diff --git a/milli/Cargo.toml b/milli/Cargo.toml
index 6b830c29e..9197fa818 100644
--- a/milli/Cargo.toml
+++ b/milli/Cargo.toml
@@ -16,7 +16,7 @@ either = "1.6.1"
 flate2 = "1.0.20"
 fst = "0.4.5"
 fxhash = "0.2.1"
-grenad = { version = "0.3.1", default-features = false, features = ["tempfile"] }
+grenad = { version = "0.4.1", default-features = false, features = ["tempfile"] }
 geoutils = "0.4.1"
 heed = { git = "https://github.com/Kerollmops/heed", tag = "v0.12.1", default-features = false, features = ["lmdb", "sync-read-txn"] }
 human_format = "1.0.3"
diff --git a/milli/src/error.rs b/milli/src/error.rs
index 47c9a5993..dce23582a 100644
--- a/milli/src/error.rs
+++ b/milli/src/error.rs
@@ -29,6 +29,7 @@ pub enum InternalError {
     FieldIdMapMissingEntry(FieldIdMapMissingEntry),
     Fst(fst::Error),
     GrenadInvalidCompressionType,
+    GrenadInvalidFormatVersion,
     IndexingMergingKeys { process: &'static str },
     InvalidDatabaseTyping,
     RayonThreadPool(ThreadPoolBuildError),
@@ -97,6 +98,9 @@ where
             grenad::Error::InvalidCompressionType => {
                 Error::InternalError(InternalError::GrenadInvalidCompressionType)
             }
+            grenad::Error::InvalidFormatVersion => {
+                Error::InternalError(InternalError::GrenadInvalidFormatVersion)
+            }
         }
     }
 }
@@ -186,6 +190,9 @@ impl fmt::Display for InternalError {
             Self::GrenadInvalidCompressionType => {
                 f.write_str("Invalid compression type have been specified to grenad.")
             }
+            Self::GrenadInvalidFormatVersion => {
+                f.write_str("Invalid grenad file with an invalid version format.")
+            }
             Self::IndexingMergingKeys { process } => {
                 write!(f, "Invalid merge while processing {}.", process)
             }
diff --git a/milli/src/update/facets.rs b/milli/src/update/facets.rs
index 19684c6ea..53305cdee 100644
--- a/milli/src/update/facets.rs
+++ b/milli/src/update/facets.rs
@@ -160,8 +160,7 @@ fn compute_facet_number_levels<'t>(
 
     // It is forbidden to keep a cursor and write in a database at the same time with LMDB
     // therefore we write the facet levels entries into a grenad file before transfering them.
-    let mut writer = tempfile::tempfile()
-        .and_then(|file| create_writer(compression_type, compression_level, file))?;
+    let mut writer = create_writer(compression_type, compression_level, tempfile::tempfile()?);
 
     let level_0_range = {
         let left = (field_id, 0, f64::MIN, f64::MIN);
@@ -279,8 +278,7 @@ fn compute_facet_string_levels<'t>(
 
     // It is forbidden to keep a cursor and write in a database at the same time with LMDB
     // therefore we write the facet levels entries into a grenad file before transfering them.
-    let mut writer = tempfile::tempfile()
-        .and_then(|file| create_writer(compression_type, compression_level, file))?;
+    let mut writer = create_writer(compression_type, compression_level, tempfile::tempfile()?);
 
     // Groups sizes are always a power of the original level_group_size and therefore a group
     // always maps groups of the previous level and never splits previous levels groups in half.
diff --git a/milli/src/update/index_documents/extract/extract_docid_word_positions.rs b/milli/src/update/index_documents/extract/extract_docid_word_positions.rs
index fa1381412..44bf9dbf7 100644
--- a/milli/src/update/index_documents/extract/extract_docid_word_positions.rs
+++ b/milli/src/update/index_documents/extract/extract_docid_word_positions.rs
@@ -18,8 +18,8 @@ use crate::{absolute_from_relative_position, FieldId, Result, MAX_POSITION_PER_A
 /// Returns the generated internal documents ids and a grenad reader
 /// with the list of extracted words from the given chunk of documents.
 #[logging_timer::time]
-pub fn extract_docid_word_positions<R: io::Read>(
-    mut obkv_documents: grenad::Reader<R>,
+pub fn extract_docid_word_positions<R: io::Read + io::Seek>(
+    obkv_documents: grenad::Reader<R>,
     indexer: GrenadParameters,
     searchable_fields: &Option<HashSet<FieldId>>,
     stop_words: Option<&fst::Set<&[u8]>>,
@@ -46,7 +46,8 @@ pub fn extract_docid_word_positions<R: io::Read>(
     }
     let analyzer = Analyzer::<Vec<u8>>::new(AnalyzerConfig::default());
 
-    while let Some((key, value)) = obkv_documents.next()? {
+    let mut cursor = obkv_documents.into_cursor()?;
+    while let Some((key, value)) = cursor.move_on_next()? {
         let document_id = key
             .try_into()
             .map(u32::from_be_bytes)
diff --git a/milli/src/update/index_documents/extract/extract_facet_number_docids.rs b/milli/src/update/index_documents/extract/extract_facet_number_docids.rs
index 5480bd605..fa63d9549 100644
--- a/milli/src/update/index_documents/extract/extract_facet_number_docids.rs
+++ b/milli/src/update/index_documents/extract/extract_facet_number_docids.rs
@@ -14,8 +14,8 @@ use crate::Result;
 /// Returns a grenad reader with the list of extracted facet numbers and
 /// documents ids from the given chunk of docid facet number positions.
 #[logging_timer::time]
-pub fn extract_facet_number_docids<R: io::Read>(
-    mut docid_fid_facet_number: grenad::Reader<R>,
+pub fn extract_facet_number_docids<R: io::Read + io::Seek>(
+    docid_fid_facet_number: grenad::Reader<R>,
     indexer: GrenadParameters,
 ) -> Result<grenad::Reader<File>> {
     let max_memory = indexer.max_memory_by_thread();
@@ -28,7 +28,8 @@ pub fn extract_facet_number_docids<R: io::Read>(
         max_memory,
     );
 
-    while let Some((key_bytes, _)) = docid_fid_facet_number.next()? {
+    let mut cursor = docid_fid_facet_number.into_cursor()?;
+    while let Some((key_bytes, _)) = cursor.move_on_next()? {
         let (field_id, document_id, number) =
             FieldDocIdFacetF64Codec::bytes_decode(key_bytes).unwrap();
 
diff --git a/milli/src/update/index_documents/extract/extract_facet_string_docids.rs b/milli/src/update/index_documents/extract/extract_facet_string_docids.rs
index e08d062cf..8209d817b 100644
--- a/milli/src/update/index_documents/extract/extract_facet_string_docids.rs
+++ b/milli/src/update/index_documents/extract/extract_facet_string_docids.rs
@@ -16,8 +16,8 @@ use crate::{FieldId, Result};
 /// Returns a grenad reader with the list of extracted facet strings and
 /// documents ids from the given chunk of docid facet string positions.
 #[logging_timer::time]
-pub fn extract_facet_string_docids<R: io::Read>(
-    mut docid_fid_facet_string: grenad::Reader<R>,
+pub fn extract_facet_string_docids<R: io::Read + io::Seek>(
+    docid_fid_facet_string: grenad::Reader<R>,
     indexer: GrenadParameters,
 ) -> Result<grenad::Reader<File>> {
     let max_memory = indexer.max_memory_by_thread();
@@ -32,7 +32,8 @@ pub fn extract_facet_string_docids<R: io::Read>(
 
     let mut key_buffer = Vec::new();
     let mut value_buffer = Vec::new();
-    while let Some((key, original_value_bytes)) = docid_fid_facet_string.next()? {
+    let mut cursor = docid_fid_facet_string.into_cursor()?;
+    while let Some((key, original_value_bytes)) = cursor.move_on_next()? {
         let (field_id_bytes, bytes) = try_split_array_at(key).unwrap();
         let field_id = FieldId::from_be_bytes(field_id_bytes);
         let (document_id_bytes, normalized_value_bytes) = try_split_array_at(bytes).unwrap();
diff --git a/milli/src/update/index_documents/extract/extract_fid_docid_facet_values.rs b/milli/src/update/index_documents/extract/extract_fid_docid_facet_values.rs
index a1bf0b1e3..628636f78 100644
--- a/milli/src/update/index_documents/extract/extract_fid_docid_facet_values.rs
+++ b/milli/src/update/index_documents/extract/extract_fid_docid_facet_values.rs
@@ -16,8 +16,8 @@ use crate::{DocumentId, FieldId, Result};
 /// Returns the generated grenad reader containing the docid the fid and the orginal value as key
 /// and the normalized value as value extracted from the given chunk of documents.
 #[logging_timer::time]
-pub fn extract_fid_docid_facet_values<R: io::Read>(
-    mut obkv_documents: grenad::Reader<R>,
+pub fn extract_fid_docid_facet_values<R: io::Read + io::Seek>(
+    obkv_documents: grenad::Reader<R>,
     indexer: GrenadParameters,
     faceted_fields: &HashSet<FieldId>,
 ) -> Result<(grenad::Reader<File>, grenad::Reader<File>)> {
@@ -40,7 +40,8 @@ pub fn extract_fid_docid_facet_values<R: io::Read>(
     );
 
     let mut key_buffer = Vec::new();
-    while let Some((docid_bytes, value)) = obkv_documents.next()? {
+    let mut cursor = obkv_documents.into_cursor()?;
+    while let Some((docid_bytes, value)) = cursor.move_on_next()? {
         let obkv = obkv::KvReader::new(value);
 
         for (field_id, field_bytes) in obkv.iter() {
diff --git a/milli/src/update/index_documents/extract/extract_fid_word_count_docids.rs b/milli/src/update/index_documents/extract/extract_fid_word_count_docids.rs
index 4e25cb4f6..85a65ee14 100644
--- a/milli/src/update/index_documents/extract/extract_fid_word_count_docids.rs
+++ b/milli/src/update/index_documents/extract/extract_fid_word_count_docids.rs
@@ -18,8 +18,8 @@ use crate::{relative_from_absolute_position, DocumentId, FieldId, Result};
 /// Returns a grenad reader with the list of extracted field id word counts
 /// and documents ids from the given chunk of docid word positions.
 #[logging_timer::time]
-pub fn extract_fid_word_count_docids<R: io::Read>(
-    mut docid_word_positions: grenad::Reader<R>,
+pub fn extract_fid_word_count_docids<R: io::Read + io::Seek>(
+    docid_word_positions: grenad::Reader<R>,
     indexer: GrenadParameters,
 ) -> Result<grenad::Reader<File>> {
     let max_memory = indexer.max_memory_by_thread();
@@ -36,7 +36,8 @@ pub fn extract_fid_word_count_docids<R: io::Read>(
     let mut document_fid_wordcount = HashMap::new();
     let mut current_document_id = None;
 
-    while let Some((key, value)) = docid_word_positions.next()? {
+    let mut cursor = docid_word_positions.into_cursor()?;
+    while let Some((key, value)) = cursor.move_on_next()? {
         let (document_id_bytes, _word_bytes) = try_split_array_at(key)
             .ok_or_else(|| SerializationError::Decoding { db_name: Some(DOCID_WORD_POSITIONS) })?;
         let document_id = u32::from_be_bytes(document_id_bytes);
diff --git a/milli/src/update/index_documents/extract/extract_geo_points.rs b/milli/src/update/index_documents/extract/extract_geo_points.rs
index a36b608ee..e58d351d6 100644
--- a/milli/src/update/index_documents/extract/extract_geo_points.rs
+++ b/milli/src/update/index_documents/extract/extract_geo_points.rs
@@ -10,17 +10,20 @@ use crate::{FieldId, InternalError, Result, UserError};
 /// Extracts the geographical coordinates contained in each document under the `_geo` field.
 ///
 /// Returns the generated grenad reader containing the docid as key associated to the (latitude, longitude)
-pub fn extract_geo_points<R: io::Read>(
-    mut obkv_documents: grenad::Reader<R>,
+pub fn extract_geo_points<R: io::Read + io::Seek>(
+    obkv_documents: grenad::Reader<R>,
     indexer: GrenadParameters,
     primary_key_id: FieldId,
     geo_field_id: FieldId,
 ) -> Result<grenad::Reader<File>> {
-    let mut writer = tempfile::tempfile().and_then(|file| {
-        create_writer(indexer.chunk_compression_type, indexer.chunk_compression_level, file)
-    })?;
+    let mut writer = create_writer(
+        indexer.chunk_compression_type,
+        indexer.chunk_compression_level,
+        tempfile::tempfile()?,
+    );
 
-    while let Some((docid_bytes, value)) = obkv_documents.next()? {
+    let mut cursor = obkv_documents.into_cursor()?;
+    while let Some((docid_bytes, value)) = cursor.move_on_next()? {
         let obkv = obkv::KvReader::new(value);
         let point: Value = match obkv.get(geo_field_id) {
             Some(point) => serde_json::from_slice(point).map_err(InternalError::SerdeJson)?,
diff --git a/milli/src/update/index_documents/extract/extract_word_docids.rs b/milli/src/update/index_documents/extract/extract_word_docids.rs
index 6d99fda44..80d68298a 100644
--- a/milli/src/update/index_documents/extract/extract_word_docids.rs
+++ b/milli/src/update/index_documents/extract/extract_word_docids.rs
@@ -17,8 +17,8 @@ use crate::Result;
 /// Returns a grenad reader with the list of extracted words and
 /// documents ids from the given chunk of docid word positions.
 #[logging_timer::time]
-pub fn extract_word_docids<R: io::Read>(
-    mut docid_word_positions: grenad::Reader<R>,
+pub fn extract_word_docids<R: io::Read + io::Seek>(
+    docid_word_positions: grenad::Reader<R>,
     indexer: GrenadParameters,
 ) -> Result<grenad::Reader<File>> {
     let max_memory = indexer.max_memory_by_thread();
@@ -32,7 +32,8 @@ pub fn extract_word_docids<R: io::Read>(
     );
 
     let mut value_buffer = Vec::new();
-    while let Some((key, _value)) = docid_word_positions.next()? {
+    let mut cursor = docid_word_positions.into_cursor()?;
+    while let Some((key, _value)) = cursor.move_on_next()? {
         let (document_id_bytes, word_bytes) = try_split_array_at(key)
             .ok_or_else(|| SerializationError::Decoding { db_name: Some(DOCID_WORD_POSITIONS) })?;
         let document_id = u32::from_be_bytes(document_id_bytes);
diff --git a/milli/src/update/index_documents/extract/extract_word_pair_proximity_docids.rs b/milli/src/update/index_documents/extract/extract_word_pair_proximity_docids.rs
index f3667694a..90349eb93 100644
--- a/milli/src/update/index_documents/extract/extract_word_pair_proximity_docids.rs
+++ b/milli/src/update/index_documents/extract/extract_word_pair_proximity_docids.rs
@@ -17,8 +17,8 @@ use crate::{DocumentId, Result};
 /// Returns a grenad reader with the list of extracted word pairs proximities and
 /// documents ids from the given chunk of docid word positions.
 #[logging_timer::time]
-pub fn extract_word_pair_proximity_docids<R: io::Read>(
-    mut docid_word_positions: grenad::Reader<R>,
+pub fn extract_word_pair_proximity_docids<R: io::Read + io::Seek>(
+    docid_word_positions: grenad::Reader<R>,
     indexer: GrenadParameters,
 ) -> Result<grenad::Reader<File>> {
     let max_memory = indexer.max_memory_by_thread();
@@ -35,7 +35,8 @@ pub fn extract_word_pair_proximity_docids<R: io::Read>(
     let mut document_word_positions_heap = BinaryHeap::new();
     let mut current_document_id = None;
 
-    while let Some((key, value)) = docid_word_positions.next()? {
+    let mut cursor = docid_word_positions.into_cursor()?;
+    while let Some((key, value)) = cursor.move_on_next()? {
         let (document_id_bytes, word_bytes) = try_split_array_at(key)
             .ok_or_else(|| SerializationError::Decoding { db_name: Some(DOCID_WORD_POSITIONS) })?;
         let document_id = u32::from_be_bytes(document_id_bytes);
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 4ca8537ac..a4720ba2b 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
@@ -14,8 +14,8 @@ use crate::{DocumentId, Result};
 /// Returns a grenad reader with the list of extracted words at positions and
 /// documents ids from the given chunk of docid word positions.
 #[logging_timer::time]
-pub fn extract_word_position_docids<R: io::Read>(
-    mut docid_word_positions: grenad::Reader<R>,
+pub fn extract_word_position_docids<R: io::Read + io::Seek>(
+    docid_word_positions: grenad::Reader<R>,
     indexer: GrenadParameters,
 ) -> Result<grenad::Reader<File>> {
     let max_memory = indexer.max_memory_by_thread();
@@ -29,7 +29,8 @@ pub fn extract_word_position_docids<R: io::Read>(
     );
 
     let mut key_buffer = Vec::new();
-    while let Some((key, value)) = docid_word_positions.next()? {
+    let mut cursor = docid_word_positions.into_cursor()?;
+    while let Some((key, value)) = cursor.move_on_next()? {
         let (document_id_bytes, word_bytes) = try_split_array_at(key)
             .ok_or_else(|| SerializationError::Decoding { db_name: Some(DOCID_WORD_POSITIONS) })?;
         let document_id = DocumentId::from_be_bytes(document_id_bytes);
diff --git a/milli/src/update/index_documents/helpers/grenad_helpers.rs b/milli/src/update/index_documents/helpers/grenad_helpers.rs
index eef067122..ec4a32755 100644
--- a/milli/src/update/index_documents/helpers/grenad_helpers.rs
+++ b/milli/src/update/index_documents/helpers/grenad_helpers.rs
@@ -17,7 +17,7 @@ pub fn create_writer<R: io::Write>(
     typ: grenad::CompressionType,
     level: Option<u32>,
     file: R,
-) -> io::Result<grenad::Writer<R>> {
+) -> grenad::Writer<R> {
     let mut builder = grenad::Writer::builder();
     builder.compression_type(typ);
     if let Some(level) = level {
@@ -52,10 +52,13 @@ pub fn sorter_into_reader(
     sorter: grenad::Sorter<MergeFn>,
     indexer: GrenadParameters,
 ) -> Result<grenad::Reader<File>> {
-    let mut writer = tempfile::tempfile().and_then(|file| {
-        create_writer(indexer.chunk_compression_type, indexer.chunk_compression_level, file)
-    })?;
-    sorter.write_into(&mut writer)?;
+    let mut writer = create_writer(
+        indexer.chunk_compression_type,
+        indexer.chunk_compression_level,
+        tempfile::tempfile()?,
+    );
+    sorter.write_into_stream_writer(&mut writer)?;
+
     Ok(writer_into_reader(writer)?)
 }
 
@@ -75,20 +78,25 @@ pub unsafe fn into_clonable_grenad(
     Ok(reader)
 }
 
-pub fn merge_readers<R: io::Read>(
+pub fn merge_readers<R: io::Read + io::Seek>(
     readers: Vec<grenad::Reader<R>>,
     merge_fn: MergeFn,
     indexer: GrenadParameters,
 ) -> Result<grenad::Reader<File>> {
     let mut merger_builder = grenad::MergerBuilder::new(merge_fn);
-    merger_builder.extend(readers);
+    for reader in readers {
+        merger_builder.push(reader.into_cursor()?);
+    }
+
     let merger = merger_builder.build();
-    let mut writer = tempfile::tempfile().and_then(|file| {
-        create_writer(indexer.chunk_compression_type, indexer.chunk_compression_level, file)
-    })?;
-    merger.write_into(&mut writer)?;
-    let reader = writer_into_reader(writer)?;
-    Ok(reader)
+    let mut writer = create_writer(
+        indexer.chunk_compression_type,
+        indexer.chunk_compression_level,
+        tempfile::tempfile()?,
+    );
+    merger.write_into_stream_writer(&mut writer)?;
+
+    Ok(writer_into_reader(writer)?)
 }
 
 #[derive(Debug, Clone, Copy)]
@@ -125,12 +133,13 @@ impl GrenadParameters {
 /// The grenad obkv entries are composed of an incremental document id big-endian
 /// encoded as the key and an obkv object with an `u8` for the field as the key
 /// and a simple UTF-8 encoded string as the value.
-pub fn grenad_obkv_into_chunks<R: io::Read>(
-    mut reader: grenad::Reader<R>,
+pub fn grenad_obkv_into_chunks<R: io::Read + io::Seek>(
+    reader: grenad::Reader<R>,
     indexer: GrenadParameters,
     documents_chunk_size: usize,
 ) -> Result<impl Iterator<Item = Result<grenad::Reader<File>>>> {
     let mut continue_reading = true;
+    let mut cursor = reader.into_cursor()?;
 
     let indexer_clone = indexer.clone();
     let mut transposer = move || {
@@ -139,15 +148,13 @@ pub fn grenad_obkv_into_chunks<R: io::Read>(
         }
 
         let mut current_chunk_size = 0u64;
-        let mut obkv_documents = tempfile::tempfile().and_then(|file| {
-            create_writer(
-                indexer_clone.chunk_compression_type,
-                indexer_clone.chunk_compression_level,
-                file,
-            )
-        })?;
+        let mut obkv_documents = create_writer(
+            indexer_clone.chunk_compression_type,
+            indexer_clone.chunk_compression_level,
+            tempfile::tempfile()?,
+        );
 
-        while let Some((document_id, obkv)) = reader.next()? {
+        while let Some((document_id, obkv)) = cursor.move_on_next()? {
             obkv_documents.insert(document_id, obkv)?;
             current_chunk_size += document_id.len() as u64 + obkv.len() as u64;
 
@@ -166,13 +173,14 @@ pub fn grenad_obkv_into_chunks<R: io::Read>(
 pub fn write_into_lmdb_database(
     wtxn: &mut heed::RwTxn,
     database: heed::PolyDatabase,
-    mut reader: Reader<File>,
+    reader: Reader<File>,
     merge: MergeFn,
 ) -> Result<()> {
     debug!("Writing MTBL stores...");
     let before = Instant::now();
 
-    while let Some((k, v)) = reader.next()? {
+    let mut cursor = reader.into_cursor()?;
+    while let Some((k, v)) = cursor.move_on_next()? {
         let mut iter = database.prefix_iter_mut::<_, ByteSlice, ByteSlice>(wtxn, k)?;
         match iter.next().transpose()? {
             Some((key, old_val)) if key == k => {
@@ -201,19 +209,19 @@ pub fn sorter_into_lmdb_database(
     debug!("Writing MTBL sorter...");
     let before = Instant::now();
 
-    merger_iter_into_lmdb_database(wtxn, database, sorter.into_merger_iter()?, merge)?;
+    merger_iter_into_lmdb_database(wtxn, database, sorter.into_stream_merger_iter()?, merge)?;
 
     debug!("MTBL sorter writen in {:.02?}!", before.elapsed());
     Ok(())
 }
 
-fn merger_iter_into_lmdb_database<R: io::Read>(
+fn merger_iter_into_lmdb_database<R: io::Read + io::Seek>(
     wtxn: &mut heed::RwTxn,
     database: heed::PolyDatabase,
-    mut sorter: MergerIter<R, MergeFn>,
+    mut merger_iter: MergerIter<R, MergeFn>,
     merge: MergeFn,
 ) -> Result<()> {
-    while let Some((k, v)) = sorter.next()? {
+    while let Some((k, v)) = merger_iter.next()? {
         let mut iter = database.prefix_iter_mut::<_, ByteSlice, ByteSlice>(wtxn, k)?;
         match iter.next().transpose()? {
             Some((key, old_val)) if key == k => {
diff --git a/milli/src/update/index_documents/transform.rs b/milli/src/update/index_documents/transform.rs
index f5fb1ec01..4ec34c0c6 100644
--- a/milli/src/update/index_documents/transform.rs
+++ b/milli/src/update/index_documents/transform.rs
@@ -277,7 +277,7 @@ impl<'a, 'i> Transform<'a, 'i> {
         let mut available_documents_ids = AvailableDocumentsIds::from_documents_ids(&documents_ids);
 
         // consume sorter, in order to free the internal allocation, before creating a new one.
-        let mut iter = self.sorter.into_merger_iter()?;
+        let mut iter = self.sorter.into_stream_merger_iter()?;
 
         // Once we have sort and deduplicated the documents we write them into a final file.
         let mut final_sorter = create_sorter(
@@ -374,16 +374,15 @@ impl<'a, 'i> Transform<'a, 'i> {
         });
 
         // We create a final writer to write the new documents in order from the sorter.
-        let file = tempfile::tempfile()?;
         let mut writer = create_writer(
             self.indexer_settings.chunk_compression_type,
             self.indexer_settings.chunk_compression_level,
-            file,
-        )?;
+            tempfile::tempfile()?,
+        );
 
         // Once we have written all the documents into the final sorter, we write the documents
         // into this writer, extract the file and reset the seek to be able to read it again.
-        final_sorter.write_into(&mut writer)?;
+        final_sorter.write_into_stream_writer(&mut writer)?;
         let mut documents_file = writer.into_inner()?;
         documents_file.seek(SeekFrom::Start(0))?;
 
@@ -424,12 +423,11 @@ impl<'a, 'i> Transform<'a, 'i> {
         let documents_count = documents_ids.len() as usize;
 
         // We create a final writer to write the new documents in order from the sorter.
-        let file = tempfile::tempfile()?;
         let mut writer = create_writer(
             self.indexer_settings.chunk_compression_type,
             self.indexer_settings.chunk_compression_level,
-            file,
-        )?;
+            tempfile::tempfile()?,
+        );
 
         let mut obkv_buffer = Vec::new();
         for result in self.index.documents.iter(wtxn)? {
diff --git a/milli/src/update/index_documents/typed_chunk.rs b/milli/src/update/index_documents/typed_chunk.rs
index 7f0cfcab3..3c77de7a1 100644
--- a/milli/src/update/index_documents/typed_chunk.rs
+++ b/milli/src/update/index_documents/typed_chunk.rs
@@ -1,6 +1,7 @@
 use std::borrow::Cow;
 use std::convert::TryInto;
 use std::fs::File;
+use std::io;
 
 use heed::types::ByteSlice;
 use heed::{BytesDecode, RwTxn};
@@ -65,8 +66,9 @@ pub(crate) fn write_typed_chunk_into_index(
                 },
             )?;
         }
-        TypedChunk::Documents(mut obkv_documents_iter) => {
-            while let Some((key, value)) = obkv_documents_iter.next()? {
+        TypedChunk::Documents(obkv_documents_iter) => {
+            let mut cursor = obkv_documents_iter.into_cursor()?;
+            while let Some((key, value)) = cursor.move_on_next()? {
                 index.documents.remap_types::<ByteSlice, ByteSlice>().put(wtxn, key, value)?;
             }
         }
@@ -85,7 +87,7 @@ pub(crate) fn write_typed_chunk_into_index(
             return Ok((documents_ids, is_merged_database))
         }
         TypedChunk::WordDocids(word_docids_iter) => {
-            let mut word_docids_iter = unsafe { into_clonable_grenad(word_docids_iter) }?;
+            let word_docids_iter = unsafe { into_clonable_grenad(word_docids_iter) }?;
             append_entries_into_database(
                 word_docids_iter.clone(),
                 &index.word_docids,
@@ -97,7 +99,8 @@ pub(crate) fn write_typed_chunk_into_index(
 
             // create fst from word docids
             let mut builder = fst::SetBuilder::memory();
-            while let Some((word, _value)) = word_docids_iter.next()? {
+            let mut cursor = word_docids_iter.into_cursor()?;
+            while let Some((word, _value)) = cursor.move_on_next()? {
                 // This is a lexicographically ordered word position
                 // we use the key to construct the words fst.
                 builder.insert(word)?;
@@ -146,19 +149,21 @@ pub(crate) fn write_typed_chunk_into_index(
             )?;
             is_merged_database = true;
         }
-        TypedChunk::FieldIdDocidFacetNumbers(mut fid_docid_facet_number) => {
+        TypedChunk::FieldIdDocidFacetNumbers(fid_docid_facet_number) => {
             let index_fid_docid_facet_numbers =
                 index.field_id_docid_facet_f64s.remap_types::<ByteSlice, ByteSlice>();
-            while let Some((key, value)) = fid_docid_facet_number.next()? {
+            let mut cursor = fid_docid_facet_number.into_cursor()?;
+            while let Some((key, value)) = cursor.move_on_next()? {
                 if valid_lmdb_key(key) {
                     index_fid_docid_facet_numbers.put(wtxn, key, &value)?;
                 }
             }
         }
-        TypedChunk::FieldIdDocidFacetStrings(mut fid_docid_facet_string) => {
+        TypedChunk::FieldIdDocidFacetStrings(fid_docid_facet_string) => {
             let index_fid_docid_facet_strings =
                 index.field_id_docid_facet_strings.remap_types::<ByteSlice, ByteSlice>();
-            while let Some((key, value)) = fid_docid_facet_string.next()? {
+            let mut cursor = fid_docid_facet_string.into_cursor()?;
+            while let Some((key, value)) = cursor.move_on_next()? {
                 if valid_lmdb_key(key) {
                     index_fid_docid_facet_strings.put(wtxn, key, &value)?;
                 }
@@ -183,11 +188,12 @@ pub(crate) fn write_typed_chunk_into_index(
             )?;
             is_merged_database = true;
         }
-        TypedChunk::GeoPoints(mut geo_points) => {
+        TypedChunk::GeoPoints(geo_points) => {
             let mut rtree = index.geo_rtree(wtxn)?.unwrap_or_default();
             let mut geo_faceted_docids = index.geo_faceted_documents_ids(wtxn)?;
 
-            while let Some((key, value)) = geo_points.next()? {
+            let mut cursor = geo_points.into_cursor()?;
+            while let Some((key, value)) = cursor.move_on_next()? {
                 // convert the key back to a u32 (4 bytes)
                 let docid = key.try_into().map(DocumentId::from_be_bytes).unwrap();
 
@@ -229,7 +235,7 @@ fn merge_cbo_roaring_bitmaps(
 /// Write provided entries in database using serialize_value function.
 /// merge_values function is used if an entry already exist in the database.
 fn write_entries_into_database<R, K, V, FS, FM>(
-    mut data: grenad::Reader<R>,
+    data: grenad::Reader<R>,
     database: &heed::Database<K, V>,
     wtxn: &mut RwTxn,
     index_is_empty: bool,
@@ -237,14 +243,15 @@ fn write_entries_into_database<R, K, V, FS, FM>(
     merge_values: FM,
 ) -> Result<()>
 where
-    R: std::io::Read,
+    R: io::Read + io::Seek,
     FS: for<'a> Fn(&'a [u8], &'a mut Vec<u8>) -> Result<&'a [u8]>,
     FM: Fn(&[u8], &[u8], &mut Vec<u8>) -> Result<()>,
 {
     let mut buffer = Vec::new();
     let database = database.remap_types::<ByteSlice, ByteSlice>();
 
-    while let Some((key, value)) = data.next()? {
+    let mut cursor = data.into_cursor()?;
+    while let Some((key, value)) = cursor.move_on_next()? {
         if valid_lmdb_key(key) {
             buffer.clear();
             let value = if index_is_empty {
@@ -270,7 +277,7 @@ where
 /// All provided entries must be ordered.
 /// If the index is not empty, write_entries_into_database is called instead.
 fn append_entries_into_database<R, K, V, FS, FM>(
-    mut data: grenad::Reader<R>,
+    data: grenad::Reader<R>,
     database: &heed::Database<K, V>,
     wtxn: &mut RwTxn,
     index_is_empty: bool,
@@ -278,7 +285,7 @@ fn append_entries_into_database<R, K, V, FS, FM>(
     merge_values: FM,
 ) -> Result<()>
 where
-    R: std::io::Read,
+    R: io::Read + io::Seek,
     FS: for<'a> Fn(&'a [u8], &'a mut Vec<u8>) -> Result<&'a [u8]>,
     FM: Fn(&[u8], &[u8], &mut Vec<u8>) -> Result<()>,
 {
@@ -296,7 +303,8 @@ where
     let mut buffer = Vec::new();
     let mut database = database.iter_mut(wtxn)?.remap_types::<ByteSlice, ByteSlice>();
 
-    while let Some((key, value)) = data.next()? {
+    let mut cursor = data.into_cursor()?;
+    while let Some((key, value)) = cursor.move_on_next()? {
         if valid_lmdb_key(key) {
             buffer.clear();
             let value = serialize_value(value, &mut buffer)?;
diff --git a/milli/src/update/word_prefix_docids.rs b/milli/src/update/word_prefix_docids.rs
index 624037f8f..0bb5edb9a 100644
--- a/milli/src/update/word_prefix_docids.rs
+++ b/milli/src/update/word_prefix_docids.rs
@@ -51,8 +51,10 @@ impl<'t, 'u, 'i> WordPrefixDocids<'t, 'u, 'i> {
         );
 
         let mut word_docids_merger = MergerBuilder::new(merge_roaring_bitmaps);
-        word_docids_merger.extend(new_word_docids);
-        let mut word_docids_iter = word_docids_merger.build().into_merger_iter()?;
+        for reader in new_word_docids {
+            word_docids_merger.push(reader.into_cursor()?);
+        }
+        let mut word_docids_iter = word_docids_merger.build().into_stream_merger_iter()?;
 
         let mut current_prefixes: Option<&&[String]> = None;
         let mut prefixes_cache = HashMap::new();
diff --git a/milli/src/update/word_prefix_pair_proximity_docids.rs b/milli/src/update/word_prefix_pair_proximity_docids.rs
index 530c2867e..b498d5850 100644
--- a/milli/src/update/word_prefix_pair_proximity_docids.rs
+++ b/milli/src/update/word_prefix_pair_proximity_docids.rs
@@ -77,8 +77,10 @@ impl<'t, 'u, 'i> WordPrefixPairProximityDocids<'t, 'u, 'i> {
         // We retrieve and merge the created word pair proximities docids entries
         // for the newly added documents.
         let mut wppd_merger = MergerBuilder::new(merge_cbo_roaring_bitmaps);
-        wppd_merger.extend(new_word_pair_proximity_docids);
-        let mut wppd_iter = wppd_merger.build().into_merger_iter()?;
+        for reader in new_word_pair_proximity_docids {
+            wppd_merger.push(reader.into_cursor()?);
+        }
+        let mut wppd_iter = wppd_merger.build().into_stream_merger_iter()?;
 
         let mut word_prefix_pair_proximity_docids_sorter = create_sorter(
             merge_cbo_roaring_bitmaps,
diff --git a/milli/src/update/words_prefix_position_docids.rs b/milli/src/update/words_prefix_position_docids.rs
index c992d01ec..9e15f4d6c 100644
--- a/milli/src/update/words_prefix_position_docids.rs
+++ b/milli/src/update/words_prefix_position_docids.rs
@@ -73,9 +73,11 @@ impl<'t, 'u, 'i> WordPrefixPositionDocids<'t, 'u, 'i> {
         );
 
         let mut word_position_docids_merger = MergerBuilder::new(merge_cbo_roaring_bitmaps);
-        word_position_docids_merger.extend(new_word_position_docids);
+        for reader in new_word_position_docids {
+            word_position_docids_merger.push(reader.into_cursor()?);
+        }
         let mut word_position_docids_iter =
-            word_position_docids_merger.build().into_merger_iter()?;
+            word_position_docids_merger.build().into_stream_merger_iter()?;
 
         // We fetch all the new common prefixes between the previous and new prefix fst.
         let mut buffer = Vec::new();