Polish some details

milli/src/heed_codec/facet/field_doc_id_facet_codec.rs

@@ -1,8 +1,10 @@
-use crate::{try_split_array_at, DocumentId, FieldId};
-use heed::{BytesDecode, BytesEncode};
 use std::borrow::Cow;
 use std::marker::PhantomData;
 
+use heed::{BytesDecode, BytesEncode};
+
+use crate::{try_split_array_at, DocumentId, FieldId};
+
 pub struct FieldDocIdFacetCodec<C>(PhantomData<C>);
 
 impl<'a, C> BytesDecode<'a> for FieldDocIdFacetCodec<C>

milli/src/heed_codec/facet/mod.rs

@@ -40,6 +40,8 @@ pub struct FacetGroupKey<T> {
     pub left_bound: T,
 }
 
+/// The value in the [`facet_id_string_docids` and `facet_id_f64_docids`][`Index::facet_id_string_docids`]
+/// databases.
 #[derive(Debug)]
 pub struct FacetGroupValue {
     pub size: u8,
@@ -102,6 +104,8 @@ impl<'a> heed::BytesDecode<'a> for FacetGroupValueCodec {
     }
 }
 
+/// A codec for values of type `&[u8]`. Unlike `ByteSlice`, its `EItem` and `DItem` associated
+/// types are equivalent (= `&'a [u8]`) and these values can reside within another structure.
 pub struct ByteSliceRef;
 
 impl<'a> BytesEncode<'a> for ByteSliceRef {

milli/src/heed_codec/facet/str_ref.rs

@@ -2,6 +2,8 @@ use std::borrow::Cow;
 
 use heed::{BytesDecode, BytesEncode};
 
+/// A codec for values of type `&str`. Unlike `Str`, its `EItem` and `DItem` associated
+/// types are equivalent (= `&'a str`) and these values can reside within another structure.
 pub struct StrRefCodec;
 impl<'a> BytesEncode<'a> for StrRefCodec {
     type EItem = &'a str;

milli/src/update/index_documents/extract/extract_facet_string_docids.rs

@@ -33,10 +33,6 @@ pub fn extract_facet_string_docids<R: io::Read + io::Seek>(
         let (field_id_bytes, bytes) = try_split_array_at(key).unwrap();
         let field_id = FieldId::from_be_bytes(field_id_bytes);
 
-        // document_id_bytes is a big-endian u32
-        // merge_cbo_roaring_bitmap works with native endian u32s
-        // that is a problem, I think
-
         let (document_id_bytes, normalized_value_bytes) =
             try_split_array_at::<_, 4>(bytes).unwrap();
         let document_id = u32::from_be_bytes(document_id_bytes);
@@ -45,6 +41,7 @@ pub fn extract_facet_string_docids<R: io::Read + io::Seek>(
         let key = FacetGroupKey { field_id, level: 0, left_bound: normalised_value };
         let key_bytes = FacetGroupKeyCodec::<StrRefCodec>::bytes_encode(&key).unwrap();
 
+        // document id is encoded in native-endian because of the CBO roaring bitmap codec
         facet_string_docids_sorter.insert(&key_bytes, &document_id.to_ne_bytes())?;
     }
 

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

@@ -5,7 +5,6 @@ use std::result::Result as StdResult;
 use roaring::RoaringBitmap;
 
 use super::read_u32_ne_bytes;
-// use crate::heed_codec::facet::{decode_prefix_string, encode_prefix_string};
 use crate::heed_codec::CboRoaringBitmapCodec;
 use crate::Result;
 
@@ -49,33 +48,6 @@ pub fn merge_roaring_bitmaps<'a>(_key: &[u8], values: &[Cow<'a, [u8]>]) -> Resul
     }
 }
 
-// pub fn keep_first_prefix_value_merge_roaring_bitmaps<'a>(
-//     _key: &[u8],
-//     values: &[Cow<'a, [u8]>],
-// ) -> Result<Cow<'a, [u8]>> {
-//     if values.len() == 1 {
-//         Ok(values[0].clone())
-//     } else {
-//         let original = decode_prefix_string(&values[0]).unwrap().0;
-//         let merged_bitmaps = values
-//             .iter()
-//             .map(AsRef::as_ref)
-//             .map(decode_prefix_string)
-//             .map(Option::unwrap)
-//             .map(|(_, bitmap_bytes)| bitmap_bytes)
-//             .map(RoaringBitmap::deserialize_from)
-//             .map(StdResult::unwrap)
-//             .reduce(|a, b| a | b)
-//             .unwrap();
-
-//         let cap = std::mem::size_of::<u16>() + original.len() + merged_bitmaps.serialized_size();
-//         let mut buffer = Vec::with_capacity(cap);
-//         encode_prefix_string(original, &mut buffer)?;
-//         merged_bitmaps.serialize_into(&mut buffer)?;
-//         Ok(Cow::Owned(buffer))
-//     }
-// }
-
 pub fn keep_first<'a>(_key: &[u8], values: &[Cow<'a, [u8]>]) -> Result<Cow<'a, [u8]>> {
     Ok(values[0].clone())
 }