[GitHub] [lucene] msokolov commented on a change in pull request #413: LUCENE-9614: Fix KnnVectorQuery failure when numDocs is 0

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

msokolov commented on a change in pull request #413:
URL: https://github.com/apache/lucene/pull/413#discussion_r737073221



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File path: lucene/core/src/java/org/apache/lucene/search/KnnVectorQuery.java
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@@ -60,7 +60,8 @@ public KnnVectorQuery(String field, float[] target, int k) {
   public Query rewrite(IndexReader reader) throws IOException {
     TopDocs[] perLeafResults = new TopDocs[reader.leaves().size()];
     for (LeafReaderContext ctx : reader.leaves()) {
-      perLeafResults[ctx.ord] = searchLeaf(ctx, Math.min(k, reader.numDocs()));
+      int numDocs = ctx.reader().numDocs();
+      perLeafResults[ctx.ord] = numDocs > 0 ? searchLeaf(ctx, Math.min(k, numDocs)) : NO_RESULTS;

Review comment:
       Thanks for fixing this - it makes sense to me use `size()` instead of `numDocs()`, or even simply `k`; I wasn't aware of the costly nature of that call. Indeed the idea here was just to avoid spending extra work on tiny segments; something I noticed all the time in tests, but which is probably not much of an issue in reality.




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