diff --git a/Cargo.lock b/Cargo.lock
index 899893044..3c0f0456e 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1624,7 +1624,6 @@ dependencies = [
  "sdset",
  "serde",
  "serde_json",
- "siphasher",
  "slice-group-by",
  "structopt",
  "tempfile",
diff --git a/meilisearch-core/Cargo.toml b/meilisearch-core/Cargo.toml
index d9b88f89b..341c6336a 100644
--- a/meilisearch-core/Cargo.toml
+++ b/meilisearch-core/Cargo.toml
@@ -35,7 +35,6 @@ regex = "1.3.6"
 sdset = "0.4.0"
 serde = { version = "1.0.105", features = ["derive"] }
 serde_json = { version = "1.0.50", features = ["preserve_order"] }
-siphasher = "0.3.2"
 slice-group-by = "0.2.6"
 unicase = "2.6.0"
 zerocopy = "0.3.0"
diff --git a/meilisearch-core/src/database.rs b/meilisearch-core/src/database.rs
index d7f78dca1..5672c3c1e 100644
--- a/meilisearch-core/src/database.rs
+++ b/meilisearch-core/src/database.rs
@@ -775,12 +775,12 @@ mod tests {
         assert!(document.is_none());
 
         let document: Option<IgnoredAny> = index
-            .document(&reader, None, DocumentId(7_900_334_843_754_999_545))
+            .document(&reader, None, DocumentId(0))
             .unwrap();
         assert!(document.is_some());
 
         let document: Option<IgnoredAny> = index
-            .document(&reader, None, DocumentId(8_367_468_610_878_465_872))
+            .document(&reader, None, DocumentId(1))
             .unwrap();
         assert!(document.is_some());
     }
@@ -855,12 +855,12 @@ mod tests {
         assert!(document.is_none());
 
         let document: Option<IgnoredAny> = index
-            .document(&reader, None, DocumentId(7_900_334_843_754_999_545))
+            .document(&reader, None, DocumentId(0))
             .unwrap();
         assert!(document.is_some());
 
         let document: Option<IgnoredAny> = index
-            .document(&reader, None, DocumentId(8_367_468_610_878_465_872))
+            .document(&reader, None, DocumentId(1))
             .unwrap();
         assert!(document.is_some());
 
@@ -897,7 +897,7 @@ mod tests {
 
         let reader = db.main_read_txn().unwrap();
         let document: Option<serde_json::Value> = index
-            .document(&reader, None, DocumentId(7_900_334_843_754_999_545))
+            .document(&reader, None, DocumentId(0))
             .unwrap();
 
         let new_doc1 = serde_json::json!({
@@ -908,7 +908,7 @@ mod tests {
         assert_eq!(document, Some(new_doc1));
 
         let document: Option<serde_json::Value> = index
-            .document(&reader, None, DocumentId(8_367_468_610_878_465_872))
+            .document(&reader, None, DocumentId(1))
             .unwrap();
 
         let new_doc2 = serde_json::json!({
@@ -1080,14 +1080,14 @@ mod tests {
         assert_matches!(
             iter.next(),
             Some(Document {
-                id: DocumentId(7_900_334_843_754_999_545),
+                id: DocumentId(0),
                 ..
             })
         );
         assert_matches!(
             iter.next(),
             Some(Document {
-                id: DocumentId(8_367_468_610_878_465_872),
+                id: DocumentId(1),
                 ..
             })
         );
diff --git a/meilisearch-core/src/lib.rs b/meilisearch-core/src/lib.rs
index 38a1a3c34..1a4b0d2e6 100644
--- a/meilisearch-core/src/lib.rs
+++ b/meilisearch-core/src/lib.rs
@@ -191,6 +191,6 @@ mod tests {
 
     #[test]
     fn docindex_mem_size() {
-        assert_eq!(mem::size_of::<DocIndex>(), 16);
+        assert_eq!(mem::size_of::<DocIndex>(), 12);
     }
 }
diff --git a/meilisearch-core/src/query_builder.rs b/meilisearch-core/src/query_builder.rs
index 1f1ef28e3..d1b35273d 100644
--- a/meilisearch-core/src/query_builder.rs
+++ b/meilisearch-core/src/query_builder.rs
@@ -228,7 +228,7 @@ mod tests {
         builder.into_inner().and_then(Set::from_bytes).unwrap()
     }
 
-    const fn doc_index(document_id: u64, word_index: u16) -> DocIndex {
+    const fn doc_index(document_id: u32, word_index: u16) -> DocIndex {
         DocIndex {
             document_id: DocumentId(document_id),
             attribute: 0,
@@ -238,7 +238,7 @@ mod tests {
         }
     }
 
-    const fn doc_char_index(document_id: u64, word_index: u16, char_index: u16) -> DocIndex {
+    const fn doc_char_index(document_id: u32, word_index: u16, char_index: u16) -> DocIndex {
         DocIndex {
             document_id: DocumentId(document_id),
             attribute: 0,
diff --git a/meilisearch-core/src/store/docs_words.rs b/meilisearch-core/src/store/docs_words.rs
index 0ae153b3f..1e33a9bb0 100644
--- a/meilisearch-core/src/store/docs_words.rs
+++ b/meilisearch-core/src/store/docs_words.rs
@@ -1,4 +1,4 @@
-use super::BEU64;
+use super::BEU32;
 use crate::database::MainT;
 use crate::DocumentId;
 use heed::types::{ByteSlice, OwnedType};
@@ -7,7 +7,7 @@ use std::sync::Arc;
 
 #[derive(Copy, Clone)]
 pub struct DocsWords {
-    pub(crate) docs_words: heed::Database<OwnedType<BEU64>, ByteSlice>,
+    pub(crate) docs_words: heed::Database<OwnedType<BEU32>, ByteSlice>,
 }
 
 impl DocsWords {
@@ -17,13 +17,13 @@ impl DocsWords {
         document_id: DocumentId,
         words: &fst::Set,
     ) -> ZResult<()> {
-        let document_id = BEU64::new(document_id.0);
+        let document_id = BEU32::new(document_id.0);
         let bytes = words.as_fst().as_bytes();
         self.docs_words.put(writer, &document_id, bytes)
     }
 
     pub fn del_doc_words(self, writer: &mut heed::RwTxn<MainT>, document_id: DocumentId) -> ZResult<bool> {
-        let document_id = BEU64::new(document_id.0);
+        let document_id = BEU32::new(document_id.0);
         self.docs_words.delete(writer, &document_id)
     }
 
@@ -36,7 +36,7 @@ impl DocsWords {
         reader: &heed::RoTxn<MainT>,
         document_id: DocumentId,
     ) -> ZResult<Option<fst::Set>> {
-        let document_id = BEU64::new(document_id.0);
+        let document_id = BEU32::new(document_id.0);
         match self.docs_words.get(reader, &document_id)? {
             Some(bytes) => {
                 let len = bytes.len();
diff --git a/meilisearch-core/src/store/documents_ids.rs b/meilisearch-core/src/store/documents_ids.rs
new file mode 100644
index 000000000..a0628e9e2
--- /dev/null
+++ b/meilisearch-core/src/store/documents_ids.rs
@@ -0,0 +1,75 @@
+use std::borrow::Cow;
+
+use heed::{BytesDecode, BytesEncode};
+use sdset::Set;
+
+use crate::DocumentId;
+use super::cow_set::CowSet;
+
+pub struct DocumentsIds;
+
+impl BytesEncode<'_> for DocumentsIds {
+    type EItem = Set<DocumentId>;
+
+    fn bytes_encode(item: &Self::EItem) -> Option<Cow<[u8]>> {
+        CowSet::bytes_encode(item)
+    }
+}
+
+impl<'a> BytesDecode<'a> for DocumentsIds {
+    type DItem = Cow<'a, Set<DocumentId>>;
+
+    fn bytes_decode(bytes: &'a [u8]) -> Option<Self::DItem> {
+        CowSet::bytes_decode(bytes)
+    }
+}
+
+pub struct DiscoverIds<'a> {
+    ids_iter: std::slice::Iter<'a, DocumentId>,
+    left_id: Option<u32>,
+    right_id: Option<u32>,
+    available_range: std::ops::Range<u32>,
+}
+
+impl DiscoverIds<'_> {
+    pub fn new(ids: &Set<DocumentId>) -> DiscoverIds {
+        let mut ids_iter = ids.iter();
+        let right_id = ids_iter.next().map(|id| id.0);
+        let available_range = 0..right_id.unwrap_or(u32::max_value());
+        DiscoverIds { ids_iter, left_id: None, right_id, available_range }
+    }
+}
+
+impl Iterator for DiscoverIds<'_> {
+    type Item = DocumentId;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        loop {
+            match self.available_range.next() {
+                // The available range gives us a new id, we return it.
+                Some(id) => return Some(DocumentId(id)),
+                // The available range is exhausted, we need to find the next one.
+                None if self.available_range.end == u32::max_value() => return None,
+                None => loop {
+                    self.left_id = self.right_id.take();
+                    self.right_id = self.ids_iter.next().map(|id| id.0);
+                    match (self.left_id, self.right_id) {
+                        // We found a gap in the used ids, we can yield all ids
+                        // until the end of the gap
+                        (Some(l), Some(r)) => if l.saturating_add(1) != r {
+                            self.available_range = (l + 1)..r;
+                            break;
+                        },
+                        // The last used id has been reached, we can use all ids
+                        // until u32 MAX
+                        (Some(l), None) => {
+                            self.available_range = l.saturating_add(1)..u32::max_value();
+                            break;
+                        },
+                        _ => (),
+                    }
+                },
+            }
+        }
+    }
+}
diff --git a/meilisearch-core/src/store/main.rs b/meilisearch-core/src/store/main.rs
index 34a88afcd..d1f7a522c 100644
--- a/meilisearch-core/src/store/main.rs
+++ b/meilisearch-core/src/store/main.rs
@@ -3,28 +3,31 @@ use std::sync::Arc;
 use std::collections::HashMap;
 
 use chrono::{DateTime, Utc};
-use heed::types::{ByteSlice, OwnedType, SerdeBincode, Str};
 use heed::Result as ZResult;
+use heed::types::{ByteSlice, OwnedType, SerdeBincode, Str};
 use meilisearch_schema::{FieldId, Schema};
+use meilisearch_types::DocumentId;
 use sdset::Set;
 
 use crate::database::MainT;
 use crate::RankedMap;
 use crate::settings::RankingRule;
-use super::cow_set::CowSet;
+use super::{CowSet, DocumentsIds};
 
+const ATTRIBUTES_FOR_FACETING_KEY: &str = "attributes-for-faceting";
 const CREATED_AT_KEY: &str = "created-at";
-const ATTRIBUTES_FOR_FACETING: &str = "attributes-for-faceting";
-const RANKING_RULES_KEY: &str = "ranking-rules";
-const DISTINCT_ATTRIBUTE_KEY: &str = "distinct-attribute";
-const STOP_WORDS_KEY: &str = "stop-words";
-const SYNONYMS_KEY: &str = "synonyms";
 const CUSTOMS_KEY: &str = "customs";
+const DISTINCT_ATTRIBUTE_KEY: &str = "distinct-attribute";
+const EXTERNAL_DOCIDS_KEY: &str = "external-docids";
 const FIELDS_FREQUENCY_KEY: &str = "fields-frequency";
+const INTERNAL_DOCIDS_KEY: &str = "internal-docids";
 const NAME_KEY: &str = "name";
 const NUMBER_OF_DOCUMENTS_KEY: &str = "number-of-documents";
 const RANKED_MAP_KEY: &str = "ranked-map";
+const RANKING_RULES_KEY: &str = "ranking-rules";
 const SCHEMA_KEY: &str = "schema";
+const STOP_WORDS_KEY: &str = "stop-words";
+const SYNONYMS_KEY: &str = "synonyms";
 const UPDATED_AT_KEY: &str = "updated-at";
 const WORDS_KEY: &str = "words";
 
@@ -71,9 +74,90 @@ impl Main {
         self.main.get::<_, Str, SerdeDatetime>(reader, UPDATED_AT_KEY)
     }
 
+    pub fn put_internal_docids(self, writer: &mut heed::RwTxn<MainT>, ids: &sdset::Set<DocumentId>) -> ZResult<()> {
+        self.main.put::<_, Str, DocumentsIds>(writer, INTERNAL_DOCIDS_KEY, ids)
+    }
+
+    pub fn internal_docids<'txn>(self, reader: &'txn heed::RoTxn<MainT>) -> ZResult<Cow<'txn, sdset::Set<DocumentId>>> {
+        match self.main.get::<_, Str, DocumentsIds>(reader, INTERNAL_DOCIDS_KEY)? {
+            Some(ids) => Ok(ids),
+            None => Ok(Cow::default()),
+        }
+    }
+
+    pub fn merge_internal_docids(self, writer: &mut heed::RwTxn<MainT>, new_ids: &sdset::Set<DocumentId>) -> ZResult<()> {
+        use sdset::SetOperation;
+
+        // We do an union of the old and new internal ids.
+        let internal_docids = self.internal_docids(writer)?;
+        let internal_docids = sdset::duo::Union::new(&internal_docids, new_ids).into_set_buf();
+        self.put_internal_docids(writer, &internal_docids)
+    }
+
+    pub fn remove_internal_docids(self, writer: &mut heed::RwTxn<MainT>, ids: &sdset::Set<DocumentId>) -> ZResult<()> {
+        use sdset::SetOperation;
+
+        // We do a difference of the old and new internal ids.
+        let internal_docids = self.internal_docids(writer)?;
+        let internal_docids = sdset::duo::Difference::new(&internal_docids, ids).into_set_buf();
+        self.put_internal_docids(writer, &internal_docids)
+    }
+
+    pub fn put_external_docids(self, writer: &mut heed::RwTxn<MainT>, ids: &fst::Map) -> ZResult<()> {
+        self.main.put::<_, Str, ByteSlice>(writer, EXTERNAL_DOCIDS_KEY, ids.as_fst().as_bytes())
+    }
+
+    pub fn merge_external_docids(self, writer: &mut heed::RwTxn<MainT>, new_docids: &fst::Map) -> ZResult<()> {
+        use fst::{Streamer, IntoStreamer};
+
+        // Do an union of the old and the new set of external docids.
+        let external_docids = self.external_docids(writer)?;
+        let mut op = external_docids.op().add(new_docids.into_stream()).r#union();
+        let mut build = fst::MapBuilder::memory();
+        while let Some((docid, values)) = op.next() {
+            build.insert(docid, values[0].value).unwrap();
+        }
+        let external_docids = build.into_inner().unwrap();
+
+        // TODO prefer using self.put_user_ids
+        self.main.put::<_, Str, ByteSlice>(writer, EXTERNAL_DOCIDS_KEY, external_docids.as_slice())
+    }
+
+    pub fn remove_external_docids(self, writer: &mut heed::RwTxn<MainT>, ids: &fst::Map) -> ZResult<()> {
+        use fst::{Streamer, IntoStreamer};
+
+        // Do an union of the old and the new set of external docids.
+        let external_docids = self.external_docids(writer)?;
+        let mut op = external_docids.op().add(ids.into_stream()).difference();
+        let mut build = fst::MapBuilder::memory();
+        while let Some((docid, values)) = op.next() {
+            build.insert(docid, values[0].value).unwrap();
+        }
+        let external_docids = build.into_inner().unwrap();
+
+        // TODO prefer using self.put_external_docids
+        self.main.put::<_, Str, ByteSlice>(writer, EXTERNAL_DOCIDS_KEY, external_docids.as_slice())
+    }
+
+    pub fn external_docids(self, reader: &heed::RoTxn<MainT>) -> ZResult<fst::Map> {
+        match self.main.get::<_, Str, ByteSlice>(reader, EXTERNAL_DOCIDS_KEY)? {
+            Some(bytes) => {
+                let len = bytes.len();
+                let bytes = Arc::new(bytes.to_owned());
+                let fst = fst::raw::Fst::from_shared_bytes(bytes, 0, len).unwrap();
+                Ok(fst::Map::from(fst))
+            },
+            None => Ok(fst::Map::default()),
+        }
+    }
+
+    pub fn external_to_internal_docid(self, reader: &heed::RoTxn<MainT>, external_docid: &str) -> ZResult<Option<DocumentId>> {
+        let external_ids = self.external_docids(reader)?;
+        Ok(external_ids.get(external_docid).map(|id| DocumentId(id as u32)))
+    }
+
     pub fn put_words_fst(self, writer: &mut heed::RwTxn<MainT>, fst: &fst::Set) -> ZResult<()> {
-        let bytes = fst.as_fst().as_bytes();
-        self.main.put::<_, Str, ByteSlice>(writer, WORDS_KEY, bytes)
+        self.main.put::<_, Str, ByteSlice>(writer, WORDS_KEY, fst.as_fst().as_bytes())
     }
 
     pub unsafe fn static_words_fst(self, reader: &heed::RoTxn<MainT>) -> ZResult<Option<fst::Set>> {
@@ -82,7 +166,7 @@ impl Main {
                 let bytes: &'static [u8] = std::mem::transmute(bytes);
                 let set = fst::Set::from_static_slice(bytes).unwrap();
                 Ok(Some(set))
-            }
+            },
             None => Ok(None),
         }
     }
@@ -94,7 +178,7 @@ impl Main {
                 let bytes = Arc::new(bytes.to_owned());
                 let fst = fst::raw::Fst::from_shared_bytes(bytes, 0, len).unwrap();
                 Ok(Some(fst::Set::from(fst)))
-            }
+            },
             None => Ok(None),
         }
     }
@@ -193,15 +277,15 @@ impl Main {
     }
 
     pub fn attributes_for_faceting<'txn>(&self, reader: &'txn heed::RoTxn<MainT>) -> ZResult<Option<Cow<'txn, Set<FieldId>>>> {
-        self.main.get::<_, Str, CowSet<FieldId>>(reader, ATTRIBUTES_FOR_FACETING)
+        self.main.get::<_, Str, CowSet<FieldId>>(reader, ATTRIBUTES_FOR_FACETING_KEY)
     }
 
     pub fn put_attributes_for_faceting(self, writer: &mut heed::RwTxn<MainT>, attributes: &Set<FieldId>) -> ZResult<()> {
-        self.main.put::<_, Str, CowSet<FieldId>>(writer, ATTRIBUTES_FOR_FACETING, attributes)
+        self.main.put::<_, Str, CowSet<FieldId>>(writer, ATTRIBUTES_FOR_FACETING_KEY, attributes)
     }
 
     pub fn delete_attributes_for_faceting(self, writer: &mut heed::RwTxn<MainT>) -> ZResult<bool> {
-        self.main.delete::<_, Str>(writer, ATTRIBUTES_FOR_FACETING)
+        self.main.delete::<_, Str>(writer, ATTRIBUTES_FOR_FACETING_KEY)
     }
 
     pub fn ranking_rules(&self, reader: &heed::RoTxn<MainT>) -> ZResult<Option<Vec<RankingRule>>> {
diff --git a/meilisearch-core/src/store/mod.rs b/meilisearch-core/src/store/mod.rs
index 6448a3441..d19d3f7d3 100644
--- a/meilisearch-core/src/store/mod.rs
+++ b/meilisearch-core/src/store/mod.rs
@@ -1,26 +1,27 @@
 mod cow_set;
 mod docs_words;
-mod prefix_documents_cache;
-mod prefix_postings_lists_cache;
+mod documents_ids;
 mod documents_fields;
 mod documents_fields_counts;
+mod facets;
 mod main;
 mod postings_lists;
+mod prefix_documents_cache;
+mod prefix_postings_lists_cache;
 mod synonyms;
 mod updates;
 mod updates_results;
-mod facets;
 
+pub use self::cow_set::CowSet;
 pub use self::docs_words::DocsWords;
-pub use self::facets::Facets;
-pub use self::prefix_documents_cache::PrefixDocumentsCache;
-pub use self::prefix_postings_lists_cache::PrefixPostingsListsCache;
 pub use self::documents_fields::{DocumentFieldsIter, DocumentsFields};
-pub use self::documents_fields_counts::{
-    DocumentFieldsCountsIter, DocumentsFieldsCounts, DocumentsIdsIter,
-};
+pub use self::documents_fields_counts::{DocumentFieldsCountsIter, DocumentsFieldsCounts, DocumentsIdsIter};
+pub use self::documents_ids::{DocumentsIds, DiscoverIds};
+pub use self::facets::Facets;
 pub use self::main::Main;
 pub use self::postings_lists::PostingsLists;
+pub use self::prefix_documents_cache::PrefixDocumentsCache;
+pub use self::prefix_postings_lists_cache::PrefixPostingsListsCache;
 pub use self::synonyms::Synonyms;
 pub use self::updates::Updates;
 pub use self::updates_results::UpdatesResults;
@@ -44,20 +45,21 @@ use crate::serde::Deserializer;
 use crate::settings::SettingsUpdate;
 use crate::{query_builder::QueryBuilder, update, DocIndex, DocumentId, Error, MResult};
 
+type BEU32 = zerocopy::U32<byteorder::BigEndian>;
 type BEU64 = zerocopy::U64<byteorder::BigEndian>;
 pub type BEU16 = zerocopy::U16<byteorder::BigEndian>;
 
 #[derive(Debug, Copy, Clone, AsBytes, FromBytes)]
 #[repr(C)]
 pub struct DocumentFieldIndexedKey {
-    docid: BEU64,
+    docid: BEU32,
     indexed_pos: BEU16,
 }
 
 impl DocumentFieldIndexedKey {
     fn new(docid: DocumentId, indexed_pos: IndexedPos) -> DocumentFieldIndexedKey {
         DocumentFieldIndexedKey {
-            docid: BEU64::new(docid.0),
+            docid: BEU32::new(docid.0),
             indexed_pos: BEU16::new(indexed_pos.0),
         }
     }
@@ -66,14 +68,14 @@ impl DocumentFieldIndexedKey {
 #[derive(Debug, Copy, Clone, AsBytes, FromBytes)]
 #[repr(C)]
 pub struct DocumentFieldStoredKey {
-    docid: BEU64,
+    docid: BEU32,
     field_id: BEU16,
 }
 
 impl DocumentFieldStoredKey {
     fn new(docid: DocumentId, field_id: FieldId) -> DocumentFieldStoredKey {
         DocumentFieldStoredKey {
-            docid: BEU64::new(docid.0),
+            docid: BEU32::new(docid.0),
             field_id: BEU16::new(field_id.0),
         }
     }
@@ -97,7 +99,7 @@ impl<'a> BytesEncode<'a> for PostingsCodec {
 
         let mut buffer = Vec::with_capacity(u64_size + docids_size + matches_size);
 
-        let docids_len = item.docids.len();
+        let docids_len = item.docids.len() as u64;
         buffer.extend_from_slice(&docids_len.to_be_bytes());
         buffer.extend_from_slice(item.docids.as_bytes());
         buffer.extend_from_slice(item.matches.as_bytes());
diff --git a/meilisearch-core/src/store/prefix_documents_cache.rs b/meilisearch-core/src/store/prefix_documents_cache.rs
index 8cde30e95..2bb8700dc 100644
--- a/meilisearch-core/src/store/prefix_documents_cache.rs
+++ b/meilisearch-core/src/store/prefix_documents_cache.rs
@@ -4,7 +4,7 @@ use heed::types::{OwnedType, CowSlice};
 use heed::Result as ZResult;
 use zerocopy::{AsBytes, FromBytes};
 
-use super::BEU64;
+use super::{BEU64, BEU32};
 use crate::{DocumentId, Highlight};
 use crate::database::MainT;
 
@@ -13,15 +13,15 @@ use crate::database::MainT;
 pub struct PrefixKey {
     prefix: [u8; 4],
     index: BEU64,
-    docid: BEU64,
+    docid: BEU32,
 }
 
 impl PrefixKey {
-    pub fn new(prefix: [u8; 4], index: u64, docid: u64) -> PrefixKey {
+    pub fn new(prefix: [u8; 4], index: u64, docid: u32) -> PrefixKey {
         PrefixKey {
             prefix,
             index: BEU64::new(index),
-            docid: BEU64::new(docid),
+            docid: BEU32::new(docid),
         }
     }
 }
@@ -54,7 +54,7 @@ impl PrefixDocumentsCache {
         prefix: [u8; 4],
     ) -> ZResult<PrefixDocumentsIter<'txn>> {
         let start = PrefixKey::new(prefix, 0, 0);
-        let end = PrefixKey::new(prefix, u64::max_value(), u64::max_value());
+        let end = PrefixKey::new(prefix, u64::max_value(), u32::max_value());
         let iter = self.prefix_documents_cache.range(reader, &(start..=end))?;
         Ok(PrefixDocumentsIter { iter })
     }
diff --git a/meilisearch-core/src/update/clear_all.rs b/meilisearch-core/src/update/clear_all.rs
index 0c52f5190..a4c5780b9 100644
--- a/meilisearch-core/src/update/clear_all.rs
+++ b/meilisearch-core/src/update/clear_all.rs
@@ -7,6 +7,8 @@ pub fn apply_clear_all(
     index: &store::Index,
 ) -> MResult<()> {
     index.main.put_words_fst(writer, &fst::Set::default())?;
+    index.main.put_external_docids(writer, &fst::Map::default())?;
+    index.main.put_internal_docids(writer, &sdset::SetBuf::default())?;
     index.main.put_ranked_map(writer, &RankedMap::default())?;
     index.main.put_number_of_documents(writer, |_| 0)?;
     index.documents_fields.clear(writer)?;
diff --git a/meilisearch-core/src/update/documents_addition.rs b/meilisearch-core/src/update/documents_addition.rs
index d9d1af328..6858f6d2c 100644
--- a/meilisearch-core/src/update/documents_addition.rs
+++ b/meilisearch-core/src/update/documents_addition.rs
@@ -1,4 +1,4 @@
-use std::collections::HashMap;
+use std::collections::{HashMap, BTreeMap};
 
 use fst::{set::OpBuilder, SetBuilder};
 use indexmap::IndexMap;
@@ -13,7 +13,7 @@ use crate::database::{UpdateEvent, UpdateEventsEmitter};
 use crate::facets;
 use crate::raw_indexer::RawIndexer;
 use crate::serde::Deserializer;
-use crate::store::{self, DocumentsFields, DocumentsFieldsCounts};
+use crate::store::{self, DocumentsFields, DocumentsFieldsCounts, DiscoverIds};
 use crate::update::helpers::{index_value, value_to_number, extract_document_id};
 use crate::update::{apply_documents_deletion, compute_short_prefixes, next_update_id, Update};
 use crate::{Error, MResult, RankedMap};
@@ -148,23 +148,40 @@ pub fn apply_addition<'a, 'b>(
     index: &store::Index,
     new_documents: Vec<IndexMap<String, Value>>,
     partial: bool
-) -> MResult<()> {
-    let mut documents_additions = HashMap::new();
-
+) -> MResult<()>
+{
     let mut schema = match index.main.schema(writer)? {
         Some(schema) => schema,
         None => return Err(Error::SchemaMissing),
     };
 
+    // Retrieve the documents ids related structures
+    let external_docids = index.main.external_docids(writer)?;
+    let internal_docids = index.main.internal_docids(writer)?;
+    let mut available_ids = DiscoverIds::new(&internal_docids);
+
     let primary_key = schema.primary_key().ok_or(Error::MissingPrimaryKey)?;
 
     // 1. store documents ids for future deletion
+    let mut documents_additions = HashMap::new();
+    let mut new_external_docids = BTreeMap::new();
+    let mut new_internal_docids = Vec::with_capacity(new_documents.len());
+
     for mut document in new_documents {
-        let document_id = extract_document_id(&primary_key, &document)?;
+        let (internal_docid, external_docid) =
+            extract_document_id(
+                &primary_key,
+                &document,
+                &external_docids,
+                &mut available_ids,
+            )?;
+
+        new_external_docids.insert(external_docid, internal_docid.0);
+        new_internal_docids.push(internal_docid);
 
         if partial {
             let mut deserializer = Deserializer {
-                document_id,
+                document_id: internal_docid,
                 reader: writer,
                 documents_fields: index.documents_fields,
                 schema: &schema,
@@ -178,12 +195,12 @@ pub fn apply_addition<'a, 'b>(
                 }
             }
         }
-        documents_additions.insert(document_id, document);
+        documents_additions.insert(internal_docid, document);
     }
 
-    // 2. remove the documents posting lists
+    // 2. remove the documents postings lists
     let number_of_inserted_documents = documents_additions.len();
-    let documents_ids = documents_additions.iter().map(|(id, _)| *id).collect();
+    let documents_ids = new_external_docids.iter().map(|(id, _)| id.clone()).collect();
     apply_documents_deletion(writer, index, documents_ids)?;
 
     let mut ranked_map = match index.main.ranked_map(writer)? {
@@ -233,6 +250,11 @@ pub fn apply_addition<'a, 'b>(
 
     index.main.put_schema(writer, &schema)?;
 
+    let new_external_docids = fst::Map::from_iter(new_external_docids.iter().map(|(ext, id)| (ext, *id as u64)))?;
+    let new_internal_docids = sdset::SetBuf::from_dirty(new_internal_docids);
+    index.main.merge_external_docids(writer, &new_external_docids)?;
+    index.main.merge_internal_docids(writer, &new_internal_docids)?;
+
     Ok(())
 }
 
diff --git a/meilisearch-core/src/update/documents_deletion.rs b/meilisearch-core/src/update/documents_deletion.rs
index 4526d053d..a45021cae 100644
--- a/meilisearch-core/src/update/documents_deletion.rs
+++ b/meilisearch-core/src/update/documents_deletion.rs
@@ -14,7 +14,7 @@ pub struct DocumentsDeletion {
     updates_store: store::Updates,
     updates_results_store: store::UpdatesResults,
     updates_notifier: UpdateEventsEmitter,
-    documents: Vec<DocumentId>,
+    external_docids: Vec<String>,
 }
 
 impl DocumentsDeletion {
@@ -27,12 +27,12 @@ impl DocumentsDeletion {
             updates_store,
             updates_results_store,
             updates_notifier,
-            documents: Vec::new(),
+            external_docids: Vec::new(),
         }
     }
 
-    pub fn delete_document_by_id(&mut self, document_id: DocumentId) {
-        self.documents.push(document_id);
+    pub fn delete_document_by_external_docid(&mut self, document_id: String) {
+        self.external_docids.push(document_id);
     }
 
     pub fn finalize(self, writer: &mut heed::RwTxn<UpdateT>) -> MResult<u64> {
@@ -41,15 +41,15 @@ impl DocumentsDeletion {
             writer,
             self.updates_store,
             self.updates_results_store,
-            self.documents,
+            self.external_docids,
         )?;
         Ok(update_id)
     }
 }
 
-impl Extend<DocumentId> for DocumentsDeletion {
-    fn extend<T: IntoIterator<Item = DocumentId>>(&mut self, iter: T) {
-        self.documents.extend(iter)
+impl Extend<String> for DocumentsDeletion {
+    fn extend<T: IntoIterator<Item=String>>(&mut self, iter: T) {
+        self.external_docids.extend(iter)
     }
 }
 
@@ -57,11 +57,11 @@ pub fn push_documents_deletion(
     writer: &mut heed::RwTxn<UpdateT>,
     updates_store: store::Updates,
     updates_results_store: store::UpdatesResults,
-    deletion: Vec<DocumentId>,
+    external_docids: Vec<String>,
 ) -> MResult<u64> {
     let last_update_id = next_update_id(writer, updates_store, updates_results_store)?;
 
-    let update = Update::documents_deletion(deletion);
+    let update = Update::documents_deletion(external_docids);
     updates_store.put_update(writer, last_update_id, &update)?;
 
     Ok(last_update_id)
@@ -70,8 +70,24 @@ pub fn push_documents_deletion(
 pub fn apply_documents_deletion(
     writer: &mut heed::RwTxn<MainT>,
     index: &store::Index,
-    deletion: Vec<DocumentId>,
-) -> MResult<()> {
+    external_docids: Vec<String>,
+) -> MResult<()>
+{
+    let (external_docids, internal_docids) = {
+        let new_external_docids = SetBuf::from_dirty(external_docids);
+        let mut internal_docids = Vec::new();
+
+        let old_external_docids = index.main.external_docids(writer)?;
+        for external_docid in new_external_docids.as_slice() {
+            if let Some(id) = old_external_docids.get(external_docid) {
+                internal_docids.push(DocumentId(id as u32));
+            }
+        }
+
+        let new_external_docids = fst::Map::from_iter(new_external_docids.into_iter().map(|k| (k, 0))).unwrap();
+        (new_external_docids, SetBuf::from_dirty(internal_docids))
+    };
+
     let schema = match index.main.schema(writer)? {
         Some(schema) => schema,
         None => return Err(Error::SchemaMissing),
@@ -84,16 +100,15 @@ pub fn apply_documents_deletion(
 
     // facet filters deletion
     if let Some(attributes_for_facetting) = index.main.attributes_for_faceting(writer)? {
-        let facet_map = facets::facet_map_from_docids(writer, &index, &deletion, &attributes_for_facetting)?;
+        let facet_map = facets::facet_map_from_docids(writer, &index, &internal_docids, &attributes_for_facetting)?;
         index.facets.remove(writer, facet_map)?;
     }
 
     // collect the ranked attributes according to the schema
     let ranked_fields = schema.ranked();
 
-    let idset = SetBuf::from_dirty(deletion);
     let mut words_document_ids = HashMap::new();
-    for id in idset {
+    for id in internal_docids.iter().cloned() {
         // remove all the ranked attributes from the ranked_map
         for ranked_attr in ranked_fields {
             ranked_map.remove(id, *ranked_attr);
@@ -163,6 +178,10 @@ pub fn apply_documents_deletion(
     index.main.put_ranked_map(writer, &ranked_map)?;
     index.main.put_number_of_documents(writer, |old| old - deleted_documents_len)?;
 
+    // We apply the changes to the user and internal ids
+    index.main.remove_external_docids(writer, &external_docids)?;
+    index.main.remove_internal_docids(writer, &internal_docids)?;
+
     compute_short_prefixes(writer, index)?;
 
     Ok(())
diff --git a/meilisearch-core/src/update/helpers.rs b/meilisearch-core/src/update/helpers.rs
index d17bea3b2..c7bd05cec 100644
--- a/meilisearch-core/src/update/helpers.rs
+++ b/meilisearch-core/src/update/helpers.rs
@@ -1,16 +1,15 @@
 use std::fmt::Write as _;
-use std::hash::{Hash, Hasher};
 
 use indexmap::IndexMap;
 use meilisearch_schema::IndexedPos;
 use meilisearch_types::DocumentId;
 use ordered_float::OrderedFloat;
 use serde_json::Value;
-use siphasher::sip::SipHasher;
 
+use crate::Number;
 use crate::raw_indexer::RawIndexer;
 use crate::serde::SerializerError;
-use crate::Number;
+use crate::store::DiscoverIds;
 
 /// Returns the number of words indexed or `None` if the type is unindexable.
 pub fn index_value(
@@ -96,28 +95,43 @@ pub fn value_to_number(value: &Value) -> Option<Number> {
     }
 }
 
-/// Validates a string representation to be a correct document id and
-/// returns the hash of the given type, this is the way we produce documents ids.
-pub fn compute_document_id(string: &str) -> Result<DocumentId, SerializerError> {
-    if string.chars().all(|x| x.is_ascii_alphanumeric() || x == '-' || x == '_') {
-        let mut s = SipHasher::new();
-        string.hash(&mut s);
-        Ok(DocumentId(s.finish()))
+/// Validates a string representation to be a correct document id and returns
+/// the corresponding id or generate a new one, this is the way we produce documents ids.
+pub fn discover_document_id(
+    docid: &str,
+    external_docids: &fst::Map,
+    available_docids: &mut DiscoverIds<'_>,
+) -> Result<DocumentId, SerializerError>
+{
+    if docid.chars().all(|x| x.is_ascii_alphanumeric() || x == '-' || x == '_') {
+        match external_docids.get(docid) {
+            Some(id) => Ok(DocumentId(id as u32)),
+            None => {
+                let internal_id = available_docids.next().expect("no more ids available");
+                Ok(internal_id)
+            },
+        }
     } else {
         Err(SerializerError::InvalidDocumentIdFormat)
     }
 }
 
 /// Extracts and validates the document id of a document.
-pub fn extract_document_id(primary_key: &str, document: &IndexMap<String, Value>) -> Result<DocumentId, SerializerError> {
+pub fn extract_document_id(
+    primary_key: &str,
+    document: &IndexMap<String, Value>,
+    external_docids: &fst::Map,
+    available_docids: &mut DiscoverIds<'_>,
+) -> Result<(DocumentId, String), SerializerError>
+{
     match document.get(primary_key) {
         Some(value) => {
-            let string = match value {
+            let docid = match value {
                 Value::Number(number) => number.to_string(),
                 Value::String(string) => string.clone(),
                 _ => return Err(SerializerError::InvalidDocumentIdFormat),
             };
-            compute_document_id(&string)
+            discover_document_id(&docid, external_docids, available_docids).map(|id| (id, docid))
         }
         None => Err(SerializerError::DocumentIdNotFound),
     }
diff --git a/meilisearch-core/src/update/mod.rs b/meilisearch-core/src/update/mod.rs
index 5b7c33c9d..d2d771030 100644
--- a/meilisearch-core/src/update/mod.rs
+++ b/meilisearch-core/src/update/mod.rs
@@ -9,7 +9,7 @@ pub use self::clear_all::{apply_clear_all, push_clear_all};
 pub use self::customs_update::{apply_customs_update, push_customs_update};
 pub use self::documents_addition::{apply_documents_addition, apply_documents_partial_addition, DocumentsAddition};
 pub use self::documents_deletion::{apply_documents_deletion, DocumentsDeletion};
-pub use self::helpers::{index_value, value_to_string, value_to_number, compute_document_id, extract_document_id};
+pub use self::helpers::{index_value, value_to_string, value_to_number, discover_document_id, extract_document_id};
 pub use self::settings_update::{apply_settings_update, push_settings_update};
 
 use std::cmp;
@@ -24,7 +24,7 @@ use sdset::Set;
 use serde::{Deserialize, Serialize};
 use serde_json::Value;
 
-use crate::{store, DocumentId, MResult};
+use crate::{store, MResult};
 use crate::database::{MainT, UpdateT};
 use crate::settings::SettingsUpdate;
 
@@ -63,7 +63,7 @@ impl Update {
         }
     }
 
-    fn documents_deletion(data: Vec<DocumentId>) -> Update {
+    fn documents_deletion(data: Vec<String>) -> Update {
         Update {
             data: UpdateData::DocumentsDeletion(data),
             enqueued_at: Utc::now(),
@@ -84,7 +84,7 @@ pub enum UpdateData {
     Customs(Vec<u8>),
     DocumentsAddition(Vec<IndexMap<String, Value>>),
     DocumentsPartial(Vec<IndexMap<String, Value>>),
-    DocumentsDeletion(Vec<DocumentId>),
+    DocumentsDeletion(Vec<String>),
     Settings(SettingsUpdate)
 }
 
diff --git a/meilisearch-http/src/error.rs b/meilisearch-http/src/error.rs
index 295931454..27626c80b 100644
--- a/meilisearch-http/src/error.rs
+++ b/meilisearch-http/src/error.rs
@@ -22,7 +22,7 @@ pub enum ResponseError {
     NotFound(String),
     OpenIndex(String),
     FilterParsing(String),
-    RetrieveDocument(u64, String),
+    RetrieveDocument(u32, String),
     SearchDocuments(String),
     PayloadTooLarge,
     UnsupportedMediaType,
@@ -116,7 +116,7 @@ impl ResponseError {
         ResponseError::Maintenance
     }
 
-    pub fn retrieve_document(doc_id: u64, err: impl fmt::Display) -> ResponseError {
+    pub fn retrieve_document(doc_id: u32, err: impl fmt::Display) -> ResponseError {
         ResponseError::RetrieveDocument(doc_id, err.to_string())
     }
 
diff --git a/meilisearch-http/src/routes/document.rs b/meilisearch-http/src/routes/document.rs
index 3b71e656a..eca88a590 100644
--- a/meilisearch-http/src/routes/document.rs
+++ b/meilisearch-http/src/routes/document.rs
@@ -3,7 +3,7 @@ use std::collections::{BTreeSet, HashSet};
 use actix_web::{web, HttpResponse};
 use actix_web_macros::{delete, get, post, put};
 use indexmap::IndexMap;
-use meilisearch_core::{update, Error};
+use meilisearch_core::update;
 use serde::Deserialize;
 use serde_json::Value;
 
@@ -43,11 +43,13 @@ async fn get_document(
         .open_index(&path.index_uid)
         .ok_or(ResponseError::index_not_found(&path.index_uid))?;
 
-    let document_id = update::compute_document_id(&path.document_id).map_err(Error::Serializer)?;
     let reader = data.db.main_read_txn()?;
+    let internal_id = index.main
+        .external_to_internal_docid(&reader, &path.document_id)?
+        .ok_or(ResponseError::document_not_found(&path.document_id))?;
 
     let response: Document = index
-        .document(&reader, None, document_id)?
+        .document(&reader, None, internal_id)?
         .ok_or(ResponseError::document_not_found(&path.document_id))?;
 
     Ok(HttpResponse::Ok().json(response))
@@ -66,12 +68,10 @@ async fn delete_document(
         .open_index(&path.index_uid)
         .ok_or(ResponseError::index_not_found(&path.index_uid))?;
 
-    let document_id = update::compute_document_id(&path.document_id).map_err(Error::Serializer)?;
-
     let mut update_writer = data.db.update_write_txn()?;
 
     let mut documents_deletion = index.documents_deletion();
-    documents_deletion.delete_document_by_id(document_id);
+    documents_deletion.delete_document_by_external_docid(path.document_id.clone());
 
     let update_id = documents_deletion.finalize(&mut update_writer)?;
 
@@ -239,8 +239,7 @@ async fn delete_documents(
 
     for document_id in body.into_inner() {
         let document_id = update::value_to_string(&document_id);
-        let document_id = update::compute_document_id(&document_id).map_err(Error::Serializer)?;
-        documents_deletion.delete_document_by_id(document_id);
+        documents_deletion.delete_document_by_external_docid(document_id);
     }
 
     let update_id = documents_deletion.finalize(&mut writer)?;
diff --git a/meilisearch-types/src/lib.rs b/meilisearch-types/src/lib.rs
index fac361415..3e14521e0 100644
--- a/meilisearch-types/src/lib.rs
+++ b/meilisearch-types/src/lib.rs
@@ -12,7 +12,7 @@ use serde::{Deserialize, Serialize};
 #[cfg_attr(feature = "zerocopy", derive(AsBytes, FromBytes))]
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 #[repr(C)]
-pub struct DocumentId(pub u64);
+pub struct DocumentId(pub u32);
 
 /// This structure represent the position of a word
 /// in a document and its attributes.