8,7 +8,7 @@ use crate::{Index, Result, SmallString32};
 pub struct WordsPrefixesFst<'t, 'u, 'i> {
     wtxn: &'t mut heed::RwTxn<'i, 'u>,
     index: &'i Index,
-    threshold: f64,
+    threshold: u32,
     max_prefix_length: usize,
     _update_id: u64,
 }
@@ -22,20 +22,20 @@ impl<'t, 'u, 'i> WordsPrefixesFst<'t, 'u, 'i> {
         WordsPrefixesFst {
             wtxn,
             index,
-            threshold: 0.1 / 100.0, // .01%
+            threshold: 100,
             max_prefix_length: 4,
             _update_id: update_id,
         }
     }
 
-    /// Set the ratio of concerned words required to make a prefix be part of the words prefixes
+    /// Set the number of words required to make a prefix be part of the words prefixes
     /// database. If a word prefix is supposed to match more than this number of words in the
     /// dictionnary, therefore this prefix is added to the words prefixes datastructures.
     ///
-    /// Default value is `0.01` or `1%`. This value must be between 0 and 1 and will be clamped
+    /// Default value is 100. This value must be higher than 50 and will be clamped
-    /// to these bounds otherwise.
+    /// to this bound otherwise.
-    pub fn threshold(&mut self, value: f64) -> &mut Self {
+    pub fn threshold(&mut self, value: u32) -> &mut Self {
-        self.threshold = value.min(1.0).max(0.0); // clamp [0, 1]
+        self.threshold = value.max(50);
         self
     }
 
@@ -48,10 +48,9 @@ impl<'t, 'u, 'i> WordsPrefixesFst<'t, 'u, 'i> {
         self
     }
 
+    #[logging_timer::time("WordsPrefixesFst::{}")]
     pub fn execute(self) -> Result<()> {
         let words_fst = self.index.words_fst(&self.wtxn)?;
-        let number_of_words = words_fst.len();
-        let min_number_of_words = (number_of_words as f64 * self.threshold) as usize;
 
         let mut prefix_fsts = Vec::with_capacity(self.max_prefix_length);
         for n in 1..=self.max_prefix_length {
@@ -80,7 +79,7 @@ impl<'t, 'u, 'i> WordsPrefixesFst<'t, 'u, 'i> {
                 current_prefix_count += 1;
 
                 // There is enough words corresponding to this prefix to add it to the cache.
-                if current_prefix_count == min_number_of_words {
+                if current_prefix_count >= self.threshold {
                     builder.insert(prefix)?;
                 }
             }

milli/tests/search/mod.rs

@@ -5,7 +5,7 @@ use big_s::S;
 use either::{Either, Left, Right};
 use heed::EnvOpenOptions;
 use maplit::{hashmap, hashset};
-use milli::update::{IndexDocuments, Settings, UpdateFormat};
+use milli::update::{Settings, UpdateBuilder, UpdateFormat};
 use milli::{AscDesc, Criterion, DocumentId, Index};
 use serde::Deserialize;
 use slice_group_by::GroupBy;
@@ -50,7 +50,9 @@ pub fn setup_search_index_with_criteria(criteria: &[Criterion]) -> Index {
     builder.execute(|_, _| ()).unwrap();
 
     // index documents
-    let mut builder = IndexDocuments::new(&mut wtxn, &index, 0);
+    let mut builder = UpdateBuilder::new(0);
+    builder.max_memory(10 * 1024 * 1024); // 10MiB
+    let mut builder = builder.index_documents(&mut wtxn, &index);
     builder.update_format(UpdateFormat::JsonStream);
     builder.enable_autogenerate_docids();
     builder.execute(CONTENT.as_bytes(), |_, _| ()).unwrap();