diff --git a/milli/src/update/new/channel.rs b/milli/src/update/new/channel.rs
index 4123e568c..6780be72e 100644
--- a/milli/src/update/new/channel.rs
+++ b/milli/src/update/new/channel.rs
@@ -1,6 +1,7 @@
+use core::slice::SlicePattern;
 use std::fs::File;
 
-use crossbeam_channel::{Receiver, RecvError, SendError, Sender};
+use crossbeam_channel::{IntoIter, Receiver, SendError, Sender};
 use heed::types::Bytes;
 
 use super::indexer::KvReaderFieldId;
@@ -8,20 +9,9 @@ use super::StdResult;
 use crate::{DocumentId, Index};
 
 /// The capacity of the channel is currently in number of messages.
-pub fn merger_writer_channels(cap: usize) -> MergerWriterChannels {
+pub fn merger_writer_channels(cap: usize) -> (MergerSender, WriterReceiver) {
     let (sender, receiver) = crossbeam_channel::bounded(cap);
-
-    MergerWriterChannels {
-        writer_receiver: WriterReceiver(receiver),
-        merger_sender: MergerSender(sender.clone()),
-        document_sender: DocumentSender(sender),
-    }
-}
-
-pub struct MergerWriterChannels {
-    pub writer_receiver: WriterReceiver,
-    pub merger_sender: MergerSender,
-    pub document_sender: DocumentSender,
+    (MergerSender(sender), WriterReceiver(receiver))
 }
 
 /// The capacity of the channel is currently in number of messages.
@@ -53,8 +43,12 @@ impl KeyValueEntry {
         KeyValueEntry { key_length: key.len(), data: data.into_boxed_slice() }
     }
 
-    pub fn entry(&self) -> (&[u8], &[u8]) {
-        self.data.split_at(self.key_length)
+    pub fn key(&self) -> &[u8] {
+        &self.data.as_slice()[..self.key_length]
+    }
+
+    pub fn value(&self) -> &[u8] {
+        &self.data.as_slice()[self.key_length..]
     }
 }
 
@@ -72,7 +66,7 @@ impl KeyEntry {
     }
 }
 
-enum EntryOperation {
+pub enum EntryOperation {
     Delete(KeyEntry),
     Write(KeyValueEntry),
 }
@@ -91,9 +85,12 @@ impl DocumentEntry {
         DocumentEntry { docid, content }
     }
 
-    pub fn entry(&self) -> ([u8; 4], &[u8]) {
-        let docid = self.docid.to_be_bytes();
-        (docid, &self.content)
+    pub fn key(&self) -> [u8; 4] {
+        self.docid.to_be_bytes()
+    }
+
+    pub fn content(&self) -> &[u8] {
+        &self.content
     }
 }
 
@@ -113,9 +110,12 @@ impl WriterOperation {
 
 pub struct WriterReceiver(Receiver<WriterOperation>);
 
-impl WriterReceiver {
-    pub fn recv(&self) -> StdResult<WriterOperation, RecvError> {
-        self.0.recv()
+impl IntoIterator for WriterReceiver {
+    type Item = WriterOperation;
+    type IntoIter = IntoIter<Self::Item>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.0.into_iter()
     }
 }
 
@@ -167,7 +167,7 @@ pub struct MergerReceiver(Receiver<MergerOperation>);
 
 impl IntoIterator for MergerReceiver {
     type Item = MergerOperation;
-    type IntoIter = crossbeam_channel::IntoIter<Self::Item>;
+    type IntoIter = IntoIter<Self::Item>;
 
     fn into_iter(self) -> Self::IntoIter {
         self.0.into_iter()
diff --git a/milli/src/update/new/mod.rs b/milli/src/update/new/mod.rs
index 24e9c95db..da76bdfee 100644
--- a/milli/src/update/new/mod.rs
+++ b/milli/src/update/new/mod.rs
@@ -15,15 +15,21 @@ mod indexer {
     use std::io::Cursor;
     use std::os::unix::fs::MetadataExt;
     use std::sync::Arc;
+    use std::thread;
 
+    use big_s::S;
     use heed::types::Bytes;
-    use heed::RoTxn;
+    use heed::{RoTxn, RwTxn};
     use memmap2::Mmap;
     use rayon::iter::{IntoParallelIterator, ParallelBridge, ParallelIterator};
     use roaring::RoaringBitmap;
     use serde_json::Value;
 
-    use super::channel::{MergerReceiver, MergerSender};
+    use super::channel::{
+        extractors_merger_channels, merger_writer_channels, EntryOperation,
+        ExtractorsMergerChannels, MergerReceiver, MergerSender, MergerWriterChannels,
+        WriterOperation,
+    };
     use super::document_change::{Deletion, DocumentChange, Insertion, Update};
     use super::items_pool::ItemsPool;
     use super::merge;
@@ -363,6 +369,44 @@ mod indexer {
 
     pub struct UpdateByFunctionIndexer;
 
+    /// TODO return stats
+    /// TODO take the rayon ThreadPool
+    pub fn index<PI>(wtxn: &mut RwTxn, index: &Index, document_changes: PI) -> Result<()>
+    where
+        PI: IntoParallelIterator<Item = Result<DocumentChange>> + Send,
+        PI::Iter: Clone,
+    {
+        let (merger_sender, writer_receiver) = merger_writer_channels(100);
+        let ExtractorsMergerChannels { merger_receiver, deladd_cbo_roaring_bitmap_sender } =
+            extractors_merger_channels(100);
+
+        thread::scope(|s| {
+            thread::Builder::new().name(S("indexer-extractors")).spawn_scoped(s, || {
+                document_changes.into_par_iter().for_each(|_dc| ());
+            });
+
+            // TODO manage the errors correctly
+            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()
+            });
+
+            // TODO Split this code into another function
+            for operation in writer_receiver {
+                let database = operation.database(index);
+                match operation {
+                    WriterOperation::WordDocids(operation) => match operation {
+                        EntryOperation::Delete(e) => database.delete(wtxn, e.entry()).map(drop)?,
+                        EntryOperation::Write(e) => database.put(wtxn, e.key(), e.value())?,
+                    },
+                    WriterOperation::Document(e) => database.put(wtxn, &e.key(), e.content())?,
+                }
+            }
+
+            Ok(())
+        })
+    }
+
     enum Operation {
         Write(RoaringBitmap),
         Delete,