diff --git a/milli/src/update/index_documents/extract/extract_word_position_docids.rs b/milli/src/update/index_documents/extract/extract_word_position_docids.rs
index 220dca960..2ff2f2ad5 100644
--- a/milli/src/update/index_documents/extract/extract_word_position_docids.rs
+++ b/milli/src/update/index_documents/extract/extract_word_position_docids.rs
@@ -1,15 +1,17 @@
-use std::collections::HashSet;
+use std::collections::BTreeSet;
 use std::fs::File;
 use std::io::{self, BufReader};
 
 use obkv::KvReaderU16;
 
 use super::helpers::{
-    create_sorter, merge_cbo_roaring_bitmaps, sorter_into_reader, try_split_array_at,
+    create_sorter, merge_deladd_cbo_roaring_bitmaps, sorter_into_reader, try_split_array_at,
     GrenadParameters,
 };
 use crate::error::SerializationError;
 use crate::index::db_name::DOCID_WORD_POSITIONS;
+use crate::update::del_add::{DelAdd, KvReaderDelAdd, KvWriterDelAdd};
+use crate::update::MergeFn;
 use crate::{bucketed_position, DocumentId, Result};
 
 /// Extracts the word positions and the documents ids where this word appear.
@@ -27,14 +29,15 @@ pub fn extract_word_position_docids<R: io::Read + io::Seek>(
 
     let mut word_position_docids_sorter = create_sorter(
         grenad::SortAlgorithm::Unstable,
-        merge_cbo_roaring_bitmaps,
+        merge_deladd_cbo_roaring_bitmaps,
         indexer.chunk_compression_type,
         indexer.chunk_compression_level,
         indexer.max_nb_chunks,
         max_memory,
     );
 
-    let mut word_positions: HashSet<(u16, Vec<u8>)> = HashSet::new();
+    let mut del_word_positions: BTreeSet<(u16, Vec<u8>)> = BTreeSet::new();
+    let mut add_word_positions: BTreeSet<(u16, Vec<u8>)> = BTreeSet::new();
     let mut current_document_id: Option<u32> = None;
     let mut key_buffer = Vec::new();
     let mut cursor = docid_word_positions.into_cursor()?;
@@ -44,36 +47,92 @@ pub fn extract_word_position_docids<R: io::Read + io::Seek>(
         let document_id = DocumentId::from_be_bytes(document_id_bytes);
 
         if current_document_id.map_or(false, |id| document_id != id) {
-            for (position, word_bytes) in word_positions.iter() {
-                key_buffer.clear();
-                key_buffer.extend_from_slice(word_bytes);
-                key_buffer.push(0);
-                key_buffer.extend_from_slice(&position.to_be_bytes());
-                word_position_docids_sorter
-                    .insert(&key_buffer, current_document_id.unwrap().to_ne_bytes())?;
-            }
-            word_positions.clear();
+            words_position_into_sorter(
+                current_document_id.unwrap(),
+                &mut key_buffer,
+                &del_word_positions,
+                &add_word_positions,
+                &mut word_position_docids_sorter,
+            )?;
+            del_word_positions.clear();
+            add_word_positions.clear();
         }
 
         current_document_id = Some(document_id);
 
-        for (position, word_bytes) in KvReaderU16::new(&value).iter() {
-            let position = bucketed_position(position);
-            word_positions.insert((position, word_bytes.to_vec()));
+        let del_add_reader = KvReaderDelAdd::new(&value);
+        // extract all unique words to remove.
+        if let Some(deletion) = del_add_reader.get(DelAdd::Deletion) {
+            for (position, word_bytes) in KvReaderU16::new(deletion).iter() {
+                let position = bucketed_position(position);
+                del_word_positions.insert((position, word_bytes.to_vec()));
+            }
+        }
+
+        // extract all unique additional words.
+        if let Some(addition) = del_add_reader.get(DelAdd::Addition) {
+            for (position, word_bytes) in KvReaderU16::new(addition).iter() {
+                let position = bucketed_position(position);
+                add_word_positions.insert((position, word_bytes.to_vec()));
+            }
         }
     }
 
     if let Some(document_id) = current_document_id {
-        for (position, word_bytes) in word_positions {
-            key_buffer.clear();
-            key_buffer.extend_from_slice(&word_bytes);
-            key_buffer.push(0);
-            key_buffer.extend_from_slice(&position.to_be_bytes());
-            word_position_docids_sorter.insert(&key_buffer, document_id.to_ne_bytes())?;
-        }
+        words_position_into_sorter(
+            document_id,
+            &mut key_buffer,
+            &del_word_positions,
+            &add_word_positions,
+            &mut word_position_docids_sorter,
+        )?;
     }
 
+    // TODO remove noop DelAdd OBKV
     let word_position_docids_reader = sorter_into_reader(word_position_docids_sorter, indexer)?;
 
     Ok(word_position_docids_reader)
 }
+
+fn words_position_into_sorter(
+    document_id: DocumentId,
+    key_buffer: &mut Vec<u8>,
+    del_word_positions: &BTreeSet<(u16, Vec<u8>)>,
+    add_word_positions: &BTreeSet<(u16, Vec<u8>)>,
+    word_position_docids_sorter: &mut grenad::Sorter<MergeFn>,
+) -> Result<()> {
+    puffin::profile_function!();
+
+    use itertools::merge_join_by;
+    use itertools::EitherOrBoth::{Both, Left, Right};
+
+    let mut buffer = Vec::new();
+    for eob in merge_join_by(del_word_positions.iter(), add_word_positions.iter(), |d, a| d.cmp(a))
+    {
+        buffer.clear();
+        let mut value_writer = KvWriterDelAdd::new(&mut buffer);
+        let (position, word_bytes) = match eob {
+            Left(key) => {
+                value_writer.insert(DelAdd::Deletion, document_id.to_ne_bytes()).unwrap();
+                key
+            }
+            Right(key) => {
+                value_writer.insert(DelAdd::Addition, document_id.to_ne_bytes()).unwrap();
+                key
+            }
+            Both(key, _) => {
+                value_writer.insert(DelAdd::Deletion, document_id.to_ne_bytes()).unwrap();
+                value_writer.insert(DelAdd::Addition, document_id.to_ne_bytes()).unwrap();
+                key
+            }
+        };
+
+        key_buffer.clear();
+        key_buffer.extend_from_slice(word_bytes);
+        key_buffer.push(0);
+        key_buffer.extend_from_slice(&position.to_be_bytes());
+        word_position_docids_sorter.insert(&key_buffer, value_writer.into_inner().unwrap())?;
+    }
+
+    Ok(())
+}