Recycling buffer in PrefixPhraseScorer (#2443)

src/postings/postings.rs

@@ -15,6 +15,7 @@ pub trait Postings: DocSet + 'static {
     fn term_freq(&self) -> u32;
 
     /// Returns the positions offsetted with a given value.
+    /// It is not necessary to clear the `output` before calling this method.
     /// The output vector will be resized to the `term_freq`.
     fn positions_with_offset(&mut self, offset: u32, output: &mut Vec<u32>);
 

src/query/phrase_prefix_query/phrase_prefix_scorer.rs

@@ -97,6 +97,7 @@ pub struct PhrasePrefixScorer<TPostings: Postings> {
     suffixes: Vec<TPostings>,
     suffix_offset: u32,
     phrase_count: u32,
+    suffix_position_buffer: Vec<u32>,
 }
 
 impl<TPostings: Postings> PhrasePrefixScorer<TPostings> {
@@ -140,6 +141,7 @@ impl<TPostings: Postings> PhrasePrefixScorer<TPostings> {
             suffixes,
             suffix_offset: (max_offset - suffix_pos) as u32,
             phrase_count: 0,
+            suffix_position_buffer: Vec::with_capacity(100),
         };
         if phrase_prefix_scorer.doc() != TERMINATED && !phrase_prefix_scorer.matches_prefix() {
             phrase_prefix_scorer.advance();
@@ -153,7 +155,6 @@ impl<TPostings: Postings> PhrasePrefixScorer<TPostings> {
 
     fn matches_prefix(&mut self) -> bool {
         let mut count = 0;
-        let mut positions = Vec::new();
         let current_doc = self.doc();
         let pos_matching = self.phrase_scorer.get_intersection();
         for suffix in &mut self.suffixes {
@@ -162,8 +163,8 @@ impl<TPostings: Postings> PhrasePrefixScorer<TPostings> {
             }
             let doc = suffix.seek(current_doc);
             if doc == current_doc {
-                suffix.positions_with_offset(self.suffix_offset, &mut positions);
-                count += intersection_count(pos_matching, &positions);
+                suffix.positions_with_offset(self.suffix_offset, &mut self.suffix_position_buffer);
+                count += intersection_count(pos_matching, &self.suffix_position_buffer);
             }
         }
         self.phrase_count = count as u32;