diff --git a/milli/src/update/new/channel.rs b/milli/src/update/new/channel.rs
index 98538ea9e..6a47dc606 100644
--- a/milli/src/update/new/channel.rs
+++ b/milli/src/update/new/channel.rs
@@ -16,7 +16,14 @@ use crate::{DocumentId, Index};
 /// The capacity of the channel is currently in number of messages.
 pub fn merger_writer_channel(cap: usize) -> (MergerSender, WriterReceiver) {
     let (sender, receiver) = crossbeam_channel::bounded(cap);
-    (MergerSender(sender), WriterReceiver(receiver))
+    (
+        MergerSender {
+            sender,
+            send_count: Default::default(),
+            contentious_count: Default::default(),
+        },
+        WriterReceiver(receiver),
+    )
 }
 
 /// The capacity of the channel is currently in number of messages.
@@ -169,23 +176,40 @@ impl IntoIterator for WriterReceiver {
     }
 }
 
-pub struct MergerSender(Sender<WriterOperation>);
+pub struct MergerSender {
+    sender: Sender<WriterOperation>,
+    /// The number of message we send in total in the channel.
+    send_count: std::cell::Cell<usize>,
+    /// The number of times we sent something in a channel that was full.
+    contentious_count: std::cell::Cell<usize>,
+}
+
+impl Drop for MergerSender {
+    fn drop(&mut self) {
+        tracing::info!(
+            "Merger channel stats: {} sends, {} were contentious (ratio {})",
+            self.send_count.get(),
+            self.contentious_count.get(),
+            self.contentious_count.get() as f64 / self.send_count.get() as f64
+        )
+    }
+}
 
 impl MergerSender {
     pub fn main(&self) -> MainSender<'_> {
-        MainSender(&self.0)
+        MainSender(self)
     }
 
     pub fn docids<D: DatabaseType>(&self) -> WordDocidsSender<'_, D> {
-        WordDocidsSender { sender: &self.0, _marker: PhantomData }
+        WordDocidsSender { sender: self, _marker: PhantomData }
     }
 
     pub fn facet_docids(&self) -> FacetDocidsSender<'_> {
-        FacetDocidsSender { sender: &self.0 }
+        FacetDocidsSender { sender: self }
     }
 
     pub fn documents(&self) -> DocumentsSender<'_> {
-        DocumentsSender(&self.0)
+        DocumentsSender(self)
     }
 
     pub fn send_documents_ids(&self, bitmap: &[u8]) -> StdResult<(), SendError<()>> {
@@ -193,14 +217,25 @@ impl MergerSender {
             DOCUMENTS_IDS_KEY.as_bytes(),
             bitmap,
         ));
-        match self.0.send(WriterOperation { database: Database::Main, entry }) {
+        match self.send(WriterOperation { database: Database::Main, entry }) {
+            Ok(()) => Ok(()),
+            Err(SendError(_)) => Err(SendError(())),
+        }
+    }
+
+    fn send(&self, op: WriterOperation) -> StdResult<(), SendError<()>> {
+        if self.sender.is_full() {
+            self.contentious_count.set(self.contentious_count.get() + 1);
+        }
+        self.send_count.set(self.send_count.get() + 1);
+        match self.sender.send(op) {
             Ok(()) => Ok(()),
             Err(SendError(_)) => Err(SendError(())),
         }
     }
 }
 
-pub struct MainSender<'a>(&'a Sender<WriterOperation>);
+pub struct MainSender<'a>(&'a MergerSender);
 
 impl MainSender<'_> {
     pub fn write_words_fst(&self, value: Mmap) -> StdResult<(), SendError<()>> {
@@ -311,7 +346,7 @@ pub trait DocidsSender {
 }
 
 pub struct WordDocidsSender<'a, D> {
-    sender: &'a Sender<WriterOperation>,
+    sender: &'a MergerSender,
     _marker: PhantomData<D>,
 }
 
@@ -334,7 +369,7 @@ impl<D: DatabaseType> DocidsSender for WordDocidsSender<'_, D> {
 }
 
 pub struct FacetDocidsSender<'a> {
-    sender: &'a Sender<WriterOperation>,
+    sender: &'a MergerSender,
 }
 
 impl DocidsSender for FacetDocidsSender<'_> {
@@ -370,7 +405,7 @@ impl FacetDocidsSender<'_> {
     }
 }
 
-pub struct DocumentsSender<'a>(&'a Sender<WriterOperation>);
+pub struct DocumentsSender<'a>(&'a MergerSender);
 
 impl DocumentsSender<'_> {
     /// TODO do that efficiently
@@ -426,7 +461,7 @@ pub struct ExtractorSender(Sender<MergerOperation>);
 
 impl ExtractorSender {
     pub fn document_sender(&self) -> DocumentSender<'_> {
-        DocumentSender(&self.0)
+        DocumentSender(Some(&self.0))
     }
 
     pub fn send_searchable<D: MergerOperationType>(
@@ -440,7 +475,7 @@ impl ExtractorSender {
     }
 }
 
-pub struct DocumentSender<'a>(&'a Sender<MergerOperation>);
+pub struct DocumentSender<'a>(Option<&'a Sender<MergerOperation>>);
 
 impl DocumentSender<'_> {
     pub fn insert(
@@ -448,21 +483,24 @@ impl DocumentSender<'_> {
         docid: DocumentId,
         document: Box<KvReaderFieldId>,
     ) -> StdResult<(), SendError<()>> {
-        match self.0.send(MergerOperation::InsertDocument { docid, document }) {
+        let sender = self.0.unwrap();
+        match sender.send(MergerOperation::InsertDocument { docid, document }) {
             Ok(()) => Ok(()),
             Err(SendError(_)) => Err(SendError(())),
         }
     }
 
     pub fn delete(&self, docid: DocumentId) -> StdResult<(), SendError<()>> {
-        match self.0.send(MergerOperation::DeleteDocument { docid }) {
+        let sender = self.0.unwrap();
+        match sender.send(MergerOperation::DeleteDocument { docid }) {
             Ok(()) => Ok(()),
             Err(SendError(_)) => Err(SendError(())),
         }
     }
 
-    pub fn finish(self) -> StdResult<(), SendError<()>> {
-        match self.0.send(MergerOperation::FinishedDocument) {
+    pub fn finish(mut self) -> StdResult<(), SendError<()>> {
+        let sender = self.0.take().unwrap();
+        match sender.send(MergerOperation::FinishedDocument) {
             Ok(()) => Ok(()),
             Err(SendError(_)) => Err(SendError(())),
         }
@@ -471,6 +509,8 @@ impl DocumentSender<'_> {
 
 impl Drop for DocumentSender<'_> {
     fn drop(&mut self) {
-        self.0.send(MergerOperation::FinishedDocument);
+        if let Some(sender) = self.0.take() {
+            sender.send(MergerOperation::FinishedDocument);
+        }
     }
 }
diff --git a/milli/src/update/new/indexer/mod.rs b/milli/src/update/new/indexer/mod.rs
index b40ddbc4d..3a9db79b6 100644
--- a/milli/src/update/new/indexer/mod.rs
+++ b/milli/src/update/new/indexer/mod.rs
@@ -17,7 +17,7 @@ use super::extract::*;
 use super::merger::merge_grenad_entries;
 use super::StdResult;
 use crate::documents::{PrimaryKey, DEFAULT_PRIMARY_KEY};
-use crate::update::new::channel::{DatabaseType, ExtractorSender};
+use crate::update::new::channel::ExtractorSender;
 use crate::update::GrenadParameters;
 use crate::{FieldsIdsMap, GlobalFieldsIdsMap, Index, Result, UserError};