[Backport 2.x] Refactor the filter rewrite optimization

server/src/main/java/org/opensearch/search/aggregations/bucket/composite/CompositeAggregator.java

@@ -73,8 +73,8 @@
 import org.opensearch.search.aggregations.MultiBucketCollector;
 import org.opensearch.search.aggregations.MultiBucketConsumerService;
 import org.opensearch.search.aggregations.bucket.BucketsAggregator;
-import org.opensearch.search.aggregations.bucket.FastFilterRewriteHelper;
-import org.opensearch.search.aggregations.bucket.FastFilterRewriteHelper.AbstractDateHistogramAggregationType;
+import org.opensearch.search.aggregations.bucket.filterrewrite.CompositeAggregatorBridge;
+import org.opensearch.search.aggregations.bucket.filterrewrite.FilterRewriteOptimizationContext;
 import org.opensearch.search.aggregations.bucket.missing.MissingOrder;
 import org.opensearch.search.aggregations.bucket.terms.LongKeyedBucketOrds;
 import org.opensearch.search.internal.SearchContext;
@@ -89,13 +89,15 @@
 import java.util.List;
 import java.util.Map;
 import java.util.function.BiConsumer;
+import java.util.function.Function;
 import java.util.function.LongUnaryOperator;
 import java.util.stream.Collectors;
 
 import static org.opensearch.search.aggregations.MultiBucketConsumerService.MAX_BUCKET_SETTING;
+import static org.opensearch.search.aggregations.bucket.filterrewrite.DateHistogramAggregatorBridge.segmentMatchAll;
 
 /**
- * Main aggregator that aggregates docs from mulitple aggregations
+ * Main aggregator that aggregates docs from multiple aggregations
  *
  * @opensearch.internal
  */
@@ -118,9 +120,8 @@ public final class CompositeAggregator extends BucketsAggregator {
 
     private boolean earlyTerminated;
 
-    private final FastFilterRewriteHelper.FastFilterContext fastFilterContext;
-    private LongKeyedBucketOrds bucketOrds = null;
-    private Rounding.Prepared preparedRounding = null;
+    private final FilterRewriteOptimizationContext filterRewriteOptimizationContext;
+    private LongKeyedBucketOrds bucketOrds;
 
     CompositeAggregator(
         String name,
@@ -166,57 +167,62 @@ public final class CompositeAggregator extends BucketsAggregator {
         this.queue = new CompositeValuesCollectorQueue(context.bigArrays(), sources, size, rawAfterKey);
         this.rawAfterKey = rawAfterKey;
 
-        fastFilterContext = new FastFilterRewriteHelper.FastFilterContext(context);
-        if (!FastFilterRewriteHelper.isCompositeAggRewriteable(sourceConfigs)) {
-            return;
-        }
-        fastFilterContext.setAggregationType(new CompositeAggregationType());
-        if (fastFilterContext.isRewriteable(parent, subAggregators.length)) {
-            // bucketOrds is used for saving date histogram results
-            bucketOrds = LongKeyedBucketOrds.build(context.bigArrays(), CardinalityUpperBound.ONE);
-            preparedRounding = ((CompositeAggregationType) fastFilterContext.getAggregationType()).getRoundingPrepared();
-            fastFilterContext.buildRanges(sourceConfigs[0].fieldType());
-        }
-    }
+        CompositeAggregatorBridge bridge = new CompositeAggregatorBridge() {
+            private RoundingValuesSource valuesSource;
+            private long afterKey = -1L;
 
-    /**
-     * Currently the filter rewrite is only supported for date histograms
-     */
-    public class CompositeAggregationType extends AbstractDateHistogramAggregationType {
-        private final RoundingValuesSource valuesSource;
-        private long afterKey = -1L;
-
-        public CompositeAggregationType() {
-            super(sourceConfigs[0].fieldType(), sourceConfigs[0].missingBucket(), sourceConfigs[0].hasScript());
-            this.valuesSource = (RoundingValuesSource) sourceConfigs[0].valuesSource();
-            if (rawAfterKey != null) {
-                assert rawAfterKey.size() == 1 && formats.size() == 1;
-                this.afterKey = formats.get(0).parseLong(rawAfterKey.get(0).toString(), false, () -> {
-                    throw new IllegalArgumentException("now() is not supported in [after] key");
-                });
+            @Override
+            protected boolean canOptimize() {
+                if (canOptimize(sourceConfigs)) {
+                    this.valuesSource = (RoundingValuesSource) sourceConfigs[0].valuesSource();
+                    if (rawAfterKey != null) {
+                        assert rawAfterKey.size() == 1 && formats.size() == 1;
+                        this.afterKey = formats.get(0).parseLong(rawAfterKey.get(0).toString(), false, () -> {
+                            throw new IllegalArgumentException("now() is not supported in [after] key");
+                        });
+                    }
+
+                    // bucketOrds is used for saving the date histogram results got from the optimization path
+                    bucketOrds = LongKeyedBucketOrds.build(context.bigArrays(), CardinalityUpperBound.ONE);
+                    return true;
+                }
+                return false;
             }
-        }
 
-        public Rounding getRounding(final long low, final long high) {
-            return valuesSource.getRounding();
-        }
+            @Override
+            protected void prepare() throws IOException {
+                buildRanges(context);
+            }
 
-        public Rounding.Prepared getRoundingPrepared() {
-            return valuesSource.getPreparedRounding();
-        }
+            protected Rounding getRounding(final long low, final long high) {
+                return valuesSource.getRounding();
+            }
 
-        @Override
-        protected void processAfterKey(long[] bound, long interval) {
-            // afterKey is the last bucket key in previous response, and the bucket key
-            // is the minimum of all values in the bucket, so need to add the interval
-            if (afterKey != -1L) {
-                bound[0] = afterKey + interval;
+            protected Rounding.Prepared getRoundingPrepared() {
+                return valuesSource.getPreparedRounding();
             }
-        }
 
-        public int getSize() {
-            return size;
-        }
+            @Override
+            protected long[] processAfterKey(long[] bounds, long interval) {
+                // afterKey is the last bucket key in previous response, and the bucket key
+                // is the minimum of all values in the bucket, so need to add the interval
+                if (afterKey != -1L) {
+                    bounds[0] = afterKey + interval;
+                }
+                return bounds;
+            }
+
+            @Override
+            protected int getSize() {
+                return size;
+            }
+
+            @Override
+            protected Function<Long, Long> bucketOrdProducer() {
+                return (key) -> bucketOrds.add(0, getRoundingPrepared().round((long) key));
+            }
+        };
+        filterRewriteOptimizationContext = new FilterRewriteOptimizationContext(bridge, parent, subAggregators.length, context);
     }
 
     @Override
@@ -368,7 +374,7 @@ private boolean isMaybeMultivalued(LeafReaderContext context, SortField sortFiel
                 return v2 != null && DocValues.unwrapSingleton(v2) == null;
 
             default:
-                // we have no clue whether the field is multi-valued or not so we assume it is.
+                // we have no clue whether the field is multivalued or not so we assume it is.
                 return true;
         }
     }
@@ -551,11 +557,7 @@ private void processLeafFromQuery(LeafReaderContext ctx, Sort indexSortPrefix) t
 
     @Override
     protected LeafBucketCollector getLeafCollector(LeafReaderContext ctx, LeafBucketCollector sub) throws IOException {
-        boolean optimized = fastFilterContext.tryFastFilterAggregation(
-            ctx,
-            this::incrementBucketDocCount,
-            (key) -> bucketOrds.add(0, preparedRounding.round((long) key))
-        );
+        boolean optimized = filterRewriteOptimizationContext.tryOptimize(ctx, this::incrementBucketDocCount, segmentMatchAll(context, ctx));
         if (optimized) throw new CollectionTerminatedException();
 
         finishLeaf();
@@ -709,11 +711,6 @@ private static class Entry {
 
     @Override
     public void collectDebugInfo(BiConsumer<String, Object> add) {
-        if (fastFilterContext.optimizedSegments > 0) {
-            add.accept("optimized_segments", fastFilterContext.optimizedSegments);
-            add.accept("unoptimized_segments", fastFilterContext.segments - fastFilterContext.optimizedSegments);
-            add.accept("leaf_visited", fastFilterContext.leaf);
-            add.accept("inner_visited", fastFilterContext.inner);
-        }
+        filterRewriteOptimizationContext.populateDebugInfo(add);
     }
 }

server/src/main/java/org/opensearch/search/aggregations/bucket/filterrewrite/AggregatorBridge.java

@@ -0,0 +1,84 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+
+package org.opensearch.search.aggregations.bucket.filterrewrite;
+
+import org.apache.lucene.index.LeafReaderContext;
+import org.apache.lucene.index.PointValues;
+import org.opensearch.index.mapper.MappedFieldType;
+
+import java.io.IOException;
+import java.util.function.BiConsumer;
+import java.util.function.Consumer;
+
+/**
+ * This interface provides a bridge between an aggregator and the optimization context, allowing
+ * the aggregator to provide data and optimize the aggregation process.
+ *
+ * <p>The main purpose of this interface is to encapsulate the aggregator-specific optimization
+ * logic and provide access to the data in Aggregator that is required for optimization, while keeping the optimization
+ * business logic separate from the aggregator implementation.
+ *
+ * <p>To use this interface to optimize an aggregator, you should subclass this interface in this package
+ * and put any specific optimization business logic in it. Then implement this subclass in the aggregator
+ * to provide data that is needed for doing the optimization
+ *
+ * @opensearch.internal
+ */
+public abstract class AggregatorBridge {
+
+    /**
+     * The field type associated with this aggregator bridge.
+     */
+    MappedFieldType fieldType;
+
+    Consumer<Ranges> setRanges;
+
+    void setRangesConsumer(Consumer<Ranges> setRanges) {
+        this.setRanges = setRanges;
+    }
+
+    /**
+     * Checks whether the aggregator can be optimized.
+     * <p>
+     * This method is supposed to be implemented in a specific aggregator to take in fields from there
+     *
+     * @return {@code true} if the aggregator can be optimized, {@code false} otherwise.
+     * The result will be saved in the optimization context.
+     */
+    protected abstract boolean canOptimize();
+
+    /**
+     * Prepares the optimization at shard level after checking aggregator is optimizable.
+     * <p>
+     * For example, figure out what are the ranges from the aggregation to do the optimization later
+     * <p>
+     * This method is supposed to be implemented in a specific aggregator to take in fields from there
+     */
+    protected abstract void prepare() throws IOException;
+
+    /**
+     * Prepares the optimization for a specific segment when the segment is functionally matching all docs
+     *
+     * @param leaf the leaf reader context for the segment
+     */
+    abstract Ranges tryBuildRangesFromSegment(LeafReaderContext leaf) throws IOException;
+
+    /**
+     * Attempts to build aggregation results for a segment
+     *
+     * @param values            the point values (index structure for numeric values) for a segment
+     * @param incrementDocCount a consumer to increment the document count for a range bucket. The First parameter is document count, the second is the key of the bucket
+     * @param ranges
+     */
+    abstract FilterRewriteOptimizationContext.DebugInfo tryOptimize(
+        PointValues values,
+        BiConsumer<Long, Long> incrementDocCount,
+        Ranges ranges
+    ) throws IOException;
+}

server/src/main/java/org/opensearch/search/aggregations/bucket/filterrewrite/CompositeAggregatorBridge.java

@@ -0,0 +1,36 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+
+package org.opensearch.search.aggregations.bucket.filterrewrite;
+
+import org.opensearch.index.mapper.DateFieldMapper;
+import org.opensearch.index.mapper.MappedFieldType;
+import org.opensearch.search.aggregations.bucket.composite.CompositeValuesSourceConfig;
+import org.opensearch.search.aggregations.bucket.composite.RoundingValuesSource;
+
+/**
+ * For composite aggregation to do optimization when it only has a single date histogram source
+ */
+public abstract class CompositeAggregatorBridge extends DateHistogramAggregatorBridge {
+    protected boolean canOptimize(CompositeValuesSourceConfig[] sourceConfigs) {
+        if (sourceConfigs.length != 1 || !(sourceConfigs[0].valuesSource() instanceof RoundingValuesSource)) return false;
+        return canOptimize(sourceConfigs[0].missingBucket(), sourceConfigs[0].hasScript(), sourceConfigs[0].fieldType());
+    }
+
+    private boolean canOptimize(boolean missing, boolean hasScript, MappedFieldType fieldType) {
+        if (!missing && !hasScript) {
+            if (fieldType instanceof DateFieldMapper.DateFieldType) {
+                if (fieldType.isSearchable()) {
+                    this.fieldType = fieldType;
+                    return true;
+                }
+            }
+        }
+        return false;
+    }
+}