introduce exact_word_docids db

milli/src/update/index_documents/helpers/grenad_helpers.rs

@@ -277,3 +277,8 @@ pub fn sorter_into_lmdb_database(
     debug!("MTBL sorter writen in {:.02?}!", before.elapsed());
     Ok(())
 }
+
+/// Used when trying to merge readers, but you don't actually care about the values.
+pub fn merge_nothing<'a>(_key: &[u8], _values: &[Cow<'a, [u8]>]) -> Result<Cow<'a, [u8]>> {
+    Ok(Cow::Owned(Vec::new()))
+}

milli/src/update/index_documents/helpers/mod.rs

@@ -8,7 +8,7 @@ use std::convert::{TryFrom, TryInto};
 pub use clonable_mmap::{ClonableMmap, CursorClonableMmap};
 use fst::{IntoStreamer, Streamer};
 pub use grenad_helpers::{
-    as_cloneable_grenad, create_sorter, create_writer, grenad_obkv_into_chunks,
+    as_cloneable_grenad, create_sorter, create_writer, grenad_obkv_into_chunks, merge_nothing,
     sorter_into_lmdb_database, sorter_into_reader, write_into_lmdb_database, writer_into_reader,
     GrenadParameters, MergeableReader,
 };