mayya-sharipova commented on code in PR #14094:
URL: https://github.com/apache/lucene/pull/14094#discussion_r1903151661


##########
lucene/core/src/java/org/apache/lucene/search/HnswQueueSaturationCollector.java:
##########
@@ -0,0 +1,119 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.lucene.search;
+
+/**
+ * A {@link HnswKnnCollector} that early exits when nearest neighbor queue 
keeps saturating beyond a
+ * 'patience' parameter.
+ */
+public class HnswQueueSaturationCollector implements HnswKnnCollector {
+
+  private static final double DEFAULT_SATURATION_THRESHOLD = 0.995d;
+
+  private final KnnCollector delegate;
+  private double saturationThreshold;
+  private int patience;
+  private boolean patienceFinished;
+  private int countSaturated;
+  private int previousQueueSize;
+  private int currentQueueSize;
+
+  public HnswQueueSaturationCollector(
+      KnnCollector delegate, double saturationThreshold, int patience) {
+    this.delegate = delegate;
+    this.previousQueueSize = 0;
+    this.currentQueueSize = 0;
+    this.countSaturated = 0;
+    this.patienceFinished = false;
+    this.saturationThreshold = saturationThreshold;
+    this.patience = patience;
+  }
+
+  public HnswQueueSaturationCollector(KnnCollector delegate) {
+    this.delegate = delegate;
+    this.previousQueueSize = 0;
+    this.currentQueueSize = 0;
+    this.countSaturated = 0;
+    this.patienceFinished = false;
+    this.saturationThreshold = DEFAULT_SATURATION_THRESHOLD;
+    this.patience = defaultPatience();
+  }
+
+  private int defaultPatience() {
+    return Math.max(7, (int) (k() * 0.3));
+  }
+
+  @Override
+  public boolean earlyTerminated() {
+    return delegate.earlyTerminated() || patienceFinished;
+  }
+
+  @Override
+  public void incVisitedCount(int count) {
+    delegate.incVisitedCount(count);
+  }
+
+  @Override
+  public long visitedCount() {
+    return delegate.visitedCount();
+  }
+
+  @Override
+  public long visitLimit() {
+    return delegate.visitLimit();
+  }
+
+  @Override
+  public int k() {
+    return delegate.k();
+  }
+
+  @Override
+  public boolean collect(int docId, float similarity) {
+    boolean collect = delegate.collect(docId, similarity);
+    if (collect) {
+      currentQueueSize++;
+    }
+    return collect;
+  }
+
+  @Override
+  public float minCompetitiveSimilarity() {
+    return delegate.minCompetitiveSimilarity();
+  }
+
+  @Override
+  public TopDocs topDocs() {
+    return delegate.topDocs();
+  }
+
+  @Override
+  public void nextCandidate() {
+    double queueSaturation =
+        (double) Math.min(currentQueueSize, previousQueueSize) / 
currentQueueSize;

Review Comment:
   Should we look at the intersection of nodes in previous queue vs current 
queue or is it enough just to look at row numbers?



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