Differentiate short words as prefix or exact matches

meilisearch-core/src/query_tree.rs

@@ -380,7 +380,7 @@ pub fn traverse_query_tree<'o, 'txn>(
         let before = Instant::now();
 
         let Query { id, prefix, kind } = query;
-        let docids = match kind {
+        let docids: Cow<Set<_>> = match kind {
             QueryKind::Tolerant(word) => {
                 if *prefix && word.len() <= 2 {
                     let prefix = {
@@ -390,10 +390,29 @@ pub fn traverse_query_tree<'o, 'txn>(
                         array
                     };
 
+                    let mut docids = Vec::new();
+
+                    // We retrieve the cached postings list for all
+                    // the words that starts with this short prefix.
                     let result = ctx.prefix_postings_lists.prefix_postings_list(reader, prefix)?.unwrap_or_default();
                     let distance = 0;
                     postings.insert((query, word.clone().into_bytes(), distance), result.matches);
-                    result.docids
+                    docids.extend_from_slice(&result.docids);
+
+                    // We retrieve the exact postings list for the prefix,
+                    // because we must consider these matches as exact.
+                    if let Some(result) = ctx.postings_lists.postings_list(reader, word.as_bytes())? {
+                        let distance = 0;
+                        postings.insert((query, word.clone().into_bytes(), distance), result.matches);
+                        docids.extend_from_slice(&result.docids);
+                    }
+
+                    let before = Instant::now();
+                    let docids = SetBuf::from_dirty(docids);
+                    println!("{:2$}prefix docids construction took {:.02?}", "", before.elapsed(), depth * 2);
+
+                    Cow::Owned(docids)
+
                 } else {
                     let dfa = if *prefix { build_prefix_dfa(word) } else { build_dfa(word) };
 
@@ -442,7 +461,11 @@ pub fn traverse_query_tree<'o, 'txn>(
                     }
                 }
 
-                Cow::Owned(SetBuf::from_dirty(docids))
+                let before = Instant::now();
+                let docids = SetBuf::from_dirty(docids);
+                println!("{:2$}docids construction took {:.02?}", "", before.elapsed(), depth * 2);
+
+                Cow::Owned(docids)
             },
             QueryKind::Phrase(words) => {
                 // TODO support prefix and non-prefix exact DFA

meilisearch-core/src/update/documents_addition.rs

@@ -195,11 +195,16 @@ pub fn apply_documents_addition<'a, 'b>(
     pplc_store.clear(writer)?;
 
     for prefix_len in 1..=2 {
-        // compute prefixes and store those in the PrefixPostingsListsCache.
+        // compute prefixes and store those in the PrefixPostingsListsCache store.
         let mut previous_prefix: Option<([u8; 4], Vec<_>)> = None;
         let mut stream = words_fst.into_stream();
         while let Some(input) = stream.next() {
-            if input.len() < prefix_len { continue }
+
+            // We skip the prefixes that are shorter than the current length
+            // we want to cache (<). We must ignore the input when it is exactly the
+            // same word as the prefix because if we match exactly on it we need
+            // to consider it as an exact match and not as a prefix (=).
+            if input.len() <= prefix_len { continue }
 
             if let Some(postings_list) = postings_lists_store.postings_list(writer, input)?.map(|p| p.matches.into_owned()) {
                 let prefix = &input[..prefix_len];
@@ -208,38 +213,33 @@ pub fn apply_documents_addition<'a, 'b>(
                 arr_prefix[..prefix_len].copy_from_slice(prefix);
 
                 match previous_prefix {
-                    Some((ref mut prev_prefix, ref mut prev_postings_list)) if *prev_prefix != arr_prefix => {
+                    Some((ref mut prev_prefix, ref mut prev_pl)) if *prev_prefix != arr_prefix => {
-                        prev_postings_list.sort_unstable();
+                        prev_pl.sort_unstable();
-                        prev_postings_list.dedup();
+                        prev_pl.dedup();
 
                         if let Ok(prefix) = std::str::from_utf8(&prev_prefix[..prefix_len]) {
-                            debug!("writing the prefix of {:?} of length {}",
+                            debug!("writing the prefix of {:?} of length {}", prefix, prev_pl.len());
-                                prefix, prev_postings_list.len());
                         }
 
-                        let pls = Set::new_unchecked(&prev_postings_list);
+                        let pls = Set::new_unchecked(&prev_pl);
                         pplc_store.put_prefix_postings_list(writer, *prev_prefix, &pls)?;
 
                         *prev_prefix = arr_prefix;
-                        prev_postings_list.clear();
+                        prev_pl.clear();
-                        prev_postings_list.extend_from_slice(&postings_list);
+                        prev_pl.extend_from_slice(&postings_list);
-                    },
-                    Some((_, ref mut prev_postings_list)) => {
-                        prev_postings_list.extend_from_slice(&postings_list);
-                    },
-                    None => {
-                        previous_prefix = Some((arr_prefix, postings_list.to_vec()));
                     },
+                    Some((_, ref mut prev_pl)) => prev_pl.extend_from_slice(&postings_list),
+                    None => previous_prefix = Some((arr_prefix, postings_list.to_vec())),
                 }
             }
         }
 
         // write the last prefix postings lists
-        if let Some((prev_prefix, mut prev_postings_list)) = previous_prefix.take() {
+        if let Some((prev_prefix, mut prev_pl)) = previous_prefix.take() {
-            prev_postings_list.sort_unstable();
+            prev_pl.sort_unstable();
-            prev_postings_list.dedup();
+            prev_pl.dedup();
 
-            let pls = Set::new_unchecked(&prev_postings_list);
+            let pls = Set::new_unchecked(&prev_pl);
             pplc_store.put_prefix_postings_list(writer, prev_prefix, &pls)?;
         }
     }