diff --git a/milli/src/update/new/mod.rs b/milli/src/update/new/mod.rs
index 6dc600545..02b61dde4 100644
--- a/milli/src/update/new/mod.rs
+++ b/milli/src/update/new/mod.rs
@@ -22,6 +22,7 @@ mod indexer {
     use heed::{RoTxn, RwTxn};
     use memmap2::Mmap;
     use rayon::iter::{IntoParallelIterator, ParallelBridge, ParallelIterator};
+    use rayon::ThreadPool;
     use roaring::RoaringBitmap;
     use serde_json::Value;
 
@@ -31,7 +32,6 @@ mod indexer {
     };
     use super::document_change::{Deletion, DocumentChange, Insertion, Update};
     use super::items_pool::ItemsPool;
-    use super::merge;
     use crate::documents::{
         obkv_to_object, DocumentIdExtractionError, DocumentsBatchReader, PrimaryKey,
     };
@@ -52,7 +52,7 @@ mod indexer {
 
     pub struct DocumentOperationIndexer {
         operations: Vec<Payload>,
-        method: IndexDocumentsMethod,
+        index_documents_method: IndexDocumentsMethod,
     }
 
     enum Payload {
@@ -81,7 +81,7 @@ mod indexer {
 
     impl DocumentOperationIndexer {
         pub fn new(method: IndexDocumentsMethod) -> Self {
-            Self { operations: Default::default(), method }
+            Self { operations: Default::default(), index_documents_method: method }
         }
 
         /// TODO please give me a type
@@ -104,7 +104,7 @@ mod indexer {
             self,
             index: &'a Index,
             rtxn: &'a RoTxn,
-            mut fields_ids_map: FieldsIdsMap,
+            fields_ids_map: &'a mut FieldsIdsMap,
             primary_key: &'a PrimaryKey<'a>,
         ) -> Result<impl ParallelIterator<Item = Result<Option<DocumentChange>>> + 'a> {
             let documents_ids = index.documents_ids(rtxn)?;
@@ -198,33 +198,27 @@ mod indexer {
                 }
             }
 
-            let items = Arc::new(ItemsPool::new(|| index.read_txn().map_err(crate::Error::from)));
-            docids_version_offsets.into_par_iter().map_with(
-                items,
-                |context_pool, (external_docid, (internal_docid, operations))| {
-                    context_pool.with(|rtxn| match self.method {
-                        IndexDocumentsMethod::ReplaceDocuments => merge_document_for_replacements(
+            Ok(docids_version_offsets.into_par_iter().map_with(
+                Arc::new(ItemsPool::new(|| index.read_txn().map_err(crate::Error::from))),
+                move |context_pool, (external_docid, (internal_docid, operations))| {
+                    context_pool.with(|rtxn| {
+                        use IndexDocumentsMethod as Idm;
+                        let document_merge_function = match self.index_documents_method {
+                            Idm::ReplaceDocuments => merge_document_for_replacements,
+                            Idm::UpdateDocuments => merge_document_for_updates,
+                        };
+
+                        document_merge_function(
                             rtxn,
                             index,
-                            &fields_ids_map,
+                            fields_ids_map,
                             internal_docid,
                             external_docid,
                             &operations,
-                        ),
-                        // TODO Remap the documents to match the db fields_ids_map
-                        IndexDocumentsMethod::UpdateDocuments => merge_document_for_updates(
-                            rtxn,
-                            index,
-                            &fields_ids_map,
-                            internal_docid,
-                            external_docid,
-                            &operations,
-                        ),
+                        )
                     })
                 },
-            );
-
-            Ok(vec![].into_par_iter())
+            ))
         }
     }
 
@@ -253,7 +247,7 @@ mod indexer {
         //         process: "external_id_of",
         //     })
         // })?;
-        pub fn document_changes<'a, F>(
+        pub fn document_changes<'a>(
             self,
             index: &'a Index,
             fields: &'a FieldsIdsMap,
@@ -263,7 +257,7 @@ mod indexer {
             Ok(self.to_delete.into_iter().par_bridge().map_with(items, |items, docid| {
                 items.with(|rtxn| {
                     let current = index.document(rtxn, docid)?;
-                    let external_docid = match primary_key.document_id(&current, fields)? {
+                    let external_docid = match primary_key.document_id(current, fields)? {
                         Ok(document_id) => Ok(document_id) as Result<_>,
                         Err(_) => Err(InternalError::DocumentsError(
                             crate::documents::Error::InvalidDocumentFormat,
@@ -325,7 +319,12 @@ mod indexer {
 
     /// TODO return stats
     /// TODO take the rayon ThreadPool
-    pub fn index<PI>(wtxn: &mut RwTxn, index: &Index, document_changes: PI) -> Result<()>
+    pub fn index<PI>(
+        wtxn: &mut RwTxn,
+        index: &Index,
+        pool: &ThreadPool,
+        document_changes: PI,
+    ) -> Result<()>
     where
         PI: IntoParallelIterator<Item = Result<DocumentChange>> + Send,
         PI::Iter: Clone,
@@ -336,7 +335,9 @@ mod indexer {
 
         thread::scope(|s| {
             thread::Builder::new().name(S("indexer-extractors")).spawn_scoped(s, || {
-                document_changes.into_par_iter().for_each(|_dc| ());
+                pool.in_place_scope(|_s| {
+                    document_changes.into_par_iter().for_each(|_dc| ());
+                })
             })?;
 
             // TODO manage the errors correctly