diff --git a/milli/src/update/new/extract/searchable/extract_word_pair_proximity_docids.rs b/milli/src/update/new/extract/searchable/extract_word_pair_proximity_docids.rs
index 7b3706424..82007f9ba 100644
--- a/milli/src/update/new/extract/searchable/extract_word_pair_proximity_docids.rs
+++ b/milli/src/update/new/extract/searchable/extract_word_pair_proximity_docids.rs
@@ -1,4 +1,4 @@
-use std::collections::{BTreeMap, VecDeque};
+use std::collections::{HashMap, VecDeque};
 
 use heed::RoTxn;
 use itertools::merge_join_by;
@@ -35,10 +35,8 @@ impl SearchableExtractor for WordPairProximityDocidsExtractor {
         cached_sorter: &mut CboCachedSorter<MergeDeladdCboRoaringBitmaps>,
         document_change: DocumentChange,
     ) -> Result<()> {
-        /// TODO: mutualize those buffers
         let mut key_buffer = Vec::new();
-        let mut add_word_pair_proximity = BTreeMap::new();
-        let mut del_word_pair_proximity = BTreeMap::new();
+        let mut word_pair_proximity = HashMap::new();
         let mut word_positions: VecDeque<(String, u16)> =
             VecDeque::with_capacity(MAX_DISTANCE as usize);
 
@@ -51,7 +49,14 @@ impl SearchableExtractor for WordPairProximityDocidsExtractor {
                     document_tokenizer,
                     fields_ids_map,
                     &mut word_positions,
-                    &mut del_word_pair_proximity,
+                    &mut |(w1, w2), prox| {
+                        word_pair_proximity
+                            .entry((w1, w2))
+                            .and_modify(|(del_p, _add_p)| {
+                                *del_p = std::cmp::min(*del_p, prox);
+                            })
+                            .or_insert((prox, 0));
+                    },
                 )?;
             }
             DocumentChange::Update(inner) => {
@@ -61,7 +66,14 @@ impl SearchableExtractor for WordPairProximityDocidsExtractor {
                     document_tokenizer,
                     fields_ids_map,
                     &mut word_positions,
-                    &mut del_word_pair_proximity,
+                    &mut |(w1, w2), prox| {
+                        word_pair_proximity
+                            .entry((w1, w2))
+                            .and_modify(|(del_p, _add_p)| {
+                                *del_p = std::cmp::min(*del_p, prox);
+                            })
+                            .or_insert((prox, 0));
+                    },
                 )?;
                 let document = inner.new();
                 process_document_tokens(
@@ -69,7 +81,14 @@ impl SearchableExtractor for WordPairProximityDocidsExtractor {
                     document_tokenizer,
                     fields_ids_map,
                     &mut word_positions,
-                    &mut add_word_pair_proximity,
+                    &mut |(w1, w2), prox| {
+                        word_pair_proximity
+                            .entry((w1, w2))
+                            .and_modify(|(_del_p, add_p)| {
+                                *add_p = std::cmp::min(*add_p, prox);
+                            })
+                            .or_insert((0, prox));
+                    },
                 )?;
             }
             DocumentChange::Insertion(inner) => {
@@ -79,35 +98,23 @@ impl SearchableExtractor for WordPairProximityDocidsExtractor {
                     document_tokenizer,
                     fields_ids_map,
                     &mut word_positions,
-                    &mut add_word_pair_proximity,
+                    &mut |(w1, w2), prox| {
+                        word_pair_proximity
+                            .entry((w1, w2))
+                            .and_modify(|(_del_p, add_p)| {
+                                *add_p = std::cmp::min(*add_p, prox);
+                            })
+                            .or_insert((0, prox));
+                    },
                 )?;
             }
         }
 
-        use itertools::EitherOrBoth::*;
-        for eob in
-            merge_join_by(del_word_pair_proximity.iter(), add_word_pair_proximity.iter(), |d, a| {
-                d.cmp(a)
-            })
-        {
-            match eob {
-                Left(((w1, w2), prox)) => {
-                    let key = build_key(*prox, w1, w2, &mut key_buffer);
-                    cached_sorter.insert_del_u32(key, docid)?;
-                }
-                Right(((w1, w2), prox)) => {
-                    let key = build_key(*prox, w1, w2, &mut key_buffer);
-                    cached_sorter.insert_add_u32(key, docid)?;
-                }
-                Both(((w1, w2), del_prox), (_, add_prox)) => {
-                    if del_prox != add_prox {
-                        let key = build_key(*del_prox, w1, w2, &mut key_buffer);
-                        cached_sorter.insert_del_u32(key, docid)?;
-                        let key = build_key(*add_prox, w1, w2, &mut key_buffer);
-                        cached_sorter.insert_add_u32(key, docid)?;
-                    }
-                }
-            }
+        for ((w1, w2), (del_p, add_p)) in word_pair_proximity.iter() {
+            let key = build_key(*del_p, w1, w2, &mut key_buffer);
+            cached_sorter.insert_del_u32(key, docid)?;
+            let key = build_key(*add_p, w1, w2, &mut key_buffer);
+            cached_sorter.insert_add_u32(key, docid)?;
         }
 
         Ok(())
@@ -125,18 +132,19 @@ fn build_key<'a>(prox: u8, w1: &str, w2: &str, key_buffer: &'a mut Vec<u8>) -> &
 
 fn word_positions_into_word_pair_proximity(
     word_positions: &mut VecDeque<(String, u16)>,
-    word_pair_proximity: &mut BTreeMap<(String, String), u8>,
+    word_pair_proximity: &mut dyn FnMut((String, String), u8),
 ) -> Result<()> {
     let (head_word, head_position) = word_positions.pop_front().unwrap();
     for (word, position) in word_positions.iter() {
         let prox = index_proximity(head_position as u32, *position as u32) as u8;
         if prox > 0 && prox < MAX_DISTANCE as u8 {
-            word_pair_proximity
-                .entry((head_word.clone(), word.clone()))
-                .and_modify(|p| {
-                    *p = std::cmp::min(*p, prox);
-                })
-                .or_insert(prox);
+            word_pair_proximity((head_word.clone(), word.clone()), prox);
+            // word_pair_proximity
+            //     .entry((head_word.clone(), word.clone()))
+            //     .and_modify(|p| {
+            //         *p = std::cmp::min(*p, prox);
+            //     })
+            //     .or_insert(prox);
         }
     }
     Ok(())
@@ -147,7 +155,7 @@ fn process_document_tokens(
     document_tokenizer: &DocumentTokenizer,
     fields_ids_map: &mut GlobalFieldsIdsMap,
     word_positions: &mut VecDeque<(String, u16)>,
-    word_pair_proximity: &mut BTreeMap<(String, String), u8>,
+    word_pair_proximity: &mut dyn FnMut((String, String), u8),
 ) -> Result<()> {
     let mut token_fn = |_fname: &str, _fid: FieldId, pos: u16, word: &str| {
         // drain the proximity window until the head word is considered close to the word we are inserting.