diff --git a/milli/src/update/new/extract/cache.rs b/milli/src/update/new/extract/cache.rs
index 878150eb3..684b67daa 100644
--- a/milli/src/update/new/extract/cache.rs
+++ b/milli/src/update/new/extract/cache.rs
@@ -1,13 +1,13 @@
-use std::borrow::Cow;
 use std::num::NonZeroUsize;
-use std::{io, mem};
+use std::mem;
 
 use grenad::{MergeFunction, Sorter};
 use lru::LruCache;
 use roaring::RoaringBitmap;
 use smallvec::SmallVec;
 
-use crate::update::del_add::{DelAdd, KvReaderDelAdd, KvWriterDelAdd};
+use crate::update::del_add::{DelAdd, KvWriterDelAdd};
+use crate::CboRoaringBitmapCodec;
 
 #[derive(Debug)]
 pub struct CachedSorter<MF> {
@@ -123,26 +123,27 @@ impl<MF: MergeFunction> CachedSorter<MF> {
         key: A,
         deladd: DelAddRoaringBitmap,
     ) -> grenad::Result<(), MF::Error> {
+        /// TODO we must create a serialization trait to correctly serialize bitmaps
         self.deladd_buffer.clear();
         let mut value_writer = KvWriterDelAdd::new(&mut self.deladd_buffer);
         match deladd {
             DelAddRoaringBitmap { del: Some(del), add: None } => {
                 self.cbo_buffer.clear();
-                RoaringBitmap::serialize_into(&del, &mut self.cbo_buffer)?;
+                CboRoaringBitmapCodec::serialize_into(&del, &mut self.cbo_buffer);
                 value_writer.insert(DelAdd::Deletion, &self.cbo_buffer)?;
             }
             DelAddRoaringBitmap { del: None, add: Some(add) } => {
                 self.cbo_buffer.clear();
-                RoaringBitmap::serialize_into(&add, &mut self.cbo_buffer)?;
+                CboRoaringBitmapCodec::serialize_into(&add, &mut self.cbo_buffer);
                 value_writer.insert(DelAdd::Addition, &self.cbo_buffer)?;
             }
             DelAddRoaringBitmap { del: Some(del), add: Some(add) } => {
                 self.cbo_buffer.clear();
-                RoaringBitmap::serialize_into(&del, &mut self.cbo_buffer)?;
+                CboRoaringBitmapCodec::serialize_into(&del, &mut self.cbo_buffer);
                 value_writer.insert(DelAdd::Deletion, &self.cbo_buffer)?;
 
                 self.cbo_buffer.clear();
-                RoaringBitmap::serialize_into(&add, &mut self.cbo_buffer)?;
+                CboRoaringBitmapCodec::serialize_into(&add, &mut self.cbo_buffer);
                 value_writer.insert(DelAdd::Addition, &self.cbo_buffer)?;
             }
             DelAddRoaringBitmap { del: None, add: None } => return Ok(()),
@@ -193,56 +194,4 @@ impl DelAddRoaringBitmap {
     fn new_add_u32(n: u32) -> Self {
         DelAddRoaringBitmap { del: None, add: Some(RoaringBitmap::from([n])) }
     }
-}
-
-/// Do a union of CboRoaringBitmaps on both sides of a DelAdd obkv
-/// separately and outputs a new DelAdd with both unions.
-pub struct DelAddRoaringBitmapMerger;
-
-impl MergeFunction for DelAddRoaringBitmapMerger {
-    type Error = io::Error;
-
-    fn merge<'a>(
-        &self,
-        _key: &[u8],
-        values: &[Cow<'a, [u8]>],
-    ) -> std::result::Result<Cow<'a, [u8]>, Self::Error> {
-        if values.len() == 1 {
-            Ok(values[0].clone())
-        } else {
-            // Retrieve the bitmaps from both sides
-            let mut del_bitmaps_bytes = Vec::new();
-            let mut add_bitmaps_bytes = Vec::new();
-            for value in values {
-                let obkv: &KvReaderDelAdd = value.as_ref().into();
-                if let Some(bitmap_bytes) = obkv.get(DelAdd::Deletion) {
-                    del_bitmaps_bytes.push(bitmap_bytes);
-                }
-                if let Some(bitmap_bytes) = obkv.get(DelAdd::Addition) {
-                    add_bitmaps_bytes.push(bitmap_bytes);
-                }
-            }
-
-            let mut output_deladd_obkv = KvWriterDelAdd::memory();
-
-            // Deletion
-            let mut buffer = Vec::new();
-            let mut merged = RoaringBitmap::new();
-            for bytes in del_bitmaps_bytes {
-                merged |= RoaringBitmap::deserialize_unchecked_from(bytes)?;
-            }
-            merged.serialize_into(&mut buffer)?;
-            output_deladd_obkv.insert(DelAdd::Deletion, &buffer)?;
-
-            // Addition
-            buffer.clear();
-            merged.clear();
-            for bytes in add_bitmaps_bytes {
-                merged |= RoaringBitmap::deserialize_unchecked_from(bytes)?;
-            }
-            output_deladd_obkv.insert(DelAdd::Addition, &buffer)?;
-
-            output_deladd_obkv.into_inner().map(Cow::from).map_err(Into::into)
-        }
-    }
-}
+}
\ No newline at end of file