Forcess ann only search with delete docs filter

src/main/java/org/opensearch/knn/index/query/KNNWeight.java

@@ -20,6 +20,7 @@
 import org.apache.lucene.util.BitSetIterator;
 import org.apache.lucene.util.Bits;
 import org.apache.lucene.util.FixedBitSet;
+import org.opensearch.common.StopWatch;
 import org.opensearch.common.lucene.Lucene;
 import org.opensearch.knn.common.FieldInfoExtractor;
 import org.opensearch.knn.common.KNNConstants;
@@ -40,6 +41,7 @@
 import org.opensearch.knn.indices.ModelUtil;
 import org.opensearch.knn.jni.JNIService;
 import org.opensearch.knn.plugin.stats.KNNCounter;
+import org.opensearch.knn.plugin.stats.KNNTimer;
 
 import java.io.IOException;
 import java.util.Arrays;
@@ -128,7 +130,12 @@ public Scorer scorer(LeafReaderContext context) throws IOException {
      * @return A Map of docId to scores for top k results
      */
     public PerLeafResult searchLeaf(LeafReaderContext context, int k) throws IOException {
+        StopWatch stopWatch = new StopWatch().start();
+        KNNTimer.FILTER_SCORER_TIME.start();
         final BitSet filterBitSet = getFilteredDocsBitSet(context);
+        KNNTimer.FILTER_SCORER_TIME.stop();
+        log.debug("Filter Query execution time {} ms", stopWatch.stop().totalTime().millis());
+
         final int maxDoc = context.reader().maxDoc();
         int cardinality = filterBitSet.cardinality();
         // We don't need to go to JNI layer if no documents are found which satisfy the filters
@@ -137,41 +144,38 @@ public PerLeafResult searchLeaf(LeafReaderContext context, int k) throws IOExcep
         if (filterWeight != null && cardinality == 0) {
             return PerLeafResult.EMPTY_RESULT;
         }
-        /*
-         * The idea for this optimization is to get K results, we need to at least look at K vectors in the HNSW graph
-         * . Hence, if filtered results are less than K and filter query is present we should shift to exact search.
-         * This improves the recall.
-         */
-        if (isFilteredExactSearchPreferred(cardinality)) {
-            Map<Integer, Float> result = doExactSearch(context, new BitSetIterator(filterBitSet, cardinality), cardinality, k);
-            return new PerLeafResult(filterWeight == null ? null : filterBitSet, result);
-        }
 
         /*
          * If filters match all docs in this segment, then null should be passed as filterBitSet
          * so that it will not do a bitset look up in bottom search layer.
          */
         final BitSet annFilter = (filterWeight != null && cardinality == maxDoc) ? null : filterBitSet;
-        final Map<Integer, Float> docIdsToScoreMap = doANNSearch(context, annFilter, cardinality, k);
-
-        // See whether we have to perform exact search based on approx search results
-        // This is required if there are no native engine files or if approximate search returned
-        // results less than K, though we have more than k filtered docs
-        if (isExactSearchRequire(context, cardinality, docIdsToScoreMap.size())) {
-            final BitSetIterator docs = filterWeight != null ? new BitSetIterator(filterBitSet, cardinality) : null;
-            Map<Integer, Float> result = doExactSearch(context, docs, cardinality, k);
-            return new PerLeafResult(filterWeight == null ? null : filterBitSet, result);
-        }
-        return new PerLeafResult(filterWeight == null ? null : filterBitSet, docIdsToScoreMap);
+        stopWatch = new StopWatch().start();
+        KNNTimer.ANN_TIME.start();
+        Map<Integer, Float> result = doANNSearch(context, annFilter, cardinality, k);
+        KNNTimer.ANN_TIME.stop();
+        log.debug("Ann search time {} ms", stopWatch.stop().totalTime().millis());
+
+        return new PerLeafResult(filterWeight == null ? null : filterBitSet, result);
     }
 
     private BitSet getFilteredDocsBitSet(final LeafReaderContext ctx) throws IOException {
-        if (this.filterWeight == null) {
+        final Bits liveDocs = ctx.reader().getLiveDocs();
+        if (this.filterWeight == null && liveDocs == null) {
             return new FixedBitSet(0);
         }
 
-        final Bits liveDocs = ctx.reader().getLiveDocs();
         final int maxDoc = ctx.reader().maxDoc();
+        if (filterWeight == null) {
+            // done only to not do refactor, we can always pass bits
+            final FixedBitSet fixedBitSet = new FixedBitSet(maxDoc);
+            for (int index = 0; index < liveDocs.length(); index++) {
+                if (liveDocs.get(index)) {
+                    fixedBitSet.set(index);
+                }
+            }
+            return fixedBitSet;
+        }
 
         final Scorer scorer = filterWeight.scorer(ctx);
         if (scorer == null) {

src/main/java/org/opensearch/knn/plugin/stats/KNNStats.java

@@ -16,6 +16,7 @@
 import org.opensearch.knn.plugin.stats.suppliers.KNNCircuitBreakerSupplier;
 import org.opensearch.knn.plugin.stats.suppliers.KNNCounterSupplier;
 import org.opensearch.knn.plugin.stats.suppliers.KNNInnerCacheStatsSupplier;
+import org.opensearch.knn.plugin.stats.suppliers.KNNTimerSupplier;
 import org.opensearch.knn.plugin.stats.suppliers.LibraryInitializedSupplier;
 import org.opensearch.knn.plugin.stats.suppliers.ModelIndexStatusSupplier;
 import org.opensearch.knn.plugin.stats.suppliers.ModelIndexingDegradingSupplier;
@@ -116,6 +117,10 @@ private void addQueryStats(ImmutableMap.Builder<String, KNNStat<?>> builder) {
                 StatNames.MAX_DISTANCE_QUERY_WITH_FILTER_REQUESTS.getName(),
                 new KNNStat<>(false, new KNNCounterSupplier(KNNCounter.MAX_DISTANCE_QUERY_WITH_FILTER_REQUESTS))
             );
+
+        for (KNNTimer timer : KNNTimer.values()) {
+            builder.put(timer.getName(), new KNNStat<>(false, new KNNTimerSupplier(timer)));
+        }
     }
 
     private void addNativeMemoryStats(ImmutableMap.Builder<String, KNNStat<?>> builder) {

src/main/java/org/opensearch/knn/plugin/stats/KNNTimer.java

@@ -0,0 +1,39 @@
+/*
+ * Copyright OpenSearch Contributors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package org.opensearch.knn.plugin.stats;
+
+import lombok.Getter;
+import lombok.RequiredArgsConstructor;
+import org.opensearch.search.profile.Timer;
+
+@Getter
+@RequiredArgsConstructor
+public enum KNNTimer {
+
+    FILTER_WEIGHT_TIME("filter_weight", new Timer()),
+    FILTER_SCORER_TIME("filter_scorer", new Timer()),
+    EXACT_SEARCH_TIME("exact_search", new Timer()),
+    FILTER_ID_SELECTOR_TIME("filter_id_selector", new Timer()),
+    ANN_TIME("ann_search", new Timer());
+
+    private final String name;
+    private final Timer timer;
+
+    public void start() {
+        timer.start();
+    }
+
+    public void stop() {
+        timer.stop();
+    }
+
+    public long average() {
+        if (timer.getCount() > 1) {
+            return timer.getApproximateTiming() / timer.getCount();
+        }
+        return timer.getApproximateTiming();
+    }
+}

src/main/java/org/opensearch/knn/plugin/stats/StatNames.java

@@ -76,6 +76,11 @@ public static Set<String> getNames() {
         for (StatNames statName : StatNames.values()) {
             names.add(statName.getName());
         }
+
+        for (KNNTimer knnTimer : KNNTimer.values()) {
+            names.add(knnTimer.getName());
+        }
+
         return names;
     }
 }

src/main/java/org/opensearch/knn/plugin/stats/suppliers/KNNTimerSupplier.java

@@ -0,0 +1,22 @@
+/*
+ * Copyright OpenSearch Contributors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package org.opensearch.knn.plugin.stats.suppliers;
+
+import lombok.RequiredArgsConstructor;
+import org.opensearch.knn.plugin.stats.KNNTimer;
+
+import java.util.function.Supplier;
+
+@RequiredArgsConstructor
+public class KNNTimerSupplier implements Supplier<Long> {
+
+    private final KNNTimer knnTimer;
+
+    @Override
+    public Long get() {
+        return knnTimer.average();
+    }
+}