[GitHub] [lucene] jpountz commented on pull request #242: LUCENE-9620 Add Weight#count(LeafReaderContext)

[GitBox <gi...@apache.org>]

jpountz commented on pull request #242:
URL: https://github.com/apache/lucene/pull/242#issuecomment-904741873


   > Note: This method is probably slower than the pre-existing one because it is not slice-level multithreaded like the previous one
   
   FWIW I was thinking that we could benefit from this new shortcut and from multithreaded search at the same time by doing something like this in the end:
   
   ```java
     private static class ShortcutHitCountCollector implements Collector {
       private final Weight weight;
       private final TotalHitCountCollector totalHitCountCollector = new TotalHitCountCollector();
       private int weightCount;
   
       ShortcutHitCountCollector(Weight weight) {
         this.weight = weight;
       }
       
       @Override
       public LeafCollector getLeafCollector(LeafReaderContext context) throws IOException {
         int count = weight.count(context);
         if (count == -1) {
           return totalHitCountCollector.getLeafCollector(context);
         } else {
           weightCount += count;
           throw new CollectionTerminatedException();
         }
       }
     }
   
     /** Count how many documents match the given query. */
     public int count(Query query) throws IOException {
       query = rewrite(query);
       Weight weight = createWeight(query, ScoreMode.COMPLETE_NO_SCORES, 1f);
       return search(weight, new CollectorManager<ShortcutHitCountCollector, Integer>() {
   
         @Override
         public ShortcutHitCountCollector newCollector() throws IOException {
           return new ShortcutHitCountCollector(weight);
         }
   
         @Override
         public Integer reduce(Collection<ShortcutHitCountCollector> collectors) throws IOException {
           int totalHitCount;
           for (ShortcutHitCountCollector c : collectors) {
             totalHitCount += c.weightCount + c.totalHitCountCollector.getTotalHits();
           }
         }
       });
     }
   ```


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