mikemccand commented on code in PR #13149:
URL: https://github.com/apache/lucene/pull/13149#discussion_r1517878022
##########
lucene/core/src/java/org/apache/lucene/util/bkd/DocIdsWriter.java:
##########
@@ -36,6 +36,66 @@ final class DocIdsWriter {
private final int[] scratch;
+ private final ScratchDocIdSetIterator scratchDocIdSetIterator = new
ScratchDocIdSetIterator();
+
+ /**
+ * DocIdSetIterator to be used to iterate over the scratch buffer. A single
instance is reused to
+ * avoid re-allocating the object. The reset method should be called before
each use with the
+ * count.
+ *
+ * <p>The main reason for existing is to be able to call the {@link
+ * IntersectVisitor#visit(DocIdSetIterator)} method rather than the {@link
+ * IntersectVisitor#visit(int)} method. This seems to make a difference in
performance, probably
+ * due to fewer virtual calls then happening (once per read call rather than
once per doc).
+ */
+ private class ScratchDocIdSetIterator extends DocIdSetIterator {
+
+ private int index = -1;
+ private int count = -1;
+
+ @Override
+ public int docID() {
+ if (index < 0) {
+ return -1;
+ }
+ if (index >= count) {
+ return NO_MORE_DOCS;
+ }
+ return scratch[index];
+ }
+
+ @Override
+ public int nextDoc() throws IOException {
+ index++;
+ if (index >= count) {
+ return NO_MORE_DOCS;
+ }
+ return scratch[index];
+ }
+
+ @Override
+ public int advance(int target) throws IOException {
+ while (index < count && scratch[index] < target) {
Review Comment:
> It might be that a DISI is not the right interface for visiting docids
within the BKD tree - but I'm guessing changing that would be larger and more
controversial.
Yeah indeed DISI may not be right, but let's not try to fix that here/now?
Perhaps there are use cases that might want to call `.advance` on the DISI?
Maybe some sort of curious combined filtering / points query?
OK you convinced me!: let's leave the method as is. You're right that if
such a use case existed today, it is suffering through the linear scan of
`.visit` calls already, so this is no worse.
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