abiesps commented on code in PR #15376:
URL: https://github.com/apache/lucene/pull/15376#discussion_r2585700702
##########
lucene/core/src/java/org/apache/lucene/util/bkd/BKDReader.java:
##########
@@ -1076,4 +1137,123 @@ public long cost() {
return length;
}
}
+
+ /**
+ * We can recurse the {@link BKDPointTree} using {@link
TwoPhaseIntersectVisitor}. This visitor
+ * travere {@link BKDPointTree} in two phases. In the first phase, it
recurses over the {@link
+ * BKDPointTree} optionally triggering IO for some of the blocks and caching
them. In the second
+ * phase, once the recursion is over it visits the cached blocks one by one.
+ *
+ * @lucene.experimental
+ */
+ public interface TwoPhaseIntersectVisitor extends IntersectVisitor {
+ /** return the last deferred block ordinal during recursion. */
+ public int lastDeferredBlockOrdinal();
+
+ /** set last deferred block ordinal */
+ public void setLastDeferredBlockOrdinal(int leafNodeOrdinal);
+
+ /** Defer this block for processing in the second phase. */
+ public void deferBlock(long leafFp);
+
+ /** Returns a snapshot of the currently deferred blocks. */
+ public List<Long> deferredBlocks();
+
+ /** Mark the given block as processed and remove it from the deferred set.
*/
+ public void onProcessingDeferredBlock(long leafFp);
+ }
+
+ /**
+ * Base implementation of {@link TwoPhaseIntersectVisitor} that maintains a
list of deferred
+ * blocks from first phase of traversal and visits them in the second phase.
+ *
+ * @lucene.experimental
+ */
+ public abstract static class BaseTwoPhaseIntersectVisitor implements
TwoPhaseIntersectVisitor {
+
+ int lastDeferredBlockOrdinal = -1;
+ List<Long> deferredBlocks = new ArrayList<>();
Review Comment:
Actually list can grow upto total number of leaf nodes in worst case. Num of
leaves /2 +1 is the maximum number of prefetch calls in worst case.
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