diff --git a/milli/src/update/new/channel.rs b/milli/src/update/new/channel.rs
index 088303fb3..4041fcc6a 100644
--- a/milli/src/update/new/channel.rs
+++ b/milli/src/update/new/channel.rs
@@ -8,7 +8,7 @@ use crate::update::new::KvReaderFieldId;
 use crate::{DocumentId, Index};
 
 /// The capacity of the channel is currently in number of messages.
-pub fn merger_writer_channels(cap: usize) -> (MergerSender, WriterReceiver) {
+pub fn merger_writer_channel(cap: usize) -> (MergerSender, WriterReceiver) {
     let (sender, receiver) = crossbeam_channel::bounded(cap);
     (MergerSender(sender), WriterReceiver(receiver))
 }
diff --git a/milli/src/update/new/indexer/document_deletion.rs b/milli/src/update/new/indexer/document_deletion.rs
index 2b4bdaeb7..c16299e9a 100644
--- a/milli/src/update/new/indexer/document_deletion.rs
+++ b/milli/src/update/new/indexer/document_deletion.rs
@@ -3,7 +3,7 @@ use std::sync::Arc;
 use rayon::iter::{ParallelBridge, ParallelIterator};
 use roaring::RoaringBitmap;
 
-use super::Indexer;
+use super::DocumentChanges;
 use crate::documents::PrimaryKey;
 use crate::update::new::{Deletion, DocumentChange, ItemsPool};
 use crate::{FieldsIdsMap, Index, InternalError, Result};
@@ -22,7 +22,7 @@ impl DocumentDeletion {
     }
 }
 
-impl<'p> Indexer<'p> for DocumentDeletion {
+impl<'p> DocumentChanges<'p> for DocumentDeletion {
     type Parameter = (&'p Index, &'p FieldsIdsMap, &'p PrimaryKey<'p>);
 
     fn document_changes(
diff --git a/milli/src/update/new/indexer/document_operation.rs b/milli/src/update/new/indexer/document_operation.rs
index fdcb84c7b..5d9755211 100644
--- a/milli/src/update/new/indexer/document_operation.rs
+++ b/milli/src/update/new/indexer/document_operation.rs
@@ -11,7 +11,7 @@ use rayon::iter::{IntoParallelIterator, ParallelIterator};
 
 use super::super::document_change::DocumentChange;
 use super::super::items_pool::ItemsPool;
-use super::Indexer;
+use super::DocumentChanges;
 use crate::documents::{
     obkv_to_object, DocumentIdExtractionError, DocumentsBatchReader, PrimaryKey,
 };
@@ -70,7 +70,7 @@ impl DocumentOperation {
     }
 }
 
-impl<'p> Indexer<'p> for DocumentOperation {
+impl<'p> DocumentChanges<'p> for DocumentOperation {
     type Parameter = (&'p Index, &'p RoTxn<'static>, &'p mut FieldsIdsMap, &'p PrimaryKey<'p>);
 
     fn document_changes(
diff --git a/milli/src/update/new/indexer/mod.rs b/milli/src/update/new/indexer/mod.rs
index 85d4dbcb1..69ccc0451 100644
--- a/milli/src/update/new/indexer/mod.rs
+++ b/milli/src/update/new/indexer/mod.rs
@@ -10,7 +10,7 @@ use rayon::ThreadPool;
 pub use update_by_function::UpdateByFunction;
 
 use super::channel::{
-    extractors_merger_channels, merger_writer_channels, EntryOperation, ExtractorsMergerChannels,
+    extractors_merger_channels, merger_writer_channel, EntryOperation, ExtractorsMergerChannels,
     WriterOperation,
 };
 use super::document_change::DocumentChange;
@@ -22,7 +22,7 @@ mod document_operation;
 mod partial_dump;
 mod update_by_function;
 
-pub trait Indexer<'p> {
+pub trait DocumentChanges<'p> {
     type Parameter: 'p;
 
     fn document_changes(
@@ -36,7 +36,6 @@ pub trait Indexer<'p> {
 /// Give it the output of the [`Indexer::document_changes`] method and it will execute it in the [`rayon::ThreadPool`].
 ///
 /// TODO return stats
-/// TODO take the rayon ThreadPool
 pub fn index<PI>(
     wtxn: &mut RwTxn,
     index: &Index,
@@ -44,25 +43,31 @@ pub fn index<PI>(
     document_changes: PI,
 ) -> Result<()>
 where
-    PI: IntoParallelIterator<Item = Result<DocumentChange>> + Send,
+    PI: IntoParallelIterator<Item = Result<Option<DocumentChange>>> + Send,
     PI::Iter: Clone,
 {
-    let (merger_sender, writer_receiver) = merger_writer_channels(100);
+    let (merger_sender, writer_receiver) = merger_writer_channel(100);
     let ExtractorsMergerChannels { merger_receiver, deladd_cbo_roaring_bitmap_sender } =
         extractors_merger_channels(100);
 
     thread::scope(|s| {
         // TODO manage the errors correctly
-        thread::Builder::new().name(S("indexer-extractors")).spawn_scoped(s, || {
-            pool.in_place_scope(|_s| {
-                document_changes.into_par_iter().for_each(|_dc| ());
-            })
-        })?;
+        let handle =
+            thread::Builder::new().name(S("indexer-extractors")).spawn_scoped(s, || {
+                pool.in_place_scope(|_s| {
+                    // word docids
+                    // document_changes.into_par_iter().try_for_each(|_dc| Ok(()) as Result<_>)
+                    // let grenads = extractor_function(document_changes)?;
+                    // deladd_cbo_roaring_bitmap_sender.word_docids(grenads)?;
+
+                    Ok(()) as Result<_>
+                })
+            })?;
 
         // TODO manage the errors correctly
-        thread::Builder::new().name(S("indexer-merger")).spawn_scoped(s, || {
+        let handle2 = thread::Builder::new().name(S("indexer-merger")).spawn_scoped(s, || {
             let rtxn = index.read_txn().unwrap();
-            merge_grenad_entries(merger_receiver, merger_sender, &rtxn, index).unwrap()
+            merge_grenad_entries(merger_receiver, merger_sender, &rtxn, index)
         })?;
 
         // TODO Split this code into another function
@@ -77,6 +82,10 @@ where
             }
         }
 
+        /// TODO handle the panicking threads
+        handle.join().unwrap()?;
+        handle2.join().unwrap()?;
+
         Ok(())
     })
 }
diff --git a/milli/src/update/new/indexer/partial_dump.rs b/milli/src/update/new/indexer/partial_dump.rs
index 7afb96d65..11c9fbd0e 100644
--- a/milli/src/update/new/indexer/partial_dump.rs
+++ b/milli/src/update/new/indexer/partial_dump.rs
@@ -1,6 +1,6 @@
 use rayon::iter::{ParallelBridge, ParallelIterator};
 
-use super::Indexer;
+use super::DocumentChanges;
 use crate::documents::{DocumentIdExtractionError, PrimaryKey};
 use crate::update::concurrent_available_ids::ConcurrentAvailableIds;
 use crate::update::new::{DocumentChange, Insertion, KvWriterFieldId};
@@ -16,7 +16,7 @@ impl<I> PartialDump<I> {
     }
 }
 
-impl<'p, I> Indexer<'p> for PartialDump<I>
+impl<'p, I> DocumentChanges<'p> for PartialDump<I>
 where
     I: IntoIterator<Item = Object>,
     I::IntoIter: Send + 'p,
diff --git a/milli/src/update/new/indexer/update_by_function.rs b/milli/src/update/new/indexer/update_by_function.rs
index e9bdf3640..035f95c02 100644
--- a/milli/src/update/new/indexer/update_by_function.rs
+++ b/milli/src/update/new/indexer/update_by_function.rs
@@ -1,12 +1,12 @@
 use rayon::iter::{IntoParallelIterator, ParallelIterator};
 
-use super::Indexer;
+use super::DocumentChanges;
 use crate::update::new::DocumentChange;
 use crate::Result;
 
 pub struct UpdateByFunction;
 
-impl<'p> Indexer<'p> for UpdateByFunction {
+impl<'p> DocumentChanges<'p> for UpdateByFunction {
     type Parameter = ();
 
     fn document_changes(