Merge pull request #39 from meilisearch/speedup-documents-ids-merging

Speedup documents ids merging

http-ui/src/main.rs

@@ -605,14 +605,14 @@ async fn main() -> anyhow::Result<()> {
             let index = index_cloned.clone();
             let rtxn = index.read_txn().unwrap();
 
-            let users_ids_documents_ids = index.users_ids_documents_ids(&rtxn).unwrap();
+            let external_documents_ids = index.external_documents_ids(&rtxn).unwrap();
             let fields_ids_map = index.fields_ids_map(&rtxn).unwrap();
             let displayed_fields = match index.displayed_fields(&rtxn).unwrap() {
                 Some(fields) => Cow::Borrowed(fields),
                 None => Cow::Owned(fields_ids_map.iter().map(|(id, _)| id).collect()),
             };
 
-            match users_ids_documents_ids.get(&id) {
+            match external_documents_ids.get(&id) {
                 Some(document_id) => {
                     let document_id = document_id as u32;
                     let (_, obkv) = index.documents(&rtxn, Some(document_id)).unwrap().pop().unwrap();

src/external_documents_ids.rs

@@ -0,0 +1,156 @@
+use std::borrow::Cow;
+use std::convert::TryInto;
+use fst::{Streamer, IntoStreamer};
+
+pub struct ExternalDocumentsIds<'a> {
+    pub(crate) hard: fst::Map<Cow<'a, [u8]>>,
+    pub(crate) soft: fst::Map<Cow<'a, [u8]>>,
+}
+
+impl<'a> ExternalDocumentsIds<'a> {
+    pub fn new(hard: fst::Map<Cow<'a, [u8]>>, soft: fst::Map<Cow<'a, [u8]>>) -> ExternalDocumentsIds<'a> {
+        ExternalDocumentsIds { hard, soft }
+    }
+
+    pub fn into_static(self) -> ExternalDocumentsIds<'static> {
+        ExternalDocumentsIds {
+            hard: self.hard.map_data(|c| Cow::Owned(c.into_owned())).unwrap(),
+            soft: self.soft.map_data(|c| Cow::Owned(c.into_owned())).unwrap(),
+        }
+    }
+
+    pub fn get<A: AsRef<[u8]>>(&self, external_id: A) -> Option<u32> {
+        let external_id = external_id.as_ref();
+        match self.soft.get(external_id).or_else(|| self.hard.get(external_id)) {
+            // u64 MAX means deleted in the soft fst map
+            Some(id) if id != u64::MAX => Some(id.try_into().unwrap()),
+            _otherwise => None
+        }
+    }
+
+    pub fn delete_ids<A: AsRef<[u8]>>(&mut self, other: fst::Set<A>) -> fst::Result<()> {
+        let other = fst::Map::from(other.into_fst());
+        let union_op = self.soft.op().add(&other).r#union();
+
+        let mut iter = union_op.into_stream();
+        let mut new_soft_builder = fst::MapBuilder::memory();
+        while let Some((external_id, docids)) = iter.next() {
+            if docids.iter().any(|v| v.index == 1) {
+                // If the `other` set returns a value here it means
+                // that it must be marked as deleted.
+                new_soft_builder.insert(external_id, u64::MAX)?;
+            } else {
+                new_soft_builder.insert(external_id, docids[0].value)?;
+            }
+        }
+
+        drop(iter);
+
+        // We save this new map as the new soft map.
+        self.soft = new_soft_builder.into_map().map_data(Cow::Owned)?;
+        self.merge_soft_into_hard()
+    }
+
+    pub fn insert_ids<A: AsRef<[u8]>>(&mut self, other: &fst::Map<A>) -> fst::Result<()> {
+        let union_op = self.soft.op().add(other).r#union();
+
+        let mut new_soft_builder = fst::MapBuilder::memory();
+        let mut iter = union_op.into_stream();
+        while let Some((external_id, docids)) = iter.next() {
+            let id = docids.last().unwrap().value;
+            new_soft_builder.insert(external_id, id)?;
+        }
+
+        drop(iter);
+
+        // We save the new map as the new soft map.
+        self.soft = new_soft_builder.into_map().map_data(Cow::Owned)?;
+        self.merge_soft_into_hard()
+    }
+
+    fn merge_soft_into_hard(&mut self) -> fst::Result<()> {
+        if self.soft.len() >= self.hard.len() / 2 {
+            let union_op = self.hard.op().add(&self.soft).r#union();
+
+            let mut iter = union_op.into_stream();
+            let mut new_hard_builder = fst::MapBuilder::memory();
+            while let Some((external_id, docids)) = iter.next() {
+                if docids.len() == 2 {
+                    if docids[1].value != u64::MAX {
+                        new_hard_builder.insert(external_id, docids[1].value)?;
+                    }
+                } else {
+                    new_hard_builder.insert(external_id, docids[0].value)?;
+                }
+            }
+
+            drop(iter);
+
+            self.hard = new_hard_builder.into_map().map_data(Cow::Owned)?;
+            self.soft = fst::Map::default().map_data(Cow::Owned)?;
+        }
+
+        Ok(())
+    }
+}
+
+impl Default for ExternalDocumentsIds<'static> {
+    fn default() -> Self {
+        ExternalDocumentsIds {
+            hard: fst::Map::default().map_data(Cow::Owned).unwrap(),
+            soft: fst::Map::default().map_data(Cow::Owned).unwrap(),
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn simple_insert_delete_ids() {
+        let mut external_documents_ids = ExternalDocumentsIds::default();
+
+        let new_ids = fst::Map::from_iter(vec![("a", 1), ("b", 2), ("c", 3), ("d", 4)]).unwrap();
+        external_documents_ids.insert_ids(&new_ids).unwrap();
+
+        assert_eq!(external_documents_ids.get("a"), Some(1));
+        assert_eq!(external_documents_ids.get("b"), Some(2));
+        assert_eq!(external_documents_ids.get("c"), Some(3));
+        assert_eq!(external_documents_ids.get("d"), Some(4));
+
+        let new_ids = fst::Map::from_iter(vec![("e", 5), ("f", 6), ("g", 7)]).unwrap();
+        external_documents_ids.insert_ids(&new_ids).unwrap();
+
+        assert_eq!(external_documents_ids.get("a"), Some(1));
+        assert_eq!(external_documents_ids.get("b"), Some(2));
+        assert_eq!(external_documents_ids.get("c"), Some(3));
+        assert_eq!(external_documents_ids.get("d"), Some(4));
+        assert_eq!(external_documents_ids.get("e"), Some(5));
+        assert_eq!(external_documents_ids.get("f"), Some(6));
+        assert_eq!(external_documents_ids.get("g"), Some(7));
+
+        let del_ids = fst::Set::from_iter(vec!["a", "c", "f"]).unwrap();
+        external_documents_ids.delete_ids(del_ids).unwrap();
+
+        assert_eq!(external_documents_ids.get("a"), None);
+        assert_eq!(external_documents_ids.get("b"), Some(2));
+        assert_eq!(external_documents_ids.get("c"), None);
+        assert_eq!(external_documents_ids.get("d"), Some(4));
+        assert_eq!(external_documents_ids.get("e"), Some(5));
+        assert_eq!(external_documents_ids.get("f"), None);
+        assert_eq!(external_documents_ids.get("g"), Some(7));
+
+        let new_ids = fst::Map::from_iter(vec![("a", 5), ("b", 6), ("h", 8)]).unwrap();
+        external_documents_ids.insert_ids(&new_ids).unwrap();
+
+        assert_eq!(external_documents_ids.get("a"), Some(5));
+        assert_eq!(external_documents_ids.get("b"), Some(6));
+        assert_eq!(external_documents_ids.get("c"), None);
+        assert_eq!(external_documents_ids.get("d"), Some(4));
+        assert_eq!(external_documents_ids.get("e"), Some(5));
+        assert_eq!(external_documents_ids.get("f"), None);
+        assert_eq!(external_documents_ids.get("g"), Some(7));
+        assert_eq!(external_documents_ids.get("h"), Some(8));
+    }
+}

src/index.rs

@@ -10,7 +10,7 @@ use roaring::RoaringBitmap;
 use crate::facet::FacetType;
 use crate::fields_ids_map::FieldsIdsMap;
 use crate::Search;
-use crate::{BEU32, DocumentId};
+use crate::{BEU32, DocumentId, ExternalDocumentsIds};
 use crate::{
     RoaringBitmapCodec, BEU32StrCodec, StrStrU8Codec, ObkvCodec,
     BoRoaringBitmapCodec, CboRoaringBitmapCodec,
@@ -22,7 +22,8 @@ pub const FACETED_FIELDS_KEY: &str = "faceted-fields";
 pub const FIELDS_IDS_MAP_KEY: &str = "fields-ids-map";
 pub const PRIMARY_KEY_KEY: &str = "primary-key";
 pub const SEARCHABLE_FIELDS_KEY: &str = "searchable-fields";
-pub const USERS_IDS_DOCUMENTS_IDS_KEY: &str = "users-ids-documents-ids";
+pub const HARD_EXTERNAL_DOCUMENTS_IDS_KEY: &str = "hard-external-documents-ids";
+pub const SOFT_EXTERNAL_DOCUMENTS_IDS_KEY: &str = "soft-external-documents-ids";
 pub const WORDS_FST_KEY: &str = "words-fst";
 
 #[derive(Clone)]
@@ -119,21 +120,37 @@ impl Index {
         self.main.get::<_, Str, OwnedType<u8>>(rtxn, PRIMARY_KEY_KEY)
     }
 
-    /* users ids documents ids */
+    /* external documents ids */
 
-    /// Writes the users ids documents ids, a user id is a byte slice (i.e. `[u8]`)
+    /// Writes the external documents ids and internal ids (i.e. `u32`).
-    /// and refers to an internal id (i.e. `u32`).
+    pub fn put_external_documents_ids<'a>(
-    pub fn put_users_ids_documents_ids<A: AsRef<[u8]>>(&self, wtxn: &mut RwTxn, fst: &fst::Map<A>) -> heed::Result<()> {
+        &self,
-        self.main.put::<_, Str, ByteSlice>(wtxn, USERS_IDS_DOCUMENTS_IDS_KEY, fst.as_fst().as_bytes())
+        wtxn: &mut RwTxn,
+        external_documents_ids: &ExternalDocumentsIds<'a>,
+    ) -> heed::Result<()>
+    {
+        let ExternalDocumentsIds { hard, soft } = external_documents_ids;
+        let hard = hard.as_fst().as_bytes();
+        let soft = soft.as_fst().as_bytes();
+        self.main.put::<_, Str, ByteSlice>(wtxn, HARD_EXTERNAL_DOCUMENTS_IDS_KEY, hard)?;
+        self.main.put::<_, Str, ByteSlice>(wtxn, SOFT_EXTERNAL_DOCUMENTS_IDS_KEY, soft)?;
+        Ok(())
     }
 
-    /// Returns the user ids documents ids map which associate the user ids (i.e. `[u8]`)
+    /// Returns the external documents ids map which associate the external ids
     /// with the internal ids (i.e. `u32`).
-    pub fn users_ids_documents_ids<'t>(&self, rtxn: &'t RoTxn) -> anyhow::Result<fst::Map<Cow<'t, [u8]>>> {
+    pub fn external_documents_ids<'t>(&self, rtxn: &'t RoTxn) -> anyhow::Result<ExternalDocumentsIds<'t>> {
-        match self.main.get::<_, Str, ByteSlice>(rtxn, USERS_IDS_DOCUMENTS_IDS_KEY)? {
+        let hard = self.main.get::<_, Str, ByteSlice>(rtxn, HARD_EXTERNAL_DOCUMENTS_IDS_KEY)?;
-            Some(bytes) => Ok(fst::Map::new(bytes)?.map_data(Cow::Borrowed)?),
+        let soft = self.main.get::<_, Str, ByteSlice>(rtxn, SOFT_EXTERNAL_DOCUMENTS_IDS_KEY)?;
-            None => Ok(fst::Map::default().map_data(Cow::Owned)?),
+        let hard = match hard {
-        }
+            Some(hard) => fst::Map::new(hard)?.map_data(Cow::Borrowed)?,
+            None => fst::Map::default().map_data(Cow::Owned)?,
+        };
+        let soft = match soft {
+            Some(soft) => fst::Map::new(soft)?.map_data(Cow::Borrowed)?,
+            None => fst::Map::default().map_data(Cow::Owned)?,
+        };
+        Ok(ExternalDocumentsIds::new(hard, soft))
     }
 
     /* fields ids map */

src/lib.rs

@@ -1,4 +1,5 @@
 mod criterion;
+mod external_documents_ids;
 mod fields_ids_map;
 mod index;
 mod mdfs;
@@ -20,6 +21,7 @@ use fxhash::{FxHasher32, FxHasher64};
 use serde_json::{Map, Value};
 
 pub use self::criterion::{Criterion, default_criteria};
+pub use self::external_documents_ids::ExternalDocumentsIds;
 pub use self::fields_ids_map::FieldsIdsMap;
 pub use self::index::Index;
 pub use self::search::{Search, SearchResult};

src/subcommand/infos.rs

@@ -13,6 +13,7 @@ const WORD_DOCIDS_DB_NAME: &str = "word-docids";
 const DOCID_WORD_POSITIONS_DB_NAME: &str = "docid-word-positions";
 const WORD_PAIR_PROXIMITY_DOCIDS_DB_NAME: &str = "word-pair-proximity-docids";
 const DOCUMENTS_DB_NAME: &str = "documents";
+const USERS_IDS_DOCUMENTS_IDS: &[u8] = b"users-ids-documents-ids";
 
 const ALL_DATABASE_NAMES: &[&str] = &[
     MAIN_DB_NAME,
@@ -137,6 +138,10 @@ enum Command {
         #[structopt(short, long, default_value = "words.fst")]
         output: PathBuf,
     },
+
+    /// A command that patches the old external ids
+    /// into the new external ids format.
+    PatchToNewExternalIds,
 }
 
 pub fn run(opt: Opt) -> anyhow::Result<()> {
@@ -171,9 +176,32 @@ pub fn run(opt: Opt) -> anyhow::Result<()> {
             word_pair_proximities_docids(&index, &rtxn, !full_display, word1, word2)
         },
         ExportWordsFst { output } => export_words_fst(&index, &rtxn, output),
+        PatchToNewExternalIds => {
+            drop(rtxn);
+            let mut wtxn = index.write_txn()?;
+            let result = patch_to_new_external_ids(&index, &mut wtxn);
+            wtxn.commit()?;
+            result
+        }
     }
 }
 
+fn patch_to_new_external_ids(index: &Index, wtxn: &mut heed::RwTxn) -> anyhow::Result<()> {
+    use heed::types::ByteSlice;
+
+    if let Some(documents_ids) = index.main.get::<_, ByteSlice, ByteSlice>(wtxn, USERS_IDS_DOCUMENTS_IDS)? {
+        let documents_ids = documents_ids.to_owned();
+        index.main.put::<_, ByteSlice, ByteSlice>(
+            wtxn,
+            crate::index::HARD_EXTERNAL_DOCUMENTS_IDS_KEY.as_bytes(),
+            &documents_ids,
+        )?;
+        index.main.delete::<_, ByteSlice>(wtxn, USERS_IDS_DOCUMENTS_IDS)?;
+    }
+
+    Ok(())
+}
+
 fn most_common_words(index: &Index, rtxn: &heed::RoTxn, limit: usize) -> anyhow::Result<()> {
     use std::collections::BinaryHeap;
     use std::cmp::Reverse;

src/update/clear_documents.rs

@@ -1,5 +1,5 @@
 use roaring::RoaringBitmap;
-use crate::Index;
+use crate::{ExternalDocumentsIds, Index};
 
 pub struct ClearDocuments<'t, 'u, 'i> {
     wtxn: &'t mut heed::RwTxn<'i, 'u>,
@@ -27,7 +27,7 @@ impl<'t, 'u, 'i> ClearDocuments<'t, 'u, 'i> {
 
         // We clean some of the main engine datastructures.
         self.index.put_words_fst(self.wtxn, &fst::Set::default())?;
-        self.index.put_users_ids_documents_ids(self.wtxn, &fst::Map::default())?;
+        self.index.put_external_documents_ids(self.wtxn, &ExternalDocumentsIds::default())?;
         self.index.put_documents_ids(self.wtxn, &RoaringBitmap::default())?;
 
         // Clear the other databases.

src/update/delete_documents.rs

@@ -1,16 +1,13 @@
-use std::borrow::Cow;
+use fst::IntoStreamer;
-use std::convert::TryFrom;
-
-use fst::{IntoStreamer, Streamer};
 use roaring::RoaringBitmap;
 
-use crate::{Index, BEU32, SmallString32};
+use crate::{Index, BEU32, SmallString32, ExternalDocumentsIds};
 use super::ClearDocuments;
 
 pub struct DeleteDocuments<'t, 'u, 'i> {
     wtxn: &'t mut heed::RwTxn<'i, 'u>,
     index: &'i Index,
-    users_ids_documents_ids: fst::Map<Vec<u8>>,
+    external_documents_ids: ExternalDocumentsIds<'static>,
     documents_ids: RoaringBitmap,
 }
 
@@ -20,14 +17,14 @@ impl<'t, 'u, 'i> DeleteDocuments<'t, 'u, 'i> {
         index: &'i Index,
     ) -> anyhow::Result<DeleteDocuments<'t, 'u, 'i>>
     {
-        let users_ids_documents_ids = index
+        let external_documents_ids = index
-            .users_ids_documents_ids(wtxn)?
+            .external_documents_ids(wtxn)?
-            .map_data(Cow::into_owned)?;
+            .into_static();
 
         Ok(DeleteDocuments {
             wtxn,
             index,
-            users_ids_documents_ids,
+            external_documents_ids,
             documents_ids: RoaringBitmap::new(),
         })
     }
@@ -40,8 +37,8 @@ impl<'t, 'u, 'i> DeleteDocuments<'t, 'u, 'i> {
         self.documents_ids.union_with(docids);
     }
 
-    pub fn delete_user_id(&mut self, user_id: &str) -> Option<u32> {
+    pub fn delete_external_id(&mut self, external_id: &str) -> Option<u32> {
-        let docid = self.users_ids_documents_ids.get(user_id).map(|id| u32::try_from(id).unwrap())?;
+        let docid = self.external_documents_ids.get(external_id)?;
         self.delete_document(docid);
         Some(docid)
     }
@@ -80,9 +77,9 @@ impl<'t, 'u, 'i> DeleteDocuments<'t, 'u, 'i> {
             documents,
         } = self.index;
 
-        // Retrieve the words and the users ids contained in the documents.
+        // Retrieve the words and the external documents ids contained in the documents.
         let mut words = Vec::new();
-        let mut users_ids = Vec::new();
+        let mut external_ids = Vec::new();
         for docid in &self.documents_ids {
             // We create an iterator to be able to get the content and delete the document
             // content itself. It's faster to acquire a cursor to get and delete,
@@ -91,8 +88,8 @@ impl<'t, 'u, 'i> DeleteDocuments<'t, 'u, 'i> {
             let mut iter = documents.range_mut(self.wtxn, &(key..=key))?;
             if let Some((_key, obkv)) = iter.next().transpose()? {
                 if let Some(content) = obkv.get(id_field) {
-                    let user_id: SmallString32 = serde_json::from_slice(content).unwrap();
+                    let external_id: SmallString32 = serde_json::from_slice(content).unwrap();
-                    users_ids.push(user_id);
+                    external_ids.push(external_id);
                 }
                 iter.del_current()?;
             }
@@ -109,30 +106,18 @@ impl<'t, 'u, 'i> DeleteDocuments<'t, 'u, 'i> {
             }
         }
 
-        // We create the FST map of the users ids that we must delete.
+        // We create the FST map of the external ids that we must delete.
-        users_ids.sort_unstable();
+        external_ids.sort_unstable();
-        let users_ids_to_delete = fst::Set::from_iter(users_ids.iter().map(AsRef::as_ref))?;
+        let external_ids_to_delete = fst::Set::from_iter(external_ids.iter().map(AsRef::as_ref))?;
-        let users_ids_to_delete = fst::Map::from(users_ids_to_delete.into_fst());
 
-        let new_users_ids_documents_ids = {
+        // We acquire the current external documents ids map...
-            // We acquire the current users ids documents ids map and create
+        let mut new_external_documents_ids = self.index.external_documents_ids(self.wtxn)?;
-            // a difference operation between the current and to-delete users ids.
+        // ...and remove the to-delete external ids.
-            let users_ids_documents_ids = self.index.users_ids_documents_ids(self.wtxn)?;
+        new_external_documents_ids.delete_ids(external_ids_to_delete)?;
-            let difference = users_ids_documents_ids.op().add(&users_ids_to_delete).difference();
 
-            // We stream the new users ids that does no more contains the to-delete users ids.
+        // We write the new external ids into the main database.
-            let mut iter = difference.into_stream();
+        let new_external_documents_ids = new_external_documents_ids.into_static();
-            let mut new_users_ids_documents_ids_builder = fst::MapBuilder::memory();
+        self.index.put_external_documents_ids(self.wtxn, &new_external_documents_ids)?;
-            while let Some((userid, docids)) = iter.next() {
-                new_users_ids_documents_ids_builder.insert(userid, docids[0].value)?;
-            }
-
-            // We create an FST map from the above builder.
-            new_users_ids_documents_ids_builder.into_map()
-        };
-
-        // We write the new users ids into the main database.
-        self.index.put_users_ids_documents_ids(self.wtxn, &new_users_ids_documents_ids)?;
 
         // Maybe we can improve the get performance of the words
         // if we sort the words first, keeping the LMDB pages in cache.
@@ -169,7 +154,7 @@ impl<'t, 'u, 'i> DeleteDocuments<'t, 'u, 'i> {
             let words_fst = self.index.words_fst(self.wtxn)?;
             let difference = words_fst.op().add(&words_to_delete).difference();
 
-            // We stream the new users ids that does no more contains the to-delete users ids.
+            // We stream the new external ids that does no more contains the to-delete external ids.
             let mut new_words_fst_builder = fst::SetBuilder::memory();
             new_words_fst_builder.extend_stream(difference.into_stream())?;
 

src/update/index_documents/mod.rs

@@ -287,7 +287,7 @@ impl<'t, 'u, 'i, 'a> IndexDocuments<'t, 'u, 'i, 'a> {
         let TransformOutput {
             primary_key,
             fields_ids_map,
-            users_ids_documents_ids,
+            external_documents_ids,
             new_documents_ids,
             replaced_documents_ids,
             documents_count,
@@ -472,8 +472,8 @@ impl<'t, 'u, 'i, 'a> IndexDocuments<'t, 'u, 'i, 'a> {
         // We write the primary key field id into the main database
         self.index.put_primary_key(self.wtxn, primary_key)?;
 
-        // We write the users_ids_documents_ids into the main database.
+        // We write the external documents ids into the main database.
-        self.index.put_users_ids_documents_ids(self.wtxn, &users_ids_documents_ids)?;
+        self.index.put_external_documents_ids(self.wtxn, &external_documents_ids)?;
 
         // We merge the new documents ids with the existing ones.
         documents_ids.union_with(&new_documents_ids);

src/update/index_documents/transform.rs

@@ -3,14 +3,15 @@ use std::convert::TryFrom;
 use std::fs::File;
 use std::io::{Read, Seek, SeekFrom};
 use std::iter::Peekable;
+use std::time::Instant;
 
 use anyhow::{anyhow, Context};
-use fst::{IntoStreamer, Streamer};
 use grenad::CompressionType;
+use log::info;
 use roaring::RoaringBitmap;
 use serde_json::{Map, Value};
 
-use crate::{BEU32, MergeFn, Index, FieldsIdsMap};
+use crate::{BEU32, MergeFn, Index, FieldsIdsMap, ExternalDocumentsIds};
 use crate::update::{AvailableDocumentsIds, UpdateIndexingStep};
 use super::merge_function::merge_two_obkvs;
 use super::{create_writer, create_sorter, IndexDocumentsMethod};
@@ -18,14 +19,14 @@ use super::{create_writer, create_sorter, IndexDocumentsMethod};
 pub struct TransformOutput {
     pub primary_key: u8,
     pub fields_ids_map: FieldsIdsMap,
-    pub users_ids_documents_ids: fst::Map<Vec<u8>>,
+    pub external_documents_ids: ExternalDocumentsIds<'static>,
     pub new_documents_ids: RoaringBitmap,
     pub replaced_documents_ids: RoaringBitmap,
     pub documents_count: usize,
     pub documents_file: File,
 }
 
-/// Extract the users ids, deduplicate and compute the new internal documents ids
+/// Extract the external ids, deduplicate and compute the new internal documents ids
 /// and fields ids, writing all the documents under their internal ids into a final file.
 ///
 /// Outputs the new `FieldsIdsMap`, the new `UsersIdsDocumentsIds` map, the new documents ids,
@@ -72,7 +73,7 @@ impl Transform<'_, '_> {
         F: Fn(UpdateIndexingStep) + Sync,
     {
         let mut fields_ids_map = self.index.fields_ids_map(self.rtxn)?;
-        let users_ids_documents_ids = self.index.users_ids_documents_ids(self.rtxn).unwrap();
+        let external_documents_ids = self.index.external_documents_ids(self.rtxn).unwrap();
         let primary_key = self.index.primary_key(self.rtxn)?;
 
         // Deserialize the whole batch of documents in memory.
@@ -114,7 +115,7 @@ impl Transform<'_, '_> {
             return Ok(TransformOutput {
                 primary_key,
                 fields_ids_map,
-                users_ids_documents_ids: fst::Map::default(),
+                external_documents_ids: ExternalDocumentsIds::default(),
                 new_documents_ids: RoaringBitmap::new(),
                 replaced_documents_ids: RoaringBitmap::new(),
                 documents_count: 0,
@@ -170,7 +171,7 @@ impl Transform<'_, '_> {
 
             // We retrieve the user id from the document based on the primary key name,
             // if the document id isn't present we generate a uuid.
-            let user_id = match document.get(&primary_key_name) {
+            let external_id = match document.get(&primary_key_name) {
                 Some(value) => match value {
                     Value::String(string) => Cow::Borrowed(string.as_str()),
                     Value::Number(number) => Cow::Owned(number.to_string()),
@@ -198,19 +199,19 @@ impl Transform<'_, '_> {
                 }
                 else if field_id == primary_key {
                     // We validate the document id [a-zA-Z0-9\-_].
-                    let user_id = match validate_document_id(&user_id) {
+                    let external_id = match validate_document_id(&external_id) {
                         Some(valid) => valid,
-                        None => return Err(anyhow!("invalid document id: {:?}", user_id)),
+                        None => return Err(anyhow!("invalid document id: {:?}", external_id)),
                     };
 
                     // We serialize the document id.
-                    serde_json::to_writer(&mut json_buffer, &user_id)?;
+                    serde_json::to_writer(&mut json_buffer, &external_id)?;
                     writer.insert(field_id, &json_buffer)?;
                 }
             }
 
             // We use the extracted/generated user id as the key for this document.
-            sorter.insert(user_id.as_bytes(), &obkv_buffer)?;
+            sorter.insert(external_id.as_bytes(), &obkv_buffer)?;
             documents_count += 1;
         }
 
@@ -225,7 +226,7 @@ impl Transform<'_, '_> {
             primary_key,
             fields_ids_map,
             documents_count,
-            users_ids_documents_ids,
+            external_documents_ids,
             progress_callback,
         )
     }
@@ -236,7 +237,7 @@ impl Transform<'_, '_> {
         F: Fn(UpdateIndexingStep) + Sync,
     {
         let mut fields_ids_map = self.index.fields_ids_map(self.rtxn)?;
-        let users_ids_documents_ids = self.index.users_ids_documents_ids(self.rtxn).unwrap();
+        let external_documents_ids = self.index.external_documents_ids(self.rtxn).unwrap();
 
         let mut csv = csv::Reader::from_reader(reader);
         let headers = csv.headers()?;
@@ -250,7 +251,7 @@ impl Transform<'_, '_> {
         }
 
         // Extract the position of the primary key in the current headers, None if not found.
-        let user_id_pos = match primary_key {
+        let external_id_pos = match primary_key {
             Some(primary_key) => {
                 // Te primary key have is known so we must find the position in the CSV headers.
                 let name = fields_ids_map.name(primary_key).expect("found the primary key name");
@@ -261,7 +262,7 @@ impl Transform<'_, '_> {
 
         // Returns the field id in the fileds ids map, create an "id" field
         // in case it is not in the current headers.
-        let primary_key_field_id = match user_id_pos {
+        let primary_key_field_id = match external_id_pos {
             Some(pos) => fields_ids_map.id(&headers[pos]).expect("found the primary key"),
             None => {
                 if !self.autogenerate_docids {
@@ -292,7 +293,7 @@ impl Transform<'_, '_> {
         );
 
         // We write into the sorter to merge and deduplicate the documents
-        // based on the users ids.
+        // based on the external ids.
         let mut json_buffer = Vec::new();
         let mut obkv_buffer = Vec::new();
         let mut uuid_buffer = [0; uuid::adapter::Hyphenated::LENGTH];
@@ -310,13 +311,13 @@ impl Transform<'_, '_> {
             }
 
             // We extract the user id if we know where it is or generate an UUID V4 otherwise.
-            let user_id = match user_id_pos {
+            let external_id = match external_id_pos {
                 Some(pos) => {
-                    let user_id = &record[pos];
+                    let external_id = &record[pos];
                     // We validate the document id [a-zA-Z0-9\-_].
-                    match validate_document_id(&user_id) {
+                    match validate_document_id(&external_id) {
                         Some(valid) => valid,
-                        None => return Err(anyhow!("invalid document id: {:?}", user_id)),
+                        None => return Err(anyhow!("invalid document id: {:?}", external_id)),
                     }
                 },
                 None => uuid::Uuid::new_v4().to_hyphenated().encode_lower(&mut uuid_buffer),
@@ -326,7 +327,7 @@ impl Transform<'_, '_> {
             // we return the generated document id instead of the record field.
             let iter = fields_ids.iter()
                 .map(|(fi, i)| {
-                    let field = if *fi == primary_key_field_id { user_id } else { &record[*i] };
+                    let field = if *fi == primary_key_field_id { external_id } else { &record[*i] };
                     (fi, field)
                 });
 
@@ -339,7 +340,7 @@ impl Transform<'_, '_> {
             }
 
             // We use the extracted/generated user id as the key for this document.
-            sorter.insert(user_id, &obkv_buffer)?;
+            sorter.insert(external_id, &obkv_buffer)?;
             documents_count += 1;
         }
 
@@ -354,7 +355,7 @@ impl Transform<'_, '_> {
             primary_key_field_id,
             fields_ids_map,
             documents_count,
-            users_ids_documents_ids,
+            external_documents_ids,
             progress_callback,
         )
     }
@@ -368,7 +369,7 @@ impl Transform<'_, '_> {
         primary_key: u8,
         fields_ids_map: FieldsIdsMap,
         approximate_number_of_documents: usize,
-        users_ids_documents_ids: fst::Map<Cow<'_, [u8]>>,
+        mut external_documents_ids: ExternalDocumentsIds<'_>,
         progress_callback: F,
     ) -> anyhow::Result<TransformOutput>
     where
@@ -386,7 +387,7 @@ impl Transform<'_, '_> {
             self.max_nb_chunks,
             self.max_memory,
         );
-        let mut new_users_ids_documents_ids_builder = fst::MapBuilder::memory();
+        let mut new_external_documents_ids_builder = fst::MapBuilder::memory();
         let mut replaced_documents_ids = RoaringBitmap::new();
         let mut new_documents_ids = RoaringBitmap::new();
         let mut obkv_buffer = Vec::new();
@@ -394,7 +395,7 @@ impl Transform<'_, '_> {
         // While we write into final file we get or generate the internal documents ids.
         let mut documents_count = 0;
         let mut iter = sorter.into_iter()?;
-        while let Some((user_id, update_obkv)) = iter.next()? {
+        while let Some((external_id, update_obkv)) = iter.next()? {
 
             if self.log_every_n.map_or(false, |len| documents_count % len == 0) {
                 progress_callback(UpdateIndexingStep::ComputeIdsAndMergeDocuments {
@@ -403,9 +404,9 @@ impl Transform<'_, '_> {
                 });
             }
 
-            let (docid, obkv) = match users_ids_documents_ids.get(user_id) {
+            let (docid, obkv) = match external_documents_ids.get(external_id) {
                 Some(docid) => {
-                    // If we find the user id in the current users ids documents ids map
+                    // If we find the user id in the current external documents ids map
                     // we use it and insert it in the list of replaced documents.
                     let docid = u32::try_from(docid).expect("valid document id");
                     replaced_documents_ids.insert(docid);
@@ -425,11 +426,11 @@ impl Transform<'_, '_> {
                     }
                 },
                 None => {
-                    // If this user id is new we add it to the users ids documents ids map
+                    // If this user id is new we add it to the external documents ids map
                     // for new ids and into the list of new documents.
                     let new_docid = available_documents_ids.next()
                         .context("no more available documents ids")?;
-                    new_users_ids_documents_ids_builder.insert(user_id, new_docid as u64)?;
+                    new_external_documents_ids_builder.insert(external_id, new_docid as u64)?;
                     new_documents_ids.insert(new_docid);
                     (new_docid, update_obkv)
                 },
@@ -455,25 +456,17 @@ impl Transform<'_, '_> {
         let mut documents_file = writer.into_inner()?;
         documents_file.seek(SeekFrom::Start(0))?;
 
-        // We create the union between the existing users ids documents ids with the new ones.
+        let before_docids_merging = Instant::now();
-        let new_users_ids_documents_ids = new_users_ids_documents_ids_builder.into_map();
+        // We merge the new external ids with existing external documents ids.
-        let union_ = fst::map::OpBuilder::new()
+        let new_external_documents_ids = new_external_documents_ids_builder.into_map();
-            .add(&users_ids_documents_ids)
+        external_documents_ids.insert_ids(&new_external_documents_ids)?;
-            .add(&new_users_ids_documents_ids)
-            .r#union();
 
-        // We stream and merge the new users ids documents ids map with the existing one.
+        info!("Documents external merging took {:.02?}", before_docids_merging.elapsed());
-        let mut users_ids_documents_ids_builder = fst::MapBuilder::memory();
-        let mut iter = union_.into_stream();
-        while let Some((user_id, vals)) = iter.next() {
-            assert_eq!(vals.len(), 1, "there must be exactly one document id");
-            users_ids_documents_ids_builder.insert(user_id, vals[0].value)?;
-        }
 
         Ok(TransformOutput {
             primary_key,
             fields_ids_map,
-            users_ids_documents_ids: users_ids_documents_ids_builder.into_map(),
+            external_documents_ids: external_documents_ids.into_static(),
             new_documents_ids,
             replaced_documents_ids,
             documents_count,
@@ -491,7 +484,7 @@ impl Transform<'_, '_> {
     ) -> anyhow::Result<TransformOutput>
     {
         let current_fields_ids_map = self.index.fields_ids_map(self.rtxn)?;
-        let users_ids_documents_ids = self.index.users_ids_documents_ids(self.rtxn)?;
+        let external_documents_ids = self.index.external_documents_ids(self.rtxn)?;
         let documents_ids = self.index.documents_ids(self.rtxn)?;
         let documents_count = documents_ids.len() as usize;
 
@@ -526,7 +519,7 @@ impl Transform<'_, '_> {
         Ok(TransformOutput {
             primary_key,
             fields_ids_map,
-            users_ids_documents_ids: users_ids_documents_ids.map_data(Cow::into_owned)?,
+            external_documents_ids: external_documents_ids.into_static(),
             new_documents_ids: documents_ids,
             replaced_documents_ids: RoaringBitmap::default(),
             documents_count,