Invert the word docid positions key order

src/bin/indexer.rs

@@ -13,10 +13,7 @@ use bstr::ByteSlice as _;
 use csv::StringRecord;
 use flate2::read::GzDecoder;
 use fst::IntoStreamer;
-use heed::BytesDecode;
-use heed::BytesEncode;
-use heed::EnvOpenOptions;
-use heed::types::*;
+use heed::{EnvOpenOptions, BytesEncode, types::*};
 use log::{debug, info};
 use memmap::Mmap;
 use oxidized_mtbl::{Reader, Writer, Merger, Sorter, CompressionType};
@@ -26,7 +23,7 @@ use structopt::StructOpt;
 
 use milli::heed_codec::CsvStringRecordCodec;
 use milli::tokenizer::{simple_tokenizer, only_words};
-use milli::{SmallVec32, Index, DocumentId, BEU32, StrBEU32Codec};
+use milli::{SmallVec32, Index, DocumentId, BEU32};
 
 const LMDB_MAX_KEY_LENGTH: usize = 511;
 const ONE_MILLION: usize = 1_000_000;
@@ -202,12 +199,13 @@ impl Store {
         let mut key = vec![WORD_DOCID_POSITIONS_BYTE];
         let mut buffer = Vec::new();
 
-        for (word, positions) in iter {
-            key.truncate(1);
-            key.extend_from_slice(word.as_bytes());
+        // We serialize the document ids into a buffer
         // We prefix the words by the document id.
         key.extend_from_slice(&id.to_be_bytes());
-            // We serialize the document ids into a buffer
+
+        for (word, positions) in iter {
+            key.truncate(1 + 4);
+            key.extend_from_slice(word.as_bytes());
             buffer.clear();
             buffer.reserve(positions.serialized_size());
             positions.serialize_into(&mut buffer)?;
@@ -350,7 +348,7 @@ fn lmdb_writer(wtxn: &mut heed::RwTxn, index: &Index, key: &[u8], val: &[u8]) ->
     }
     else if key.starts_with(&[WORD_DOCID_POSITIONS_BYTE]) {
         // Write the postings lists
-        index.word_docid_positions.as_polymorph()
+        index.docid_word_positions.as_polymorph()
             .put::<_, ByteSlice, ByteSlice>(wtxn, &key[1..], val)?;
     }
 

src/heed_codec/beu32_str_codec.rs

@@ -2,26 +2,26 @@ use std::borrow::Cow;
 use std::convert::TryInto;
 use std::str;
 
-pub struct StrBEU32Codec;
+pub struct BEU32StrCodec;
 
-impl<'a> heed::BytesDecode<'a> for StrBEU32Codec {
-    type DItem = (&'a str, u32);
+impl<'a> heed::BytesDecode<'a> for BEU32StrCodec {
+    type DItem = (u32, &'a str);
 
     fn bytes_decode(bytes: &'a [u8]) -> Option<Self::DItem> {
-        let (str_bytes, n_bytes) = bytes.split_at(bytes.len() - 4);
-        let s = str::from_utf8(str_bytes).ok()?;
+        let (n_bytes, str_bytes) = bytes.split_at(4);
         let n = n_bytes.try_into().map(u32::from_be_bytes).ok()?;
-        Some((s, n))
+        let s = str::from_utf8(str_bytes).ok()?;
+        Some((n, s))
     }
 }
 
-impl<'a> heed::BytesEncode<'a> for StrBEU32Codec {
-    type EItem = (&'a str, u32);
+impl<'a> heed::BytesEncode<'a> for BEU32StrCodec {
+    type EItem = (u32, &'a str);
 
-    fn bytes_encode((s, n): &Self::EItem) -> Option<Cow<[u8]>> {
+    fn bytes_encode((n, s): &Self::EItem) -> Option<Cow<[u8]>> {
         let mut bytes = Vec::with_capacity(s.len() + 4);
-        bytes.extend_from_slice(s.as_bytes());
         bytes.extend_from_slice(&n.to_be_bytes());
+        bytes.extend_from_slice(s.as_bytes());
         Some(Cow::Owned(bytes))
     }
 }

src/heed_codec/mod.rs

@@ -1,7 +1,7 @@
 mod csv_string_record_codec;
 mod roaring_bitmap_codec;
-mod str_beu32_codec;
+mod beu32_str_codec;
 
 pub use self::csv_string_record_codec::CsvStringRecordCodec;
 pub use self::roaring_bitmap_codec::RoaringBitmapCodec;
-pub use self::str_beu32_codec::StrBEU32Codec;
+pub use self::beu32_str_codec::BEU32StrCodec;

src/lib.rs

@@ -15,7 +15,7 @@ use heed::{PolyDatabase, Database};
 
 pub use self::search::{Search, SearchResult};
 pub use self::criterion::{Criterion, default_criteria};
-pub use self::heed_codec::{RoaringBitmapCodec, StrBEU32Codec, CsvStringRecordCodec};
+pub use self::heed_codec::{RoaringBitmapCodec, BEU32StrCodec, CsvStringRecordCodec};
 
 pub type FastMap4<K, V> = HashMap<K, V, BuildHasherDefault<FxHasher32>>;
 pub type FastMap8<K, V> = HashMap<K, V, BuildHasherDefault<FxHasher64>>;
@@ -38,7 +38,7 @@ pub struct Index {
     /// A word and all the documents ids containing the word.
     pub word_docids: Database<Str, RoaringBitmapCodec>,
     /// Maps a word and a document id (u32) to all the positions where the given word appears.
-    pub word_docid_positions: Database<StrBEU32Codec, RoaringBitmapCodec>,
+    pub docid_word_positions: Database<BEU32StrCodec, RoaringBitmapCodec>,
     /// Maps the document id to the document as a CSV line.
     pub documents: Database<OwnedType<BEU32>, ByteSlice>,
 }
@@ -48,7 +48,7 @@ impl Index {
         Ok(Index {
             main: env.create_poly_database(None)?,
             word_docids: env.create_database(Some("word-docids"))?,
-            word_docid_positions: env.create_database(Some("word-docid-positions"))?,
+            docid_word_positions: env.create_database(Some("docid-word-positions"))?,
             documents: env.create_database(Some("documents"))?,
         })
     }

src/search.rs

@@ -151,7 +151,7 @@ impl<'a> Search<'a> {
             for (word, (_distance, docids)) in words {
 
                 if docids.contains(candidate) {
-                    match index.word_docid_positions.get(rtxn, &(word, candidate))? {
+                    match index.docid_word_positions.get(rtxn, &(candidate, word))? {
                         Some(positions) => union_positions.union_with(&positions),
                         None => error!("position missing for candidate {} and word {}", candidate, word),
                     }