Return the original string values for the inverted facet index database

milli/src/update/index_documents/merge_function.rs

@@ -2,8 +2,11 @@ use std::borrow::Cow;
 use std::result::Result as StdResult;
 
 use fst::IntoStreamer;
+use heed::{BytesDecode, BytesEncode};
 use roaring::RoaringBitmap;
 
+use crate::error::SerializationError;
+use crate::heed_codec::facet::FacetStringLevelZeroValueCodec;
 use crate::heed_codec::CboRoaringBitmapCodec;
 use crate::Result;
 
@@ -69,6 +72,26 @@ pub fn roaring_bitmap_merge(_key: &[u8], values: &[Cow<[u8]>]) -> Result<Vec<u8>
     Ok(vec)
 }
 
+/// Uses the FacetStringLevelZeroValueCodec to merge the values.
+pub fn tuple_string_cbo_roaring_bitmap_merge(_key: &[u8], values: &[Cow<[u8]>]) -> Result<Vec<u8>> {
+    let (head, tail) = values.split_first().unwrap();
+    let (head_string, mut head_rb) =
+        FacetStringLevelZeroValueCodec::<CboRoaringBitmapCodec>::bytes_decode(&head[..])
+            .ok_or(SerializationError::Decoding { db_name: None })?;
+
+    for value in tail {
+        let (_string, rb) =
+            FacetStringLevelZeroValueCodec::<CboRoaringBitmapCodec>::bytes_decode(&value[..])
+                .ok_or(SerializationError::Decoding { db_name: None })?;
+        head_rb |= rb;
+    }
+
+    FacetStringLevelZeroValueCodec::<CboRoaringBitmapCodec>::bytes_encode(&(head_string, head_rb))
+        .map(|cow| cow.into_owned())
+        .ok_or(SerializationError::Encoding { db_name: None })
+        .map_err(Into::into)
+}
+
 pub fn cbo_roaring_bitmap_merge(_key: &[u8], values: &[Cow<[u8]>]) -> Result<Vec<u8>> {
     let (head, tail) = values.split_first().unwrap();
     let mut head = CboRoaringBitmapCodec::deserialize_from(&head[..])?;

milli/src/update/index_documents/mod.rs

@@ -20,6 +20,7 @@ use serde::{Deserialize, Serialize};
 
 pub use self::merge_function::{
     cbo_roaring_bitmap_merge, fst_merge, keep_first, roaring_bitmap_merge,
+    tuple_string_cbo_roaring_bitmap_merge,
 };
 use self::store::{Readers, Store};
 pub use self::transform::{Transform, TransformOutput};
@@ -655,7 +656,7 @@ impl<'t, 'u, 'i, 'a> IndexDocuments<'t, 'u, 'i, 'a> {
             self.wtxn,
             *self.index.facet_id_string_docids.as_polymorph(),
             facet_field_strings_docids_readers,
-            cbo_roaring_bitmap_merge,
+            tuple_string_cbo_roaring_bitmap_merge,
             write_method,
         )?;
 

milli/src/update/index_documents/store.rs

@@ -22,12 +22,13 @@ use tempfile::tempfile;
 
 use super::merge_function::{
     cbo_roaring_bitmap_merge, fst_merge, keep_first, roaring_bitmap_merge,
+    tuple_string_cbo_roaring_bitmap_merge,
 };
 use super::{create_sorter, create_writer, writer_into_reader, MergeFn};
 use crate::error::{Error, InternalError, SerializationError};
 use crate::heed_codec::facet::{
-    FacetLevelValueF64Codec, FacetStringLevelZeroCodec, FieldDocIdFacetF64Codec,
-    FieldDocIdFacetStringCodec,
+    FacetLevelValueF64Codec, FacetStringLevelZeroCodec, FacetStringLevelZeroValueCodec,
+    FieldDocIdFacetF64Codec, FieldDocIdFacetStringCodec,
 };
 use crate::heed_codec::{BoRoaringBitmapCodec, CboRoaringBitmapCodec};
 use crate::update::UpdateIndexingStep;
@@ -153,7 +154,7 @@ impl<'s, A: AsRef<[u8]>> Store<'s, A> {
             max_memory,
         );
         let facet_field_strings_docids_sorter = create_sorter(
-            cbo_roaring_bitmap_merge,
+            tuple_string_cbo_roaring_bitmap_merge,
             chunk_compression_type,
             chunk_compression_level,
             chunk_fusing_shrink_size,
@@ -528,17 +529,18 @@ impl<'s, A: AsRef<[u8]>> Store<'s, A> {
         Error: From<E>,
     {
         let mut key_buffer = Vec::new();
-        let mut data_buffer = Vec::new();
 
         for ((field_id, normalized_value), (original_value, docids)) in iter {
             key_buffer.clear();
-            data_buffer.clear();
 
             FacetStringLevelZeroCodec::serialize_into(field_id, &normalized_value, &mut key_buffer);
-            CboRoaringBitmapCodec::serialize_into(&docids, &mut data_buffer);
+
+            let data = (original_value.as_str(), docids);
+            let data = FacetStringLevelZeroValueCodec::<CboRoaringBitmapCodec>::bytes_encode(&data)
+                .ok_or(SerializationError::Encoding { db_name: Some("facet-id-string-docids") })?;
 
             if lmdb_key_valid_size(&key_buffer) {
-                sorter.insert(&key_buffer, &data_buffer)?;
+                sorter.insert(&key_buffer, &data)?;
             } else {
                 warn!("facet value {:?} is too large to be saved", original_value);
             }