Merge branch 'indexer-edition-2024' into indexer-edition-2024-doc-chunks

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

@@ -0,0 +1,319 @@
+use std::convert::TryInto;
+use std::fs::File;
+use std::io::BufReader;
+use std::{io, mem, str};
+
+use charabia::{SeparatorKind, Token, TokenKind, Tokenizer, TokenizerBuilder};
+use obkv::{KvReader, KvWriterU16};
+use roaring::RoaringBitmap;
+use serde_json::Value;
+
+use super::helpers::{create_sorter, sorter_into_reader, GrenadParameters, KeepLatestObkv};
+use crate::error::{InternalError, SerializationError};
+use crate::update::del_add::{del_add_from_two_obkvs, DelAdd, KvReaderDelAdd};
+use crate::update::settings::{InnerIndexSettings, InnerIndexSettingsDiff};
+use crate::{FieldId, Result, MAX_POSITION_PER_ATTRIBUTE, MAX_WORD_LENGTH};
+
+/// 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.
+#[tracing::instrument(level = "trace", skip_all, target = "indexing::extract")]
+pub fn extract_docid_word_positions<R: io::Read + io::Seek>(
+    obkv_documents: grenad::Reader<R>,
+    indexer: GrenadParameters,
+    settings_diff: &InnerIndexSettingsDiff,
+    max_positions_per_attributes: Option<u32>,
+) -> Result<grenad::Reader<BufReader<File>>> {
+    let max_positions_per_attributes = max_positions_per_attributes
+        .map_or(MAX_POSITION_PER_ATTRIBUTE, |max| max.min(MAX_POSITION_PER_ATTRIBUTE));
+    let max_memory = indexer.max_memory_by_thread();
+    let force_reindexing = settings_diff.reindex_searchable();
+
+    // initialize destination values.
+    let mut documents_ids = RoaringBitmap::new();
+    let mut docid_word_positions_sorter = create_sorter(
+        grenad::SortAlgorithm::Stable,
+        KeepLatestObkv,
+        indexer.chunk_compression_type,
+        indexer.chunk_compression_level,
+        indexer.max_nb_chunks,
+        max_memory,
+        true,
+    );
+
+    // initialize buffers.
+    let mut del_buffers = Buffers::default();
+    let mut add_buffers = Buffers::default();
+    let mut key_buffer = Vec::new();
+    let mut value_buffer = Vec::new();
+
+    // initialize tokenizer.
+    let old_stop_words = settings_diff.old.stop_words.as_ref();
+    let old_separators: Option<Vec<_>> = settings_diff
+        .old
+        .allowed_separators
+        .as_ref()
+        .map(|s| s.iter().map(String::as_str).collect());
+    let old_dictionary: Option<Vec<_>> =
+        settings_diff.old.dictionary.as_ref().map(|s| s.iter().map(String::as_str).collect());
+    let del_builder =
+        tokenizer_builder(old_stop_words, old_separators.as_deref(), old_dictionary.as_deref());
+    let del_tokenizer = del_builder.into_tokenizer();
+
+    let new_stop_words = settings_diff.new.stop_words.as_ref();
+    let new_separators: Option<Vec<_>> = settings_diff
+        .new
+        .allowed_separators
+        .as_ref()
+        .map(|s| s.iter().map(String::as_str).collect());
+    let new_dictionary: Option<Vec<_>> =
+        settings_diff.new.dictionary.as_ref().map(|s| s.iter().map(String::as_str).collect());
+    let add_builder =
+        tokenizer_builder(new_stop_words, new_separators.as_deref(), new_dictionary.as_deref());
+    let add_tokenizer = add_builder.into_tokenizer();
+
+    // iterate over documents.
+    let mut cursor = obkv_documents.into_cursor()?;
+    while let Some((key, value)) = cursor.move_on_next()? {
+        let document_id = key
+            .try_into()
+            .map(u32::from_be_bytes)
+            .map_err(|_| SerializationError::InvalidNumberSerialization)?;
+        let obkv = KvReader::<FieldId>::from_slice(value);
+
+        // if the searchable fields didn't change, skip the searchable indexing for this document.
+        if !force_reindexing && !searchable_fields_changed(obkv, settings_diff) {
+            continue;
+        }
+
+        documents_ids.push(document_id);
+
+        // Update key buffer prefix.
+        key_buffer.clear();
+        key_buffer.extend_from_slice(&document_id.to_be_bytes());
+
+        // Tokenize deletions and additions in 2 diffferent threads.
+        let (del, add): (Result<_>, Result<_>) = rayon::join(
+            || {
+                // deletions
+                tokens_from_document(
+                    obkv,
+                    &settings_diff.old,
+                    &del_tokenizer,
+                    max_positions_per_attributes,
+                    DelAdd::Deletion,
+                    &mut del_buffers,
+                )
+            },
+            || {
+                // additions
+                tokens_from_document(
+                    obkv,
+                    &settings_diff.new,
+                    &add_tokenizer,
+                    max_positions_per_attributes,
+                    DelAdd::Addition,
+                    &mut add_buffers,
+                )
+            },
+        );
+
+        let del_obkv = del?;
+        let add_obkv = add?;
+
+        // merge deletions and additions.
+        // transforming two KV<FieldId, KV<u16, String>> into one KV<FieldId, KV<DelAdd, KV<u16, String>>>
+        value_buffer.clear();
+        del_add_from_two_obkvs(
+            KvReader::<FieldId>::from_slice(del_obkv),
+            KvReader::<FieldId>::from_slice(add_obkv),
+            &mut value_buffer,
+        )?;
+
+        // write each KV<DelAdd, KV<u16, String>> into the sorter, field by field.
+        let obkv = KvReader::<FieldId>::from_slice(&value_buffer);
+        for (field_id, value) in obkv.iter() {
+            key_buffer.truncate(mem::size_of::<u32>());
+            key_buffer.extend_from_slice(&field_id.to_be_bytes());
+            docid_word_positions_sorter.insert(&key_buffer, value)?;
+        }
+    }
+
+    // the returned sorter is serialized as: key: (DocId, FieldId), value: KV<DelAdd, KV<u16, String>>.
+    sorter_into_reader(docid_word_positions_sorter, indexer)
+}
+
+/// Check if any searchable fields of a document changed.
+fn searchable_fields_changed(
+    obkv: &KvReader<FieldId>,
+    settings_diff: &InnerIndexSettingsDiff,
+) -> bool {
+    let searchable_fields = &settings_diff.new.searchable_fields_ids;
+    for (field_id, field_bytes) in obkv.iter() {
+        if searchable_fields.contains(&field_id) {
+            let del_add = KvReaderDelAdd::from_slice(field_bytes);
+            match (del_add.get(DelAdd::Deletion), del_add.get(DelAdd::Addition)) {
+                // if both fields are None, check the next field.
+                (None, None) => (),
+                // if both contains a value and values are the same, check the next field.
+                (Some(del), Some(add)) if del == add => (),
+                // otherwise the fields are different, return true.
+                _otherwise => return true,
+            }
+        }
+    }
+
+    false
+}
+
+/// Factorize tokenizer building.
+fn tokenizer_builder<'a>(
+    stop_words: Option<&'a fst::Set<Vec<u8>>>,
+    allowed_separators: Option<&'a [&str]>,
+    dictionary: Option<&'a [&str]>,
+) -> TokenizerBuilder<'a, Vec<u8>> {
+    let mut tokenizer_builder = TokenizerBuilder::new();
+    if let Some(stop_words) = stop_words {
+        tokenizer_builder.stop_words(stop_words);
+    }
+    if let Some(dictionary) = dictionary {
+        tokenizer_builder.words_dict(dictionary);
+    }
+    if let Some(separators) = allowed_separators {
+        tokenizer_builder.separators(separators);
+    }
+
+    tokenizer_builder
+}
+
+/// Extract words mapped with their positions of a document.
+fn tokens_from_document<'a>(
+    obkv: &'a KvReader<FieldId>,
+    settings: &InnerIndexSettings,
+    tokenizer: &Tokenizer<'_>,
+    max_positions_per_attributes: u32,
+    del_add: DelAdd,
+    buffers: &'a mut Buffers,
+) -> Result<&'a [u8]> {
+    buffers.obkv_buffer.clear();
+    let mut document_writer = KvWriterU16::new(&mut buffers.obkv_buffer);
+    for (field_id, field_bytes) in obkv.iter() {
+        // if field is searchable.
+        if settings.searchable_fields_ids.contains(&field_id) {
+            // extract deletion or addition only.
+            if let Some(field_bytes) = KvReaderDelAdd::from_slice(field_bytes).get(del_add) {
+                // parse json.
+                let value =
+                    serde_json::from_slice(field_bytes).map_err(InternalError::SerdeJson)?;
+
+                // prepare writing destination.
+                buffers.obkv_positions_buffer.clear();
+                let mut writer = KvWriterU16::new(&mut buffers.obkv_positions_buffer);
+
+                // convert json into a unique string.
+                buffers.field_buffer.clear();
+                if let Some(field) = json_to_string(&value, &mut buffers.field_buffer) {
+                    // create an iterator of token with their positions.
+                    let locales = settings.localized_searchable_fields_ids.locales(field_id);
+                    let tokens = process_tokens(tokenizer.tokenize_with_allow_list(field, locales))
+                        .take_while(|(p, _)| (*p as u32) < max_positions_per_attributes);
+
+                    for (index, token) in tokens {
+                        // keep a word only if it is not empty and fit in a LMDB key.
+                        let token = token.lemma().trim();
+                        if !token.is_empty() && token.len() <= MAX_WORD_LENGTH {
+                            let position: u16 = index
+                                .try_into()
+                                .map_err(|_| SerializationError::InvalidNumberSerialization)?;
+                            writer.insert(position, token.as_bytes())?;
+                        }
+                    }
+
+                    // write positions into document.
+                    let positions = writer.into_inner()?;
+                    document_writer.insert(field_id, positions)?;
+                }
+            }
+        }
+    }
+
+    // returns a KV<FieldId, KV<u16, String>>
+    Ok(document_writer.into_inner().map(|v| v.as_slice())?)
+}
+
+/// 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 | Value::Object(_) => 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
+            }
+        }
+    }
+
+    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 standard 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())
+        .scan((0, None), |(offset, prev_kind), mut token| {
+            match token.kind {
+                TokenKind::Word | TokenKind::StopWord if !token.lemma().is_empty() => {
+                    *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);
+                }
+                _ => token.kind = TokenKind::Unknown,
+            }
+            Some((*offset, token))
+        })
+        .filter(|(_, t)| t.is_word())
+}
+
+#[derive(Default)]
+struct Buffers {
+    // the field buffer for each fields desserialization, and must be cleared between each field.
+    field_buffer: String,
+    // buffer used to store the value data containing an obkv.
+    obkv_buffer: Vec<u8>,
+    // buffer used to store the value data containing an obkv of tokens with their positions.
+    obkv_positions_buffer: Vec<u8>,
+}

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

@@ -0,0 +1,58 @@
+use std::fs::File;
+use std::io::{self, BufReader};
+
+use heed::{BytesDecode, BytesEncode};
+
+use super::helpers::{
+    create_sorter, sorter_into_reader, GrenadParameters, MergeDeladdCboRoaringBitmaps,
+};
+use crate::heed_codec::facet::{
+    FacetGroupKey, FacetGroupKeyCodec, FieldDocIdFacetF64Codec, OrderedF64Codec,
+};
+use crate::update::del_add::{KvReaderDelAdd, KvWriterDelAdd};
+use crate::update::settings::InnerIndexSettingsDiff;
+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.
+#[tracing::instrument(level = "trace", skip_all, target = "indexing::extract")]
+pub fn extract_facet_number_docids<R: io::Read + io::Seek>(
+    fid_docid_facet_number: grenad::Reader<R>,
+    indexer: GrenadParameters,
+    _settings_diff: &InnerIndexSettingsDiff,
+) -> Result<grenad::Reader<BufReader<File>>> {
+    let max_memory = indexer.max_memory_by_thread();
+
+    let mut facet_number_docids_sorter = create_sorter(
+        grenad::SortAlgorithm::Unstable,
+        MergeDeladdCboRoaringBitmaps,
+        indexer.chunk_compression_type,
+        indexer.chunk_compression_level,
+        indexer.max_nb_chunks,
+        max_memory,
+        true,
+    );
+
+    let mut buffer = Vec::new();
+    let mut cursor = fid_docid_facet_number.into_cursor()?;
+    while let Some((key_bytes, deladd_obkv_bytes)) = cursor.move_on_next()? {
+        let (field_id, document_id, number) =
+            FieldDocIdFacetF64Codec::bytes_decode(key_bytes).unwrap();
+
+        let key = FacetGroupKey { field_id, level: 0, left_bound: number };
+        let key_bytes = FacetGroupKeyCodec::<OrderedF64Codec>::bytes_encode(&key).unwrap();
+
+        buffer.clear();
+        let mut obkv = KvWriterDelAdd::new(&mut buffer);
+        for (deladd_key, _) in KvReaderDelAdd::from_slice(deladd_obkv_bytes).iter() {
+            obkv.insert(deladd_key, document_id.to_ne_bytes())?;
+        }
+        obkv.finish()?;
+
+        facet_number_docids_sorter.insert(key_bytes, &buffer)?;
+    }
+
+    sorter_into_reader(facet_number_docids_sorter, indexer)
+}

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

@@ -0,0 +1,303 @@
+use std::collections::BTreeSet;
+use std::fs::File;
+use std::io::BufReader;
+use std::iter::FromIterator;
+use std::{io, str};
+
+use charabia::normalizer::{Normalize, NormalizerOption};
+use charabia::{Language, StrDetection, Token};
+use heed::types::SerdeJson;
+use heed::BytesEncode;
+
+use super::helpers::{create_sorter, sorter_into_reader, try_split_array_at, GrenadParameters};
+use crate::heed_codec::facet::{FacetGroupKey, FacetGroupKeyCodec};
+use crate::heed_codec::{BEU16StrCodec, StrRefCodec};
+use crate::localized_attributes_rules::LocalizedFieldIds;
+use crate::update::del_add::{DelAdd, KvReaderDelAdd, KvWriterDelAdd};
+use crate::update::index_documents::helpers::{
+    MergeDeladdBtreesetString, MergeDeladdCboRoaringBitmaps,
+};
+use crate::update::settings::InnerIndexSettingsDiff;
+use crate::{FieldId, Result, MAX_FACET_VALUE_LENGTH};
+
+/// 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.
+#[tracing::instrument(level = "trace", skip_all, target = "indexing::extract")]
+pub fn extract_facet_string_docids<R: io::Read + io::Seek>(
+    docid_fid_facet_string: grenad::Reader<R>,
+    indexer: GrenadParameters,
+    settings_diff: &InnerIndexSettingsDiff,
+) -> Result<(grenad::Reader<BufReader<File>>, grenad::Reader<BufReader<File>>)> {
+    if settings_diff.settings_update_only() {
+        extract_facet_string_docids_settings(docid_fid_facet_string, indexer, settings_diff)
+    } else {
+        let localized_field_ids = &settings_diff.new.localized_faceted_fields_ids;
+        extract_facet_string_docids_document_update(
+            docid_fid_facet_string,
+            indexer,
+            localized_field_ids,
+        )
+    }
+}
+
+/// 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.
+#[tracing::instrument(level = "trace", skip_all, target = "indexing::extract")]
+fn extract_facet_string_docids_document_update<R: io::Read + io::Seek>(
+    docid_fid_facet_string: grenad::Reader<R>,
+    indexer: GrenadParameters,
+    localized_field_ids: &LocalizedFieldIds,
+) -> Result<(grenad::Reader<BufReader<File>>, grenad::Reader<BufReader<File>>)> {
+    let max_memory = indexer.max_memory_by_thread();
+
+    let mut facet_string_docids_sorter = create_sorter(
+        grenad::SortAlgorithm::Stable,
+        MergeDeladdCboRoaringBitmaps,
+        indexer.chunk_compression_type,
+        indexer.chunk_compression_level,
+        indexer.max_nb_chunks,
+        max_memory.map(|m| m / 2),
+        true,
+    );
+
+    let mut normalized_facet_string_docids_sorter = create_sorter(
+        grenad::SortAlgorithm::Stable,
+        MergeDeladdBtreesetString,
+        indexer.chunk_compression_type,
+        indexer.chunk_compression_level,
+        indexer.max_nb_chunks,
+        max_memory.map(|m| m / 2),
+        true,
+    );
+
+    let mut buffer = Vec::new();
+    let mut cursor = docid_fid_facet_string.into_cursor()?;
+    while let Some((key, deladd_original_value_bytes)) = cursor.move_on_next()? {
+        let deladd_reader = KvReaderDelAdd::from_slice(deladd_original_value_bytes);
+
+        let is_same_value = deladd_reader.get(DelAdd::Deletion).is_some()
+            && deladd_reader.get(DelAdd::Addition).is_some();
+
+        if is_same_value {
+            continue;
+        }
+
+        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::<_, 4>(bytes).unwrap();
+        let document_id = u32::from_be_bytes(document_id_bytes);
+
+        let normalized_value = str::from_utf8(normalized_value_bytes)?;
+
+        // Facet search normalization
+        {
+            let locales = localized_field_ids.locales(field_id);
+            let hyper_normalized_value = normalize_facet_string(normalized_value, locales);
+
+            let set = BTreeSet::from_iter(std::iter::once(normalized_value));
+
+            // as the facet string is the same, we can put the deletion and addition in the same obkv.
+            buffer.clear();
+            let mut obkv = KvWriterDelAdd::new(&mut buffer);
+            for (deladd_key, _) in deladd_reader.iter() {
+                let val = SerdeJson::bytes_encode(&set).map_err(heed::Error::Encoding)?;
+                obkv.insert(deladd_key, val)?;
+            }
+            obkv.finish()?;
+
+            let key: (u16, &str) = (field_id, hyper_normalized_value.as_ref());
+            let key_bytes = BEU16StrCodec::bytes_encode(&key).map_err(heed::Error::Encoding)?;
+            normalized_facet_string_docids_sorter.insert(key_bytes, &buffer)?;
+        }
+
+        let key = FacetGroupKey { field_id, level: 0, left_bound: normalized_value };
+        let key_bytes = FacetGroupKeyCodec::<StrRefCodec>::bytes_encode(&key).unwrap();
+
+        buffer.clear();
+        let mut obkv = KvWriterDelAdd::new(&mut buffer);
+        for (deladd_key, _) in deladd_reader.iter() {
+            obkv.insert(deladd_key, document_id.to_ne_bytes())?;
+        }
+        obkv.finish()?;
+        facet_string_docids_sorter.insert(&key_bytes, &buffer)?;
+    }
+
+    let normalized = sorter_into_reader(normalized_facet_string_docids_sorter, indexer)?;
+    sorter_into_reader(facet_string_docids_sorter, indexer).map(|s| (s, normalized))
+}
+
+/// 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.
+#[tracing::instrument(level = "trace", skip_all, target = "indexing::extract")]
+fn extract_facet_string_docids_settings<R: io::Read + io::Seek>(
+    docid_fid_facet_string: grenad::Reader<R>,
+    indexer: GrenadParameters,
+    settings_diff: &InnerIndexSettingsDiff,
+) -> Result<(grenad::Reader<BufReader<File>>, grenad::Reader<BufReader<File>>)> {
+    let max_memory = indexer.max_memory_by_thread();
+
+    let mut facet_string_docids_sorter = create_sorter(
+        grenad::SortAlgorithm::Stable,
+        MergeDeladdCboRoaringBitmaps,
+        indexer.chunk_compression_type,
+        indexer.chunk_compression_level,
+        indexer.max_nb_chunks,
+        max_memory.map(|m| m / 2),
+        true,
+    );
+
+    let mut normalized_facet_string_docids_sorter = create_sorter(
+        grenad::SortAlgorithm::Stable,
+        MergeDeladdBtreesetString,
+        indexer.chunk_compression_type,
+        indexer.chunk_compression_level,
+        indexer.max_nb_chunks,
+        max_memory.map(|m| m / 2),
+        true,
+    );
+
+    let mut buffer = Vec::new();
+    let mut cursor = docid_fid_facet_string.into_cursor()?;
+    while let Some((key, deladd_original_value_bytes)) = cursor.move_on_next()? {
+        let deladd_reader = KvReaderDelAdd::from_slice(deladd_original_value_bytes);
+
+        let is_same_value = deladd_reader.get(DelAdd::Deletion).is_some()
+            && deladd_reader.get(DelAdd::Addition).is_some();
+
+        let (field_id_bytes, bytes) = try_split_array_at(key).unwrap();
+        let field_id = FieldId::from_be_bytes(field_id_bytes);
+
+        let old_locales = settings_diff.old.localized_faceted_fields_ids.locales(field_id);
+        let new_locales = settings_diff.new.localized_faceted_fields_ids.locales(field_id);
+
+        let are_same_locales = old_locales == new_locales;
+
+        if is_same_value && are_same_locales {
+            continue;
+        }
+
+        let (document_id_bytes, normalized_value_bytes) =
+            try_split_array_at::<_, 4>(bytes).unwrap();
+        let document_id = u32::from_be_bytes(document_id_bytes);
+
+        let normalized_value = str::from_utf8(normalized_value_bytes)?;
+
+        // Facet search normalization
+        {
+            let old_hyper_normalized_value = normalize_facet_string(normalized_value, old_locales);
+            let new_hyper_normalized_value = if are_same_locales {
+                &old_hyper_normalized_value
+            } else {
+                &normalize_facet_string(normalized_value, new_locales)
+            };
+
+            let set = BTreeSet::from_iter(std::iter::once(normalized_value));
+
+            // if the facet string is the same, we can put the deletion and addition in the same obkv.
+            if old_hyper_normalized_value == new_hyper_normalized_value.as_str() {
+                // nothing to do if we delete and re-add the value.
+                if is_same_value {
+                    continue;
+                }
+
+                buffer.clear();
+                let mut obkv = KvWriterDelAdd::new(&mut buffer);
+                for (deladd_key, _) in deladd_reader.iter() {
+                    let val = SerdeJson::bytes_encode(&set).map_err(heed::Error::Encoding)?;
+                    obkv.insert(deladd_key, val)?;
+                }
+                obkv.finish()?;
+
+                let key: (u16, &str) = (field_id, new_hyper_normalized_value.as_ref());
+                let key_bytes = BEU16StrCodec::bytes_encode(&key).map_err(heed::Error::Encoding)?;
+                normalized_facet_string_docids_sorter.insert(key_bytes, &buffer)?;
+            } else {
+                // if the facet string is different, we need to insert the deletion and addition in different obkv because the related key is different.
+                // deletion
+                if deladd_reader.get(DelAdd::Deletion).is_some() {
+                    // insert old value
+                    let val = SerdeJson::bytes_encode(&set).map_err(heed::Error::Encoding)?;
+                    buffer.clear();
+                    let mut obkv = KvWriterDelAdd::new(&mut buffer);
+                    obkv.insert(DelAdd::Deletion, val)?;
+                    obkv.finish()?;
+                    let key: (u16, &str) = (field_id, old_hyper_normalized_value.as_ref());
+                    let key_bytes =
+                        BEU16StrCodec::bytes_encode(&key).map_err(heed::Error::Encoding)?;
+                    normalized_facet_string_docids_sorter.insert(key_bytes, &buffer)?;
+                }
+
+                // addition
+                if deladd_reader.get(DelAdd::Addition).is_some() {
+                    // insert new value
+                    let val = SerdeJson::bytes_encode(&set).map_err(heed::Error::Encoding)?;
+                    buffer.clear();
+                    let mut obkv = KvWriterDelAdd::new(&mut buffer);
+                    obkv.insert(DelAdd::Addition, val)?;
+                    obkv.finish()?;
+                    let key: (u16, &str) = (field_id, new_hyper_normalized_value.as_ref());
+                    let key_bytes =
+                        BEU16StrCodec::bytes_encode(&key).map_err(heed::Error::Encoding)?;
+                    normalized_facet_string_docids_sorter.insert(key_bytes, &buffer)?;
+                }
+            }
+        }
+
+        // nothing to do if we delete and re-add the value.
+        if is_same_value {
+            continue;
+        }
+
+        let key = FacetGroupKey { field_id, level: 0, left_bound: normalized_value };
+        let key_bytes = FacetGroupKeyCodec::<StrRefCodec>::bytes_encode(&key).unwrap();
+
+        buffer.clear();
+        let mut obkv = KvWriterDelAdd::new(&mut buffer);
+        for (deladd_key, _) in deladd_reader.iter() {
+            obkv.insert(deladd_key, document_id.to_ne_bytes())?;
+        }
+        obkv.finish()?;
+        facet_string_docids_sorter.insert(&key_bytes, &buffer)?;
+    }
+
+    let normalized = sorter_into_reader(normalized_facet_string_docids_sorter, indexer)?;
+    sorter_into_reader(facet_string_docids_sorter, indexer).map(|s| (s, normalized))
+}
+
+/// Normalizes the facet string and truncates it to the max length.
+fn normalize_facet_string(facet_string: &str, locales: Option<&[Language]>) -> String {
+    let options: NormalizerOption = NormalizerOption { lossy: true, ..Default::default() };
+    let mut detection = StrDetection::new(facet_string, locales);
+
+    let script = detection.script();
+    // Detect the language of the facet string only if several locales are explicitly provided.
+    let language = match locales {
+        Some(&[language]) => Some(language),
+        Some(multiple_locales) if multiple_locales.len() > 1 => detection.language(),
+        _ => None,
+    };
+
+    let token = Token {
+        lemma: std::borrow::Cow::Borrowed(facet_string),
+        script,
+        language,
+        ..Default::default()
+    };
+
+    // truncate the facet string to the max length
+    token
+        .normalize(&options)
+        .lemma
+        .char_indices()
+        .take_while(|(idx, _)| *idx < MAX_FACET_VALUE_LENGTH)
+        .map(|(_, c)| c)
+        .collect()
+}

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

@@ -0,0 +1,574 @@
+use std::collections::{BTreeMap, BTreeSet};
+use std::convert::TryInto;
+use std::fs::File;
+use std::io::{self, BufReader};
+use std::mem::size_of;
+
+use bytemuck::bytes_of;
+use grenad::Sorter;
+use heed::BytesEncode;
+use itertools::{merge_join_by, EitherOrBoth, Itertools};
+use ordered_float::OrderedFloat;
+use roaring::RoaringBitmap;
+use serde_json::{from_slice, Value};
+use FilterableValues::{Empty, Null, Values};
+
+use super::helpers::{create_sorter, sorter_into_reader, GrenadParameters, KeepFirst};
+use crate::error::InternalError;
+use crate::facet::value_encoding::f64_into_bytes;
+use crate::update::del_add::{DelAdd, KvReaderDelAdd, KvWriterDelAdd};
+use crate::update::index_documents::{create_writer, writer_into_reader};
+use crate::update::settings::InnerIndexSettingsDiff;
+use crate::{CboRoaringBitmapCodec, DocumentId, FieldId, Result, MAX_FACET_VALUE_LENGTH};
+
+/// The length of the elements that are always in the buffer when inserting new values.
+const TRUNCATE_SIZE: usize = size_of::<FieldId>() + size_of::<DocumentId>();
+
+/// The extracted facet values stored in grenad files by type.
+pub struct ExtractedFacetValues {
+    pub fid_docid_facet_numbers_chunk: grenad::Reader<BufReader<File>>,
+    pub fid_docid_facet_strings_chunk: grenad::Reader<BufReader<File>>,
+    pub fid_facet_is_null_docids_chunk: grenad::Reader<BufReader<File>>,
+    pub fid_facet_is_empty_docids_chunk: grenad::Reader<BufReader<File>>,
+    pub fid_facet_exists_docids_chunk: grenad::Reader<BufReader<File>>,
+}
+
+/// Extracts the facet values of each faceted field of each document.
+///
+/// Returns the generated grenad reader containing the docid the fid and the original value as key
+/// and the normalized value as value extracted from the given chunk of documents.
+/// We need the fid of the geofields to correctly parse them as numbers if they were sent as strings initially.
+#[tracing::instrument(level = "trace", skip_all, target = "indexing::extract")]
+pub fn extract_fid_docid_facet_values<R: io::Read + io::Seek>(
+    obkv_documents: grenad::Reader<R>,
+    indexer: GrenadParameters,
+    settings_diff: &InnerIndexSettingsDiff,
+) -> Result<ExtractedFacetValues> {
+    let max_memory = indexer.max_memory_by_thread();
+
+    let mut fid_docid_facet_numbers_sorter = create_sorter(
+        grenad::SortAlgorithm::Stable,
+        KeepFirst,
+        indexer.chunk_compression_type,
+        indexer.chunk_compression_level,
+        indexer.max_nb_chunks,
+        max_memory.map(|m| m / 2),
+        true,
+    );
+
+    let mut fid_docid_facet_strings_sorter = create_sorter(
+        grenad::SortAlgorithm::Stable,
+        KeepFirst,
+        indexer.chunk_compression_type,
+        indexer.chunk_compression_level,
+        indexer.max_nb_chunks,
+        max_memory.map(|m| m / 2),
+        true,
+    );
+
+    // The tuples represents the Del and Add side for a bitmap
+    let mut facet_exists_docids = BTreeMap::<FieldId, (RoaringBitmap, RoaringBitmap)>::new();
+    let mut facet_is_null_docids = BTreeMap::<FieldId, (RoaringBitmap, RoaringBitmap)>::new();
+    let mut facet_is_empty_docids = BTreeMap::<FieldId, (RoaringBitmap, RoaringBitmap)>::new();
+
+    // We create two buffers for mutable ref issues with closures.
+    let mut numbers_key_buffer = Vec::new();
+    let mut strings_key_buffer = Vec::new();
+
+    let old_faceted_fids: BTreeSet<_> =
+        settings_diff.old.faceted_fields_ids.iter().copied().collect();
+    let new_faceted_fids: BTreeSet<_> =
+        settings_diff.new.faceted_fields_ids.iter().copied().collect();
+
+    if !settings_diff.settings_update_only || old_faceted_fids != new_faceted_fids {
+        let mut cursor = obkv_documents.into_cursor()?;
+        while let Some((docid_bytes, value)) = cursor.move_on_next()? {
+            let obkv = obkv::KvReader::from_slice(value);
+            let get_document_json_value = move |field_id, side| {
+                obkv.get(field_id)
+                    .map(KvReaderDelAdd::from_slice)
+                    .and_then(|kv| kv.get(side))
+                    .map(from_slice)
+                    .transpose()
+                    .map_err(InternalError::SerdeJson)
+            };
+            // iterate over the faceted fields instead of over the whole document.
+            for eob in
+                merge_join_by(old_faceted_fids.iter(), new_faceted_fids.iter(), |old, new| {
+                    old.cmp(new)
+                })
+            {
+                let (field_id, del_value, add_value) = match eob {
+                    EitherOrBoth::Left(&field_id) => {
+                        let del_value = get_document_json_value(field_id, DelAdd::Deletion)?;
+
+                        // deletion only
+                        (field_id, del_value, None)
+                    }
+                    EitherOrBoth::Right(&field_id) => {
+                        let add_value = get_document_json_value(field_id, DelAdd::Addition)?;
+
+                        // addition only
+                        (field_id, None, add_value)
+                    }
+                    EitherOrBoth::Both(&field_id, _) => {
+                        // during settings update, recompute the changing settings only.
+                        if settings_diff.settings_update_only {
+                            continue;
+                        }
+
+                        let del_value = get_document_json_value(field_id, DelAdd::Deletion)?;
+                        let add_value = get_document_json_value(field_id, DelAdd::Addition)?;
+
+                        (field_id, del_value, add_value)
+                    }
+                };
+
+                if del_value.is_some() || add_value.is_some() {
+                    numbers_key_buffer.clear();
+                    strings_key_buffer.clear();
+
+                    // Set key to the field_id
+                    // Note: this encoding is consistent with FieldIdCodec
+                    numbers_key_buffer.extend_from_slice(&field_id.to_be_bytes());
+                    strings_key_buffer.extend_from_slice(&field_id.to_be_bytes());
+
+                    let document: [u8; 4] = docid_bytes[..4].try_into().ok().unwrap();
+                    let document = DocumentId::from_be_bytes(document);
+
+                    // For the other extraction tasks, prefix the key with the field_id and the document_id
+                    numbers_key_buffer.extend_from_slice(docid_bytes);
+                    strings_key_buffer.extend_from_slice(docid_bytes);
+
+                    // We insert the document id on the Del and the Add side if the field exists.
+                    let (ref mut del_exists, ref mut add_exists) =
+                        facet_exists_docids.entry(field_id).or_default();
+                    let (ref mut del_is_null, ref mut add_is_null) =
+                        facet_is_null_docids.entry(field_id).or_default();
+                    let (ref mut del_is_empty, ref mut add_is_empty) =
+                        facet_is_empty_docids.entry(field_id).or_default();
+
+                    if del_value.is_some() {
+                        del_exists.insert(document);
+                    }
+                    if add_value.is_some() {
+                        add_exists.insert(document);
+                    }
+
+                    let del_geo_support = settings_diff
+                        .old
+                        .geo_fields_ids
+                        .map_or(false, |(lat, lng)| field_id == lat || field_id == lng);
+                    let add_geo_support = settings_diff
+                        .new
+                        .geo_fields_ids
+                        .map_or(false, |(lat, lng)| field_id == lat || field_id == lng);
+                    let del_filterable_values =
+                        del_value.map(|value| extract_facet_values(&value, del_geo_support));
+                    let add_filterable_values =
+                        add_value.map(|value| extract_facet_values(&value, add_geo_support));
+
+                    // Those closures are just here to simplify things a bit.
+                    let mut insert_numbers_diff = |del_numbers, add_numbers| {
+                        insert_numbers_diff(
+                            &mut fid_docid_facet_numbers_sorter,
+                            &mut numbers_key_buffer,
+                            del_numbers,
+                            add_numbers,
+                        )
+                    };
+                    let mut insert_strings_diff = |del_strings, add_strings| {
+                        insert_strings_diff(
+                            &mut fid_docid_facet_strings_sorter,
+                            &mut strings_key_buffer,
+                            del_strings,
+                            add_strings,
+                        )
+                    };
+
+                    match (del_filterable_values, add_filterable_values) {
+                        (None, None) => (),
+                        (Some(del_filterable_values), None) => match del_filterable_values {
+                            Null => {
+                                del_is_null.insert(document);
+                            }
+                            Empty => {
+                                del_is_empty.insert(document);
+                            }
+                            Values { numbers, strings } => {
+                                insert_numbers_diff(numbers, vec![])?;
+                                insert_strings_diff(strings, vec![])?;
+                            }
+                        },
+                        (None, Some(add_filterable_values)) => match add_filterable_values {
+                            Null => {
+                                add_is_null.insert(document);
+                            }
+                            Empty => {
+                                add_is_empty.insert(document);
+                            }
+                            Values { numbers, strings } => {
+                                insert_numbers_diff(vec![], numbers)?;
+                                insert_strings_diff(vec![], strings)?;
+                            }
+                        },
+                        (Some(del_filterable_values), Some(add_filterable_values)) => {
+                            match (del_filterable_values, add_filterable_values) {
+                                (Null, Null) | (Empty, Empty) => (),
+                                (Null, Empty) => {
+                                    del_is_null.insert(document);
+                                    add_is_empty.insert(document);
+                                }
+                                (Empty, Null) => {
+                                    del_is_empty.insert(document);
+                                    add_is_null.insert(document);
+                                }
+                                (Null, Values { numbers, strings }) => {
+                                    insert_numbers_diff(vec![], numbers)?;
+                                    insert_strings_diff(vec![], strings)?;
+                                    del_is_null.insert(document);
+                                }
+                                (Empty, Values { numbers, strings }) => {
+                                    insert_numbers_diff(vec![], numbers)?;
+                                    insert_strings_diff(vec![], strings)?;
+                                    del_is_empty.insert(document);
+                                }
+                                (Values { numbers, strings }, Null) => {
+                                    add_is_null.insert(document);
+                                    insert_numbers_diff(numbers, vec![])?;
+                                    insert_strings_diff(strings, vec![])?;
+                                }
+                                (Values { numbers, strings }, Empty) => {
+                                    add_is_empty.insert(document);
+                                    insert_numbers_diff(numbers, vec![])?;
+                                    insert_strings_diff(strings, vec![])?;
+                                }
+                                (
+                                    Values { numbers: del_numbers, strings: del_strings },
+                                    Values { numbers: add_numbers, strings: add_strings },
+                                ) => {
+                                    insert_numbers_diff(del_numbers, add_numbers)?;
+                                    insert_strings_diff(del_strings, add_strings)?;
+                                }
+                            }
+                        }
+                    }
+                }
+            }
+        }
+    }
+
+    let mut buffer = Vec::new();
+    let mut facet_exists_docids_writer = create_writer(
+        indexer.chunk_compression_type,
+        indexer.chunk_compression_level,
+        tempfile::tempfile()?,
+    );
+    for (fid, (del_bitmap, add_bitmap)) in facet_exists_docids.into_iter() {
+        deladd_obkv_cbo_roaring_bitmaps(&mut buffer, &del_bitmap, &add_bitmap)?;
+        facet_exists_docids_writer.insert(fid.to_be_bytes(), &buffer)?;
+    }
+    let facet_exists_docids_reader = writer_into_reader(facet_exists_docids_writer)?;
+
+    let mut facet_is_null_docids_writer = create_writer(
+        indexer.chunk_compression_type,
+        indexer.chunk_compression_level,
+        tempfile::tempfile()?,
+    );
+    for (fid, (del_bitmap, add_bitmap)) in facet_is_null_docids.into_iter() {
+        deladd_obkv_cbo_roaring_bitmaps(&mut buffer, &del_bitmap, &add_bitmap)?;
+        facet_is_null_docids_writer.insert(fid.to_be_bytes(), &buffer)?;
+    }
+    let facet_is_null_docids_reader = writer_into_reader(facet_is_null_docids_writer)?;
+
+    let mut facet_is_empty_docids_writer = create_writer(
+        indexer.chunk_compression_type,
+        indexer.chunk_compression_level,
+        tempfile::tempfile()?,
+    );
+    for (fid, (del_bitmap, add_bitmap)) in facet_is_empty_docids.into_iter() {
+        deladd_obkv_cbo_roaring_bitmaps(&mut buffer, &del_bitmap, &add_bitmap)?;
+        facet_is_empty_docids_writer.insert(fid.to_be_bytes(), &buffer)?;
+    }
+    let facet_is_empty_docids_reader = writer_into_reader(facet_is_empty_docids_writer)?;
+
+    Ok(ExtractedFacetValues {
+        fid_docid_facet_numbers_chunk: sorter_into_reader(fid_docid_facet_numbers_sorter, indexer)?,
+        fid_docid_facet_strings_chunk: sorter_into_reader(fid_docid_facet_strings_sorter, indexer)?,
+        fid_facet_is_null_docids_chunk: facet_is_null_docids_reader,
+        fid_facet_is_empty_docids_chunk: facet_is_empty_docids_reader,
+        fid_facet_exists_docids_chunk: facet_exists_docids_reader,
+    })
+}
+
+/// Generates a vector of bytes containing a DelAdd obkv with two bitmaps.
+fn deladd_obkv_cbo_roaring_bitmaps(
+    buffer: &mut Vec<u8>,
+    del_bitmap: &RoaringBitmap,
+    add_bitmap: &RoaringBitmap,
+) -> io::Result<()> {
+    buffer.clear();
+    let mut obkv = KvWriterDelAdd::new(buffer);
+    let del_bitmap_bytes = CboRoaringBitmapCodec::bytes_encode(del_bitmap).unwrap();
+    let add_bitmap_bytes = CboRoaringBitmapCodec::bytes_encode(add_bitmap).unwrap();
+    obkv.insert(DelAdd::Deletion, del_bitmap_bytes)?;
+    obkv.insert(DelAdd::Addition, add_bitmap_bytes)?;
+    obkv.finish()
+}
+
+/// Truncates a string to the biggest valid LMDB key size.
+fn truncate_str(s: &str) -> &str {
+    let index = s
+        .char_indices()
+        .map(|(idx, _)| idx)
+        .chain(std::iter::once(s.len()))
+        .take_while(|idx| idx <= &MAX_FACET_VALUE_LENGTH)
+        .last();
+
+    &s[..index.unwrap_or(0)]
+}
+
+/// Computes the diff between both Del and Add numbers and
+/// only inserts the parts that differ in the sorter.
+fn insert_numbers_diff(
+    fid_docid_facet_numbers_sorter: &mut Sorter<KeepFirst>,
+    key_buffer: &mut Vec<u8>,
+    mut del_numbers: Vec<f64>,
+    mut add_numbers: Vec<f64>,
+) -> Result<()> {
+    // We sort and dedup the float numbers
+    del_numbers.sort_unstable_by_key(|f| OrderedFloat(*f));
+    add_numbers.sort_unstable_by_key(|f| OrderedFloat(*f));
+    del_numbers.dedup_by_key(|f| OrderedFloat(*f));
+    add_numbers.dedup_by_key(|f| OrderedFloat(*f));
+
+    let merged_numbers_iter = itertools::merge_join_by(
+        del_numbers.into_iter().map(OrderedFloat),
+        add_numbers.into_iter().map(OrderedFloat),
+        |del, add| del.cmp(add),
+    );
+
+    // insert facet numbers in sorter
+    for eob in merged_numbers_iter {
+        key_buffer.truncate(TRUNCATE_SIZE);
+        match eob {
+            EitherOrBoth::Both(_, _) => (), // no need to touch anything
+            EitherOrBoth::Left(OrderedFloat(number)) => {
+                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());
+
+                    // We insert only the Del part of the Obkv to inform
+                    // that we only want to remove all those numbers.
+                    let mut obkv = KvWriterDelAdd::memory();
+                    obkv.insert(DelAdd::Deletion, bytes_of(&()))?;
+                    let bytes = obkv.into_inner()?;
+                    fid_docid_facet_numbers_sorter.insert(&key_buffer, bytes)?;
+                }
+            }
+            EitherOrBoth::Right(OrderedFloat(number)) => {
+                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());
+
+                    // We insert only the Add part of the Obkv to inform
+                    // that we only want to remove all those numbers.
+                    let mut obkv = KvWriterDelAdd::memory();
+                    obkv.insert(DelAdd::Addition, bytes_of(&()))?;
+                    let bytes = obkv.into_inner()?;
+                    fid_docid_facet_numbers_sorter.insert(&key_buffer, bytes)?;
+                }
+            }
+        }
+    }
+
+    Ok(())
+}
+
+/// Computes the diff between both Del and Add strings and
+/// only inserts the parts that differ in the sorter.
+fn insert_strings_diff(
+    fid_docid_facet_strings_sorter: &mut Sorter<KeepFirst>,
+    key_buffer: &mut Vec<u8>,
+    mut del_strings: Vec<(String, String)>,
+    mut add_strings: Vec<(String, String)>,
+) -> Result<()> {
+    // We sort and dedup the normalized and original strings
+    del_strings.sort_unstable();
+    add_strings.sort_unstable();
+    del_strings.dedup();
+    add_strings.dedup();
+
+    let del_strings = del_strings.iter().chunk_by(|(normalized, _)| normalized);
+    let add_strings = add_strings.iter().chunk_by(|(normalized, _)| normalized);
+
+    let merged_strings_iter = itertools::merge_join_by(
+        del_strings.into_iter().filter(|(n, _)| !n.is_empty()),
+        add_strings.into_iter().filter(|(n, _)| !n.is_empty()),
+        |(normalized_del, _), (normalized_add, _)| normalized_del.cmp(normalized_add),
+    );
+
+    // insert normalized and original facet string in sorter
+    for eob in merged_strings_iter {
+        key_buffer.truncate(TRUNCATE_SIZE);
+        let (side, normalized, original) = match eob {
+            EitherOrBoth::Both((normalized, del), (_, add)) => {
+                let merged_strings_iter =
+                    itertools::merge_join_by(del, add, |(_, original_del), (_, original_add)| {
+                        original_del.cmp(original_add)
+                    });
+
+                // FIXME: we're in a bit of a pickle here, because we're only saving **one** original value per side,
+                // but we possibly have multiple original values that changed in the case where the field is an
+                // array of multiple values that normalize to the same value.
+                // (e.g. "foo" = ["bar", "Bar", "bAr", "baR"]. I'm not judging why you would do that ¯\_(ツ)_/¯)
+                //
+                // We'll work best effort by ignoring when the same value appears in both sides, deleting the first
+                // value that is only in the old version, and adding the first value that is only in the new version
+                let mut obkv = KvWriterDelAdd::memory();
+                let mut del = None;
+                let mut add = None;
+                let mut both = None;
+
+                for eob in merged_strings_iter {
+                    match eob {
+                        EitherOrBoth::Both((_normalized, original), _) => {
+                            both = match both {
+                                Some(both) => Some(both),
+                                None => Some(original),
+                            }
+                        }
+                        EitherOrBoth::Left((_normalized, original)) => {
+                            del = match del {
+                                Some(del) => Some(del),
+                                None => Some(original),
+                            };
+                        }
+                        EitherOrBoth::Right((_normalized, original)) => {
+                            add = match add {
+                                Some(add) => Some(add),
+                                None => Some(original),
+                            }
+                        }
+                    }
+                }
+
+                if let Some(del) = del {
+                    obkv.insert(DelAdd::Deletion, del)?;
+                }
+                if let Some(add) = add
+                    // prefer the newly added, but if there is none, keep a value in the list of values
+                    // since the normalized value appears both in old and new, we should never remove it.
+                    .or(both)
+                {
+                    obkv.insert(DelAdd::Addition, add)?;
+                }
+
+                let truncated = truncate_str(normalized);
+                key_buffer.extend_from_slice(truncated.as_bytes());
+
+                let bytes = obkv.into_inner()?;
+                fid_docid_facet_strings_sorter.insert(&key_buffer, bytes)?;
+                continue;
+            }
+            EitherOrBoth::Left((_normalized, mut original)) => {
+                // FIXME: we only consider the first value for the purpose of facet search
+                // another structure is needed, able to retain all originals associated with a normalized value.
+                let Some((normalized, original)) = original.next() else {
+                    continue;
+                };
+                (DelAdd::Deletion, normalized, original)
+            }
+            EitherOrBoth::Right((_normalized, mut original)) => {
+                // FIXME: we only consider the first value for the purpose of facet search
+                // another structure is needed, able to retain all originals associated with a normalized value.
+                let Some((normalized, original)) = original.next() else {
+                    continue;
+                };
+                (DelAdd::Addition, normalized, original)
+            }
+        };
+        let truncated = truncate_str(normalized);
+        key_buffer.extend_from_slice(truncated.as_bytes());
+
+        let mut obkv = KvWriterDelAdd::memory();
+        obkv.insert(side, original)?;
+        let bytes = obkv.into_inner()?;
+        fid_docid_facet_strings_sorter.insert(&key_buffer, bytes)?;
+    }
+
+    Ok(())
+}
+
+/// Represent what a document field contains.
+enum FilterableValues {
+    /// Corresponds to the JSON `null` value.
+    Null,
+    /// Corresponds to either, an empty string `""`, an empty array `[]`, or an empty object `{}`.
+    Empty,
+    /// Represents all the numbers and strings values found in this document field.
+    Values { numbers: Vec<f64>, strings: Vec<(String, String)> },
+}
+
+/// Extracts the facet values of a JSON field.
+fn extract_facet_values(value: &Value, geo_field: bool) -> FilterableValues {
+    fn inner_extract_facet_values(
+        value: &Value,
+        can_recurse: bool,
+        output_numbers: &mut Vec<f64>,
+        output_strings: &mut Vec<(String, String)>,
+        geo_field: bool,
+    ) {
+        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) => {
+                // if we're working on a geofield it MUST be something we can parse or else there was an internal error
+                // in the enrich pipeline. But since the enrich pipeline worked, we want to avoid crashing at all costs.
+                if geo_field {
+                    if let Ok(float) = original.parse() {
+                        output_numbers.push(float);
+                    } else {
+                        tracing::warn!(
+                            "Internal error, could not parse a geofield that has been validated. Please open an issue."
+                        )
+                    }
+                }
+                let normalized = crate::normalize_facet(original);
+                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,
+                            geo_field,
+                        );
+                    }
+                }
+            }
+            Value::Object(_) => (),
+        }
+    }
+
+    match value {
+        Value::Null => FilterableValues::Null,
+        Value::String(s) if s.is_empty() => FilterableValues::Empty,
+        Value::Array(a) if a.is_empty() => FilterableValues::Empty,
+        Value::Object(o) if o.is_empty() => FilterableValues::Empty,
+        otherwise => {
+            let mut numbers = Vec::new();
+            let mut strings = Vec::new();
+            inner_extract_facet_values(otherwise, true, &mut numbers, &mut strings, geo_field);
+            FilterableValues::Values { numbers, strings }
+        }
+    }
+}

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

@@ -0,0 +1,96 @@
+use std::fs::File;
+use std::io::{self, BufReader};
+
+use obkv::KvReaderU16;
+
+use super::helpers::{
+    create_sorter, sorter_into_reader, try_split_array_at, GrenadParameters,
+    MergeDeladdCboRoaringBitmaps,
+};
+use crate::error::SerializationError;
+use crate::index::db_name::DOCID_WORD_POSITIONS;
+use crate::update::del_add::{DelAdd, KvReaderDelAdd, KvWriterDelAdd};
+use crate::update::settings::InnerIndexSettingsDiff;
+use crate::Result;
+
+const MAX_COUNTED_WORDS: usize = 30;
+
+/// 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.
+#[tracing::instrument(level = "trace", skip_all, target = "indexing::extract")]
+pub fn extract_fid_word_count_docids<R: io::Read + io::Seek>(
+    docid_word_positions: grenad::Reader<R>,
+    indexer: GrenadParameters,
+    _settings_diff: &InnerIndexSettingsDiff,
+) -> Result<grenad::Reader<BufReader<File>>> {
+    let max_memory = indexer.max_memory_by_thread();
+
+    let mut fid_word_count_docids_sorter = create_sorter(
+        grenad::SortAlgorithm::Unstable,
+        MergeDeladdCboRoaringBitmaps,
+        indexer.chunk_compression_type,
+        indexer.chunk_compression_level,
+        indexer.max_nb_chunks,
+        max_memory,
+        true,
+    );
+
+    let mut key_buffer = Vec::new();
+    let mut value_buffer = Vec::new();
+    let mut cursor = docid_word_positions.into_cursor()?;
+    while let Some((key, value)) = cursor.move_on_next()? {
+        let (document_id_bytes, fid_bytes) = try_split_array_at(key)
+            .ok_or(SerializationError::Decoding { db_name: Some(DOCID_WORD_POSITIONS) })?;
+        let document_id = u32::from_be_bytes(document_id_bytes);
+
+        let del_add_reader = KvReaderDelAdd::from_slice(value);
+        let deletion = del_add_reader
+            // get deleted words
+            .get(DelAdd::Deletion)
+            // count deleted words
+            .map(|deletion| {
+                KvReaderU16::from_slice(deletion).iter().take(MAX_COUNTED_WORDS + 1).count()
+            })
+            // keep the count if under or equal to MAX_COUNTED_WORDS
+            .filter(|&word_count| word_count <= MAX_COUNTED_WORDS);
+        let addition = del_add_reader
+            // get added words
+            .get(DelAdd::Addition)
+            // count added words
+            .map(|addition| {
+                KvReaderU16::from_slice(addition).iter().take(MAX_COUNTED_WORDS + 1).count()
+            })
+            // keep the count if under or equal to MAX_COUNTED_WORDS
+            .filter(|&word_count| word_count <= MAX_COUNTED_WORDS);
+
+        if deletion != addition {
+            // Insert deleted word count in sorter if exist.
+            if let Some(word_count) = deletion {
+                value_buffer.clear();
+                let mut value_writer = KvWriterDelAdd::new(&mut value_buffer);
+                value_writer.insert(DelAdd::Deletion, document_id.to_ne_bytes()).unwrap();
+                key_buffer.clear();
+                key_buffer.extend_from_slice(fid_bytes);
+                key_buffer.push(word_count as u8);
+                fid_word_count_docids_sorter
+                    .insert(&key_buffer, value_writer.into_inner().unwrap())?;
+            }
+            // Insert added word count in sorter if exist.
+            if let Some(word_count) = addition {
+                value_buffer.clear();
+                let mut value_writer = KvWriterDelAdd::new(&mut value_buffer);
+                value_writer.insert(DelAdd::Addition, document_id.to_ne_bytes()).unwrap();
+                key_buffer.clear();
+                key_buffer.extend_from_slice(fid_bytes);
+                key_buffer.push(word_count as u8);
+                fid_word_count_docids_sorter
+                    .insert(&key_buffer, value_writer.into_inner().unwrap())?;
+            }
+        }
+    }
+
+    sorter_into_reader(fid_word_count_docids_sorter, indexer)
+}

crates/milli/src/update/index_documents/extract/extract_geo_points.rs

@@ -0,0 +1,103 @@
+use std::fs::File;
+use std::io::{self, BufReader};
+
+use concat_arrays::concat_arrays;
+use serde_json::Value;
+
+use super::helpers::{create_writer, writer_into_reader, GrenadParameters};
+use crate::error::GeoError;
+use crate::update::del_add::{DelAdd, KvReaderDelAdd, KvWriterDelAdd};
+use crate::update::index_documents::extract_finite_float_from_value;
+use crate::update::settings::{InnerIndexSettings, InnerIndexSettingsDiff};
+use crate::{FieldId, InternalError, Result};
+
+/// Extracts the geographical coordinates contained in each document under the `_geo` field.
+///
+/// Returns the generated grenad reader containing the docid as key associated to the (latitude, longitude)
+#[tracing::instrument(level = "trace", skip_all, target = "indexing::extract")]
+pub fn extract_geo_points<R: io::Read + io::Seek>(
+    obkv_documents: grenad::Reader<R>,
+    indexer: GrenadParameters,
+    primary_key_id: FieldId,
+    settings_diff: &InnerIndexSettingsDiff,
+) -> Result<grenad::Reader<BufReader<File>>> {
+    let mut writer = create_writer(
+        indexer.chunk_compression_type,
+        indexer.chunk_compression_level,
+        tempfile::tempfile()?,
+    );
+
+    let mut cursor = obkv_documents.into_cursor()?;
+    while let Some((docid_bytes, value)) = cursor.move_on_next()? {
+        let obkv = obkv::KvReader::from_slice(value);
+        // since we only need the primary key when we throw an error
+        // we create this getter to lazily get it when needed
+        let document_id = || -> Value {
+            let reader = KvReaderDelAdd::from_slice(obkv.get(primary_key_id).unwrap());
+            let document_id =
+                reader.get(DelAdd::Deletion).or(reader.get(DelAdd::Addition)).unwrap();
+            serde_json::from_slice(document_id).unwrap()
+        };
+
+        // extract old version
+        let del_lat_lng = extract_lat_lng(obkv, &settings_diff.old, DelAdd::Deletion, document_id)?;
+        // extract new version
+        let add_lat_lng = extract_lat_lng(obkv, &settings_diff.new, DelAdd::Addition, document_id)?;
+
+        if del_lat_lng != add_lat_lng {
+            let mut obkv = KvWriterDelAdd::memory();
+            if let Some([lat, lng]) = del_lat_lng {
+                #[allow(clippy::drop_non_drop)]
+                let bytes: [u8; 16] = concat_arrays![lat.to_ne_bytes(), lng.to_ne_bytes()];
+                obkv.insert(DelAdd::Deletion, bytes)?;
+            }
+            if let Some([lat, lng]) = add_lat_lng {
+                #[allow(clippy::drop_non_drop)]
+                let bytes: [u8; 16] = concat_arrays![lat.to_ne_bytes(), lng.to_ne_bytes()];
+                obkv.insert(DelAdd::Addition, bytes)?;
+            }
+            let bytes = obkv.into_inner()?;
+            writer.insert(docid_bytes, bytes)?;
+        }
+    }
+
+    writer_into_reader(writer)
+}
+
+/// Extract the finite floats lat and lng from two bytes slices.
+fn extract_lat_lng(
+    document: &obkv::KvReader<FieldId>,
+    settings: &InnerIndexSettings,
+    deladd: DelAdd,
+    document_id: impl Fn() -> Value,
+) -> Result<Option<[f64; 2]>> {
+    match settings.geo_fields_ids {
+        Some((lat_fid, lng_fid)) => {
+            let lat =
+                document.get(lat_fid).map(KvReaderDelAdd::from_slice).and_then(|r| r.get(deladd));
+            let lng =
+                document.get(lng_fid).map(KvReaderDelAdd::from_slice).and_then(|r| r.get(deladd));
+            let (lat, lng) = match (lat, lng) {
+                (Some(lat), Some(lng)) => (lat, lng),
+                (Some(_), None) => {
+                    return Err(GeoError::MissingLatitude { document_id: document_id() }.into())
+                }
+                (None, Some(_)) => {
+                    return Err(GeoError::MissingLongitude { document_id: document_id() }.into())
+                }
+                (None, None) => return Ok(None),
+            };
+            let lat = extract_finite_float_from_value(
+                serde_json::from_slice(lat).map_err(InternalError::SerdeJson)?,
+            )
+            .map_err(|lat| GeoError::BadLatitude { document_id: document_id(), value: lat })?;
+
+            let lng = extract_finite_float_from_value(
+                serde_json::from_slice(lng).map_err(InternalError::SerdeJson)?,
+            )
+            .map_err(|lng| GeoError::BadLongitude { document_id: document_id(), value: lng })?;
+            Ok(Some([lat, lng]))
+        }
+        None => Ok(None),
+    }
+}

crates/milli/src/update/index_documents/extract/extract_vector_points.rs

@@ -0,0 +1,841 @@
+use std::cmp::Ordering;
+use std::convert::{TryFrom, TryInto};
+use std::fs::File;
+use std::io::{self, BufReader, BufWriter};
+use std::mem::size_of;
+use std::str::from_utf8;
+use std::sync::Arc;
+
+use bytemuck::cast_slice;
+use grenad::Writer;
+use ordered_float::OrderedFloat;
+use roaring::RoaringBitmap;
+use serde_json::Value;
+
+use super::helpers::{create_writer, writer_into_reader, GrenadParameters};
+use crate::error::FaultSource;
+use crate::index::IndexEmbeddingConfig;
+use crate::prompt::{FieldsIdsMapWithMetadata, Prompt};
+use crate::update::del_add::{DelAdd, KvReaderDelAdd, KvWriterDelAdd};
+use crate::update::settings::InnerIndexSettingsDiff;
+use crate::vector::error::{EmbedErrorKind, PossibleEmbeddingMistakes, UnusedVectorsDistribution};
+use crate::vector::parsed_vectors::{ParsedVectorsDiff, VectorState, RESERVED_VECTORS_FIELD_NAME};
+use crate::vector::settings::ReindexAction;
+use crate::vector::{Embedder, Embedding};
+use crate::{try_split_array_at, DocumentId, FieldId, Result, ThreadPoolNoAbort};
+
+/// The length of the elements that are always in the buffer when inserting new values.
+const TRUNCATE_SIZE: usize = size_of::<DocumentId>();
+
+pub struct ExtractedVectorPoints {
+    // docid, _index -> KvWriterDelAdd -> Vector
+    pub manual_vectors: grenad::Reader<BufReader<File>>,
+    // docid -> ()
+    pub remove_vectors: grenad::Reader<BufReader<File>>,
+    // docid -> prompt
+    pub prompts: grenad::Reader<BufReader<File>>,
+
+    // embedder
+    pub embedder_name: String,
+    pub embedder: Arc<Embedder>,
+    pub add_to_user_provided: RoaringBitmap,
+    pub remove_from_user_provided: RoaringBitmap,
+}
+
+enum VectorStateDelta {
+    NoChange,
+    // Remove all vectors, generated or manual, from this document
+    NowRemoved,
+
+    NowManual(Vec<Vec<f32>>),
+
+    // Add the vector computed from the specified prompt
+    // Remove any previous vector
+    // Note: changing the value of the prompt **does require** recording this delta
+    NowGenerated(String),
+}
+
+impl VectorStateDelta {
+    fn into_values(self) -> (bool, String, Vec<Vec<f32>>) {
+        match self {
+            VectorStateDelta::NoChange => Default::default(),
+            VectorStateDelta::NowRemoved => (true, Default::default(), Default::default()),
+            // We always delete the previous vectors
+            VectorStateDelta::NowManual(add) => (true, Default::default(), add),
+            VectorStateDelta::NowGenerated(prompt) => (true, prompt, Default::default()),
+        }
+    }
+}
+
+struct EmbedderVectorExtractor {
+    embedder_name: String,
+    embedder: Arc<Embedder>,
+    prompt: Arc<Prompt>,
+
+    // (docid) -> (prompt)
+    prompts_writer: Writer<BufWriter<File>>,
+    // (docid) -> ()
+    remove_vectors_writer: Writer<BufWriter<File>>,
+    // (docid, _index) -> KvWriterDelAdd -> Vector
+    manual_vectors_writer: Writer<BufWriter<File>>,
+    // The docids of the documents that contains a user defined embedding
+    add_to_user_provided: RoaringBitmap,
+
+    action: ExtractionAction,
+}
+
+struct DocumentOperation {
+    // The docids of the documents that contains an auto-generated embedding
+    remove_from_user_provided: RoaringBitmap,
+}
+
+enum ExtractionAction {
+    SettingsFullReindex,
+    SettingsRegeneratePrompts { old_prompt: Arc<Prompt> },
+    DocumentOperation(DocumentOperation),
+}
+
+struct ManualEmbedderErrors {
+    embedder_name: String,
+    docid: String,
+    other_docids: usize,
+}
+
+impl ManualEmbedderErrors {
+    pub fn push_error(
+        errors: &mut Option<ManualEmbedderErrors>,
+        embedder_name: &str,
+        document_id: impl Fn() -> Value,
+    ) {
+        match errors {
+            Some(errors) => {
+                if errors.embedder_name == embedder_name {
+                    errors.other_docids = errors.other_docids.saturating_add(1)
+                }
+            }
+            None => {
+                *errors = Some(Self {
+                    embedder_name: embedder_name.to_owned(),
+                    docid: document_id().to_string(),
+                    other_docids: 0,
+                });
+            }
+        }
+    }
+
+    pub fn to_result(
+        errors: Option<ManualEmbedderErrors>,
+        possible_embedding_mistakes: &PossibleEmbeddingMistakes,
+        unused_vectors_distribution: &UnusedVectorsDistribution,
+    ) -> Result<()> {
+        match errors {
+            Some(errors) => {
+                let embedder_name = &errors.embedder_name;
+                let mut msg = format!(
+                    r"While embedding documents for embedder `{embedder_name}`: no vectors provided for document {}{}",
+                    errors.docid,
+                    if errors.other_docids != 0 {
+                        format!(" and at least {} other document(s)", errors.other_docids)
+                    } else {
+                        "".to_string()
+                    }
+                );
+
+                msg += &format!("\n- Note: `{embedder_name}` has `source: userProvided`, so documents must provide embeddings as an array in `_vectors.{embedder_name}`.");
+
+                let mut hint_count = 0;
+
+                for (vector_misspelling, count) in
+                    possible_embedding_mistakes.vector_mistakes().take(2)
+                {
+                    msg += &format!("\n- Hint: try replacing `{vector_misspelling}` by `_vectors` in {count} document(s).");
+                    hint_count += 1;
+                }
+
+                for (embedder_misspelling, count) in possible_embedding_mistakes
+                    .embedder_mistakes(embedder_name, unused_vectors_distribution)
+                    .take(2)
+                {
+                    msg += &format!("\n- Hint: try replacing `_vectors.{embedder_misspelling}` by `_vectors.{embedder_name}` in {count} document(s).");
+                    hint_count += 1;
+                }
+
+                if hint_count == 0 {
+                    msg += &format!(
+                        "\n- Hint: opt-out for a document with `_vectors.{embedder_name}: null`"
+                    );
+                }
+
+                Err(crate::Error::UserError(crate::UserError::DocumentEmbeddingError(msg)))
+            }
+            None => Ok(()),
+        }
+    }
+}
+
+/// Extracts the embedding vector contained in each document under the `_vectors` field.
+///
+/// Returns the generated grenad reader containing the docid as key associated to the Vec<f32>
+#[tracing::instrument(level = "trace", skip_all, target = "indexing::extract")]
+pub fn extract_vector_points<R: io::Read + io::Seek>(
+    obkv_documents: grenad::Reader<R>,
+    indexer: GrenadParameters,
+    embedders_configs: &[IndexEmbeddingConfig],
+    settings_diff: &InnerIndexSettingsDiff,
+    possible_embedding_mistakes: &PossibleEmbeddingMistakes,
+) -> Result<(Vec<ExtractedVectorPoints>, UnusedVectorsDistribution)> {
+    let mut unused_vectors_distribution = UnusedVectorsDistribution::new();
+    let mut manual_errors = None;
+    let reindex_vectors = settings_diff.reindex_vectors();
+
+    let old_fields_ids_map = &settings_diff.old.fields_ids_map;
+    let old_fields_ids_map =
+        FieldsIdsMapWithMetadata::new(old_fields_ids_map, &settings_diff.old.searchable_fields_ids);
+
+    let new_fields_ids_map = &settings_diff.new.fields_ids_map;
+    let new_fields_ids_map =
+        FieldsIdsMapWithMetadata::new(new_fields_ids_map, &settings_diff.new.searchable_fields_ids);
+
+    // the vector field id may have changed
+    let old_vectors_fid = old_fields_ids_map.id(RESERVED_VECTORS_FIELD_NAME);
+
+    let new_vectors_fid = new_fields_ids_map.id(RESERVED_VECTORS_FIELD_NAME);
+
+    let mut extractors = Vec::new();
+
+    let mut configs = settings_diff.new.embedding_configs.clone().into_inner();
+    let old_configs = &settings_diff.old.embedding_configs;
+
+    if reindex_vectors {
+        for (name, action) in settings_diff.embedding_config_updates.iter() {
+            if let Some(action) = action.reindex() {
+                let Some((embedder_name, (embedder, prompt, _quantized))) =
+                    configs.remove_entry(name)
+                else {
+                    tracing::error!(embedder = name, "Requested embedder config not found");
+                    continue;
+                };
+
+                // (docid, _index) -> KvWriterDelAdd -> Vector
+                let manual_vectors_writer = create_writer(
+                    indexer.chunk_compression_type,
+                    indexer.chunk_compression_level,
+                    tempfile::tempfile()?,
+                );
+
+                // (docid) -> (prompt)
+                let prompts_writer = create_writer(
+                    indexer.chunk_compression_type,
+                    indexer.chunk_compression_level,
+                    tempfile::tempfile()?,
+                );
+
+                // (docid) -> ()
+                let remove_vectors_writer = create_writer(
+                    indexer.chunk_compression_type,
+                    indexer.chunk_compression_level,
+                    tempfile::tempfile()?,
+                );
+
+                let action = match action {
+                    ReindexAction::FullReindex => ExtractionAction::SettingsFullReindex,
+                    ReindexAction::RegeneratePrompts => {
+                        let Some((_, old_prompt, _quantized)) = old_configs.get(name) else {
+                            tracing::error!(embedder = name, "Old embedder config not found");
+                            continue;
+                        };
+
+                        ExtractionAction::SettingsRegeneratePrompts { old_prompt }
+                    }
+                };
+
+                extractors.push(EmbedderVectorExtractor {
+                    embedder_name,
+                    embedder,
+                    prompt,
+                    prompts_writer,
+                    remove_vectors_writer,
+                    manual_vectors_writer,
+                    add_to_user_provided: RoaringBitmap::new(),
+                    action,
+                });
+            } else {
+                continue;
+            }
+        }
+    } else {
+        // document operation
+
+        for (embedder_name, (embedder, prompt, _quantized)) in configs.into_iter() {
+            // (docid, _index) -> KvWriterDelAdd -> Vector
+            let manual_vectors_writer = create_writer(
+                indexer.chunk_compression_type,
+                indexer.chunk_compression_level,
+                tempfile::tempfile()?,
+            );
+
+            // (docid) -> (prompt)
+            let prompts_writer = create_writer(
+                indexer.chunk_compression_type,
+                indexer.chunk_compression_level,
+                tempfile::tempfile()?,
+            );
+
+            // (docid) -> ()
+            let remove_vectors_writer = create_writer(
+                indexer.chunk_compression_type,
+                indexer.chunk_compression_level,
+                tempfile::tempfile()?,
+            );
+
+            extractors.push(EmbedderVectorExtractor {
+                embedder_name,
+                embedder,
+                prompt,
+                prompts_writer,
+                remove_vectors_writer,
+                manual_vectors_writer,
+                add_to_user_provided: RoaringBitmap::new(),
+                action: ExtractionAction::DocumentOperation(DocumentOperation {
+                    remove_from_user_provided: RoaringBitmap::new(),
+                }),
+            });
+        }
+    }
+
+    let mut key_buffer = Vec::new();
+    let mut cursor = obkv_documents.into_cursor()?;
+    while let Some((key, value)) = cursor.move_on_next()? {
+        // this must always be serialized as (docid, external_docid);
+        const SIZE_OF_DOCUMENTID: usize = std::mem::size_of::<DocumentId>();
+        let (docid_bytes, external_id_bytes) =
+            try_split_array_at::<u8, SIZE_OF_DOCUMENTID>(key).unwrap();
+        debug_assert!(from_utf8(external_id_bytes).is_ok());
+        let docid = DocumentId::from_be_bytes(docid_bytes);
+
+        let obkv = obkv::KvReader::from_slice(value);
+        key_buffer.clear();
+        key_buffer.extend_from_slice(docid_bytes.as_slice());
+
+        // since we only need the primary key when we throw an error we create this getter to
+        // lazily get it when needed
+        let document_id = || -> Value { from_utf8(external_id_bytes).unwrap().into() };
+
+        let mut parsed_vectors = ParsedVectorsDiff::new(
+            docid,
+            embedders_configs,
+            obkv,
+            old_vectors_fid,
+            new_vectors_fid,
+        )
+        .map_err(|error| error.to_crate_error(document_id().to_string()))?;
+
+        for EmbedderVectorExtractor {
+            embedder_name,
+            embedder,
+            prompt,
+            prompts_writer,
+            remove_vectors_writer,
+            manual_vectors_writer,
+            add_to_user_provided,
+            action,
+        } in extractors.iter_mut()
+        {
+            let embedder_is_manual = matches!(**embedder, Embedder::UserProvided(_));
+
+            let (old, new) = parsed_vectors.remove(embedder_name);
+            let delta = match action {
+                ExtractionAction::SettingsFullReindex => match old {
+                    // A full reindex can be triggered either by:
+                    // 1. a new embedder
+                    // 2. an existing embedder changed so that it must regenerate all generated embeddings.
+                    // For a new embedder, there can be `_vectors.embedder` embeddings to add to the DB
+                    VectorState::Inline(vectors) => {
+                        if !vectors.must_regenerate() {
+                            add_to_user_provided.insert(docid);
+                        }
+
+                        match vectors.into_array_of_vectors() {
+                            Some(add_vectors) => {
+                                if add_vectors.len() > usize::from(u8::MAX) {
+                                    return Err(crate::Error::UserError(
+                                        crate::UserError::TooManyVectors(
+                                            document_id().to_string(),
+                                            add_vectors.len(),
+                                        ),
+                                    ));
+                                }
+                                VectorStateDelta::NowManual(add_vectors)
+                            }
+                            None => VectorStateDelta::NoChange,
+                        }
+                    }
+                    // this happens only when an existing embedder changed. We cannot regenerate userProvided vectors
+                    VectorState::Manual => VectorStateDelta::NoChange,
+                    // generated vectors must be regenerated
+                    VectorState::Generated => {
+                        if embedder_is_manual {
+                            ManualEmbedderErrors::push_error(
+                                &mut manual_errors,
+                                embedder_name.as_str(),
+                                document_id,
+                            );
+                            continue;
+                        }
+                        regenerate_prompt(obkv, prompt, &new_fields_ids_map)?
+                    }
+                },
+                // prompt regeneration is only triggered for existing embedders
+                ExtractionAction::SettingsRegeneratePrompts { old_prompt } => {
+                    if old.must_regenerate() {
+                        if embedder_is_manual {
+                            ManualEmbedderErrors::push_error(
+                                &mut manual_errors,
+                                embedder_name.as_str(),
+                                document_id,
+                            );
+                            continue;
+                        }
+                        regenerate_if_prompt_changed(
+                            obkv,
+                            (old_prompt, prompt),
+                            (&old_fields_ids_map, &new_fields_ids_map),
+                        )?
+                    } else {
+                        // we can simply ignore user provided vectors as they are not regenerated and are
+                        // already in the DB since this is an existing embedder
+                        VectorStateDelta::NoChange
+                    }
+                }
+                ExtractionAction::DocumentOperation(DocumentOperation {
+                    remove_from_user_provided,
+                }) => extract_vector_document_diff(
+                    docid,
+                    obkv,
+                    prompt,
+                    (add_to_user_provided, remove_from_user_provided),
+                    (old, new),
+                    (&old_fields_ids_map, &new_fields_ids_map),
+                    document_id,
+                    embedder_name,
+                    embedder_is_manual,
+                    &mut manual_errors,
+                )?,
+            };
+            // and we finally push the unique vectors into the writer
+            push_vectors_diff(
+                remove_vectors_writer,
+                prompts_writer,
+                manual_vectors_writer,
+                &mut key_buffer,
+                delta,
+            )?;
+        }
+
+        unused_vectors_distribution.append(parsed_vectors);
+    }
+
+    ManualEmbedderErrors::to_result(
+        manual_errors,
+        possible_embedding_mistakes,
+        &unused_vectors_distribution,
+    )?;
+
+    let mut results = Vec::new();
+
+    for EmbedderVectorExtractor {
+        embedder_name,
+        embedder,
+        prompt: _,
+        prompts_writer,
+        remove_vectors_writer,
+        action,
+        manual_vectors_writer,
+        add_to_user_provided,
+    } in extractors
+    {
+        let remove_from_user_provided =
+            if let ExtractionAction::DocumentOperation(DocumentOperation {
+                remove_from_user_provided,
+            }) = action
+            {
+                remove_from_user_provided
+            } else {
+                Default::default()
+            };
+
+        results.push(ExtractedVectorPoints {
+            manual_vectors: writer_into_reader(manual_vectors_writer)?,
+            remove_vectors: writer_into_reader(remove_vectors_writer)?,
+            prompts: writer_into_reader(prompts_writer)?,
+            embedder,
+            embedder_name,
+            add_to_user_provided,
+            remove_from_user_provided,
+        })
+    }
+
+    Ok((results, unused_vectors_distribution))
+}
+
+#[allow(clippy::too_many_arguments)] // feel free to find efficient way to factor arguments
+fn extract_vector_document_diff(
+    docid: DocumentId,
+    obkv: &obkv::KvReader<FieldId>,
+    prompt: &Prompt,
+    (add_to_user_provided, remove_from_user_provided): (&mut RoaringBitmap, &mut RoaringBitmap),
+    (old, new): (VectorState, VectorState),
+    (old_fields_ids_map, new_fields_ids_map): (
+        &FieldsIdsMapWithMetadata,
+        &FieldsIdsMapWithMetadata,
+    ),
+    document_id: impl Fn() -> Value,
+    embedder_name: &str,
+    embedder_is_manual: bool,
+    manual_errors: &mut Option<ManualEmbedderErrors>,
+) -> Result<VectorStateDelta> {
+    match (old.must_regenerate(), new.must_regenerate()) {
+        (true, true) | (false, false) => {}
+        (true, false) => {
+            add_to_user_provided.insert(docid);
+        }
+        (false, true) => {
+            remove_from_user_provided.insert(docid);
+        }
+    }
+
+    let delta = match (old, new) {
+        // regardless of the previous state, if a document now contains inline _vectors, they must
+        // be extracted manually
+        (_old, VectorState::Inline(new)) => match new.into_array_of_vectors() {
+            Some(add_vectors) => {
+                if add_vectors.len() > usize::from(u8::MAX) {
+                    return Err(crate::Error::UserError(crate::UserError::TooManyVectors(
+                        document_id().to_string(),
+                        add_vectors.len(),
+                    )));
+                }
+
+                VectorStateDelta::NowManual(add_vectors)
+            }
+            None => VectorStateDelta::NoChange,
+        },
+        // no `_vectors` anywhere, we check for document removal and otherwise we regenerate the prompt if the
+        // document changed
+        (VectorState::Generated, VectorState::Generated) => {
+            // Do we keep this document?
+            let document_is_kept = obkv
+                .iter()
+                .map(|(_, deladd)| KvReaderDelAdd::from_slice(deladd))
+                .any(|deladd| deladd.get(DelAdd::Addition).is_some());
+
+            if document_is_kept {
+                if embedder_is_manual {
+                    ManualEmbedderErrors::push_error(manual_errors, embedder_name, document_id);
+                    return Ok(VectorStateDelta::NoChange);
+                }
+                // Don't give up if the old prompt was failing
+                let old_prompt = Some(&prompt).map(|p| {
+                    p.render_kvdeladd(obkv, DelAdd::Deletion, old_fields_ids_map)
+                        .unwrap_or_default()
+                });
+                let new_prompt =
+                    prompt.render_kvdeladd(obkv, DelAdd::Addition, new_fields_ids_map)?;
+                if old_prompt.as_ref() != Some(&new_prompt) {
+                    let old_prompt = old_prompt.unwrap_or_default();
+                    tracing::trace!(
+                        "🚀 Changing prompt from\n{old_prompt}\n===to===\n{new_prompt}"
+                    );
+                    VectorStateDelta::NowGenerated(new_prompt)
+                } else {
+                    tracing::trace!("⏭️ Prompt unmodified, skipping");
+                    VectorStateDelta::NoChange
+                }
+            } else {
+                VectorStateDelta::NowRemoved
+            }
+        }
+        // inline to the left is not supposed to be possible because the embedder is not new, so `_vectors` was removed from
+        // the previous version of the document.
+        // Manual -> Generated is also not possible without an Inline to the right (which is handled above)
+        // Generated -> Generated is handled above, so not possible
+        // As a result, this code is unreachable
+        (_not_generated, VectorState::Generated) => {
+            // Do we keep this document?
+            let document_is_kept = obkv
+                .iter()
+                .map(|(_, deladd)| KvReaderDelAdd::from_slice(deladd))
+                .any(|deladd| deladd.get(DelAdd::Addition).is_some());
+            if document_is_kept {
+                if embedder_is_manual {
+                    ManualEmbedderErrors::push_error(manual_errors, embedder_name, document_id);
+                    return Ok(VectorStateDelta::NoChange);
+                }
+                // becomes autogenerated
+                VectorStateDelta::NowGenerated(prompt.render_kvdeladd(
+                    obkv,
+                    DelAdd::Addition,
+                    new_fields_ids_map,
+                )?)
+            } else {
+                // make sure the document is always removed from user provided on removal
+                remove_from_user_provided.insert(docid);
+                VectorStateDelta::NowRemoved
+            }
+        }
+        // inline to the left is not possible because the embedder is not new, and so `_vectors` was removed from the previous
+        // version of the document.
+        // however the Rust type system cannot know that.
+        (_manual, VectorState::Manual) => {
+            // Do we keep this document?
+            let document_is_kept = obkv
+                .iter()
+                .map(|(_, deladd)| KvReaderDelAdd::from_slice(deladd))
+                .any(|deladd| deladd.get(DelAdd::Addition).is_some());
+            if document_is_kept {
+                // if the new version of documents has the vectors in the DB,
+                // then they are user-provided and nothing possibly changed
+                VectorStateDelta::NoChange
+            } else {
+                // make sure the document is always removed from user provided on removal
+                remove_from_user_provided.insert(docid);
+                VectorStateDelta::NowRemoved
+            }
+        }
+    };
+
+    Ok(delta)
+}
+
+fn regenerate_if_prompt_changed(
+    obkv: &obkv::KvReader<FieldId>,
+    (old_prompt, new_prompt): (&Prompt, &Prompt),
+    (old_fields_ids_map, new_fields_ids_map): (
+        &FieldsIdsMapWithMetadata,
+        &FieldsIdsMapWithMetadata,
+    ),
+) -> Result<VectorStateDelta> {
+    let old_prompt = old_prompt
+        .render_kvdeladd(obkv, DelAdd::Deletion, old_fields_ids_map)
+        .unwrap_or(Default::default());
+    let new_prompt = new_prompt.render_kvdeladd(obkv, DelAdd::Addition, new_fields_ids_map)?;
+
+    if new_prompt == old_prompt {
+        return Ok(VectorStateDelta::NoChange);
+    }
+    Ok(VectorStateDelta::NowGenerated(new_prompt))
+}
+
+fn regenerate_prompt(
+    obkv: &obkv::KvReader<FieldId>,
+    prompt: &Prompt,
+    new_fields_ids_map: &FieldsIdsMapWithMetadata,
+) -> Result<VectorStateDelta> {
+    let prompt = prompt.render_kvdeladd(obkv, DelAdd::Addition, new_fields_ids_map)?;
+
+    Ok(VectorStateDelta::NowGenerated(prompt))
+}
+
+/// We cannot compute the diff between both Del and Add vectors.
+/// We'll push every vector and compute the difference later in TypedChunk.
+fn push_vectors_diff(
+    remove_vectors_writer: &mut Writer<BufWriter<File>>,
+    prompts_writer: &mut Writer<BufWriter<File>>,
+    manual_vectors_writer: &mut Writer<BufWriter<File>>,
+    key_buffer: &mut Vec<u8>,
+    delta: VectorStateDelta,
+) -> Result<()> {
+    let (must_remove, prompt, mut add_vectors) = delta.into_values();
+    if must_remove {
+        key_buffer.truncate(TRUNCATE_SIZE);
+        remove_vectors_writer.insert(&key_buffer, [])?;
+    }
+    if !prompt.is_empty() {
+        key_buffer.truncate(TRUNCATE_SIZE);
+        prompts_writer.insert(&key_buffer, prompt.as_bytes())?;
+    }
+
+    // We sort and dedup the vectors
+    add_vectors.sort_unstable_by(|a, b| compare_vectors(a, b));
+    add_vectors.dedup_by(|a, b| compare_vectors(a, b).is_eq());
+
+    // insert vectors into the writer
+    for (i, vector) in add_vectors.into_iter().enumerate().take(u16::MAX as usize) {
+        // Generate the key by extending the unique index to it.
+        key_buffer.truncate(TRUNCATE_SIZE);
+        let index = u16::try_from(i).unwrap();
+        key_buffer.extend_from_slice(&index.to_be_bytes());
+
+        // We insert only the Add part of the Obkv to inform
+        // that we only want to remove all those vectors.
+        let mut obkv = KvWriterDelAdd::memory();
+        obkv.insert(DelAdd::Addition, cast_slice(&vector))?;
+        let bytes = obkv.into_inner()?;
+        manual_vectors_writer.insert(&key_buffer, bytes)?;
+    }
+
+    Ok(())
+}
+
+/// Compares two vectors by using the OrderingFloat helper.
+fn compare_vectors(a: &[f32], b: &[f32]) -> Ordering {
+    a.iter().copied().map(OrderedFloat).cmp(b.iter().copied().map(OrderedFloat))
+}
+
+#[tracing::instrument(level = "trace", skip_all, target = "indexing::extract")]
+pub fn extract_embeddings<R: io::Read + io::Seek>(
+    // docid, prompt
+    prompt_reader: grenad::Reader<R>,
+    indexer: GrenadParameters,
+    embedder: Arc<Embedder>,
+    embedder_name: &str,
+    possible_embedding_mistakes: &PossibleEmbeddingMistakes,
+    unused_vectors_distribution: &UnusedVectorsDistribution,
+    request_threads: &ThreadPoolNoAbort,
+) -> Result<grenad::Reader<BufReader<File>>> {
+    let n_chunks = embedder.chunk_count_hint(); // chunk level parallelism
+    let n_vectors_per_chunk = embedder.prompt_count_in_chunk_hint(); // number of vectors in a single chunk
+
+    // docid, state with embedding
+    let mut state_writer = create_writer(
+        indexer.chunk_compression_type,
+        indexer.chunk_compression_level,
+        tempfile::tempfile()?,
+    );
+
+    let mut chunks = Vec::with_capacity(n_chunks);
+    let mut current_chunk = Vec::with_capacity(n_vectors_per_chunk);
+    let mut current_chunk_ids = Vec::with_capacity(n_vectors_per_chunk);
+    let mut chunks_ids = Vec::with_capacity(n_chunks);
+    let mut cursor = prompt_reader.into_cursor()?;
+
+    while let Some((key, value)) = cursor.move_on_next()? {
+        let docid = key.try_into().map(DocumentId::from_be_bytes).unwrap();
+        // SAFETY: precondition, the grenad value was saved from a string
+        let prompt = unsafe { std::str::from_utf8_unchecked(value) };
+        if current_chunk.len() == current_chunk.capacity() {
+            chunks.push(std::mem::replace(
+                &mut current_chunk,
+                Vec::with_capacity(n_vectors_per_chunk),
+            ));
+            chunks_ids.push(std::mem::replace(
+                &mut current_chunk_ids,
+                Vec::with_capacity(n_vectors_per_chunk),
+            ));
+        };
+        current_chunk.push(prompt.to_owned());
+        current_chunk_ids.push(docid);
+
+        if chunks.len() == chunks.capacity() {
+            let chunked_embeds = embed_chunks(
+                &embedder,
+                std::mem::replace(&mut chunks, Vec::with_capacity(n_chunks)),
+                embedder_name,
+                possible_embedding_mistakes,
+                unused_vectors_distribution,
+                request_threads,
+            )?;
+
+            for (docid, embeddings) in chunks_ids
+                .iter()
+                .flat_map(|docids| docids.iter())
+                .zip(chunked_embeds.iter().flat_map(|embeds| embeds.iter()))
+            {
+                state_writer.insert(docid.to_be_bytes(), cast_slice(embeddings))?;
+            }
+            chunks_ids.clear();
+        }
+    }
+
+    // send last chunk
+    if !chunks.is_empty() {
+        let chunked_embeds = embed_chunks(
+            &embedder,
+            std::mem::take(&mut chunks),
+            embedder_name,
+            possible_embedding_mistakes,
+            unused_vectors_distribution,
+            request_threads,
+        )?;
+        for (docid, embeddings) in chunks_ids
+            .iter()
+            .flat_map(|docids| docids.iter())
+            .zip(chunked_embeds.iter().flat_map(|embeds| embeds.iter()))
+        {
+            state_writer.insert(docid.to_be_bytes(), cast_slice(embeddings))?;
+        }
+    }
+
+    if !current_chunk.is_empty() {
+        let embeds = embed_chunks(
+            &embedder,
+            vec![std::mem::take(&mut current_chunk)],
+            embedder_name,
+            possible_embedding_mistakes,
+            unused_vectors_distribution,
+            request_threads,
+        )?;
+
+        if let Some(embeds) = embeds.first() {
+            for (docid, embeddings) in current_chunk_ids.iter().zip(embeds.iter()) {
+                state_writer.insert(docid.to_be_bytes(), cast_slice(embeddings))?;
+            }
+        }
+    }
+
+    writer_into_reader(state_writer)
+}
+
+fn embed_chunks(
+    embedder: &Embedder,
+    text_chunks: Vec<Vec<String>>,
+    embedder_name: &str,
+    possible_embedding_mistakes: &PossibleEmbeddingMistakes,
+    unused_vectors_distribution: &UnusedVectorsDistribution,
+    request_threads: &ThreadPoolNoAbort,
+) -> Result<Vec<Vec<Embedding>>> {
+    match embedder.embed_chunks(text_chunks, request_threads) {
+        Ok(chunks) => Ok(chunks),
+        Err(error) => {
+            if let FaultSource::Bug = error.fault {
+                Err(crate::Error::InternalError(crate::InternalError::VectorEmbeddingError(
+                    error.into(),
+                )))
+            } else {
+                let mut msg =
+                    format!(r"While embedding documents for embedder `{embedder_name}`: {error}");
+
+                if let EmbedErrorKind::ManualEmbed(_) = &error.kind {
+                    msg += &format!("\n- Note: `{embedder_name}` has `source: userProvided`, so documents must provide embeddings as an array in `_vectors.{embedder_name}`.");
+                }
+
+                let mut hint_count = 0;
+
+                for (vector_misspelling, count) in
+                    possible_embedding_mistakes.vector_mistakes().take(2)
+                {
+                    msg += &format!("\n- Hint: try replacing `{vector_misspelling}` by `_vectors` in {count} document(s).");
+                    hint_count += 1;
+                }
+
+                for (embedder_misspelling, count) in possible_embedding_mistakes
+                    .embedder_mistakes(embedder_name, unused_vectors_distribution)
+                    .take(2)
+                {
+                    msg += &format!("\n- Hint: try replacing `_vectors.{embedder_misspelling}` by `_vectors.{embedder_name}` in {count} document(s).");
+                    hint_count += 1;
+                }
+
+                if hint_count == 0 {
+                    if let EmbedErrorKind::ManualEmbed(_) = &error.kind {
+                        msg += &format!(
+                            "\n- Hint: opt-out for a document with `_vectors.{embedder_name}: null`"
+                        );
+                    }
+                }
+
+                Err(crate::Error::UserError(crate::UserError::DocumentEmbeddingError(msg)))
+            }
+        }
+    }
+}

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

@@ -0,0 +1,243 @@
+use std::collections::BTreeSet;
+use std::fs::File;
+use std::io::{self, BufReader};
+
+use heed::{BytesDecode, BytesEncode};
+use obkv::KvReaderU16;
+use roaring::RoaringBitmap;
+
+use super::helpers::{
+    create_sorter, create_writer, try_split_array_at, writer_into_reader, GrenadParameters,
+    MergeDeladdCboRoaringBitmaps,
+};
+use crate::error::SerializationError;
+use crate::heed_codec::StrBEU16Codec;
+use crate::index::db_name::DOCID_WORD_POSITIONS;
+use crate::update::del_add::{is_noop_del_add_obkv, DelAdd, KvReaderDelAdd, KvWriterDelAdd};
+use crate::update::index_documents::helpers::sorter_into_reader;
+use crate::update::settings::InnerIndexSettingsDiff;
+use crate::{CboRoaringBitmapCodec, DocumentId, FieldId, 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.
+///
+/// The first returned reader is the one for normal word_docids, and the second one is for
+/// exact_word_docids
+#[tracing::instrument(level = "trace", skip_all, target = "indexing::extract")]
+pub fn extract_word_docids<R: io::Read + io::Seek>(
+    docid_word_positions: grenad::Reader<R>,
+    indexer: GrenadParameters,
+    settings_diff: &InnerIndexSettingsDiff,
+) -> Result<(
+    grenad::Reader<BufReader<File>>,
+    grenad::Reader<BufReader<File>>,
+    grenad::Reader<BufReader<File>>,
+)> {
+    let max_memory = indexer.max_memory_by_thread();
+
+    let mut word_fid_docids_sorter = create_sorter(
+        grenad::SortAlgorithm::Unstable,
+        MergeDeladdCboRoaringBitmaps,
+        indexer.chunk_compression_type,
+        indexer.chunk_compression_level,
+        indexer.max_nb_chunks,
+        max_memory.map(|m| m / 3),
+        true,
+    );
+    let mut key_buffer = Vec::new();
+    let mut del_words = BTreeSet::new();
+    let mut add_words = BTreeSet::new();
+    let mut cursor = docid_word_positions.into_cursor()?;
+    while let Some((key, value)) = cursor.move_on_next()? {
+        let (document_id_bytes, fid_bytes) = try_split_array_at(key)
+            .ok_or(SerializationError::Decoding { db_name: Some(DOCID_WORD_POSITIONS) })?;
+        let (fid_bytes, _) = try_split_array_at(fid_bytes)
+            .ok_or(SerializationError::Decoding { db_name: Some(DOCID_WORD_POSITIONS) })?;
+        let document_id = u32::from_be_bytes(document_id_bytes);
+        let fid = u16::from_be_bytes(fid_bytes);
+
+        let del_add_reader = KvReaderDelAdd::from_slice(value);
+        // extract all unique words to remove.
+        if let Some(deletion) = del_add_reader.get(DelAdd::Deletion) {
+            for (_pos, word) in KvReaderU16::from_slice(deletion).iter() {
+                del_words.insert(word.to_vec());
+            }
+        }
+
+        // extract all unique additional words.
+        if let Some(addition) = del_add_reader.get(DelAdd::Addition) {
+            for (_pos, word) in KvReaderU16::from_slice(addition).iter() {
+                add_words.insert(word.to_vec());
+            }
+        }
+
+        words_into_sorter(
+            document_id,
+            fid,
+            &mut key_buffer,
+            &del_words,
+            &add_words,
+            &mut word_fid_docids_sorter,
+        )?;
+
+        del_words.clear();
+        add_words.clear();
+    }
+
+    let mut word_fid_docids_writer = create_writer(
+        indexer.chunk_compression_type,
+        indexer.chunk_compression_level,
+        tempfile::tempfile()?,
+    );
+
+    let mut word_docids_sorter = create_sorter(
+        grenad::SortAlgorithm::Unstable,
+        MergeDeladdCboRoaringBitmaps,
+        indexer.chunk_compression_type,
+        indexer.chunk_compression_level,
+        indexer.max_nb_chunks,
+        max_memory.map(|m| m / 3),
+        true,
+    );
+
+    let mut exact_word_docids_sorter = create_sorter(
+        grenad::SortAlgorithm::Unstable,
+        MergeDeladdCboRoaringBitmaps,
+        indexer.chunk_compression_type,
+        indexer.chunk_compression_level,
+        indexer.max_nb_chunks,
+        max_memory.map(|m| m / 3),
+        true,
+    );
+
+    let mut iter = word_fid_docids_sorter.into_stream_merger_iter()?;
+    let mut buffer = Vec::new();
+    // NOTE: replacing sorters by bitmap merging is less efficient, so, use sorters.
+    while let Some((key, value)) = iter.next()? {
+        // only keep the value if their is a change to apply in the DB.
+        if !is_noop_del_add_obkv(KvReaderDelAdd::from_slice(value)) {
+            word_fid_docids_writer.insert(key, value)?;
+        }
+
+        let (w, fid) = StrBEU16Codec::bytes_decode(key)
+            .map_err(|_| SerializationError::Decoding { db_name: Some(DOCID_WORD_POSITIONS) })?;
+
+        // merge all deletions
+        let obkv = KvReaderDelAdd::from_slice(value);
+        if let Some(value) = obkv.get(DelAdd::Deletion) {
+            let delete_from_exact = settings_diff.old.exact_attributes.contains(&fid);
+            buffer.clear();
+            let mut obkv = KvWriterDelAdd::new(&mut buffer);
+            obkv.insert(DelAdd::Deletion, value)?;
+            if delete_from_exact {
+                exact_word_docids_sorter.insert(w, obkv.into_inner().unwrap())?;
+            } else {
+                word_docids_sorter.insert(w, obkv.into_inner().unwrap())?;
+            }
+        }
+        // merge all additions
+        if let Some(value) = obkv.get(DelAdd::Addition) {
+            let add_in_exact = settings_diff.new.exact_attributes.contains(&fid);
+            buffer.clear();
+            let mut obkv = KvWriterDelAdd::new(&mut buffer);
+            obkv.insert(DelAdd::Addition, value)?;
+            if add_in_exact {
+                exact_word_docids_sorter.insert(w, obkv.into_inner().unwrap())?;
+            } else {
+                word_docids_sorter.insert(w, obkv.into_inner().unwrap())?;
+            }
+        }
+    }
+
+    Ok((
+        sorter_into_reader(word_docids_sorter, indexer)?,
+        sorter_into_reader(exact_word_docids_sorter, indexer)?,
+        writer_into_reader(word_fid_docids_writer)?,
+    ))
+}
+
+#[tracing::instrument(level = "trace", skip_all, target = "indexing::extract")]
+fn words_into_sorter(
+    document_id: DocumentId,
+    fid: FieldId,
+    key_buffer: &mut Vec<u8>,
+    del_words: &BTreeSet<Vec<u8>>,
+    add_words: &BTreeSet<Vec<u8>>,
+    word_fid_docids_sorter: &mut grenad::Sorter<MergeDeladdCboRoaringBitmaps>,
+) -> Result<()> {
+    use itertools::merge_join_by;
+    use itertools::EitherOrBoth::{Both, Left, Right};
+
+    let mut buffer = Vec::new();
+    for eob in merge_join_by(del_words.iter(), add_words.iter(), |d, a| d.cmp(a)) {
+        buffer.clear();
+        let mut value_writer = KvWriterDelAdd::new(&mut buffer);
+        let word_bytes = match eob {
+            Left(word_bytes) => {
+                value_writer.insert(DelAdd::Deletion, document_id.to_ne_bytes()).unwrap();
+                word_bytes
+            }
+            Right(word_bytes) => {
+                value_writer.insert(DelAdd::Addition, document_id.to_ne_bytes()).unwrap();
+                word_bytes
+            }
+            Both(word_bytes, _) => {
+                value_writer.insert(DelAdd::Deletion, document_id.to_ne_bytes()).unwrap();
+                value_writer.insert(DelAdd::Addition, document_id.to_ne_bytes()).unwrap();
+                word_bytes
+            }
+        };
+
+        key_buffer.clear();
+        key_buffer.extend_from_slice(word_bytes);
+        key_buffer.push(0);
+        key_buffer.extend_from_slice(&fid.to_be_bytes());
+        word_fid_docids_sorter.insert(&key_buffer, value_writer.into_inner().unwrap())?;
+    }
+
+    Ok(())
+}
+
+#[tracing::instrument(level = "trace", skip_all, target = "indexing::extract")]
+fn docids_into_writers<W>(
+    word: &str,
+    deletions: &RoaringBitmap,
+    additions: &RoaringBitmap,
+    writer: &mut grenad::Writer<W>,
+) -> Result<()>
+where
+    W: std::io::Write,
+{
+    if deletions == additions {
+        // if the same value is deleted and added, do nothing.
+        return Ok(());
+    }
+
+    // Write each value in the same KvDelAdd before inserting it in the final writer.
+    let mut obkv = KvWriterDelAdd::memory();
+    // deletions:
+    if !deletions.is_empty() && !deletions.is_subset(additions) {
+        obkv.insert(
+            DelAdd::Deletion,
+            CboRoaringBitmapCodec::bytes_encode(deletions).map_err(|_| {
+                SerializationError::Encoding { db_name: Some(DOCID_WORD_POSITIONS) }
+            })?,
+        )?;
+    }
+    // additions:
+    if !additions.is_empty() {
+        obkv.insert(
+            DelAdd::Addition,
+            CboRoaringBitmapCodec::bytes_encode(additions).map_err(|_| {
+                SerializationError::Encoding { db_name: Some(DOCID_WORD_POSITIONS) }
+            })?,
+        )?;
+    }
+
+    // insert everything in the same writer.
+    writer.insert(word.as_bytes(), obkv.into_inner().unwrap())?;
+
+    Ok(())
+}

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

@@ -0,0 +1,261 @@
+use std::collections::{BTreeMap, VecDeque};
+use std::fs::File;
+use std::io::BufReader;
+use std::{cmp, io};
+
+use obkv::KvReaderU16;
+
+use super::helpers::{
+    create_sorter, create_writer, try_split_array_at, writer_into_reader, GrenadParameters,
+    MergeDeladdCboRoaringBitmaps,
+};
+use crate::error::SerializationError;
+use crate::index::db_name::DOCID_WORD_POSITIONS;
+use crate::proximity::{index_proximity, ProximityPrecision, MAX_DISTANCE};
+use crate::update::del_add::{DelAdd, KvReaderDelAdd, KvWriterDelAdd};
+use crate::update::settings::InnerIndexSettingsDiff;
+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.
+#[tracing::instrument(level = "trace", skip_all, target = "indexing::extract")]
+pub fn extract_word_pair_proximity_docids<R: io::Read + io::Seek>(
+    docid_word_positions: grenad::Reader<R>,
+    indexer: GrenadParameters,
+    settings_diff: &InnerIndexSettingsDiff,
+) -> Result<grenad::Reader<BufReader<File>>> {
+    // early return if the data shouldn't be deleted nor created.
+    if settings_diff.settings_update_only && !settings_diff.reindex_proximities() {
+        let writer = create_writer(
+            indexer.chunk_compression_type,
+            indexer.chunk_compression_level,
+            tempfile::tempfile()?,
+        );
+        return writer_into_reader(writer);
+    }
+
+    let any_deletion = settings_diff.old.proximity_precision == ProximityPrecision::ByWord;
+    let any_addition = settings_diff.new.proximity_precision == ProximityPrecision::ByWord;
+
+    let max_memory = indexer.max_memory_by_thread();
+    let mut word_pair_proximity_docids_sorters: Vec<_> = (1..MAX_DISTANCE)
+        .map(|_| {
+            create_sorter(
+                grenad::SortAlgorithm::Unstable,
+                MergeDeladdCboRoaringBitmaps,
+                indexer.chunk_compression_type,
+                indexer.chunk_compression_level,
+                indexer.max_nb_chunks,
+                max_memory.map(|m| m / MAX_DISTANCE as usize),
+                true,
+            )
+        })
+        .collect();
+
+    let mut del_word_positions: VecDeque<(String, u16)> =
+        VecDeque::with_capacity(MAX_DISTANCE as usize);
+    let mut add_word_positions: VecDeque<(String, u16)> =
+        VecDeque::with_capacity(MAX_DISTANCE as usize);
+    let mut del_word_pair_proximity = BTreeMap::new();
+    let mut add_word_pair_proximity = BTreeMap::new();
+    let mut current_document_id = None;
+
+    let mut cursor = docid_word_positions.into_cursor()?;
+    while let Some((key, value)) = cursor.move_on_next()? {
+        let (document_id_bytes, _fid_bytes) = try_split_array_at(key)
+            .ok_or(SerializationError::Decoding { db_name: Some(DOCID_WORD_POSITIONS) })?;
+        let document_id = u32::from_be_bytes(document_id_bytes);
+
+        // if we change document, we fill the sorter
+        if current_document_id.map_or(false, |id| id != document_id) {
+            // FIXME: span inside of a hot loop might degrade performance and create big reports
+            let span = tracing::trace_span!(target: "indexing::details", "document_into_sorter");
+            let _entered = span.enter();
+
+            document_word_positions_into_sorter(
+                current_document_id.unwrap(),
+                &del_word_pair_proximity,
+                &add_word_pair_proximity,
+                &mut word_pair_proximity_docids_sorters,
+            )?;
+            del_word_pair_proximity.clear();
+            add_word_pair_proximity.clear();
+        }
+
+        current_document_id = Some(document_id);
+
+        let (del, add): (Result<_>, Result<_>) = rayon::join(
+            || {
+                if !any_deletion {
+                    return Ok(());
+                }
+
+                // deletions
+                if let Some(deletion) = KvReaderDelAdd::from_slice(value).get(DelAdd::Deletion) {
+                    for (position, word) in KvReaderU16::from_slice(deletion).iter() {
+                        // drain the proximity window until the head word is considered close to the word we are inserting.
+                        while del_word_positions.front().map_or(false, |(_w, p)| {
+                            index_proximity(*p as u32, position as u32) >= MAX_DISTANCE
+                        }) {
+                            word_positions_into_word_pair_proximity(
+                                &mut del_word_positions,
+                                &mut del_word_pair_proximity,
+                            )?;
+                        }
+
+                        // insert the new word.
+                        let word = std::str::from_utf8(word)?;
+                        del_word_positions.push_back((word.to_string(), position));
+                    }
+
+                    while !del_word_positions.is_empty() {
+                        word_positions_into_word_pair_proximity(
+                            &mut del_word_positions,
+                            &mut del_word_pair_proximity,
+                        )?;
+                    }
+                }
+
+                Ok(())
+            },
+            || {
+                if !any_addition {
+                    return Ok(());
+                }
+
+                // additions
+                if let Some(addition) = KvReaderDelAdd::from_slice(value).get(DelAdd::Addition) {
+                    for (position, word) in KvReaderU16::from_slice(addition).iter() {
+                        // drain the proximity window until the head word is considered close to the word we are inserting.
+                        while add_word_positions.front().map_or(false, |(_w, p)| {
+                            index_proximity(*p as u32, position as u32) >= MAX_DISTANCE
+                        }) {
+                            word_positions_into_word_pair_proximity(
+                                &mut add_word_positions,
+                                &mut add_word_pair_proximity,
+                            )?;
+                        }
+
+                        // insert the new word.
+                        let word = std::str::from_utf8(word)?;
+                        add_word_positions.push_back((word.to_string(), position));
+                    }
+
+                    while !add_word_positions.is_empty() {
+                        word_positions_into_word_pair_proximity(
+                            &mut add_word_positions,
+                            &mut add_word_pair_proximity,
+                        )?;
+                    }
+                }
+
+                Ok(())
+            },
+        );
+
+        del?;
+        add?;
+    }
+
+    if let Some(document_id) = current_document_id {
+        // FIXME: span inside of a hot loop might degrade performance and create big reports
+        let span = tracing::trace_span!(target: "indexing::details", "final_document_into_sorter");
+        let _entered = span.enter();
+
+        document_word_positions_into_sorter(
+            document_id,
+            &del_word_pair_proximity,
+            &add_word_pair_proximity,
+            &mut word_pair_proximity_docids_sorters,
+        )?;
+    }
+    {
+        // FIXME: span inside of a hot loop might degrade performance and create big reports
+        let span = tracing::trace_span!(target: "indexing::details", "sorter_into_reader");
+        let _entered = span.enter();
+
+        let mut writer = create_writer(
+            indexer.chunk_compression_type,
+            indexer.chunk_compression_level,
+            tempfile::tempfile()?,
+        );
+
+        for sorter in word_pair_proximity_docids_sorters {
+            sorter.write_into_stream_writer(&mut writer)?;
+        }
+
+        writer_into_reader(writer)
+    }
+}
+
+/// 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(
+    document_id: DocumentId,
+    del_word_pair_proximity: &BTreeMap<(String, String), u8>,
+    add_word_pair_proximity: &BTreeMap<(String, String), u8>,
+    word_pair_proximity_docids_sorters: &mut [grenad::Sorter<MergeDeladdCboRoaringBitmaps>],
+) -> Result<()> {
+    use itertools::merge_join_by;
+    use itertools::EitherOrBoth::{Both, Left, Right};
+
+    let mut buffer = Vec::new();
+    let mut key_buffer = Vec::new();
+    for eob in
+        merge_join_by(del_word_pair_proximity.iter(), add_word_pair_proximity.iter(), |d, a| {
+            d.cmp(a)
+        })
+    {
+        buffer.clear();
+        let mut value_writer = KvWriterDelAdd::new(&mut buffer);
+        let ((w1, w2), prox) = match eob {
+            Left(key_value) => {
+                value_writer.insert(DelAdd::Deletion, document_id.to_ne_bytes()).unwrap();
+                key_value
+            }
+            Right(key_value) => {
+                value_writer.insert(DelAdd::Addition, document_id.to_ne_bytes()).unwrap();
+                key_value
+            }
+            Both(key_value, _) => {
+                value_writer.insert(DelAdd::Deletion, document_id.to_ne_bytes()).unwrap();
+                value_writer.insert(DelAdd::Addition, document_id.to_ne_bytes()).unwrap();
+                key_value
+            }
+        };
+
+        key_buffer.clear();
+        key_buffer.push(*prox);
+        key_buffer.extend_from_slice(w1.as_bytes());
+        key_buffer.push(0);
+        key_buffer.extend_from_slice(w2.as_bytes());
+
+        word_pair_proximity_docids_sorters[*prox as usize - 1]
+            .insert(&key_buffer, value_writer.into_inner().unwrap())?;
+    }
+
+    Ok(())
+}
+
+fn word_positions_into_word_pair_proximity(
+    word_positions: &mut VecDeque<(String, u16)>,
+    word_pair_proximity: &mut BTreeMap<(String, String), u8>,
+) -> Result<()> {
+    let (head_word, head_position) = word_positions.pop_front().unwrap();
+    for (word, position) in word_positions.iter() {
+        let prox = index_proximity(head_position as u32, *position as u32) as u8;
+        if prox > 0 && prox < MAX_DISTANCE as u8 {
+            word_pair_proximity
+                .entry((head_word.clone(), word.clone()))
+                .and_modify(|p| {
+                    *p = cmp::min(*p, prox);
+                })
+                .or_insert(prox);
+        }
+    }
+    Ok(())
+}

crates/milli/src/update/index_documents/extract/extract_word_position_docids.rs

@@ -0,0 +1,138 @@
+use std::collections::BTreeSet;
+use std::fs::File;
+use std::io::{self, BufReader};
+
+use obkv::KvReaderU16;
+
+use super::helpers::{
+    create_sorter, sorter_into_reader, try_split_array_at, GrenadParameters,
+    MergeDeladdCboRoaringBitmaps,
+};
+use crate::error::SerializationError;
+use crate::index::db_name::DOCID_WORD_POSITIONS;
+use crate::update::del_add::{DelAdd, KvReaderDelAdd, KvWriterDelAdd};
+use crate::update::settings::InnerIndexSettingsDiff;
+use crate::{bucketed_position, 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.
+#[tracing::instrument(level = "trace", skip_all, target = "indexing::extract")]
+pub fn extract_word_position_docids<R: io::Read + io::Seek>(
+    docid_word_positions: grenad::Reader<R>,
+    indexer: GrenadParameters,
+    _settings_diff: &InnerIndexSettingsDiff,
+) -> Result<grenad::Reader<BufReader<File>>> {
+    let max_memory = indexer.max_memory_by_thread();
+
+    let mut word_position_docids_sorter = create_sorter(
+        grenad::SortAlgorithm::Unstable,
+        MergeDeladdCboRoaringBitmaps,
+        indexer.chunk_compression_type,
+        indexer.chunk_compression_level,
+        indexer.max_nb_chunks,
+        max_memory,
+        true,
+    );
+
+    let mut del_word_positions: BTreeSet<(u16, Vec<u8>)> = BTreeSet::new();
+    let mut add_word_positions: BTreeSet<(u16, Vec<u8>)> = BTreeSet::new();
+    let mut current_document_id: Option<u32> = None;
+    let mut key_buffer = Vec::new();
+    let mut cursor = docid_word_positions.into_cursor()?;
+    while let Some((key, value)) = cursor.move_on_next()? {
+        let (document_id_bytes, _fid_bytes) = try_split_array_at(key)
+            .ok_or(SerializationError::Decoding { db_name: Some(DOCID_WORD_POSITIONS) })?;
+        let document_id = DocumentId::from_be_bytes(document_id_bytes);
+
+        if current_document_id.map_or(false, |id| document_id != id) {
+            words_position_into_sorter(
+                current_document_id.unwrap(),
+                &mut key_buffer,
+                &del_word_positions,
+                &add_word_positions,
+                &mut word_position_docids_sorter,
+            )?;
+            del_word_positions.clear();
+            add_word_positions.clear();
+        }
+
+        current_document_id = Some(document_id);
+
+        let del_add_reader = KvReaderDelAdd::from_slice(value);
+        // extract all unique words to remove.
+        if let Some(deletion) = del_add_reader.get(DelAdd::Deletion) {
+            for (position, word_bytes) in KvReaderU16::from_slice(deletion).iter() {
+                let position = bucketed_position(position);
+                del_word_positions.insert((position, word_bytes.to_vec()));
+            }
+        }
+
+        // extract all unique additional words.
+        if let Some(addition) = del_add_reader.get(DelAdd::Addition) {
+            for (position, word_bytes) in KvReaderU16::from_slice(addition).iter() {
+                let position = bucketed_position(position);
+                add_word_positions.insert((position, word_bytes.to_vec()));
+            }
+        }
+    }
+
+    if let Some(document_id) = current_document_id {
+        words_position_into_sorter(
+            document_id,
+            &mut key_buffer,
+            &del_word_positions,
+            &add_word_positions,
+            &mut word_position_docids_sorter,
+        )?;
+    }
+
+    // TODO remove noop DelAdd OBKV
+    let word_position_docids_reader = sorter_into_reader(word_position_docids_sorter, indexer)?;
+
+    Ok(word_position_docids_reader)
+}
+
+#[tracing::instrument(level = "trace", skip_all, target = "indexing::extract")]
+fn words_position_into_sorter(
+    document_id: DocumentId,
+    key_buffer: &mut Vec<u8>,
+    del_word_positions: &BTreeSet<(u16, Vec<u8>)>,
+    add_word_positions: &BTreeSet<(u16, Vec<u8>)>,
+    word_position_docids_sorter: &mut grenad::Sorter<MergeDeladdCboRoaringBitmaps>,
+) -> Result<()> {
+    use itertools::merge_join_by;
+    use itertools::EitherOrBoth::{Both, Left, Right};
+
+    let mut buffer = Vec::new();
+    for eob in merge_join_by(del_word_positions.iter(), add_word_positions.iter(), |d, a| d.cmp(a))
+    {
+        buffer.clear();
+        let mut value_writer = KvWriterDelAdd::new(&mut buffer);
+        let (position, word_bytes) = match eob {
+            Left(key) => {
+                value_writer.insert(DelAdd::Deletion, document_id.to_ne_bytes()).unwrap();
+                key
+            }
+            Right(key) => {
+                value_writer.insert(DelAdd::Addition, document_id.to_ne_bytes()).unwrap();
+                key
+            }
+            Both(key, _) => {
+                // both values needs to be kept because it will be used in other extractors.
+                value_writer.insert(DelAdd::Deletion, document_id.to_ne_bytes()).unwrap();
+                value_writer.insert(DelAdd::Addition, document_id.to_ne_bytes()).unwrap();
+                key
+            }
+        };
+
+        key_buffer.clear();
+        key_buffer.extend_from_slice(word_bytes);
+        key_buffer.push(0);
+        key_buffer.extend_from_slice(&position.to_be_bytes());
+        word_position_docids_sorter.insert(&key_buffer, value_writer.into_inner().unwrap())?;
+    }
+
+    Ok(())
+}

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

@@ -0,0 +1,406 @@
+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_geo_points;
+mod extract_vector_points;
+mod extract_word_docids;
+mod extract_word_pair_proximity_docids;
+mod extract_word_position_docids;
+
+use std::fs::File;
+use std::io::BufReader;
+use std::sync::{Arc, OnceLock};
+
+use crossbeam_channel::Sender;
+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, ExtractedFacetValues};
+use self::extract_fid_word_count_docids::extract_fid_word_count_docids;
+use self::extract_geo_points::extract_geo_points;
+use self::extract_vector_points::{
+    extract_embeddings, extract_vector_points, ExtractedVectorPoints,
+};
+use self::extract_word_docids::extract_word_docids;
+use self::extract_word_pair_proximity_docids::extract_word_pair_proximity_docids;
+use self::extract_word_position_docids::extract_word_position_docids;
+use super::helpers::{as_cloneable_grenad, CursorClonableMmap, GrenadParameters};
+use super::{helpers, TypedChunk};
+use crate::index::IndexEmbeddingConfig;
+use crate::update::settings::InnerIndexSettingsDiff;
+use crate::vector::error::PossibleEmbeddingMistakes;
+use crate::{FieldId, Result, ThreadPoolNoAbort, ThreadPoolNoAbortBuilder};
+
+/// Extract data for each databases from obkv documents in parallel.
+/// Send data in grenad file over provided Sender.
+#[allow(clippy::too_many_arguments)]
+#[tracing::instrument(level = "trace", skip_all, target = "indexing::extract")]
+pub(crate) fn data_from_obkv_documents(
+    original_obkv_chunks: impl Iterator<Item = Result<grenad::Reader<BufReader<File>>>> + Send,
+    flattened_obkv_chunks: impl Iterator<Item = Result<grenad::Reader<BufReader<File>>>> + Send,
+    indexer: GrenadParameters,
+    lmdb_writer_sx: Sender<Result<TypedChunk>>,
+    primary_key_id: FieldId,
+    embedders_configs: Arc<Vec<IndexEmbeddingConfig>>,
+    settings_diff: Arc<InnerIndexSettingsDiff>,
+    max_positions_per_attributes: Option<u32>,
+    possible_embedding_mistakes: Arc<PossibleEmbeddingMistakes>,
+) -> Result<()> {
+    let (original_pipeline_result, flattened_pipeline_result): (Result<_>, Result<_>) = rayon::join(
+        || {
+            original_obkv_chunks
+                .par_bridge()
+                .map(|original_documents_chunk| {
+                    send_original_documents_data(
+                        original_documents_chunk,
+                        indexer,
+                        lmdb_writer_sx.clone(),
+                        embedders_configs.clone(),
+                        settings_diff.clone(),
+                        possible_embedding_mistakes.clone(),
+                    )
+                })
+                .collect::<Result<()>>()
+        },
+        || {
+            flattened_obkv_chunks
+                .par_bridge()
+                .map(|flattened_obkv_chunks| {
+                    send_and_extract_flattened_documents_data(
+                        flattened_obkv_chunks,
+                        indexer,
+                        lmdb_writer_sx.clone(),
+                        primary_key_id,
+                        settings_diff.clone(),
+                        max_positions_per_attributes,
+                    )
+                })
+                .map(|result| {
+                    if let Ok((
+                        ref docid_word_positions_chunk,
+                        (ref fid_docid_facet_numbers_chunk, ref fid_docid_facet_strings_chunk),
+                    )) = result
+                    {
+                        run_extraction_task::<_, _, grenad::Reader<BufReader<File>>>(
+                            docid_word_positions_chunk.clone(),
+                            indexer,
+                            settings_diff.clone(),
+                            lmdb_writer_sx.clone(),
+                            extract_fid_word_count_docids,
+                            TypedChunk::FieldIdWordCountDocids,
+                        );
+                        run_extraction_task::<
+                            _,
+                            _,
+                            (
+                                grenad::Reader<BufReader<File>>,
+                                grenad::Reader<BufReader<File>>,
+                                grenad::Reader<BufReader<File>>,
+                            ),
+                        >(
+                            docid_word_positions_chunk.clone(),
+                            indexer,
+                            settings_diff.clone(),
+                            lmdb_writer_sx.clone(),
+                            extract_word_docids,
+                            |(
+                                word_docids_reader,
+                                exact_word_docids_reader,
+                                word_fid_docids_reader,
+                            )| {
+                                TypedChunk::WordDocids {
+                                    word_docids_reader,
+                                    exact_word_docids_reader,
+                                    word_fid_docids_reader,
+                                }
+                            },
+                        );
+
+                        run_extraction_task::<_, _, grenad::Reader<BufReader<File>>>(
+                            docid_word_positions_chunk.clone(),
+                            indexer,
+                            settings_diff.clone(),
+                            lmdb_writer_sx.clone(),
+                            extract_word_position_docids,
+                            TypedChunk::WordPositionDocids,
+                        );
+
+                        run_extraction_task::<
+                            _,
+                            _,
+                            (grenad::Reader<BufReader<File>>, grenad::Reader<BufReader<File>>),
+                        >(
+                            fid_docid_facet_strings_chunk.clone(),
+                            indexer,
+                            settings_diff.clone(),
+                            lmdb_writer_sx.clone(),
+                            extract_facet_string_docids,
+                            TypedChunk::FieldIdFacetStringDocids,
+                        );
+
+                        run_extraction_task::<_, _, grenad::Reader<BufReader<File>>>(
+                            fid_docid_facet_numbers_chunk.clone(),
+                            indexer,
+                            settings_diff.clone(),
+                            lmdb_writer_sx.clone(),
+                            extract_facet_number_docids,
+                            TypedChunk::FieldIdFacetNumberDocids,
+                        );
+
+                        run_extraction_task::<_, _, grenad::Reader<BufReader<File>>>(
+                            docid_word_positions_chunk.clone(),
+                            indexer,
+                            settings_diff.clone(),
+                            lmdb_writer_sx.clone(),
+                            extract_word_pair_proximity_docids,
+                            TypedChunk::WordPairProximityDocids,
+                        );
+                    }
+
+                    Ok(())
+                })
+                .collect::<Result<()>>()
+        },
+    );
+
+    original_pipeline_result.and(flattened_pipeline_result)
+}
+
+/// 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 run_extraction_task<FE, FS, M>(
+    chunk: grenad::Reader<CursorClonableMmap>,
+    indexer: GrenadParameters,
+    settings_diff: Arc<InnerIndexSettingsDiff>,
+    lmdb_writer_sx: Sender<Result<TypedChunk>>,
+    extract_fn: FE,
+    serialize_fn: FS,
+) where
+    FE: Fn(
+            grenad::Reader<CursorClonableMmap>,
+            GrenadParameters,
+            &InnerIndexSettingsDiff,
+        ) -> Result<M>
+        + Sync
+        + Send
+        + 'static,
+    FS: Fn(M) -> TypedChunk + Sync + Send + 'static,
+    M: Send,
+{
+    let current_span = tracing::Span::current();
+
+    rayon::spawn(move || {
+        let child_span = tracing::trace_span!(target: "indexing::extract::details", parent: &current_span, "extract_multiple_chunks");
+        let _entered = child_span.enter();
+
+        match extract_fn(chunk, indexer, &settings_diff) {
+            Ok(chunk) => {
+                let _ = lmdb_writer_sx.send(Ok(serialize_fn(chunk)));
+            }
+            Err(e) => {
+                let _ = lmdb_writer_sx.send(Err(e));
+            }
+        }
+    })
+}
+
+fn request_threads() -> &'static ThreadPoolNoAbort {
+    static REQUEST_THREADS: OnceLock<ThreadPoolNoAbort> = OnceLock::new();
+
+    REQUEST_THREADS.get_or_init(|| {
+        ThreadPoolNoAbortBuilder::new()
+            .num_threads(crate::vector::REQUEST_PARALLELISM)
+            .thread_name(|index| format!("embedding-request-{index}"))
+            .build()
+            .unwrap()
+    })
+}
+
+/// Extract chunked data and send it into lmdb_writer_sx sender:
+/// - documents
+fn send_original_documents_data(
+    original_documents_chunk: Result<grenad::Reader<BufReader<File>>>,
+    indexer: GrenadParameters,
+    lmdb_writer_sx: Sender<Result<TypedChunk>>,
+    embedders_configs: Arc<Vec<IndexEmbeddingConfig>>,
+    settings_diff: Arc<InnerIndexSettingsDiff>,
+    possible_embedding_mistakes: Arc<PossibleEmbeddingMistakes>,
+) -> Result<()> {
+    let original_documents_chunk =
+        original_documents_chunk.and_then(|c| unsafe { as_cloneable_grenad(&c) })?;
+
+    let index_vectors = (settings_diff.reindex_vectors() || !settings_diff.settings_update_only())
+        // no point in indexing vectors without embedders
+        && (!settings_diff.new.embedding_configs.inner_as_ref().is_empty());
+
+    if index_vectors {
+        let settings_diff = settings_diff.clone();
+        let embedders_configs = embedders_configs.clone();
+
+        let original_documents_chunk = original_documents_chunk.clone();
+        let lmdb_writer_sx = lmdb_writer_sx.clone();
+        rayon::spawn(move || {
+            match extract_vector_points(
+                original_documents_chunk.clone(),
+                indexer,
+                &embedders_configs,
+                &settings_diff,
+                &possible_embedding_mistakes,
+            ) {
+                Ok((extracted_vectors, unused_vectors_distribution)) => {
+                    for ExtractedVectorPoints {
+                        manual_vectors,
+                        remove_vectors,
+                        prompts,
+                        embedder_name,
+                        embedder,
+                        add_to_user_provided,
+                        remove_from_user_provided,
+                    } in extracted_vectors
+                    {
+                        let embeddings = match extract_embeddings(
+                            prompts,
+                            indexer,
+                            embedder.clone(),
+                            &embedder_name,
+                            &possible_embedding_mistakes,
+                            &unused_vectors_distribution,
+                            request_threads(),
+                        ) {
+                            Ok(results) => Some(results),
+                            Err(error) => {
+                                let _ = lmdb_writer_sx.send(Err(error));
+                                None
+                            }
+                        };
+                        if !(remove_vectors.is_empty()
+                            && manual_vectors.is_empty()
+                            && embeddings.as_ref().map_or(true, |e| e.is_empty()))
+                        {
+                            let _ = lmdb_writer_sx.send(Ok(TypedChunk::VectorPoints {
+                                remove_vectors,
+                                embeddings,
+                                expected_dimension: embedder.dimensions(),
+                                manual_vectors,
+                                embedder_name,
+                                add_to_user_provided,
+                                remove_from_user_provided,
+                            }));
+                        }
+                    }
+                }
+                Err(error) => {
+                    let _ = lmdb_writer_sx.send(Err(error));
+                }
+            }
+        });
+    }
+
+    // TODO: create a custom internal error
+    let _ = lmdb_writer_sx.send(Ok(TypedChunk::Documents(original_documents_chunk)));
+    Ok(())
+}
+
+/// Extract chunked data and send it into lmdb_writer_sx sender:
+/// - documents_ids
+/// - docid_word_positions
+/// - docid_fid_facet_numbers
+/// - docid_fid_facet_strings
+/// - docid_fid_facet_exists
+#[allow(clippy::too_many_arguments)]
+#[allow(clippy::type_complexity)]
+fn send_and_extract_flattened_documents_data(
+    flattened_documents_chunk: Result<grenad::Reader<BufReader<File>>>,
+    indexer: GrenadParameters,
+    lmdb_writer_sx: Sender<Result<TypedChunk>>,
+    primary_key_id: FieldId,
+    settings_diff: Arc<InnerIndexSettingsDiff>,
+    max_positions_per_attributes: Option<u32>,
+) -> Result<(
+    grenad::Reader<CursorClonableMmap>,
+    (grenad::Reader<CursorClonableMmap>, grenad::Reader<CursorClonableMmap>),
+)> {
+    let flattened_documents_chunk =
+        flattened_documents_chunk.and_then(|c| unsafe { as_cloneable_grenad(&c) })?;
+
+    if settings_diff.run_geo_indexing() {
+        let documents_chunk_cloned = flattened_documents_chunk.clone();
+        let lmdb_writer_sx_cloned = lmdb_writer_sx.clone();
+        let settings_diff = settings_diff.clone();
+        rayon::spawn(move || {
+            let result =
+                extract_geo_points(documents_chunk_cloned, indexer, primary_key_id, &settings_diff);
+            let _ = match result {
+                Ok(geo_points) => lmdb_writer_sx_cloned.send(Ok(TypedChunk::GeoPoints(geo_points))),
+                Err(error) => lmdb_writer_sx_cloned.send(Err(error)),
+            };
+        });
+    }
+
+    let (docid_word_positions_chunk, fid_docid_facet_values_chunks): (Result<_>, Result<_>) =
+        rayon::join(
+            || {
+                let docid_word_positions_chunk = extract_docid_word_positions(
+                    flattened_documents_chunk.clone(),
+                    indexer,
+                    &settings_diff,
+                    max_positions_per_attributes,
+                )?;
+
+                // send docid_word_positions_chunk to DB writer
+                let docid_word_positions_chunk =
+                    unsafe { as_cloneable_grenad(&docid_word_positions_chunk)? };
+
+                Ok(docid_word_positions_chunk)
+            },
+            || {
+                let ExtractedFacetValues {
+                    fid_docid_facet_numbers_chunk,
+                    fid_docid_facet_strings_chunk,
+                    fid_facet_is_null_docids_chunk,
+                    fid_facet_is_empty_docids_chunk,
+                    fid_facet_exists_docids_chunk,
+                } = extract_fid_docid_facet_values(
+                    flattened_documents_chunk.clone(),
+                    indexer,
+                    &settings_diff,
+                )?;
+
+                // send fid_docid_facet_numbers_chunk to DB writer
+                let fid_docid_facet_numbers_chunk =
+                    unsafe { as_cloneable_grenad(&fid_docid_facet_numbers_chunk)? };
+
+                let _ = lmdb_writer_sx.send(Ok(TypedChunk::FieldIdDocidFacetNumbers(
+                    fid_docid_facet_numbers_chunk.clone(),
+                )));
+
+                // send fid_docid_facet_strings_chunk to DB writer
+                let fid_docid_facet_strings_chunk =
+                    unsafe { as_cloneable_grenad(&fid_docid_facet_strings_chunk)? };
+
+                let _ = lmdb_writer_sx.send(Ok(TypedChunk::FieldIdDocidFacetStrings(
+                    fid_docid_facet_strings_chunk.clone(),
+                )));
+
+                let _ = lmdb_writer_sx
+                    .send(Ok(TypedChunk::FieldIdFacetIsNullDocids(fid_facet_is_null_docids_chunk)));
+
+                let _ = lmdb_writer_sx.send(Ok(TypedChunk::FieldIdFacetIsEmptyDocids(
+                    fid_facet_is_empty_docids_chunk,
+                )));
+
+                let _ = lmdb_writer_sx
+                    .send(Ok(TypedChunk::FieldIdFacetExistsDocids(fid_facet_exists_docids_chunk)));
+
+                Ok((fid_docid_facet_numbers_chunk, fid_docid_facet_strings_chunk))
+            },
+        );
+
+    Ok((docid_word_positions_chunk?, fid_docid_facet_values_chunks?))
+}