Bring ReduceContext to top level class (#81394)

This brings `ReduceContext` to a top level class so we can add more
things to it without making `InternalAggregation` huge. It also removes
the now unused `pipelineTreeForBwcSerialization`.

benchmarks/src/main/java/org/elasticsearch/benchmark/search/aggregations/TermsReduceBenchmark.java

@@ -24,8 +24,8 @@ import org.elasticsearch.indices.breaker.NoneCircuitBreakerService;
 import org.elasticsearch.search.DocValueFormat;
 import org.elasticsearch.search.SearchShardTarget;
 import org.elasticsearch.search.aggregations.AggregationBuilders;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.BucketOrder;
-import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.search.aggregations.InternalAggregations;
 import org.elasticsearch.search.aggregations.MultiBucketConsumerService;
 import org.elasticsearch.search.aggregations.bucket.terms.StringTerms;
@@ -65,29 +65,21 @@ import java.util.concurrent.atomic.AtomicBoolean;
 @Fork(value = 1)
 public class TermsReduceBenchmark {
 
-    private final SearchPhaseController controller = new SearchPhaseController(
+    private final SearchPhaseController controller = new SearchPhaseController((task, req) -> new AggregationReduceContext.Builder() {
-        (task, req) -> new InternalAggregation.ReduceContextBuilder() {
         @Override
-            public InternalAggregation.ReduceContext forPartialReduction() {
+        public AggregationReduceContext forPartialReduction() {
-                return InternalAggregation.ReduceContext.forPartialReduction(null, null, () -> PipelineAggregator.PipelineTree.EMPTY, task);
+            return new AggregationReduceContext.ForPartial(null, null, task);
         }
 
         @Override
-            public InternalAggregation.ReduceContext forFinalReduction() {
+        public AggregationReduceContext forFinalReduction() {
             final MultiBucketConsumerService.MultiBucketConsumer bucketConsumer = new MultiBucketConsumerService.MultiBucketConsumer(
                 Integer.MAX_VALUE,
                 new NoneCircuitBreakerService().getBreaker(CircuitBreaker.REQUEST)
             );
-                return InternalAggregation.ReduceContext.forFinalReduction(
+            return new AggregationReduceContext.ForFinal(null, null, bucketConsumer, PipelineAggregator.PipelineTree.EMPTY, task);
-                    null,
-                    null,
-                    bucketConsumer,
-                    PipelineAggregator.PipelineTree.EMPTY,
-                    task
-                );
         }
-        }
+    });
-    );
 
     @State(Scope.Benchmark)
     public static class TermsList extends AbstractList<InternalAggregations> {

modules/aggs-matrix-stats/src/main/java/org/elasticsearch/search/aggregations/matrix/stats/InternalMatrixStats.java

@@ -9,6 +9,7 @@ package org.elasticsearch.search.aggregations.matrix.stats;
 
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.xcontent.XContentBuilder;
 
@@ -226,7 +227,7 @@ public class InternalMatrixStats extends InternalAggregation implements MatrixSt
     }
 
     @Override
-    public InternalAggregation reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalAggregation reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         // merge stats across all shards
         List<InternalAggregation> aggs = new ArrayList<>(aggregations);
         aggs.removeIf(p -> ((InternalMatrixStats) p).stats == null);

modules/aggs-matrix-stats/src/test/java/org/elasticsearch/search/aggregations/matrix/stats/InternalMatrixStatsTests.java

@@ -15,6 +15,7 @@ import org.elasticsearch.indices.breaker.NoneCircuitBreakerService;
 import org.elasticsearch.plugins.SearchPlugin;
 import org.elasticsearch.script.ScriptService;
 import org.elasticsearch.search.aggregations.Aggregation;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.search.aggregations.ParsedAggregation;
 import org.elasticsearch.search.aggregations.matrix.MatrixAggregationPlugin;
@@ -153,7 +154,7 @@ public class InternalMatrixStatsTests extends InternalAggregationTestCase<Intern
 
         ScriptService mockScriptService = mockScriptService();
         MockBigArrays bigArrays = new MockBigArrays(new MockPageCacheRecycler(Settings.EMPTY), new NoneCircuitBreakerService());
-        InternalAggregation.ReduceContext context = InternalAggregation.ReduceContext.forFinalReduction(
+        AggregationReduceContext context = new AggregationReduceContext.ForFinal(
             bigArrays,
             mockScriptService,
             b -> {},

server/src/main/java/org/elasticsearch/action/search/QueryPhaseResultConsumer.java

@@ -21,7 +21,7 @@ import org.elasticsearch.core.Releasable;
 import org.elasticsearch.core.Releasables;
 import org.elasticsearch.search.SearchPhaseResult;
 import org.elasticsearch.search.SearchShardTarget;
-import org.elasticsearch.search.aggregations.InternalAggregation.ReduceContextBuilder;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregations;
 import org.elasticsearch.search.builder.SearchSourceBuilder;
 import org.elasticsearch.search.query.QuerySearchResult;
@@ -57,7 +57,7 @@ public class QueryPhaseResultConsumer extends ArraySearchPhaseResults<SearchPhas
     private final CircuitBreaker circuitBreaker;
     private final SearchPhaseController controller;
     private final SearchProgressListener progressListener;
-    private final ReduceContextBuilder aggReduceContextBuilder;
+    private final AggregationReduceContext.Builder aggReduceContextBuilder;
 
     private final int topNSize;
     private final boolean hasTopDocs;

server/src/main/java/org/elasticsearch/action/search/SearchPhaseController.java

@@ -31,8 +31,7 @@ import org.elasticsearch.search.SearchHit;
 import org.elasticsearch.search.SearchHits;
 import org.elasticsearch.search.SearchPhaseResult;
 import org.elasticsearch.search.SearchService;
-import org.elasticsearch.search.aggregations.InternalAggregation;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
-import org.elasticsearch.search.aggregations.InternalAggregation.ReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregations;
 import org.elasticsearch.search.builder.SearchSourceBuilder;
 import org.elasticsearch.search.dfs.AggregatedDfs;
@@ -64,10 +63,10 @@ import java.util.stream.Collectors;
 public final class SearchPhaseController {
     private static final ScoreDoc[] EMPTY_DOCS = new ScoreDoc[0];
 
-    private final BiFunction<Supplier<Boolean>, SearchRequest, InternalAggregation.ReduceContextBuilder> requestToAggReduceContextBuilder;
+    private final BiFunction<Supplier<Boolean>, SearchRequest, AggregationReduceContext.Builder> requestToAggReduceContextBuilder;
 
     public SearchPhaseController(
-        BiFunction<Supplier<Boolean>, SearchRequest, InternalAggregation.ReduceContextBuilder> requestToAggReduceContextBuilder
+        BiFunction<Supplier<Boolean>, SearchRequest, AggregationReduceContext.Builder> requestToAggReduceContextBuilder
     ) {
         this.requestToAggReduceContextBuilder = requestToAggReduceContextBuilder;
     }
@@ -380,14 +379,14 @@ public final class SearchPhaseController {
      * @param queryResults a list of non-null query shard results
      */
     ReducedQueryPhase reducedScrollQueryPhase(Collection<? extends SearchPhaseResult> queryResults) {
-        InternalAggregation.ReduceContextBuilder aggReduceContextBuilder = new InternalAggregation.ReduceContextBuilder() {
+        AggregationReduceContext.Builder aggReduceContextBuilder = new AggregationReduceContext.Builder() {
             @Override
-            public ReduceContext forPartialReduction() {
+            public AggregationReduceContext forPartialReduction() {
                 throw new UnsupportedOperationException("Scroll requests don't have aggs");
             }
 
             @Override
-            public ReduceContext forFinalReduction() {
+            public AggregationReduceContext forFinalReduction() {
                 throw new UnsupportedOperationException("Scroll requests don't have aggs");
             }
         };
@@ -423,7 +422,7 @@ public final class SearchPhaseController {
         TopDocsStats topDocsStats,
         int numReducePhases,
         boolean isScrollRequest,
-        InternalAggregation.ReduceContextBuilder aggReduceContextBuilder,
+        AggregationReduceContext.Builder aggReduceContextBuilder,
         boolean performFinalReduce
     ) {
         assert numReducePhases >= 0 : "num reduce phases must be >= 0 but was: " + numReducePhases;
@@ -528,7 +527,7 @@ public final class SearchPhaseController {
     }
 
     private static InternalAggregations reduceAggs(
-        InternalAggregation.ReduceContextBuilder aggReduceContextBuilder,
+        AggregationReduceContext.Builder aggReduceContextBuilder,
         boolean performFinalReduce,
         List<InternalAggregations> toReduce
     ) {
@@ -679,7 +678,7 @@ public final class SearchPhaseController {
         }
     }
 
-    InternalAggregation.ReduceContextBuilder getReduceContext(Supplier<Boolean> isCanceled, SearchRequest request) {
+    AggregationReduceContext.Builder getReduceContext(Supplier<Boolean> isCanceled, SearchRequest request) {
         return requestToAggReduceContextBuilder.apply(isCanceled, request);
     }
 

server/src/main/java/org/elasticsearch/action/search/SearchResponseMerger.java

@@ -24,7 +24,7 @@ import org.elasticsearch.lucene.grouping.TopFieldGroups;
 import org.elasticsearch.search.SearchHit;
 import org.elasticsearch.search.SearchHits;
 import org.elasticsearch.search.SearchShardTarget;
-import org.elasticsearch.search.aggregations.InternalAggregation;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregations;
 import org.elasticsearch.search.internal.InternalSearchResponse;
 import org.elasticsearch.search.profile.SearchProfileResults;
@@ -69,7 +69,7 @@ final class SearchResponseMerger {
     final int size;
     final int trackTotalHitsUpTo;
     private final SearchTimeProvider searchTimeProvider;
-    private final InternalAggregation.ReduceContextBuilder aggReduceContextBuilder;
+    private final AggregationReduceContext.Builder aggReduceContextBuilder;
     private final List<SearchResponse> searchResponses = new CopyOnWriteArrayList<>();
 
     SearchResponseMerger(
@@ -77,7 +77,7 @@ final class SearchResponseMerger {
         int size,
         int trackTotalHitsUpTo,
         SearchTimeProvider searchTimeProvider,
-        InternalAggregation.ReduceContextBuilder aggReduceContextBuilder
+        AggregationReduceContext.Builder aggReduceContextBuilder
     ) {
         this.from = from;
         this.size = size;

server/src/main/java/org/elasticsearch/action/search/TransportSearchAction.java

@@ -52,7 +52,7 @@ import org.elasticsearch.indices.breaker.CircuitBreakerService;
 import org.elasticsearch.search.SearchPhaseResult;
 import org.elasticsearch.search.SearchService;
 import org.elasticsearch.search.SearchShardTarget;
-import org.elasticsearch.search.aggregations.InternalAggregation;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregations;
 import org.elasticsearch.search.builder.SearchSourceBuilder;
 import org.elasticsearch.search.internal.AliasFilter;
@@ -507,7 +507,7 @@ public class TransportSearchAction extends HandledTransportAction<SearchRequest,
         OriginalIndices localIndices,
         Map<String, OriginalIndices> remoteIndices,
         SearchTimeProvider timeProvider,
-        InternalAggregation.ReduceContextBuilder aggReduceContextBuilder,
+        AggregationReduceContext.Builder aggReduceContextBuilder,
         RemoteClusterService remoteClusterService,
         ThreadPool threadPool,
         ActionListener<SearchResponse> listener,
@@ -632,7 +632,7 @@ public class TransportSearchAction extends HandledTransportAction<SearchRequest,
     static SearchResponseMerger createSearchResponseMerger(
         SearchSourceBuilder source,
         SearchTimeProvider timeProvider,
-        InternalAggregation.ReduceContextBuilder aggReduceContextBuilder
+        AggregationReduceContext.Builder aggReduceContextBuilder
     ) {
         final int from;
         final int size;

server/src/main/java/org/elasticsearch/search/SearchService.java

@@ -70,9 +70,8 @@ import org.elasticsearch.node.ResponseCollectorService;
 import org.elasticsearch.script.FieldScript;
 import org.elasticsearch.script.ScriptService;
 import org.elasticsearch.search.aggregations.AggregationInitializationException;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.AggregatorFactories;
-import org.elasticsearch.search.aggregations.InternalAggregation;
-import org.elasticsearch.search.aggregations.InternalAggregation.ReduceContext;
 import org.elasticsearch.search.aggregations.MultiBucketConsumerService;
 import org.elasticsearch.search.aggregations.SearchContextAggregations;
 import org.elasticsearch.search.aggregations.pipeline.PipelineAggregator.PipelineTree;
@@ -1591,25 +1590,20 @@ public class SearchService extends AbstractLifecycleComponent implements IndexEv
     }
 
     /**
-     * Returns a builder for {@link InternalAggregation.ReduceContext}. This
+     * Returns a builder for {@link AggregationReduceContext}. This
      * builder retains a reference to the provided {@link SearchRequest}.
      */
-    public InternalAggregation.ReduceContextBuilder aggReduceContextBuilder(Supplier<Boolean> isCanceled, SearchRequest request) {
+    public AggregationReduceContext.Builder aggReduceContextBuilder(Supplier<Boolean> isCanceled, SearchRequest request) {
-        return new InternalAggregation.ReduceContextBuilder() {
+        return new AggregationReduceContext.Builder() {
             @Override
-            public InternalAggregation.ReduceContext forPartialReduction() {
+            public AggregationReduceContext forPartialReduction() {
-                return InternalAggregation.ReduceContext.forPartialReduction(
+                return new AggregationReduceContext.ForPartial(bigArrays, scriptService, isCanceled);
-                    bigArrays,
-                    scriptService,
-                    () -> requestToPipelineTree(request),
-                    isCanceled
-                );
             }
 
             @Override
-            public ReduceContext forFinalReduction() {
+            public AggregationReduceContext forFinalReduction() {
                 PipelineTree pipelineTree = requestToPipelineTree(request);
-                return InternalAggregation.ReduceContext.forFinalReduction(
+                return new AggregationReduceContext.ForFinal(
                     bigArrays,
                     scriptService,
                     multiBucketConsumerService.create(),

server/src/main/java/org/elasticsearch/search/aggregations/AggregationReduceContext.java

@@ -0,0 +1,141 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0 and the Server Side Public License, v 1; you may not use this file except
+ * in compliance with, at your election, the Elastic License 2.0 or the Server
+ * Side Public License, v 1.
+ */
+
+package org.elasticsearch.search.aggregations;
+
+import org.elasticsearch.common.util.BigArrays;
+import org.elasticsearch.script.ScriptService;
+import org.elasticsearch.search.aggregations.pipeline.PipelineAggregator.PipelineTree;
+import org.elasticsearch.tasks.TaskCancelledException;
+
+import java.util.function.IntConsumer;
+import java.util.function.Supplier;
+
+public abstract sealed class AggregationReduceContext permits AggregationReduceContext.ForPartial,AggregationReduceContext.ForFinal {
+    /**
+     * Builds {@link AggregationReduceContext}s.
+     */
+    public interface Builder {
+        /**
+         * Build an {@linkplain AggregationReduceContext} to perform a partial reduction.
+         */
+        AggregationReduceContext forPartialReduction();
+
+        /**
+         * Build an {@linkplain AggregationReduceContext} to perform the final reduction.
+         */
+        AggregationReduceContext forFinalReduction();
+    }
+
+    private final BigArrays bigArrays;
+    private final ScriptService scriptService;
+    private final Supplier<Boolean> isCanceled;
+
+    public AggregationReduceContext(BigArrays bigArrays, ScriptService scriptService, Supplier<Boolean> isCanceled) {
+        this.bigArrays = bigArrays;
+        this.scriptService = scriptService;
+        this.isCanceled = isCanceled;
+    }
+
+    /**
+     * Returns <code>true</code> iff the current reduce phase is the final
+     * reduce phase. This indicates if operations like pipeline aggregations
+     * should be applied or if specific features like {@code minDocCount}
+     * should be taken into account. Operations that are potentially losing
+     * information can only be applied during the final reduce phase.
+     */
+    public abstract boolean isFinalReduce();
+
+    public final BigArrays bigArrays() {
+        return bigArrays;
+    }
+
+    public final ScriptService scriptService() {
+        return scriptService;
+    }
+
+    public final Supplier<Boolean> isCanceled() {
+        return isCanceled;
+    }
+
+    /**
+     * The root of the tree of pipeline aggregations for this request.
+     */
+    public abstract PipelineTree pipelineTreeRoot();
+
+    /**
+     * Adds {@code count} buckets to the global count for the request and fails if this number is greater than
+     * the maximum number of buckets allowed in a response
+     */
+    public final void consumeBucketsAndMaybeBreak(int size) {
+        // This is a volatile read.
+        if (isCanceled.get()) {
+            throw new TaskCancelledException("Cancelled");
+        }
+        consumeBucketCountAndMaybeBreak(size);
+    }
+
+    protected abstract void consumeBucketCountAndMaybeBreak(int size);
+
+    /**
+     * A {@linkplain AggregationReduceContext} to perform a partial reduction.
+     */
+    public static final class ForPartial extends AggregationReduceContext {
+        public ForPartial(BigArrays bigArrays, ScriptService scriptService, Supplier<Boolean> isCanceled) {
+            super(bigArrays, scriptService, isCanceled);
+        }
+
+        @Override
+        public boolean isFinalReduce() {
+            return false;
+        }
+
+        @Override
+        protected void consumeBucketCountAndMaybeBreak(int size) {}
+
+        @Override
+        public PipelineTree pipelineTreeRoot() {
+            return null;
+        }
+    }
+
+    /**
+     * A {@linkplain AggregationReduceContext} to perform the final reduction.
+     */
+    public static final class ForFinal extends AggregationReduceContext {
+        private final IntConsumer multiBucketConsumer;
+        private final PipelineTree pipelineTreeRoot;
+
+        public ForFinal(
+            BigArrays bigArrays,
+            ScriptService scriptService,
+            IntConsumer multiBucketConsumer,
+            PipelineTree pipelineTreeRoot,
+            Supplier<Boolean> isCanceled
+        ) {
+            super(bigArrays, scriptService, isCanceled);
+            this.multiBucketConsumer = multiBucketConsumer;
+            this.pipelineTreeRoot = pipelineTreeRoot;
+        }
+
+        @Override
+        public boolean isFinalReduce() {
+            return true;
+        }
+
+        @Override
+        protected void consumeBucketCountAndMaybeBreak(int size) {
+            multiBucketConsumer.accept(size);
+        }
+
+        @Override
+        public PipelineTree pipelineTreeRoot() {
+            return pipelineTreeRoot;
+        }
+    }
+}

server/src/main/java/org/elasticsearch/search/aggregations/DelayedBucket.java

@@ -16,8 +16,8 @@ import java.util.function.BiFunction;
  * as long as possible. It's stateful and not even close to thread safe.
  */
 public final class DelayedBucket<B extends InternalMultiBucketAggregation.InternalBucket> {
-    private final BiFunction<List<B>, InternalAggregation.ReduceContext, B> reduce;
+    private final BiFunction<List<B>, AggregationReduceContext, B> reduce;
-    private final InternalAggregation.ReduceContext reduceContext;
+    private final AggregationReduceContext reduceContext;
     /**
      * The buckets to reduce or {@code null} if we've already reduced the buckets.
      */
@@ -40,8 +40,8 @@ public final class DelayedBucket<B extends InternalMultiBucketAggregation.Intern
      * {@link InternalMultiBucketAggregation#reduceBucket}.
      */
     public DelayedBucket(
-        BiFunction<List<B>, InternalAggregation.ReduceContext, B> reduce,
+        BiFunction<List<B>, AggregationReduceContext, B> reduce,
-        InternalAggregation.ReduceContext reduceContext,
+        AggregationReduceContext reduceContext,
         List<B> toReduce
     ) {
         this.reduce = reduce;

server/src/main/java/org/elasticsearch/search/aggregations/InternalAggregation.java

@@ -11,13 +11,10 @@ import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.io.stream.NamedWriteable;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
-import org.elasticsearch.common.util.BigArrays;
 import org.elasticsearch.rest.action.search.RestSearchAction;
-import org.elasticsearch.script.ScriptService;
 import org.elasticsearch.search.aggregations.pipeline.PipelineAggregator;
 import org.elasticsearch.search.aggregations.pipeline.PipelineAggregator.PipelineTree;
 import org.elasticsearch.search.aggregations.support.AggregationPath;
-import org.elasticsearch.tasks.TaskCancelledException;
 import org.elasticsearch.xcontent.XContentBuilder;
 
 import java.io.IOException;
@@ -27,142 +24,11 @@ import java.util.Map;
 import java.util.Objects;
 import java.util.function.Consumer;
 import java.util.function.Function;
-import java.util.function.IntConsumer;
-import java.util.function.Supplier;
-
-import static java.util.Objects.requireNonNull;
 
 /**
  * An internal implementation of {@link Aggregation}. Serves as a base class for all aggregation implementations.
  */
 public abstract class InternalAggregation implements Aggregation, NamedWriteable {
-    /**
-     * Builds {@link ReduceContext}.
-     */
-    public interface ReduceContextBuilder {
-        /**
-         * Build a {@linkplain ReduceContext} to perform a partial reduction.
-         */
-        ReduceContext forPartialReduction();
-
-        /**
-         * Build a {@linkplain ReduceContext} to perform the final reduction.
-         */
-        ReduceContext forFinalReduction();
-    }
-
-    public static class ReduceContext {
-        private final BigArrays bigArrays;
-        private final ScriptService scriptService;
-        private final IntConsumer multiBucketConsumer;
-        private final PipelineTree pipelineTreeRoot;
-        private final Supplier<Boolean> isCanceled;
-        /**
-         * Supplies the pipelines when the result of the reduce is serialized
-         * to node versions that need pipeline aggregators to be serialized
-         * to them.
-         */
-        private final Supplier<PipelineTree> pipelineTreeForBwcSerialization;
-
-        /**
-         * Build a {@linkplain ReduceContext} to perform a partial reduction.
-         */
-        public static ReduceContext forPartialReduction(
-            BigArrays bigArrays,
-            ScriptService scriptService,
-            Supplier<PipelineTree> pipelineTreeForBwcSerialization,
-            Supplier<Boolean> isCanceled
-        ) {
-            return new ReduceContext(bigArrays, scriptService, (s) -> {}, null, pipelineTreeForBwcSerialization, isCanceled);
-        }
-
-        /**
-         * Build a {@linkplain ReduceContext} to perform the final reduction.
-         * @param pipelineTreeRoot The root of tree of pipeline aggregations for this request
-         */
-        public static ReduceContext forFinalReduction(
-            BigArrays bigArrays,
-            ScriptService scriptService,
-            IntConsumer multiBucketConsumer,
-            PipelineTree pipelineTreeRoot,
-            Supplier<Boolean> isCanceled
-        ) {
-            return new ReduceContext(
-                bigArrays,
-                scriptService,
-                multiBucketConsumer,
-                requireNonNull(pipelineTreeRoot, "prefer EMPTY to null"),
-                () -> pipelineTreeRoot,
-                isCanceled
-            );
-        }
-
-        private ReduceContext(
-            BigArrays bigArrays,
-            ScriptService scriptService,
-            IntConsumer multiBucketConsumer,
-            PipelineTree pipelineTreeRoot,
-            Supplier<PipelineTree> pipelineTreeForBwcSerialization,
-            Supplier<Boolean> isCanceled
-        ) {
-            this.bigArrays = bigArrays;
-            this.scriptService = scriptService;
-            this.multiBucketConsumer = multiBucketConsumer;
-            this.pipelineTreeRoot = pipelineTreeRoot;
-            this.pipelineTreeForBwcSerialization = pipelineTreeForBwcSerialization;
-            this.isCanceled = isCanceled;
-        }
-
-        /**
-         * Returns <code>true</code> iff the current reduce phase is the final reduce phase. This indicates if operations like
-         * pipeline aggregations should be applied or if specific features like {@code minDocCount} should be taken into account.
-         * Operations that are potentially losing information can only be applied during the final reduce phase.
-         */
-        public boolean isFinalReduce() {
-            return pipelineTreeRoot != null;
-        }
-
-        public BigArrays bigArrays() {
-            return bigArrays;
-        }
-
-        public ScriptService scriptService() {
-            return scriptService;
-        }
-
-        /**
-         * The root of the tree of pipeline aggregations for this request.
-         */
-        public PipelineTree pipelineTreeRoot() {
-            return pipelineTreeRoot;
-        }
-
-        /**
-         * Supplies the pipelines when the result of the reduce is serialized
-         * to node versions that need pipeline aggregators to be serialized
-         * to them.
-         */
-        public Supplier<PipelineTree> pipelineTreeForBwcSerialization() {
-            return pipelineTreeForBwcSerialization;
-        }
-
-        /**
-         * Adds {@code count} buckets to the global count for the request and fails if this number is greater than
-         * the maximum number of buckets allowed in a response
-         */
-        public void consumeBucketsAndMaybeBreak(int size) {
-            // This is a volatile read.
-            if (isCanceled.get()) {
-                throw new TaskCancelledException("Cancelled");
-            }
-            multiBucketConsumer.accept(size);
-        }
-
-        public Supplier<Boolean> isCanceled() {
-            return isCanceled;
-        }
-    }
-
     protected final String name;
 
     protected final Map<String, Object> metadata;
@@ -234,7 +100,7 @@ public abstract class InternalAggregation implements Aggregation, NamedWriteable
      */
     public InternalAggregation reducePipelines(
         InternalAggregation reducedAggs,
-        ReduceContext reduceContext,
+        AggregationReduceContext reduceContext,
         PipelineTree pipelinesForThisAgg
     ) {
         assert reduceContext.isFinalReduce();
@@ -252,7 +118,7 @@ public abstract class InternalAggregation implements Aggregation, NamedWriteable
      *
      * @see #mustReduceOnSingleInternalAgg()
      */
-    public abstract InternalAggregation reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext);
+    public abstract InternalAggregation reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext);
 
     /**
      * Signal the framework if the {@linkplain InternalAggregation#reduce(List, ReduceContext)} phase needs to be called

server/src/main/java/org/elasticsearch/search/aggregations/InternalAggregations.java

@@ -10,7 +10,6 @@ package org.elasticsearch.search.aggregations;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.io.stream.Writeable;
-import org.elasticsearch.search.aggregations.InternalAggregation.ReduceContext;
 import org.elasticsearch.search.aggregations.pipeline.PipelineAggregator;
 import org.elasticsearch.search.aggregations.pipeline.SiblingPipelineAggregator;
 import org.elasticsearch.search.aggregations.support.AggregationPath;
@@ -99,7 +98,7 @@ public final class InternalAggregations extends Aggregations implements Writeabl
      * This method first reduces the aggregations, and if it is the final reduce, then reduce the pipeline
      * aggregations (both embedded parent/sibling as well as top-level sibling pipelines)
      */
-    public static InternalAggregations topLevelReduce(List<InternalAggregations> aggregationsList, ReduceContext context) {
+    public static InternalAggregations topLevelReduce(List<InternalAggregations> aggregationsList, AggregationReduceContext context) {
         InternalAggregations reduced = reduce(aggregationsList, context);
         if (reduced == null) {
             return null;
@@ -127,7 +126,7 @@ public final class InternalAggregations extends Aggregations implements Writeabl
      * Note that pipeline aggregations _are not_ reduced by this method.  Pipelines are handled
      * separately by {@link InternalAggregations#topLevelReduce(List, ReduceContext)}
      */
-    public static InternalAggregations reduce(List<InternalAggregations> aggregationsList, ReduceContext context) {
+    public static InternalAggregations reduce(List<InternalAggregations> aggregationsList, AggregationReduceContext context) {
         if (aggregationsList.isEmpty()) {
             return null;
         }

server/src/main/java/org/elasticsearch/search/aggregations/InternalMultiBucketAggregation.java

@@ -63,7 +63,7 @@ public abstract class InternalMultiBucketAggregation<
      * Reduce a list of same-keyed buckets (from multiple shards) to a single bucket. This
      * requires all buckets to have the same key.
      */
-    protected abstract B reduceBucket(List<B> buckets, ReduceContext context);
+    protected abstract B reduceBucket(List<B> buckets, AggregationReduceContext context);
 
     @Override
     public abstract List<B> getBuckets();
@@ -141,7 +141,7 @@ public abstract class InternalMultiBucketAggregation<
     @Override
     public final InternalAggregation reducePipelines(
         InternalAggregation reducedAggs,
-        ReduceContext reduceContext,
+        AggregationReduceContext reduceContext,
         PipelineTree pipelineTree
     ) {
         assert reduceContext.isFinalReduce();
@@ -182,7 +182,7 @@ public abstract class InternalMultiBucketAggregation<
         }
     }
 
-    private List<B> reducePipelineBuckets(ReduceContext reduceContext, PipelineTree pipelineTree) {
+    private List<B> reducePipelineBuckets(AggregationReduceContext reduceContext, PipelineTree pipelineTree) {
         List<B> reducedBuckets = new ArrayList<>();
         for (B bucket : getBuckets()) {
             List<InternalAggregation> aggs = new ArrayList<>();

server/src/main/java/org/elasticsearch/search/aggregations/bucket/InternalSingleBucketAggregation.java

@@ -10,6 +10,7 @@ package org.elasticsearch.search.aggregations.bucket;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.search.aggregations.Aggregation;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.search.aggregations.InternalAggregations;
 import org.elasticsearch.search.aggregations.pipeline.PipelineAggregator.PipelineTree;
@@ -89,7 +90,7 @@ public abstract class InternalSingleBucketAggregation extends InternalAggregatio
     protected abstract InternalSingleBucketAggregation newAggregation(String name, long docCount, InternalAggregations subAggregations);
 
     @Override
-    public InternalAggregation reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalAggregation reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         long docCount = 0L;
         List<InternalAggregations> subAggregationsList = new ArrayList<>(aggregations.size());
         for (InternalAggregation aggregation : aggregations) {
@@ -108,7 +109,7 @@ public abstract class InternalSingleBucketAggregation extends InternalAggregatio
     @Override
     public final InternalAggregation reducePipelines(
         InternalAggregation reducedAggs,
-        ReduceContext reduceContext,
+        AggregationReduceContext reduceContext,
         PipelineTree pipelineTree
     ) {
         assert reduceContext.isFinalReduce();

server/src/main/java/org/elasticsearch/search/aggregations/bucket/adjacency/InternalAdjacencyMatrix.java

@@ -10,6 +10,7 @@ package org.elasticsearch.search.aggregations.bucket.adjacency;
 
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.search.aggregations.InternalAggregations;
 import org.elasticsearch.search.aggregations.InternalMultiBucketAggregation;
@@ -167,7 +168,7 @@ public class InternalAdjacencyMatrix extends InternalMultiBucketAggregation<Inte
     }
 
     @Override
-    public InternalAggregation reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalAggregation reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         Map<String, List<InternalBucket>> bucketsMap = new HashMap<>();
         for (InternalAggregation aggregation : aggregations) {
             InternalAdjacencyMatrix filters = (InternalAdjacencyMatrix) aggregation;
@@ -197,7 +198,7 @@ public class InternalAdjacencyMatrix extends InternalMultiBucketAggregation<Inte
     }
 
     @Override
-    protected InternalBucket reduceBucket(List<InternalBucket> buckets, ReduceContext context) {
+    protected InternalBucket reduceBucket(List<InternalBucket> buckets, AggregationReduceContext context) {
         assert buckets.size() > 0;
         InternalBucket reduced = null;
         List<InternalAggregations> aggregationsList = new ArrayList<>(buckets.size());

server/src/main/java/org/elasticsearch/search/aggregations/bucket/composite/InternalComposite.java

@@ -14,6 +14,7 @@ import org.elasticsearch.Version;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.Aggregations;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.search.aggregations.InternalAggregations;
@@ -186,7 +187,7 @@ public class InternalComposite extends InternalMultiBucketAggregation<InternalCo
     }
 
     @Override
-    public InternalAggregation reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalAggregation reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         PriorityQueue<BucketIterator> pq = new PriorityQueue<>(aggregations.size()) {
             @Override
             protected boolean lessThan(BucketIterator a, BucketIterator b) {
@@ -253,7 +254,7 @@ public class InternalComposite extends InternalMultiBucketAggregation<InternalCo
     }
 
     @Override
-    protected InternalBucket reduceBucket(List<InternalBucket> buckets, ReduceContext context) {
+    protected InternalBucket reduceBucket(List<InternalBucket> buckets, AggregationReduceContext context) {
         assert buckets.size() > 0;
         List<InternalAggregations> aggregations = new ArrayList<>(buckets.size());
         long docCount = 0;

server/src/main/java/org/elasticsearch/search/aggregations/bucket/filter/InternalFilters.java

@@ -10,6 +10,7 @@ package org.elasticsearch.search.aggregations.bucket.filter;
 
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.search.aggregations.InternalAggregations;
 import org.elasticsearch.search.aggregations.InternalMultiBucketAggregation;
@@ -175,7 +176,7 @@ public class InternalFilters extends InternalMultiBucketAggregation<InternalFilt
     }
 
     @Override
-    public InternalAggregation reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalAggregation reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         List<List<InternalBucket>> bucketsList = null;
         for (InternalAggregation aggregation : aggregations) {
             InternalFilters filters = (InternalFilters) aggregation;
@@ -203,7 +204,7 @@ public class InternalFilters extends InternalMultiBucketAggregation<InternalFilt
     }
 
     @Override
-    protected InternalBucket reduceBucket(List<InternalBucket> buckets, ReduceContext context) {
+    protected InternalBucket reduceBucket(List<InternalBucket> buckets, AggregationReduceContext context) {
         assert buckets.size() > 0;
         InternalBucket reduced = null;
         List<InternalAggregations> aggregationsList = new ArrayList<>(buckets.size());

server/src/main/java/org/elasticsearch/search/aggregations/bucket/geogrid/InternalGeoGrid.java

@@ -11,6 +11,7 @@ import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.io.stream.Writeable;
 import org.elasticsearch.common.util.LongObjectPagedHashMap;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.search.aggregations.InternalAggregations;
 import org.elasticsearch.search.aggregations.InternalMultiBucketAggregation;
@@ -69,7 +70,7 @@ public abstract class InternalGeoGrid<B extends InternalGeoGridBucket> extends I
     }
 
     @Override
-    public InternalGeoGrid<B> reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalGeoGrid<B> reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         LongObjectPagedHashMap<List<InternalGeoGridBucket>> buckets = null;
         for (InternalAggregation aggregation : aggregations) {
             @SuppressWarnings("unchecked")
@@ -104,7 +105,7 @@ public abstract class InternalGeoGrid<B extends InternalGeoGridBucket> extends I
     }
 
     @Override
-    protected InternalGeoGridBucket reduceBucket(List<InternalGeoGridBucket> buckets, ReduceContext context) {
+    protected InternalGeoGridBucket reduceBucket(List<InternalGeoGridBucket> buckets, AggregationReduceContext context) {
         assert buckets.size() > 0;
         List<InternalAggregations> aggregationsList = new ArrayList<>(buckets.size());
         long docCount = 0;

server/src/main/java/org/elasticsearch/search/aggregations/bucket/histogram/InternalAutoDateHistogram.java

@@ -12,6 +12,7 @@ import org.elasticsearch.common.Rounding;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.Aggregations;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.search.aggregations.InternalAggregations;
@@ -271,7 +272,7 @@ public final class InternalAutoDateHistogram extends InternalMultiBucketAggregat
      * rounding returned across all the shards so the resolution of the buckets
      * is the same and they can be reduced together.
      */
-    private BucketReduceResult reduceBuckets(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    private BucketReduceResult reduceBuckets(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
 
         // First we need to find the highest level rounding used across all the
         // shards
@@ -338,7 +339,7 @@ public final class InternalAutoDateHistogram extends InternalMultiBucketAggregat
         return mergeBucketsIfNeeded(new BucketReduceResult(reducedBuckets, reduceRoundingIdx, 1, reduceRounding, min, max), reduceContext);
     }
 
-    private BucketReduceResult mergeBucketsIfNeeded(BucketReduceResult firstPassResult, ReduceContext reduceContext) {
+    private BucketReduceResult mergeBucketsIfNeeded(BucketReduceResult firstPassResult, AggregationReduceContext reduceContext) {
         int idx = firstPassResult.roundingIdx;
         RoundingInfo info = bucketInfo.roundingInfos[idx];
         List<Bucket> buckets = firstPassResult.buckets;
@@ -357,7 +358,11 @@ public final class InternalAutoDateHistogram extends InternalMultiBucketAggregat
         return min <= max ? rounding.prepare(min, max) : rounding.prepareForUnknown();
     }
 
-    private List<Bucket> mergeBuckets(List<Bucket> reducedBuckets, Rounding.Prepared reduceRounding, ReduceContext reduceContext) {
+    private List<Bucket> mergeBuckets(
+        List<Bucket> reducedBuckets,
+        Rounding.Prepared reduceRounding,
+        AggregationReduceContext reduceContext
+    ) {
         List<Bucket> mergedBuckets = new ArrayList<>();
 
         List<Bucket> sameKeyedBuckets = new ArrayList<>();
@@ -384,7 +389,7 @@ public final class InternalAutoDateHistogram extends InternalMultiBucketAggregat
     }
 
     @Override
-    protected Bucket reduceBucket(List<Bucket> buckets, ReduceContext context) {
+    protected Bucket reduceBucket(List<Bucket> buckets, AggregationReduceContext context) {
         assert buckets.size() > 0;
         List<InternalAggregations> aggregations = new ArrayList<>(buckets.size());
         long docCount = 0;
@@ -421,7 +426,7 @@ public final class InternalAutoDateHistogram extends InternalMultiBucketAggregat
         }
     }
 
-    private BucketReduceResult addEmptyBuckets(BucketReduceResult current, ReduceContext reduceContext) {
+    private BucketReduceResult addEmptyBuckets(BucketReduceResult current, AggregationReduceContext reduceContext) {
         List<Bucket> list = current.buckets;
         if (list.isEmpty()) {
             return current;
@@ -500,7 +505,7 @@ public final class InternalAutoDateHistogram extends InternalMultiBucketAggregat
     }
 
     @Override
-    public InternalAggregation reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalAggregation reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         BucketReduceResult reducedBucketsResult = reduceBuckets(aggregations, reduceContext);
 
         if (reduceContext.isFinalReduce()) {
@@ -531,7 +536,7 @@ public final class InternalAutoDateHistogram extends InternalMultiBucketAggregat
         );
     }
 
-    private BucketReduceResult maybeMergeConsecutiveBuckets(BucketReduceResult current, ReduceContext reduceContext) {
+    private BucketReduceResult maybeMergeConsecutiveBuckets(BucketReduceResult current, AggregationReduceContext reduceContext) {
         List<Bucket> buckets = current.buckets;
         RoundingInfo roundingInfo = bucketInfo.roundingInfos[current.roundingIdx];
         if (buckets.size() > targetBuckets) {
@@ -548,7 +553,11 @@ public final class InternalAutoDateHistogram extends InternalMultiBucketAggregat
         return current;
     }
 
-    private BucketReduceResult mergeConsecutiveBuckets(BucketReduceResult current, int mergeInterval, ReduceContext reduceContext) {
+    private BucketReduceResult mergeConsecutiveBuckets(
+        BucketReduceResult current,
+        int mergeInterval,
+        AggregationReduceContext reduceContext
+    ) {
         List<Bucket> mergedBuckets = new ArrayList<>();
         List<Bucket> sameKeyedBuckets = new ArrayList<>();
 

server/src/main/java/org/elasticsearch/search/aggregations/bucket/histogram/InternalDateHistogram.java

@@ -13,6 +13,7 @@ import org.elasticsearch.common.Rounding;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.Aggregations;
 import org.elasticsearch.search.aggregations.BucketOrder;
 import org.elasticsearch.search.aggregations.InternalAggregation;
@@ -287,7 +288,7 @@ public final class InternalDateHistogram extends InternalMultiBucketAggregation<
         return new Bucket(prototype.key, prototype.docCount, prototype.keyed, prototype.format, aggregations);
     }
 
-    private List<Bucket> reduceBuckets(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    private List<Bucket> reduceBuckets(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
 
         final PriorityQueue<IteratorAndCurrent<Bucket>> pq = new PriorityQueue<>(aggregations.size()) {
             @Override
@@ -348,7 +349,7 @@ public final class InternalDateHistogram extends InternalMultiBucketAggregation<
      * requires all buckets to have the same key.
      */
     @Override
-    protected Bucket reduceBucket(List<Bucket> buckets, ReduceContext context) {
+    protected Bucket reduceBucket(List<Bucket> buckets, AggregationReduceContext context) {
         assert buckets.size() > 0;
         List<InternalAggregations> aggregations = new ArrayList<>(buckets.size());
         long docCount = 0;
@@ -372,7 +373,7 @@ public final class InternalDateHistogram extends InternalMultiBucketAggregation<
      */
     private static final int REPORT_EMPTY_EVERY = 10_000;
 
-    private void addEmptyBuckets(List<Bucket> list, ReduceContext reduceContext) {
+    private void addEmptyBuckets(List<Bucket> list, AggregationReduceContext reduceContext) {
         /*
          * Make sure we have space for the empty buckets we're going to add by
          * counting all of the empties we plan to add and firing them into
@@ -456,7 +457,7 @@ public final class InternalDateHistogram extends InternalMultiBucketAggregation<
     }
 
     @Override
-    public InternalAggregation reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalAggregation reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         List<Bucket> reducedBuckets = reduceBuckets(aggregations, reduceContext);
         boolean alreadyAccountedForBuckets = false;
         if (reduceContext.isFinalReduce()) {

server/src/main/java/org/elasticsearch/search/aggregations/bucket/histogram/InternalHistogram.java

@@ -12,6 +12,7 @@ import org.apache.lucene.util.PriorityQueue;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.Aggregations;
 import org.elasticsearch.search.aggregations.BucketOrder;
 import org.elasticsearch.search.aggregations.InternalAggregation;
@@ -269,8 +270,7 @@ public final class InternalHistogram extends InternalMultiBucketAggregation<Inte
         return new Bucket(prototype.key, prototype.docCount, prototype.keyed, prototype.format, aggregations);
     }
 
-    private List<Bucket> reduceBuckets(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    private List<Bucket> reduceBuckets(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
-
         final PriorityQueue<IteratorAndCurrent<Bucket>> pq = new PriorityQueue<>(aggregations.size()) {
             @Override
             protected boolean lessThan(IteratorAndCurrent<Bucket> a, IteratorAndCurrent<Bucket> b) {
@@ -327,7 +327,7 @@ public final class InternalHistogram extends InternalMultiBucketAggregation<Inte
     }
 
     @Override
-    protected Bucket reduceBucket(List<Bucket> buckets, ReduceContext context) {
+    protected Bucket reduceBucket(List<Bucket> buckets, AggregationReduceContext context) {
         assert buckets.size() > 0;
         List<InternalAggregations> aggregations = new ArrayList<>(buckets.size());
         long docCount = 0;
@@ -359,7 +359,7 @@ public final class InternalHistogram extends InternalMultiBucketAggregation<Inte
      */
     private static final int REPORT_EMPTY_EVERY = 10_000;
 
-    private void addEmptyBuckets(List<Bucket> list, ReduceContext reduceContext) {
+    private void addEmptyBuckets(List<Bucket> list, AggregationReduceContext reduceContext) {
         /*
          * Make sure we have space for the empty buckets we're going to add by
          * counting all of the empties we plan to add and firing them into
@@ -431,7 +431,7 @@ public final class InternalHistogram extends InternalMultiBucketAggregation<Inte
     }
 
     @Override
-    public InternalAggregation reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalAggregation reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         List<Bucket> reducedBuckets = reduceBuckets(aggregations, reduceContext);
         boolean alreadyAccountedForBuckets = false;
         if (reduceContext.isFinalReduce()) {

server/src/main/java/org/elasticsearch/search/aggregations/bucket/histogram/InternalVariableWidthHistogram.java

@@ -12,6 +12,7 @@ import org.apache.lucene.util.PriorityQueue;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.Aggregations;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.search.aggregations.InternalAggregations;
@@ -316,7 +317,7 @@ public class InternalVariableWidthHistogram extends InternalMultiBucketAggregati
     }
 
     @Override
-    protected Bucket reduceBucket(List<Bucket> buckets, ReduceContext context) {
+    protected Bucket reduceBucket(List<Bucket> buckets, AggregationReduceContext context) {
         List<InternalAggregations> aggregations = new ArrayList<>(buckets.size());
         long docCount = 0;
         double min = Double.POSITIVE_INFINITY;
@@ -335,7 +336,7 @@ public class InternalVariableWidthHistogram extends InternalMultiBucketAggregati
         return new Bucket(centroid, bounds, docCount, format, aggs);
     }
 
-    public List<Bucket> reduceBuckets(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public List<Bucket> reduceBuckets(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         PriorityQueue<IteratorAndCurrent<Bucket>> pq = new PriorityQueue<>(aggregations.size()) {
             @Override
             protected boolean lessThan(IteratorAndCurrent<Bucket> a, IteratorAndCurrent<Bucket> b) {
@@ -420,7 +421,7 @@ public class InternalVariableWidthHistogram extends InternalMultiBucketAggregati
      * For each range {startIdx, endIdx} in <code>ranges</code>, all the buckets in that index range
      * from <code>buckets</code> are merged, and this merged bucket replaces the entire range.
      */
-    private void mergeBucketsWithPlan(List<Bucket> buckets, List<BucketRange> plan, ReduceContext reduceContext) {
+    private void mergeBucketsWithPlan(List<Bucket> buckets, List<BucketRange> plan, AggregationReduceContext reduceContext) {
         for (int i = plan.size() - 1; i >= 0; i--) {
             BucketRange range = plan.get(i);
             int endIdx = range.endIdx;
@@ -450,7 +451,7 @@ public class InternalVariableWidthHistogram extends InternalMultiBucketAggregati
      *
      * Requires: <code>buckets</code> is sorted by centroid.
      */
-    private void mergeBucketsIfNeeded(List<Bucket> buckets, int targetNumBuckets, ReduceContext reduceContext) {
+    private void mergeBucketsIfNeeded(List<Bucket> buckets, int targetNumBuckets, AggregationReduceContext reduceContext) {
         // Make a plan for getting the target number of buckets
         // Each range represents a set of adjacent bucket indices of buckets that will be merged together
         List<BucketRange> ranges = new ArrayList<>();
@@ -489,7 +490,7 @@ public class InternalVariableWidthHistogram extends InternalMultiBucketAggregati
         mergeBucketsWithPlan(buckets, ranges, reduceContext);
     }
 
-    private void mergeBucketsWithSameMin(List<Bucket> buckets, ReduceContext reduceContext) {
+    private void mergeBucketsWithSameMin(List<Bucket> buckets, AggregationReduceContext reduceContext) {
         // Create a merge plan
         List<BucketRange> ranges = new ArrayList<>();
 
@@ -526,7 +527,7 @@ public class InternalVariableWidthHistogram extends InternalMultiBucketAggregati
      *
      * After this adjustment, A will contain more values than indicated and B will have less.
      */
-    private void adjustBoundsForOverlappingBuckets(List<Bucket> buckets, ReduceContext reduceContext) {
+    private void adjustBoundsForOverlappingBuckets(List<Bucket> buckets, AggregationReduceContext reduceContext) {
         for (int i = 1; i < buckets.size(); i++) {
             Bucket curBucket = buckets.get(i);
             Bucket prevBucket = buckets.get(i - 1);
@@ -540,7 +541,7 @@ public class InternalVariableWidthHistogram extends InternalMultiBucketAggregati
     }
 
     @Override
-    public InternalAggregation reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalAggregation reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         List<Bucket> reducedBuckets = reduceBuckets(aggregations, reduceContext);
 
         if (reduceContext.isFinalReduce()) {

server/src/main/java/org/elasticsearch/search/aggregations/bucket/range/InternalBinaryRange.java

@@ -12,6 +12,7 @@ import org.apache.lucene.util.BytesRef;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.Aggregations;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.search.aggregations.InternalAggregations;
@@ -223,7 +224,7 @@ public final class InternalBinaryRange extends InternalMultiBucketAggregation<In
     }
 
     @Override
-    public InternalAggregation reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalAggregation reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         reduceContext.consumeBucketsAndMaybeBreak(buckets.size());
         long[] docCounts = new long[buckets.size()];
         InternalAggregations[][] aggs = new InternalAggregations[buckets.size()][];
@@ -260,7 +261,7 @@ public final class InternalBinaryRange extends InternalMultiBucketAggregation<In
     }
 
     @Override
-    protected Bucket reduceBucket(List<Bucket> buckets, ReduceContext context) {
+    protected Bucket reduceBucket(List<Bucket> buckets, AggregationReduceContext context) {
         assert buckets.size() > 0;
         List<InternalAggregations> aggregationsList = buckets.stream().map(bucket -> bucket.aggregations).collect(Collectors.toList());
         final InternalAggregations aggs = InternalAggregations.reduce(aggregationsList, context);

server/src/main/java/org/elasticsearch/search/aggregations/bucket/range/InternalRange.java

@@ -10,6 +10,7 @@ package org.elasticsearch.search.aggregations.bucket.range;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.search.aggregations.InternalAggregations;
 import org.elasticsearch.search.aggregations.InternalMultiBucketAggregation;
@@ -304,7 +305,7 @@ public class InternalRange<B extends InternalRange.Bucket, R extends InternalRan
 
     @SuppressWarnings("unchecked")
     @Override
-    public InternalAggregation reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalAggregation reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         reduceContext.consumeBucketsAndMaybeBreak(ranges.size());
         @SuppressWarnings("rawtypes")
         List<B>[] rangeList = new List[ranges.size()];
@@ -327,7 +328,7 @@ public class InternalRange<B extends InternalRange.Bucket, R extends InternalRan
     }
 
     @Override
-    protected B reduceBucket(List<B> buckets, ReduceContext context) {
+    protected B reduceBucket(List<B> buckets, AggregationReduceContext context) {
         assert buckets.size() > 0;
         long docCount = 0;
         List<InternalAggregations> aggregationsList = new ArrayList<>(buckets.size());

server/src/main/java/org/elasticsearch/search/aggregations/bucket/sampler/UnmappedSampler.java

@@ -9,6 +9,7 @@ package org.elasticsearch.search.aggregations.bucket.sampler;
 
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.search.aggregations.Aggregation;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.search.aggregations.InternalAggregations;
 import org.elasticsearch.xcontent.XContentBuilder;
@@ -37,7 +38,7 @@ public class UnmappedSampler extends InternalSampler {
     }
 
     @Override
-    public InternalAggregation reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalAggregation reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         return new UnmappedSampler(name, metadata);
     }
 

server/src/main/java/org/elasticsearch/search/aggregations/bucket/terms/AbstractInternalTerms.java

@@ -11,6 +11,7 @@ package org.elasticsearch.search.aggregations.bucket.terms;
 import org.apache.lucene.util.PriorityQueue;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.search.aggregations.AggregationExecutionException;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.BucketOrder;
 import org.elasticsearch.search.aggregations.DelayedBucket;
 import org.elasticsearch.search.aggregations.InternalAggregation;
@@ -84,7 +85,7 @@ public abstract class AbstractInternalTerms<A extends AbstractInternalTerms<A, B
     protected abstract B createBucket(long docCount, InternalAggregations aggs, long docCountError, B prototype);
 
     @Override
-    public B reduceBucket(List<B> buckets, ReduceContext context) {
+    public B reduceBucket(List<B> buckets, AggregationReduceContext context) {
         assert buckets.size() > 0;
         long docCount = 0;
         // For the per term doc count error we add up the errors from the
@@ -151,7 +152,7 @@ public abstract class AbstractInternalTerms<A extends AbstractInternalTerms<A, B
      */
     private BucketOrder reduceBuckets(
         List<InternalAggregation> aggregations,
-        InternalAggregation.ReduceContext reduceContext,
+        AggregationReduceContext reduceContext,
         Function<DelayedBucket<B>, Boolean> sink
     ) {
         /*
@@ -174,7 +175,7 @@ public abstract class AbstractInternalTerms<A extends AbstractInternalTerms<A, B
     private void reduceMergeSort(
         List<InternalAggregation> aggregations,
         BucketOrder thisReduceOrder,
-        InternalAggregation.ReduceContext reduceContext,
+        AggregationReduceContext reduceContext,
         Function<DelayedBucket<B>, Boolean> sink
     ) {
         assert isKeyOrder(thisReduceOrder);
@@ -231,7 +232,7 @@ public abstract class AbstractInternalTerms<A extends AbstractInternalTerms<A, B
 
     private void reduceLegacy(
         List<InternalAggregation> aggregations,
-        InternalAggregation.ReduceContext reduceContext,
+        AggregationReduceContext reduceContext,
         Function<DelayedBucket<B>, Boolean> sink
     ) {
         Map<Object, List<B>> bucketMap = new HashMap<>();
@@ -254,7 +255,7 @@ public abstract class AbstractInternalTerms<A extends AbstractInternalTerms<A, B
         }
     }
 
-    public InternalAggregation reduce(List<InternalAggregation> aggregations, InternalAggregation.ReduceContext reduceContext) {
+    public InternalAggregation reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         long sumDocCountError = 0;
         long[] otherDocCount = new long[] { 0 };
         A referenceTerms = null;

server/src/main/java/org/elasticsearch/search/aggregations/bucket/terms/DoubleTerms.java

@@ -10,6 +10,7 @@ package org.elasticsearch.search.aggregations.bucket.terms;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.BucketOrder;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.search.aggregations.InternalAggregations;
@@ -186,7 +187,7 @@ public class DoubleTerms extends InternalMappedTerms<DoubleTerms, DoubleTerms.Bu
     }
 
     @Override
-    public InternalAggregation reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalAggregation reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         boolean promoteToDouble = false;
         for (InternalAggregation agg : aggregations) {
             if (agg instanceof LongTerms

server/src/main/java/org/elasticsearch/search/aggregations/bucket/terms/InternalMappedRareTerms.java

@@ -16,6 +16,7 @@ import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.util.SetBackedScalingCuckooFilter;
 import org.elasticsearch.search.DocValueFormat;
 import org.elasticsearch.search.aggregations.AggregationExecutionException;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.BucketOrder;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.xcontent.XContentBuilder;
@@ -81,7 +82,7 @@ public abstract class InternalMappedRareTerms<A extends InternalRareTerms<A, B>,
     }
 
     @Override
-    public InternalAggregation reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalAggregation reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         Map<Object, List<B>> buckets = new HashMap<>();
         InternalRareTerms<A, B> referenceTerms = null;
         SetBackedScalingCuckooFilter filter = null;

server/src/main/java/org/elasticsearch/search/aggregations/bucket/terms/InternalRareTerms.java

@@ -11,6 +11,7 @@ import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.util.SetBackedScalingCuckooFilter;
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.Aggregations;
 import org.elasticsearch.search.aggregations.BucketOrder;
 import org.elasticsearch.search.aggregations.InternalAggregation;
@@ -144,14 +145,14 @@ public abstract class InternalRareTerms<A extends InternalRareTerms<A, B>, B ext
     public abstract B getBucketByKey(String term);
 
     @Override
-    public InternalAggregation reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalAggregation reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         throw new UnsupportedOperationException();
     }
 
     abstract B createBucket(long docCount, InternalAggregations aggs, B prototype);
 
     @Override
-    protected B reduceBucket(List<B> buckets, ReduceContext context) {
+    protected B reduceBucket(List<B> buckets, AggregationReduceContext context) {
         assert buckets.size() > 0;
         long docCount = 0;
         List<InternalAggregations> aggregationsList = new ArrayList<>(buckets.size());

server/src/main/java/org/elasticsearch/search/aggregations/bucket/terms/InternalSignificantTerms.java

@@ -10,6 +10,7 @@ package org.elasticsearch.search.aggregations.bucket.terms;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.Aggregations;
 import org.elasticsearch.search.aggregations.Aggregator;
 import org.elasticsearch.search.aggregations.InternalAggregation;
@@ -195,7 +196,7 @@ public abstract class InternalSignificantTerms<A extends InternalSignificantTerm
     public abstract List<B> getBuckets();
 
     @Override
-    public InternalAggregation reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalAggregation reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         long globalSubsetSize = 0;
         long globalSupersetSize = 0;
         // Compute the overall result set size and the corpus size using the
@@ -256,7 +257,7 @@ public abstract class InternalSignificantTerms<A extends InternalSignificantTerm
     }
 
     @Override
-    protected B reduceBucket(List<B> buckets, ReduceContext context) {
+    protected B reduceBucket(List<B> buckets, AggregationReduceContext context) {
         assert buckets.size() > 0;
         long subsetDf = 0;
         long supersetDf = 0;

server/src/main/java/org/elasticsearch/search/aggregations/bucket/terms/LongTerms.java

@@ -10,6 +10,7 @@ package org.elasticsearch.search.aggregations.bucket.terms;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.BucketOrder;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.search.aggregations.InternalAggregations;
@@ -198,7 +199,7 @@ public class LongTerms extends InternalMappedTerms<LongTerms, LongTerms.Bucket>
     }
 
     @Override
-    public InternalAggregation reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalAggregation reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         boolean unsignedLongFormat = false;
         boolean rawFormat = false;
         for (InternalAggregation agg : aggregations) {

server/src/main/java/org/elasticsearch/search/aggregations/bucket/terms/UnmappedRareTerms.java

@@ -11,6 +11,7 @@ import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.util.SetBackedScalingCuckooFilter;
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.search.aggregations.InternalAggregations;
 import org.elasticsearch.xcontent.XContentBuilder;
@@ -81,7 +82,7 @@ public class UnmappedRareTerms extends InternalRareTerms<UnmappedRareTerms, Unma
     }
 
     @Override
-    public InternalAggregation reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalAggregation reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         return new UnmappedRareTerms(name, metadata);
     }
 

server/src/main/java/org/elasticsearch/search/aggregations/bucket/terms/UnmappedSignificantTerms.java

@@ -11,6 +11,7 @@ import org.apache.lucene.util.BytesRef;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.search.aggregations.InternalAggregations;
 import org.elasticsearch.search.aggregations.bucket.terms.heuristic.SignificanceHeuristic;
@@ -103,7 +104,7 @@ public class UnmappedSignificantTerms extends InternalSignificantTerms<UnmappedS
     }
 
     @Override
-    public InternalAggregation reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalAggregation reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         return new UnmappedSignificantTerms(name, requiredSize, minDocCount, metadata);
     }
 

server/src/main/java/org/elasticsearch/search/aggregations/bucket/terms/UnmappedTerms.java

@@ -10,6 +10,7 @@ package org.elasticsearch.search.aggregations.bucket.terms;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.BucketOrder;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.search.aggregations.InternalAggregations;
@@ -91,7 +92,7 @@ public class UnmappedTerms extends InternalTerms<UnmappedTerms, UnmappedTerms.Bu
     }
 
     @Override
-    public InternalAggregation reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalAggregation reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         return new UnmappedTerms(name, order, requiredSize, minDocCount, metadata);
     }
 

server/src/main/java/org/elasticsearch/search/aggregations/bucket/terms/heuristic/ScriptHeuristic.java

@@ -12,7 +12,7 @@ import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.script.Script;
 import org.elasticsearch.script.SignificantTermsHeuristicScoreScript;
-import org.elasticsearch.search.aggregations.InternalAggregation;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.support.AggregationContext;
 import org.elasticsearch.xcontent.ConstructingObjectParser;
 import org.elasticsearch.xcontent.XContentBuilder;
@@ -87,7 +87,7 @@ public class ScriptHeuristic extends SignificanceHeuristic {
     }
 
     @Override
-    public SignificanceHeuristic rewrite(InternalAggregation.ReduceContext context) {
+    public SignificanceHeuristic rewrite(AggregationReduceContext context) {
         SignificantTermsHeuristicScoreScript.Factory factory = context.scriptService()
             .compile(script, SignificantTermsHeuristicScoreScript.CONTEXT);
         return new ExecutableScriptHeuristic(script, factory.newInstance());

server/src/main/java/org/elasticsearch/search/aggregations/bucket/terms/heuristic/SignificanceHeuristic.java

@@ -9,7 +9,7 @@
 package org.elasticsearch.search.aggregations.bucket.terms.heuristic;
 
 import org.elasticsearch.common.io.stream.NamedWriteable;
-import org.elasticsearch.search.aggregations.InternalAggregation;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.bucket.terms.SignificantTerms;
 import org.elasticsearch.search.aggregations.support.AggregationContext;
 import org.elasticsearch.xcontent.ToXContentFragment;
@@ -53,7 +53,7 @@ public abstract class SignificanceHeuristic implements NamedWriteable, ToXConten
      * @param reduceContext the reduce context on the coordinating node
      * @return a version of this heuristic suitable for execution
      */
-    public SignificanceHeuristic rewrite(InternalAggregation.ReduceContext reduceContext) {
+    public SignificanceHeuristic rewrite(AggregationReduceContext reduceContext) {
         return this;
     }
 

server/src/main/java/org/elasticsearch/search/aggregations/metrics/AbstractInternalHDRPercentiles.java

@@ -12,6 +12,7 @@ import org.HdrHistogram.DoubleHistogram;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.xcontent.XContentBuilder;
 
@@ -119,7 +120,7 @@ abstract class AbstractInternalHDRPercentiles extends InternalNumericMetricsAggr
     }
 
     @Override
-    public AbstractInternalHDRPercentiles reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public AbstractInternalHDRPercentiles reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         DoubleHistogram merged = null;
         for (InternalAggregation aggregation : aggregations) {
             final AbstractInternalHDRPercentiles percentiles = (AbstractInternalHDRPercentiles) aggregation;

server/src/main/java/org/elasticsearch/search/aggregations/metrics/AbstractInternalTDigestPercentiles.java

@@ -11,6 +11,7 @@ package org.elasticsearch.search.aggregations.metrics;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.xcontent.XContentBuilder;
 
@@ -103,7 +104,7 @@ abstract class AbstractInternalTDigestPercentiles extends InternalNumericMetrics
     }
 
     @Override
-    public AbstractInternalTDigestPercentiles reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public AbstractInternalTDigestPercentiles reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         TDigestState merged = null;
         for (InternalAggregation aggregation : aggregations) {
             final AbstractInternalTDigestPercentiles percentiles = (AbstractInternalTDigestPercentiles) aggregation;

server/src/main/java/org/elasticsearch/search/aggregations/metrics/InternalAvg.java

@@ -10,6 +10,7 @@ package org.elasticsearch.search.aggregations.metrics;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.xcontent.XContentBuilder;
 
@@ -74,7 +75,7 @@ public class InternalAvg extends InternalNumericMetricsAggregation.SingleValue i
     }
 
     @Override
-    public InternalAvg reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalAvg reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         CompensatedSum kahanSummation = new CompensatedSum(0, 0);
         long count = 0;
         // Compute the sum of double values with Kahan summation algorithm which is more

server/src/main/java/org/elasticsearch/search/aggregations/metrics/InternalCardinality.java

@@ -12,6 +12,7 @@ import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.util.BigArrays;
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.xcontent.XContentBuilder;
 
@@ -72,7 +73,7 @@ public final class InternalCardinality extends InternalNumericMetricsAggregation
     }
 
     @Override
-    public InternalAggregation reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalAggregation reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         HyperLogLogPlusPlus reduced = null;
         for (InternalAggregation aggregation : aggregations) {
             final InternalCardinality cardinality = (InternalCardinality) aggregation;

server/src/main/java/org/elasticsearch/search/aggregations/metrics/InternalExtendedStats.java

@@ -10,6 +10,7 @@ package org.elasticsearch.search.aggregations.metrics;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.xcontent.XContentBuilder;
 
@@ -256,7 +257,7 @@ public class InternalExtendedStats extends InternalStats implements ExtendedStat
     }
 
     @Override
-    public InternalExtendedStats reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalExtendedStats reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         double sumOfSqrs = 0;
         double compensationOfSqrs = 0;
         for (InternalAggregation aggregation : aggregations) {

server/src/main/java/org/elasticsearch/search/aggregations/metrics/InternalGeoBounds.java

@@ -12,6 +12,7 @@ import org.elasticsearch.common.geo.GeoBoundingBox;
 import org.elasticsearch.common.geo.GeoPoint;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.xcontent.XContentBuilder;
 
@@ -81,7 +82,7 @@ public class InternalGeoBounds extends InternalAggregation implements GeoBounds
     }
 
     @Override
-    public InternalAggregation reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalAggregation reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         double top = Double.NEGATIVE_INFINITY;
         double bottom = Double.POSITIVE_INFINITY;
         double posLeft = Double.POSITIVE_INFINITY;

server/src/main/java/org/elasticsearch/search/aggregations/metrics/InternalGeoCentroid.java

@@ -13,6 +13,7 @@ import org.elasticsearch.Version;
 import org.elasticsearch.common.geo.GeoPoint;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.xcontent.ParseField;
 import org.elasticsearch.xcontent.XContentBuilder;
@@ -102,7 +103,7 @@ public class InternalGeoCentroid extends InternalAggregation implements GeoCentr
     }
 
     @Override
-    public InternalGeoCentroid reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalGeoCentroid reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         double lonSum = Double.NaN;
         double latSum = Double.NaN;
         long totalCount = 0;

server/src/main/java/org/elasticsearch/search/aggregations/metrics/InternalMax.java

@@ -10,6 +10,7 @@ package org.elasticsearch.search.aggregations.metrics;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.xcontent.XContentBuilder;
 
@@ -58,7 +59,7 @@ public class InternalMax extends InternalNumericMetricsAggregation.SingleValue i
     }
 
     @Override
-    public InternalMax reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalMax reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         double max = Double.NEGATIVE_INFINITY;
         for (InternalAggregation aggregation : aggregations) {
             max = Math.max(max, ((InternalMax) aggregation).max);

server/src/main/java/org/elasticsearch/search/aggregations/metrics/InternalMedianAbsoluteDeviation.java

@@ -11,6 +11,7 @@ package org.elasticsearch.search.aggregations.metrics;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.xcontent.XContentBuilder;
 
@@ -63,7 +64,7 @@ public class InternalMedianAbsoluteDeviation extends InternalNumericMetricsAggre
     }
 
     @Override
-    public InternalAggregation reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalAggregation reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         final TDigestState valueMerged = new TDigestState(valuesSketch.compression());
         for (InternalAggregation aggregation : aggregations) {
             final InternalMedianAbsoluteDeviation madAggregation = (InternalMedianAbsoluteDeviation) aggregation;

server/src/main/java/org/elasticsearch/search/aggregations/metrics/InternalMin.java

@@ -10,6 +10,7 @@ package org.elasticsearch.search.aggregations.metrics;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.xcontent.XContentBuilder;
 
@@ -58,7 +59,7 @@ public class InternalMin extends InternalNumericMetricsAggregation.SingleValue i
     }
 
     @Override
-    public InternalMin reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalMin reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         double min = Double.POSITIVE_INFINITY;
         for (InternalAggregation aggregation : aggregations) {
             min = Math.min(min, ((InternalMin) aggregation).min);

server/src/main/java/org/elasticsearch/search/aggregations/metrics/InternalScriptedMetric.java

@@ -14,6 +14,7 @@ import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.util.CollectionUtils;
 import org.elasticsearch.script.Script;
 import org.elasticsearch.script.ScriptedMetricAggContexts;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.xcontent.XContentBuilder;
 
@@ -87,7 +88,7 @@ public class InternalScriptedMetric extends InternalAggregation implements Scrip
     }
 
     @Override
-    public InternalAggregation reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalAggregation reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         List<Object> aggregationObjects = new ArrayList<>();
         for (InternalAggregation aggregation : aggregations) {
             InternalScriptedMetric mapReduceAggregation = (InternalScriptedMetric) aggregation;

server/src/main/java/org/elasticsearch/search/aggregations/metrics/InternalStats.java

@@ -10,6 +10,7 @@ package org.elasticsearch.search.aggregations.metrics;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.xcontent.XContentBuilder;
 
@@ -161,7 +162,7 @@ public class InternalStats extends InternalNumericMetricsAggregation.MultiValue
     }
 
     @Override
-    public InternalStats reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalStats reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         long count = 0;
         double min = Double.POSITIVE_INFINITY;
         double max = Double.NEGATIVE_INFINITY;

server/src/main/java/org/elasticsearch/search/aggregations/metrics/InternalSum.java

@@ -10,6 +10,7 @@ package org.elasticsearch.search.aggregations.metrics;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.xcontent.XContentBuilder;
 
@@ -58,7 +59,7 @@ public class InternalSum extends InternalNumericMetricsAggregation.SingleValue i
     }
 
     @Override
-    public InternalSum reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalSum reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         // Compute the sum of double values with Kahan summation algorithm which is more
         // accurate than naive summation.
         CompensatedSum kahanSummation = new CompensatedSum(0, 0);

server/src/main/java/org/elasticsearch/search/aggregations/metrics/InternalTopHits.java

@@ -19,6 +19,7 @@ import org.elasticsearch.common.lucene.Lucene;
 import org.elasticsearch.common.lucene.search.TopDocsAndMaxScore;
 import org.elasticsearch.search.SearchHit;
 import org.elasticsearch.search.SearchHits;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.xcontent.XContentBuilder;
 
@@ -93,7 +94,7 @@ public class InternalTopHits extends InternalAggregation implements TopHits {
     }
 
     @Override
-    public InternalAggregation reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalAggregation reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         final SearchHits[] shardHits = new SearchHits[aggregations.size()];
         final int from;
         final int size;

server/src/main/java/org/elasticsearch/search/aggregations/metrics/InternalValueCount.java

@@ -9,6 +9,7 @@ package org.elasticsearch.search.aggregations.metrics;
 
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.xcontent.XContentBuilder;
 
@@ -57,7 +58,7 @@ public class InternalValueCount extends InternalNumericMetricsAggregation.Single
     }
 
     @Override
-    public InternalAggregation reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalAggregation reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         long valueCount = 0;
         for (InternalAggregation aggregation : aggregations) {
             valueCount += ((InternalValueCount) aggregation).value;

server/src/main/java/org/elasticsearch/search/aggregations/metrics/InternalWeightedAvg.java

@@ -10,6 +10,7 @@ package org.elasticsearch.search.aggregations.metrics;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.xcontent.XContentBuilder;
 
@@ -74,7 +75,7 @@ public class InternalWeightedAvg extends InternalNumericMetricsAggregation.Singl
     }
 
     @Override
-    public InternalWeightedAvg reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalWeightedAvg reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         CompensatedSum sumCompensation = new CompensatedSum(0, 0);
         CompensatedSum weightCompensation = new CompensatedSum(0, 0);
 

server/src/main/java/org/elasticsearch/search/aggregations/pipeline/BucketMetricsPipelineAggregator.java

@@ -10,9 +10,9 @@ package org.elasticsearch.search.aggregations.pipeline;
 
 import org.elasticsearch.search.DocValueFormat;
 import org.elasticsearch.search.aggregations.Aggregation;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.Aggregations;
 import org.elasticsearch.search.aggregations.InternalAggregation;
-import org.elasticsearch.search.aggregations.InternalAggregation.ReduceContext;
 import org.elasticsearch.search.aggregations.InternalMultiBucketAggregation;
 import org.elasticsearch.search.aggregations.pipeline.BucketHelpers.GapPolicy;
 import org.elasticsearch.search.aggregations.support.AggregationPath;
@@ -42,7 +42,7 @@ public abstract class BucketMetricsPipelineAggregator extends SiblingPipelineAgg
     }
 
     @Override
-    public final InternalAggregation doReduce(Aggregations aggregations, ReduceContext context) {
+    public final InternalAggregation doReduce(Aggregations aggregations, AggregationReduceContext context) {
         preCollection();
         List<String> bucketsPath = AggregationPath.parse(bucketsPaths()[0]).getPathElementsAsStringList();
         for (Aggregation aggregation : aggregations) {

server/src/main/java/org/elasticsearch/search/aggregations/pipeline/BucketScriptPipelineAggregator.java

@@ -11,8 +11,8 @@ package org.elasticsearch.search.aggregations.pipeline;
 import org.elasticsearch.script.BucketAggregationScript;
 import org.elasticsearch.script.Script;
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
-import org.elasticsearch.search.aggregations.InternalAggregation.ReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregations;
 import org.elasticsearch.search.aggregations.InternalMultiBucketAggregation;
 import org.elasticsearch.search.aggregations.pipeline.BucketHelpers.GapPolicy;
@@ -48,7 +48,7 @@ public class BucketScriptPipelineAggregator extends PipelineAggregator {
     }
 
     @Override
-    public InternalAggregation reduce(InternalAggregation aggregation, ReduceContext reduceContext) {
+    public InternalAggregation reduce(InternalAggregation aggregation, AggregationReduceContext reduceContext) {
         @SuppressWarnings({ "rawtypes", "unchecked" })
         InternalMultiBucketAggregation<InternalMultiBucketAggregation, InternalMultiBucketAggregation.InternalBucket> originalAgg =
             (InternalMultiBucketAggregation<InternalMultiBucketAggregation, InternalMultiBucketAggregation.InternalBucket>) aggregation;

server/src/main/java/org/elasticsearch/search/aggregations/pipeline/BucketSelectorPipelineAggregator.java

@@ -10,8 +10,8 @@ package org.elasticsearch.search.aggregations.pipeline;
 
 import org.elasticsearch.script.BucketAggregationSelectorScript;
 import org.elasticsearch.script.Script;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
-import org.elasticsearch.search.aggregations.InternalAggregation.ReduceContext;
 import org.elasticsearch.search.aggregations.InternalMultiBucketAggregation;
 import org.elasticsearch.search.aggregations.pipeline.BucketHelpers.GapPolicy;
 
@@ -41,7 +41,7 @@ public class BucketSelectorPipelineAggregator extends PipelineAggregator {
     }
 
     @Override
-    public InternalAggregation reduce(InternalAggregation aggregation, ReduceContext reduceContext) {
+    public InternalAggregation reduce(InternalAggregation aggregation, AggregationReduceContext reduceContext) {
         @SuppressWarnings({ "rawtypes", "unchecked" })
         InternalMultiBucketAggregation<InternalMultiBucketAggregation, InternalMultiBucketAggregation.InternalBucket> originalAgg =
             (InternalMultiBucketAggregation<InternalMultiBucketAggregation, InternalMultiBucketAggregation.InternalBucket>) aggregation;

server/src/main/java/org/elasticsearch/search/aggregations/pipeline/BucketSortPipelineAggregator.java

@@ -7,8 +7,8 @@
  */
 package org.elasticsearch.search.aggregations.pipeline;
 
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
-import org.elasticsearch.search.aggregations.InternalAggregation.ReduceContext;
 import org.elasticsearch.search.aggregations.InternalMultiBucketAggregation;
 import org.elasticsearch.search.aggregations.bucket.MultiBucketsAggregation;
 import org.elasticsearch.search.aggregations.pipeline.BucketHelpers.GapPolicy;
@@ -44,7 +44,7 @@ public class BucketSortPipelineAggregator extends PipelineAggregator {
     }
 
     @Override
-    public InternalAggregation reduce(InternalAggregation aggregation, ReduceContext reduceContext) {
+    public InternalAggregation reduce(InternalAggregation aggregation, AggregationReduceContext reduceContext) {
         @SuppressWarnings({ "rawtypes", "unchecked" })
         InternalMultiBucketAggregation<InternalMultiBucketAggregation, InternalMultiBucketAggregation.InternalBucket> originalAgg =
             (InternalMultiBucketAggregation<InternalMultiBucketAggregation, InternalMultiBucketAggregation.InternalBucket>) aggregation;

server/src/main/java/org/elasticsearch/search/aggregations/pipeline/CumulativeSumPipelineAggregator.java

@@ -9,8 +9,8 @@
 package org.elasticsearch.search.aggregations.pipeline;
 
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
-import org.elasticsearch.search.aggregations.InternalAggregation.ReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregations;
 import org.elasticsearch.search.aggregations.InternalMultiBucketAggregation;
 import org.elasticsearch.search.aggregations.bucket.MultiBucketsAggregation.Bucket;
@@ -34,7 +34,7 @@ public class CumulativeSumPipelineAggregator extends PipelineAggregator {
     }
 
     @Override
-    public InternalAggregation reduce(InternalAggregation aggregation, ReduceContext reduceContext) {
+    public InternalAggregation reduce(InternalAggregation aggregation, AggregationReduceContext reduceContext) {
         @SuppressWarnings("rawtypes")
         InternalMultiBucketAggregation<
             ? extends InternalMultiBucketAggregation,

server/src/main/java/org/elasticsearch/search/aggregations/pipeline/DerivativePipelineAggregator.java

@@ -9,8 +9,8 @@
 package org.elasticsearch.search.aggregations.pipeline;
 
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
-import org.elasticsearch.search.aggregations.InternalAggregation.ReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregations;
 import org.elasticsearch.search.aggregations.InternalMultiBucketAggregation;
 import org.elasticsearch.search.aggregations.bucket.MultiBucketsAggregation.Bucket;
@@ -45,7 +45,7 @@ public class DerivativePipelineAggregator extends PipelineAggregator {
     }
 
     @Override
-    public InternalAggregation reduce(InternalAggregation aggregation, ReduceContext reduceContext) {
+    public InternalAggregation reduce(InternalAggregation aggregation, AggregationReduceContext reduceContext) {
         @SuppressWarnings("rawtypes")
         InternalMultiBucketAggregation<
             ? extends InternalMultiBucketAggregation,

server/src/main/java/org/elasticsearch/search/aggregations/pipeline/InternalBucketMetricValue.java

@@ -11,6 +11,7 @@ package org.elasticsearch.search.aggregations.pipeline;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.search.aggregations.metrics.InternalNumericMetricsAggregation;
 import org.elasticsearch.xcontent.ParseField;
@@ -73,7 +74,7 @@ public class InternalBucketMetricValue extends InternalNumericMetricsAggregation
     }
 
     @Override
-    public InternalAggregation reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalAggregation reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         throw new UnsupportedOperationException("Not supported");
     }
 

server/src/main/java/org/elasticsearch/search/aggregations/pipeline/InternalExtendedStatsBucket.java

@@ -10,6 +10,7 @@ package org.elasticsearch.search.aggregations.pipeline;
 
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.search.aggregations.metrics.InternalExtendedStats;
 
@@ -45,7 +46,7 @@ public class InternalExtendedStatsBucket extends InternalExtendedStats implement
     }
 
     @Override
-    public InternalExtendedStats reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalExtendedStats reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         throw new UnsupportedOperationException("Not supported");
     }
 }

server/src/main/java/org/elasticsearch/search/aggregations/pipeline/InternalPercentilesBucket.java

@@ -11,6 +11,7 @@ package org.elasticsearch.search.aggregations.pipeline;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.search.aggregations.metrics.InternalMax;
 import org.elasticsearch.search.aggregations.metrics.InternalNumericMetricsAggregation;
@@ -129,7 +130,7 @@ public class InternalPercentilesBucket extends InternalNumericMetricsAggregation
     }
 
     @Override
-    public InternalMax reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalMax reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         throw new UnsupportedOperationException("Not supported");
     }
 

server/src/main/java/org/elasticsearch/search/aggregations/pipeline/InternalSimpleValue.java

@@ -11,6 +11,7 @@ package org.elasticsearch.search.aggregations.pipeline;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.search.aggregations.metrics.InternalNumericMetricsAggregation;
 import org.elasticsearch.xcontent.XContentBuilder;
@@ -64,7 +65,7 @@ public class InternalSimpleValue extends InternalNumericMetricsAggregation.Singl
     }
 
     @Override
-    public InternalSimpleValue reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalSimpleValue reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         throw new UnsupportedOperationException("Not supported");
     }
 

server/src/main/java/org/elasticsearch/search/aggregations/pipeline/InternalStatsBucket.java

@@ -10,6 +10,7 @@ package org.elasticsearch.search.aggregations.pipeline;
 
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.search.aggregations.metrics.InternalStats;
 
@@ -43,7 +44,7 @@ public class InternalStatsBucket extends InternalStats implements StatsBucket {
     }
 
     @Override
-    public InternalStats reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalStats reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         throw new UnsupportedOperationException("Not supported");
     }
 }

server/src/main/java/org/elasticsearch/search/aggregations/pipeline/MovFnPipelineAggregator.java

@@ -10,6 +10,7 @@ package org.elasticsearch.search.aggregations.pipeline;
 
 import org.elasticsearch.script.Script;
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.search.aggregations.InternalAggregations;
 import org.elasticsearch.search.aggregations.InternalMultiBucketAggregation;
@@ -70,7 +71,7 @@ public class MovFnPipelineAggregator extends PipelineAggregator {
     }
 
     @Override
-    public InternalAggregation reduce(InternalAggregation aggregation, InternalAggregation.ReduceContext reduceContext) {
+    public InternalAggregation reduce(InternalAggregation aggregation, AggregationReduceContext reduceContext) {
         @SuppressWarnings("rawtypes")
         InternalMultiBucketAggregation<
             ? extends InternalMultiBucketAggregation,

server/src/main/java/org/elasticsearch/search/aggregations/pipeline/PipelineAggregator.java

@@ -8,8 +8,8 @@
 
 package org.elasticsearch.search.aggregations.pipeline;
 
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
-import org.elasticsearch.search.aggregations.InternalAggregation.ReduceContext;
 import org.elasticsearch.search.aggregations.PipelineAggregationBuilder;
 import org.elasticsearch.xcontent.ParseField;
 import org.elasticsearch.xcontent.XContentParser;
@@ -114,5 +114,5 @@ public abstract class PipelineAggregator {
         return metadata;
     }
 
-    public abstract InternalAggregation reduce(InternalAggregation aggregation, ReduceContext reduceContext);
+    public abstract InternalAggregation reduce(InternalAggregation aggregation, AggregationReduceContext reduceContext);
 }

server/src/main/java/org/elasticsearch/search/aggregations/pipeline/SerialDiffPipelineAggregator.java

@@ -11,8 +11,8 @@ package org.elasticsearch.search.aggregations.pipeline;
 import org.elasticsearch.common.collect.EvictingQueue;
 import org.elasticsearch.core.Nullable;
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
-import org.elasticsearch.search.aggregations.InternalAggregation.ReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregations;
 import org.elasticsearch.search.aggregations.InternalMultiBucketAggregation;
 import org.elasticsearch.search.aggregations.bucket.MultiBucketsAggregation.Bucket;
@@ -47,7 +47,7 @@ public class SerialDiffPipelineAggregator extends PipelineAggregator {
     }
 
     @Override
-    public InternalAggregation reduce(InternalAggregation aggregation, ReduceContext reduceContext) {
+    public InternalAggregation reduce(InternalAggregation aggregation, AggregationReduceContext reduceContext) {
         @SuppressWarnings("rawtypes")
         InternalMultiBucketAggregation<
             ? extends InternalMultiBucketAggregation,

server/src/main/java/org/elasticsearch/search/aggregations/pipeline/SiblingPipelineAggregator.java

@@ -8,9 +8,9 @@
 
 package org.elasticsearch.search.aggregations.pipeline;
 
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.Aggregations;
 import org.elasticsearch.search.aggregations.InternalAggregation;
-import org.elasticsearch.search.aggregations.InternalAggregation.ReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregations;
 
 import java.util.List;
@@ -22,7 +22,7 @@ public abstract class SiblingPipelineAggregator extends PipelineAggregator {
     }
 
     @Override
-    public InternalAggregation reduce(InternalAggregation aggregation, ReduceContext reduceContext) {
+    public InternalAggregation reduce(InternalAggregation aggregation, AggregationReduceContext reduceContext) {
         return aggregation.copyWithRewritenBuckets(aggregations -> {
             List<InternalAggregation> aggs = aggregations.copyResults();
             aggs.add(doReduce(aggregations, reduceContext));
@@ -30,5 +30,5 @@ public abstract class SiblingPipelineAggregator extends PipelineAggregator {
         });
     }
 
-    public abstract InternalAggregation doReduce(Aggregations aggregations, ReduceContext context);
+    public abstract InternalAggregation doReduce(Aggregations aggregations, AggregationReduceContext context);
 }

server/src/test/java/org/elasticsearch/action/search/QueryPhaseResultConsumerTests.java

@@ -20,7 +20,7 @@ import org.elasticsearch.common.util.concurrent.EsThreadPoolExecutor;
 import org.elasticsearch.index.shard.ShardId;
 import org.elasticsearch.search.DocValueFormat;
 import org.elasticsearch.search.SearchShardTarget;
-import org.elasticsearch.search.aggregations.InternalAggregation;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregations;
 import org.elasticsearch.search.aggregations.pipeline.PipelineAggregator;
 import org.elasticsearch.search.query.QuerySearchResult;
@@ -46,19 +46,14 @@ public class QueryPhaseResultConsumerTests extends ESTestCase {
 
     @Before
     public void setup() {
-        searchPhaseController = new SearchPhaseController((t, s) -> new InternalAggregation.ReduceContextBuilder() {
+        searchPhaseController = new SearchPhaseController((t, s) -> new AggregationReduceContext.Builder() {
             @Override
-            public InternalAggregation.ReduceContext forPartialReduction() {
+            public AggregationReduceContext forPartialReduction() {
-                return InternalAggregation.ReduceContext.forPartialReduction(
+                return new AggregationReduceContext.ForPartial(BigArrays.NON_RECYCLING_INSTANCE, null, t);
-                    BigArrays.NON_RECYCLING_INSTANCE,
-                    null,
-                    () -> PipelineAggregator.PipelineTree.EMPTY,
-                    t
-                );
             }
 
-            public InternalAggregation.ReduceContext forFinalReduction() {
+            public AggregationReduceContext forFinalReduction() {
-                return InternalAggregation.ReduceContext.forFinalReduction(
+                return new AggregationReduceContext.ForFinal(
                     BigArrays.NON_RECYCLING_INSTANCE,
                     null,
                     b -> {},

server/src/test/java/org/elasticsearch/action/search/SearchPhaseControllerTests.java

@@ -41,8 +41,7 @@ import org.elasticsearch.search.SearchModule;
 import org.elasticsearch.search.SearchPhaseResult;
 import org.elasticsearch.search.SearchShardTarget;
 import org.elasticsearch.search.aggregations.AggregationBuilders;
-import org.elasticsearch.search.aggregations.InternalAggregation;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
-import org.elasticsearch.search.aggregations.InternalAggregation.ReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregations;
 import org.elasticsearch.search.aggregations.metrics.InternalMax;
 import org.elasticsearch.search.aggregations.pipeline.PipelineAggregator.PipelineTree;
@@ -112,27 +111,16 @@ public class SearchPhaseControllerTests extends ESTestCase {
     @Before
     public void setup() {
         reductions = new CopyOnWriteArrayList<>();
-        searchPhaseController = new SearchPhaseController((t, s) -> new InternalAggregation.ReduceContextBuilder() {
+        searchPhaseController = new SearchPhaseController((t, s) -> new AggregationReduceContext.Builder() {
             @Override
-            public ReduceContext forPartialReduction() {
+            public AggregationReduceContext forPartialReduction() {
                 reductions.add(false);
-                return InternalAggregation.ReduceContext.forPartialReduction(
+                return new AggregationReduceContext.ForPartial(BigArrays.NON_RECYCLING_INSTANCE, null, t);
-                    BigArrays.NON_RECYCLING_INSTANCE,
-                    null,
-                    () -> PipelineTree.EMPTY,
-                    t
-                );
             }
 
-            public ReduceContext forFinalReduction() {
+            public AggregationReduceContext forFinalReduction() {
                 reductions.add(true);
-                return InternalAggregation.ReduceContext.forFinalReduction(
+                return new AggregationReduceContext.ForFinal(BigArrays.NON_RECYCLING_INSTANCE, null, b -> {}, PipelineTree.EMPTY, t);
-                    BigArrays.NON_RECYCLING_INSTANCE,
-                    null,
-                    b -> {},
-                    PipelineTree.EMPTY,
-                    t
-                );
             };
         });
         threadPool = new TestThreadPool(SearchPhaseControllerTests.class.getName());

server/src/test/java/org/elasticsearch/action/search/TransportSearchActionTests.java

@@ -47,7 +47,7 @@ import org.elasticsearch.search.Scroll;
 import org.elasticsearch.search.SearchHit;
 import org.elasticsearch.search.SearchHits;
 import org.elasticsearch.search.SearchShardTarget;
-import org.elasticsearch.search.aggregations.InternalAggregation;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregations;
 import org.elasticsearch.search.builder.SearchSourceBuilder;
 import org.elasticsearch.search.collapse.CollapseBuilder;
@@ -465,7 +465,7 @@ public class TransportSearchActionTests extends ESTestCase {
         boolean local = randomBoolean();
         OriginalIndices localIndices = local ? new OriginalIndices(new String[] { "index" }, SearchRequest.DEFAULT_INDICES_OPTIONS) : null;
         TransportSearchAction.SearchTimeProvider timeProvider = new TransportSearchAction.SearchTimeProvider(0, 0, () -> 0);
-        Function<Boolean, InternalAggregation.ReduceContext> reduceContext = finalReduce -> null;
+        Function<Boolean, AggregationReduceContext> reduceContext = finalReduce -> null;
         try (MockTransportService service = MockTransportService.createNewService(settings, Version.CURRENT, threadPool, null)) {
             service.start();
             service.acceptIncomingRequests();

server/src/test/java/org/elasticsearch/search/SearchModuleTests.java

@@ -26,11 +26,11 @@ import org.elasticsearch.index.query.TypeQueryV7Builder;
 import org.elasticsearch.index.query.functionscore.GaussDecayFunctionBuilder;
 import org.elasticsearch.plugins.SearchPlugin;
 import org.elasticsearch.search.aggregations.AggregationBuilder;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.AggregatorFactories.Builder;
 import org.elasticsearch.search.aggregations.AggregatorFactory;
 import org.elasticsearch.search.aggregations.BaseAggregationBuilder;
 import org.elasticsearch.search.aggregations.InternalAggregation;
-import org.elasticsearch.search.aggregations.InternalAggregation.ReduceContext;
 import org.elasticsearch.search.aggregations.bucket.terms.TermsAggregationBuilder;
 import org.elasticsearch.search.aggregations.bucket.terms.heuristic.ChiSquare;
 import org.elasticsearch.search.aggregations.pipeline.AbstractPipelineAggregationBuilder;
@@ -588,7 +588,7 @@ public class SearchModuleTests extends ESTestCase {
         }
 
         @Override
-        public InternalAggregation reduce(InternalAggregation aggregation, ReduceContext reduceContext) {
+        public InternalAggregation reduce(InternalAggregation aggregation, AggregationReduceContext reduceContext) {
             return null;
         }
     }

server/src/test/java/org/elasticsearch/search/SearchServiceTests.java

@@ -75,7 +75,7 @@ import org.elasticsearch.script.MockScriptPlugin;
 import org.elasticsearch.script.Script;
 import org.elasticsearch.script.ScriptType;
 import org.elasticsearch.search.aggregations.AggregationBuilders;
-import org.elasticsearch.search.aggregations.InternalAggregation;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.MultiBucketConsumerService;
 import org.elasticsearch.search.aggregations.bucket.filter.FiltersAggregationBuilder;
 import org.elasticsearch.search.aggregations.bucket.global.GlobalAggregationBuilder;
@@ -1241,16 +1241,16 @@ public class SearchServiceTests extends ESSingleNodeTestCase {
 
     public void testCreateReduceContext() {
         SearchService service = getInstanceFromNode(SearchService.class);
-        InternalAggregation.ReduceContextBuilder reduceContextBuilder = service.aggReduceContextBuilder(() -> false, new SearchRequest());
+        AggregationReduceContext.Builder reduceContextBuilder = service.aggReduceContextBuilder(() -> false, new SearchRequest());
         {
-            InternalAggregation.ReduceContext reduceContext = reduceContextBuilder.forFinalReduction();
+            AggregationReduceContext reduceContext = reduceContextBuilder.forFinalReduction();
             expectThrows(
                 MultiBucketConsumerService.TooManyBucketsException.class,
                 () -> reduceContext.consumeBucketsAndMaybeBreak(MultiBucketConsumerService.DEFAULT_MAX_BUCKETS + 1)
             );
         }
         {
-            InternalAggregation.ReduceContext reduceContext = reduceContextBuilder.forPartialReduction();
+            AggregationReduceContext reduceContext = reduceContextBuilder.forPartialReduction();
             reduceContext.consumeBucketsAndMaybeBreak(MultiBucketConsumerService.DEFAULT_MAX_BUCKETS + 1);
         }
     }

server/src/test/java/org/elasticsearch/search/aggregations/DelayedBucketTests.java

@@ -10,22 +10,20 @@ package org.elasticsearch.search.aggregations;
 
 import org.apache.lucene.util.BytesRef;
 import org.elasticsearch.search.DocValueFormat;
-import org.elasticsearch.search.aggregations.InternalAggregation.ReduceContext;
 import org.elasticsearch.search.aggregations.InternalMultiBucketAggregation.InternalBucket;
 import org.elasticsearch.search.aggregations.bucket.MultiBucketsAggregation.Bucket;
 import org.elasticsearch.search.aggregations.bucket.terms.StringTerms;
 import org.elasticsearch.test.ESTestCase;
+import org.elasticsearch.test.InternalAggregationTestCase;
 
 import java.util.List;
+import java.util.concurrent.atomic.AtomicInteger;
 import java.util.function.BiFunction;
 
 import static org.hamcrest.Matchers.equalTo;
 import static org.hamcrest.Matchers.greaterThan;
 import static org.hamcrest.Matchers.lessThan;
 import static org.hamcrest.Matchers.sameInstance;
-import static org.mockito.Mockito.mock;
-import static org.mockito.Mockito.verify;
-import static org.mockito.Mockito.verifyNoMoreInteractions;
 
 public class DelayedBucketTests extends ESTestCase {
     public void testToString() {
@@ -33,18 +31,18 @@ public class DelayedBucketTests extends ESTestCase {
     }
 
     public void testReduced() {
-        ReduceContext context = mock(ReduceContext.class);
+        AtomicInteger buckets = new AtomicInteger();
+        AggregationReduceContext context = new AggregationReduceContext.ForFinal(null, null, buckets::addAndGet, null, () -> false);
         DelayedBucket<?> b = new DelayedBucket<>(mockReduce(context), context, List.of(bucket("test", 1), bucket("test", 2)));
         assertThat(b.getDocCount(), equalTo(3L));
         assertThat(b.reduced(), sameInstance(b.reduced()));
         assertThat(b.reduced().getKeyAsString(), equalTo("test"));
         assertThat(b.reduced().getDocCount(), equalTo(3L));
-        verify(context).consumeBucketsAndMaybeBreak(1);
+        assertEquals(1, buckets.get());
-        verifyNoMoreInteractions(context);
     }
 
     public void testCompareKey() {
-        ReduceContext context = mock(ReduceContext.class);
+        AggregationReduceContext context = InternalAggregationTestCase.emptyReduceContextBuilder().forFinalReduction();
         DelayedBucket<?> a = new DelayedBucket<>(mockReduce(context), context, List.of(bucket("a", 1)));
         DelayedBucket<?> b = new DelayedBucket<>(mockReduce(context), context, List.of(bucket("b", 1)));
         if (randomBoolean()) {
@@ -59,26 +57,31 @@ public class DelayedBucketTests extends ESTestCase {
     }
 
     public void testNonCompetitiveNotReduced() {
-        ReduceContext context = mock(ReduceContext.class);
+        AggregationReduceContext context = new AggregationReduceContext.ForFinal(
+            null,
+            null,
+            b -> fail("shouldn't be called"),
+            null,
+            () -> false
+        );
         new DelayedBucket<>(mockReduce(context), context, List.of(bucket("test", 1))).nonCompetitive();
-        verifyNoMoreInteractions(context);
     }
 
     public void testNonCompetitiveReduced() {
-        ReduceContext context = mock(ReduceContext.class);
+        AtomicInteger buckets = new AtomicInteger();
+        AggregationReduceContext context = new AggregationReduceContext.ForFinal(null, null, buckets::addAndGet, null, () -> false);
         DelayedBucket<?> b = new DelayedBucket<>(mockReduce(context), context, List.of(bucket("test", 1)));
         b.reduced();
-        verify(context).consumeBucketsAndMaybeBreak(1);
+        assertEquals(1, buckets.get());
         b.nonCompetitive();
-        verify(context).consumeBucketsAndMaybeBreak(-1);
+        assertEquals(0, buckets.get());
-        verifyNoMoreInteractions(context);
     }
 
     private static InternalBucket bucket(String key, long docCount) {
         return new StringTerms.Bucket(new BytesRef(key), docCount, InternalAggregations.EMPTY, false, 0, DocValueFormat.RAW);
     }
 
-    static BiFunction<List<InternalBucket>, ReduceContext, InternalBucket> mockReduce(ReduceContext context) {
+    static BiFunction<List<InternalBucket>, AggregationReduceContext, InternalBucket> mockReduce(AggregationReduceContext context) {
         return (l, c) -> {
             assertThat(c, sameInstance(context));
             return bucket(l.get(0).getKeyAsString(), l.stream().mapToLong(Bucket::getDocCount).sum());

server/src/test/java/org/elasticsearch/search/aggregations/InternalAggregationsTests.java

@@ -43,8 +43,8 @@ public class InternalAggregationsTests extends ESTestCase {
 
     public void testReduceEmptyAggs() {
         List<InternalAggregations> aggs = Collections.emptyList();
-        InternalAggregation.ReduceContextBuilder builder = InternalAggregationTestCase.emptyReduceContextBuilder();
+        AggregationReduceContext.Builder builder = InternalAggregationTestCase.emptyReduceContextBuilder();
-        InternalAggregation.ReduceContext reduceContext = randomBoolean() ? builder.forFinalReduction() : builder.forPartialReduction();
+        AggregationReduceContext reduceContext = randomBoolean() ? builder.forFinalReduction() : builder.forPartialReduction();
         assertNull(InternalAggregations.reduce(aggs, reduceContext));
     }
 
@@ -92,7 +92,7 @@ public class InternalAggregationsTests extends ESTestCase {
         assertEquals(2, reducedAggs.aggregations.size());
     }
 
-    private InternalAggregation.ReduceContextBuilder maxBucketReduceContext() {
+    private AggregationReduceContext.Builder maxBucketReduceContext() {
         MaxBucketPipelineAggregationBuilder maxBucketPipelineAggregationBuilder = new MaxBucketPipelineAggregationBuilder("test", "test");
         PipelineAggregator.PipelineTree tree = new PipelineAggregator.PipelineTree(
             emptyMap(),

server/src/test/java/org/elasticsearch/search/aggregations/TopBucketBuilderTests.java

@@ -11,10 +11,10 @@ package org.elasticsearch.search.aggregations;
 import org.apache.lucene.util.ArrayUtil;
 import org.apache.lucene.util.BytesRef;
 import org.elasticsearch.search.DocValueFormat;
-import org.elasticsearch.search.aggregations.InternalAggregation.ReduceContext;
 import org.elasticsearch.search.aggregations.InternalMultiBucketAggregation.InternalBucket;
 import org.elasticsearch.search.aggregations.bucket.terms.StringTerms;
 import org.elasticsearch.test.ESTestCase;
+import org.elasticsearch.test.InternalAggregationTestCase;
 
 import java.util.ArrayList;
 import java.util.List;
@@ -23,12 +23,11 @@ import java.util.Locale;
 import static org.elasticsearch.search.aggregations.DelayedBucketTests.mockReduce;
 import static org.hamcrest.Matchers.equalTo;
 import static org.hamcrest.Matchers.hasSize;
-import static org.mockito.Mockito.mock;
 
 public class TopBucketBuilderTests extends ESTestCase {
     public void testSizeOne() {
         int count = between(1, 1000);
-        ReduceContext context = mock(ReduceContext.class);
+        AggregationReduceContext context = InternalAggregationTestCase.emptyReduceContextBuilder().forFinalReduction();
         List<String> nonCompetitive = new ArrayList<>();
         TopBucketBuilder<InternalBucket> builder = TopBucketBuilder.build(1, BucketOrder.key(true), b -> nonCompetitive.add(b.toString()));
 
@@ -48,7 +47,7 @@ public class TopBucketBuilderTests extends ESTestCase {
     public void testAllCompetitive() {
         int size = between(3, 1000);
         int count = between(1, size);
-        ReduceContext context = mock(ReduceContext.class);
+        AggregationReduceContext context = InternalAggregationTestCase.emptyReduceContextBuilder().forFinalReduction();
         TopBucketBuilder<InternalBucket> builder = TopBucketBuilder.build(
             size,
             BucketOrder.key(true),
@@ -69,7 +68,7 @@ public class TopBucketBuilderTests extends ESTestCase {
 
     public void someNonCompetitiveTestCase(int size) {
         int count = between(size + 1, size * 30);
-        ReduceContext context = mock(ReduceContext.class);
+        AggregationReduceContext context = InternalAggregationTestCase.emptyReduceContextBuilder().forFinalReduction();
         List<String> nonCompetitive = new ArrayList<>();
         TopBucketBuilder<InternalBucket> builder = TopBucketBuilder.build(
             size,
@@ -103,7 +102,7 @@ public class TopBucketBuilderTests extends ESTestCase {
 
     public void testHuge() {
         int count = between(1, 1000);
-        ReduceContext context = mock(ReduceContext.class);
+        AggregationReduceContext context = InternalAggregationTestCase.emptyReduceContextBuilder().forFinalReduction();
         TopBucketBuilder<InternalBucket> builder = TopBucketBuilder.build(
             Integer.MAX_VALUE,
             BucketOrder.key(true),

server/src/test/java/org/elasticsearch/search/aggregations/bucket/filter/FiltersAggregatorTests.java

@@ -57,6 +57,7 @@ import org.elasticsearch.index.query.SearchExecutionContext;
 import org.elasticsearch.index.query.TermQueryBuilder;
 import org.elasticsearch.index.shard.ShardId;
 import org.elasticsearch.search.aggregations.AggregationBuilder;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.Aggregator;
 import org.elasticsearch.search.aggregations.AggregatorTestCase;
 import org.elasticsearch.search.aggregations.InternalAggregation;
@@ -540,7 +541,7 @@ public class FiltersAggregatorTests extends AggregatorTestCase {
                 InternalAggregation result = aggregator.buildTopLevel();
                 result = result.reduce(
                     List.of(result),
-                    InternalAggregation.ReduceContext.forFinalReduction(
+                    new AggregationReduceContext.ForFinal(
                         context.bigArrays(),
                         getMockScriptService(),
                         b -> {},

server/src/test/java/org/elasticsearch/search/aggregations/bucket/filter/InternalFilterTests.java

@@ -8,8 +8,8 @@
 
 package org.elasticsearch.search.aggregations.bucket.filter;
 
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
-import org.elasticsearch.search.aggregations.InternalAggregation.ReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregations;
 import org.elasticsearch.search.aggregations.InternalSingleBucketAggregationTestCase;
 import org.elasticsearch.search.aggregations.bucket.ParsedSingleBucketAggregation;
@@ -61,7 +61,7 @@ public class InternalFilterTests extends InternalSingleBucketAggregationTestCase
         InternalFilter test = createTestInstance("test", randomNonNegativeLong(), sub, emptyMap());
         PipelineAggregator mockPipeline = new PipelineAggregator(null, null, null) {
             @Override
-            public InternalAggregation reduce(InternalAggregation aggregation, ReduceContext reduceContext) {
+            public InternalAggregation reduce(InternalAggregation aggregation, AggregationReduceContext reduceContext) {
                 return dummy;
             }
         };

server/src/test/java/org/elasticsearch/search/aggregations/bucket/filter/InternalFiltersTests.java

@@ -8,8 +8,8 @@
 
 package org.elasticsearch.search.aggregations.bucket.filter;
 
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
-import org.elasticsearch.search.aggregations.InternalAggregation.ReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregations;
 import org.elasticsearch.search.aggregations.bucket.filter.InternalFilters.InternalBucket;
 import org.elasticsearch.search.aggregations.pipeline.PipelineAggregator;
@@ -124,7 +124,7 @@ public class InternalFiltersTests extends InternalMultiBucketAggregationTestCase
         InternalFilters test = createTestInstance("test", emptyMap(), sub);
         PipelineAggregator mockPipeline = new PipelineAggregator(null, null, null) {
             @Override
-            public InternalAggregation reduce(InternalAggregation aggregation, ReduceContext reduceContext) {
+            public InternalAggregation reduce(InternalAggregation aggregation, AggregationReduceContext reduceContext) {
                 return dummy;
             }
         };

server/src/test/java/org/elasticsearch/search/aggregations/bucket/histogram/DateHistogramAggregatorTests.java

@@ -27,9 +27,9 @@ import org.elasticsearch.index.mapper.BooleanFieldMapper;
 import org.elasticsearch.index.mapper.DateFieldMapper;
 import org.elasticsearch.index.mapper.FieldNamesFieldMapper;
 import org.elasticsearch.search.aggregations.AggregationBuilder;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.Aggregator;
 import org.elasticsearch.search.aggregations.BucketOrder;
-import org.elasticsearch.search.aggregations.InternalAggregation.ReduceContext;
 import org.elasticsearch.search.aggregations.bucket.range.RangeAggregator;
 import org.elasticsearch.search.aggregations.bucket.terms.StringTerms;
 import org.elasticsearch.search.aggregations.bucket.terms.TermsAggregationBuilder;
@@ -925,7 +925,7 @@ public class DateHistogramAggregatorTests extends DateHistogramAggregatorTestCas
                 InternalDateHistogram result = (InternalDateHistogram) agg.buildTopLevel();
                 result = (InternalDateHistogram) result.reduce(
                     List.of(result),
-                    ReduceContext.forFinalReduction(
+                    new AggregationReduceContext.ForFinal(
                         context.bigArrays(),
                         null,
                         context.multiBucketConsumer(),

server/src/test/java/org/elasticsearch/search/aggregations/bucket/histogram/InternalVariableWidthHistogramTests.java

@@ -16,6 +16,7 @@ import org.elasticsearch.common.util.MockPageCacheRecycler;
 import org.elasticsearch.indices.breaker.NoneCircuitBreakerService;
 import org.elasticsearch.script.ScriptService;
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.search.aggregations.InternalAggregations;
 import org.elasticsearch.search.aggregations.MultiBucketConsumerService;
@@ -153,7 +154,7 @@ public class InternalVariableWidthHistogramTests extends InternalMultiBucketAggr
             DEFAULT_MAX_BUCKETS,
             new NoneCircuitBreakerService().getBreaker(CircuitBreaker.REQUEST)
         );
-        InternalAggregation.ReduceContext context = InternalAggregation.ReduceContext.forFinalReduction(
+        AggregationReduceContext context = new AggregationReduceContext.ForFinal(
             bigArrays,
             mockScriptService,
             bucketConsumer,
@@ -207,7 +208,7 @@ public class InternalVariableWidthHistogramTests extends InternalMultiBucketAggr
             DEFAULT_MAX_BUCKETS,
             new NoneCircuitBreakerService().getBreaker(CircuitBreaker.REQUEST)
         );
-        InternalAggregation.ReduceContext context = InternalAggregation.ReduceContext.forFinalReduction(
+        AggregationReduceContext context = new AggregationReduceContext.ForFinal(
             bigArrays,
             mockScriptService,
             bucketConsumer,
@@ -297,7 +298,7 @@ public class InternalVariableWidthHistogramTests extends InternalMultiBucketAggr
             DEFAULT_MAX_BUCKETS,
             new NoneCircuitBreakerService().getBreaker(CircuitBreaker.REQUEST)
         );
-        InternalAggregation.ReduceContext context = InternalAggregation.ReduceContext.forFinalReduction(
+        AggregationReduceContext context = new AggregationReduceContext.ForFinal(
             bigArrays,
             mockScriptService,
             bucketConsumer,
@@ -353,7 +354,7 @@ public class InternalVariableWidthHistogramTests extends InternalMultiBucketAggr
             DEFAULT_MAX_BUCKETS,
             new NoneCircuitBreakerService().getBreaker(CircuitBreaker.REQUEST)
         );
-        InternalAggregation.ReduceContext context = InternalAggregation.ReduceContext.forFinalReduction(
+        AggregationReduceContext context = new AggregationReduceContext.ForFinal(
             bigArrays,
             mockScriptService,
             bucketConsumer,
@@ -414,7 +415,7 @@ public class InternalVariableWidthHistogramTests extends InternalMultiBucketAggr
             DEFAULT_MAX_BUCKETS,
             new NoneCircuitBreakerService().getBreaker(CircuitBreaker.REQUEST)
         );
-        InternalAggregation.ReduceContext context = InternalAggregation.ReduceContext.forFinalReduction(
+        AggregationReduceContext context = new AggregationReduceContext.ForFinal(
             bigArrays,
             mockScriptService,
             bucketConsumer,

server/src/test/java/org/elasticsearch/search/aggregations/bucket/terms/TermsAggregatorTests.java

@@ -77,6 +77,7 @@ import org.elasticsearch.search.SearchHit;
 import org.elasticsearch.search.aggregations.AggregationBuilder;
 import org.elasticsearch.search.aggregations.AggregationBuilders;
 import org.elasticsearch.search.aggregations.AggregationExecutionException;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.Aggregator;
 import org.elasticsearch.search.aggregations.AggregatorTestCase;
 import org.elasticsearch.search.aggregations.BucketOrder;
@@ -1268,7 +1269,7 @@ public class TermsAggregatorTests extends AggregatorTestCase {
                 }
                 dir.close();
             }
-            InternalAggregation.ReduceContext ctx = InternalAggregation.ReduceContext.forFinalReduction(
+            AggregationReduceContext ctx = new AggregationReduceContext.ForFinal(
                 new MockBigArrays(new MockPageCacheRecycler(Settings.EMPTY), new NoneCircuitBreakerService()),
                 null,
                 b -> {},
@@ -2197,7 +2198,7 @@ public class TermsAggregatorTests extends AggregatorTestCase {
             Integer.MAX_VALUE,
             new NoneCircuitBreakerService().getBreaker(CircuitBreaker.REQUEST)
         );
-        InternalAggregation.ReduceContext context = InternalAggregation.ReduceContext.forFinalReduction(
+        AggregationReduceContext context = new AggregationReduceContext.ForFinal(
             bigArrays,
             getMockScriptService(),
             reduceBucketConsumer,

server/src/test/java/org/elasticsearch/search/aggregations/metrics/InternalScriptedMetricTests.java

@@ -18,8 +18,8 @@ import org.elasticsearch.script.ScriptModule;
 import org.elasticsearch.script.ScriptService;
 import org.elasticsearch.script.ScriptType;
 import org.elasticsearch.search.aggregations.Aggregation.CommonFields;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
-import org.elasticsearch.search.aggregations.InternalAggregation.ReduceContext;
 import org.elasticsearch.search.aggregations.ParsedAggregation;
 import org.elasticsearch.search.aggregations.pipeline.PipelineAggregator.PipelineTree;
 import org.elasticsearch.test.InternalAggregationTestCase;
@@ -163,7 +163,7 @@ public class InternalScriptedMetricTests extends InternalAggregationTestCase<Int
         InternalScriptedMetric aggregation = createTestInstance();
         return (InternalScriptedMetric) aggregation.reduce(
             singletonList(aggregation),
-            ReduceContext.forFinalReduction(null, mockScriptService(), null, PipelineTree.EMPTY, () -> false)
+            new AggregationReduceContext.ForFinal(null, mockScriptService(), null, PipelineTree.EMPTY, () -> false)
         );
     }
 

test/framework/src/main/java/org/elasticsearch/search/aggregations/AggregatorTestCase.java

@@ -106,7 +106,6 @@ import org.elasticsearch.script.ScriptService;
 import org.elasticsearch.search.NestedDocuments;
 import org.elasticsearch.search.SearchModule;
 import org.elasticsearch.search.aggregations.AggregatorFactories.Builder;
-import org.elasticsearch.search.aggregations.InternalAggregation.ReduceContext;
 import org.elasticsearch.search.aggregations.MultiBucketConsumerService.MultiBucketConsumer;
 import org.elasticsearch.search.aggregations.bucket.nested.NestedAggregationBuilder;
 import org.elasticsearch.search.aggregations.metrics.MetricsAggregator;
@@ -581,10 +580,9 @@ public abstract class AggregatorTestCase extends ESTestCase {
             Collections.shuffle(aggs, random());
             int r = randomIntBetween(1, toReduceSize);
             List<InternalAggregation> toReduce = aggs.subList(0, r);
-            InternalAggregation.ReduceContext reduceContext = InternalAggregation.ReduceContext.forPartialReduction(
+            AggregationReduceContext reduceContext = new AggregationReduceContext.ForPartial(
                 context.bigArrays(),
                 getMockScriptService(),
-                () -> PipelineAggregator.PipelineTree.EMPTY,
                 () -> false
             );
             A reduced = (A) aggs.get(0).reduce(toReduce, reduceContext);
@@ -598,7 +596,7 @@ public abstract class AggregatorTestCase extends ESTestCase {
             maxBucket,
             new NoneCircuitBreakerService().getBreaker(CircuitBreaker.REQUEST)
         );
-        InternalAggregation.ReduceContext reduceContext = InternalAggregation.ReduceContext.forFinalReduction(
+        AggregationReduceContext reduceContext = new AggregationReduceContext.ForFinal(
             context.bigArrays(),
             getMockScriptService(),
             reduceBucketConsumer,
@@ -732,7 +730,7 @@ public abstract class AggregatorTestCase extends ESTestCase {
         InternalAggregation r = aggregator.buildTopLevel();
         r = r.reduce(
             List.of(r),
-            ReduceContext.forFinalReduction(
+            new AggregationReduceContext.ForFinal(
                 context.bigArrays(),
                 getMockScriptService(),
                 context.multiBucketConsumer(),
@@ -1325,7 +1323,7 @@ public abstract class AggregatorTestCase extends ESTestCase {
         }
 
         @Override
-        public InternalAggregation reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+        public InternalAggregation reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
             aggregations.forEach(ia -> { assertThat(((InternalAggCardinalityUpperBound) ia).cardinality, equalTo(cardinality)); });
             return new InternalAggCardinalityUpperBound(name, cardinality, metadata);
         }

test/framework/src/main/java/org/elasticsearch/search/aggregations/bucket/AbstractSignificanceHeuristicTestCase.java

@@ -19,6 +19,7 @@ import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.search.DocValueFormat;
 import org.elasticsearch.search.SearchModule;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.search.aggregations.InternalAggregations;
 import org.elasticsearch.search.aggregations.bucket.terms.InternalMappedSignificantTerms;
@@ -132,7 +133,7 @@ public abstract class AbstractSignificanceHeuristicTestCase extends ESTestCase {
 
     public void testReduce() {
         List<InternalAggregation> aggs = createInternalAggregations();
-        InternalAggregation.ReduceContext context = InternalAggregationTestCase.emptyReduceContextBuilder().forFinalReduction();
+        AggregationReduceContext context = InternalAggregationTestCase.emptyReduceContextBuilder().forFinalReduction();
         SignificantTerms reducedAgg = (SignificantTerms) aggs.get(0).reduce(aggs, context);
         assertThat(reducedAgg.getBuckets().size(), equalTo(2));
         assertThat(reducedAgg.getBuckets().get(0).getSubsetDf(), equalTo(8L));

test/framework/src/main/java/org/elasticsearch/test/InternalAggregationTestCase.java

@@ -27,8 +27,8 @@ import org.elasticsearch.script.ScriptService;
 import org.elasticsearch.search.DocValueFormat;
 import org.elasticsearch.search.SearchModule;
 import org.elasticsearch.search.aggregations.Aggregation;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
-import org.elasticsearch.search.aggregations.InternalAggregation.ReduceContext;
 import org.elasticsearch.search.aggregations.MultiBucketConsumerService;
 import org.elasticsearch.search.aggregations.MultiBucketConsumerService.MultiBucketConsumer;
 import org.elasticsearch.search.aggregations.ParsedAggregation;
@@ -170,37 +170,26 @@ import static org.hamcrest.Matchers.lessThanOrEqualTo;
  */
 public abstract class InternalAggregationTestCase<T extends InternalAggregation> extends AbstractNamedWriteableTestCase<T> {
     /**
-     * Builds an {@link InternalAggregation.ReduceContextBuilder} that is valid but empty.
+     * Builds an {@link AggregationReduceContext} that is valid but empty.
      */
-    public static InternalAggregation.ReduceContextBuilder emptyReduceContextBuilder() {
+    public static AggregationReduceContext.Builder emptyReduceContextBuilder() {
         return emptyReduceContextBuilder(PipelineTree.EMPTY);
     }
 
     /**
-     * Builds an {@link InternalAggregation.ReduceContextBuilder} that is valid and nearly
+     * Builds an {@link AggregationReduceContext} that is valid and nearly
      * empty <strong>except</strong> that it contain {@link PipelineAggregator}s.
      */
-    public static InternalAggregation.ReduceContextBuilder emptyReduceContextBuilder(PipelineTree pipelineTree) {
+    public static AggregationReduceContext.Builder emptyReduceContextBuilder(PipelineTree pipelineTree) {
-        return new InternalAggregation.ReduceContextBuilder() {
+        return new AggregationReduceContext.Builder() {
             @Override
-            public InternalAggregation.ReduceContext forPartialReduction() {
+            public AggregationReduceContext forPartialReduction() {
-                return InternalAggregation.ReduceContext.forPartialReduction(
+                return new AggregationReduceContext.ForPartial(BigArrays.NON_RECYCLING_INSTANCE, null, () -> false);
-                    BigArrays.NON_RECYCLING_INSTANCE,
-                    null,
-                    () -> pipelineTree,
-                    () -> false
-                );
             }
 
             @Override
-            public ReduceContext forFinalReduction() {
+            public AggregationReduceContext forFinalReduction() {
-                return InternalAggregation.ReduceContext.forFinalReduction(
+                return new AggregationReduceContext.ForFinal(BigArrays.NON_RECYCLING_INSTANCE, null, b -> {}, pipelineTree, () -> false);
-                    BigArrays.NON_RECYCLING_INSTANCE,
-                    null,
-                    b -> {},
-                    pipelineTree,
-                    () -> false
-                );
             }
         };
     }
@@ -374,12 +363,7 @@ public abstract class InternalAggregationTestCase<T extends InternalAggregation>
             List<InternalAggregation> toPartialReduce = toReduce.subList(0, r);
             // Sort aggs so that unmapped come last. This mimicks the behavior of InternalAggregations.reduce()
             toPartialReduce.sort(INTERNAL_AGG_COMPARATOR);
-            InternalAggregation.ReduceContext context = InternalAggregation.ReduceContext.forPartialReduction(
+            AggregationReduceContext context = new AggregationReduceContext.ForPartial(bigArrays, mockScriptService, () -> false);
-                bigArrays,
-                mockScriptService,
-                () -> PipelineAggregator.PipelineTree.EMPTY,
-                () -> false
-            );
             @SuppressWarnings("unchecked")
             T reduced = (T) toPartialReduce.get(0).reduce(toPartialReduce, context);
             int initialBucketCount = 0;
@@ -404,7 +388,7 @@ public abstract class InternalAggregationTestCase<T extends InternalAggregation>
             DEFAULT_MAX_BUCKETS,
             new NoneCircuitBreakerService().getBreaker(CircuitBreaker.REQUEST)
         );
-        InternalAggregation.ReduceContext context = InternalAggregation.ReduceContext.forFinalReduction(
+        AggregationReduceContext context = new AggregationReduceContext.ForFinal(
             bigArrays,
             mockScriptService,
             bucketConsumer,

test/framework/src/main/java/org/elasticsearch/test/InternalMultiBucketAggregationTestCase.java

@@ -10,6 +10,7 @@ package org.elasticsearch.test;
 
 import org.elasticsearch.common.util.BigArrays;
 import org.elasticsearch.search.aggregations.Aggregation;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.Aggregations;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.search.aggregations.InternalAggregations;
@@ -202,10 +203,10 @@ public abstract class InternalMultiBucketAggregationTestCase<T extends InternalA
     }
 
     /**
-     * Build a reuce
+     * Expect that reducing this aggregation will pass the bucket limit.
      */
     protected static void expectReduceUsesTooManyBuckets(InternalAggregation agg, int bucketLimit) {
-        InternalAggregation.ReduceContext reduceContext = InternalAggregation.ReduceContext.forFinalReduction(
+        AggregationReduceContext reduceContext = new AggregationReduceContext.ForFinal(
             BigArrays.NON_RECYCLING_INSTANCE,
             null,
             new IntConsumer() {

x-pack/plugin/analytics/src/main/java/org/elasticsearch/xpack/analytics/boxplot/InternalBoxplot.java

@@ -12,6 +12,7 @@ import com.tdunning.math.stats.Centroid;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.search.aggregations.metrics.InternalNumericMetricsAggregation;
 import org.elasticsearch.search.aggregations.metrics.TDigestState;
@@ -270,7 +271,7 @@ public class InternalBoxplot extends InternalNumericMetricsAggregation.MultiValu
     }
 
     @Override
-    public InternalBoxplot reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalBoxplot reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         TDigestState merged = null;
         for (InternalAggregation aggregation : aggregations) {
             final InternalBoxplot percentiles = (InternalBoxplot) aggregation;

x-pack/plugin/analytics/src/main/java/org/elasticsearch/xpack/analytics/cumulativecardinality/CumulativeCardinalityPipelineAggregator.java

@@ -8,8 +8,8 @@ package org.elasticsearch.xpack.analytics.cumulativecardinality;
 
 import org.elasticsearch.search.DocValueFormat;
 import org.elasticsearch.search.aggregations.AggregationExecutionException;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
-import org.elasticsearch.search.aggregations.InternalAggregation.ReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregations;
 import org.elasticsearch.search.aggregations.InternalMultiBucketAggregation;
 import org.elasticsearch.search.aggregations.bucket.MultiBucketsAggregation;
@@ -37,7 +37,7 @@ public class CumulativeCardinalityPipelineAggregator extends PipelineAggregator
     }
 
     @Override
-    public InternalAggregation reduce(InternalAggregation aggregation, ReduceContext reduceContext) {
+    public InternalAggregation reduce(InternalAggregation aggregation, AggregationReduceContext reduceContext) {
         InternalMultiBucketAggregation<?, ?> histo = (InternalMultiBucketAggregation<?, ?>) aggregation;
         List<? extends InternalMultiBucketAggregation.InternalBucket> buckets = histo.getBuckets();
         HistogramFactory factory = (HistogramFactory) histo;

x-pack/plugin/analytics/src/main/java/org/elasticsearch/xpack/analytics/cumulativecardinality/InternalSimpleLongValue.java

@@ -9,6 +9,7 @@ package org.elasticsearch.xpack.analytics.cumulativecardinality;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.search.aggregations.metrics.InternalNumericMetricsAggregation;
 import org.elasticsearch.search.aggregations.pipeline.SimpleValue;
@@ -63,7 +64,7 @@ public class InternalSimpleLongValue extends InternalNumericMetricsAggregation.S
     }
 
     @Override
-    public InternalSimpleLongValue reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalSimpleLongValue reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         throw new UnsupportedOperationException("Not supported");
     }
 

x-pack/plugin/analytics/src/main/java/org/elasticsearch/xpack/analytics/movingPercentiles/MovingPercentilesPipelineAggregator.java

@@ -9,8 +9,8 @@ package org.elasticsearch.xpack.analytics.movingPercentiles;
 import org.HdrHistogram.DoubleHistogram;
 import org.elasticsearch.search.DocValueFormat;
 import org.elasticsearch.search.aggregations.AggregationExecutionException;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
-import org.elasticsearch.search.aggregations.InternalAggregation.ReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregations;
 import org.elasticsearch.search.aggregations.InternalMultiBucketAggregation;
 import org.elasticsearch.search.aggregations.bucket.MultiBucketsAggregation;
@@ -41,7 +41,7 @@ public class MovingPercentilesPipelineAggregator extends PipelineAggregator {
     }
 
     @Override
-    public InternalAggregation reduce(InternalAggregation aggregation, ReduceContext reduceContext) {
+    public InternalAggregation reduce(InternalAggregation aggregation, AggregationReduceContext reduceContext) {
         @SuppressWarnings("unchecked")
         InternalMultiBucketAggregation<?, ?> histo = (InternalMultiBucketAggregation<?, ?>) aggregation;
         List<? extends InternalMultiBucketAggregation.InternalBucket> buckets = histo.getBuckets();

x-pack/plugin/analytics/src/main/java/org/elasticsearch/xpack/analytics/multiterms/InternalMultiTerms.java

@@ -13,6 +13,7 @@ import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.search.DocValueFormat;
 import org.elasticsearch.search.aggregations.AggregationExecutionException;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.Aggregations;
 import org.elasticsearch.search.aggregations.BucketOrder;
 import org.elasticsearch.search.aggregations.InternalAggregation;
@@ -558,7 +559,7 @@ public class InternalMultiTerms extends AbstractInternalTerms<InternalMultiTerms
 
     public InternalAggregation reduce(
         List<InternalAggregation> aggregations,
-        ReduceContext reduceContext,
+        AggregationReduceContext reduceContext,
         boolean[] needsPromotionToDouble
     ) {
         if (needsPromotionToDouble != null) {
@@ -573,7 +574,7 @@ public class InternalMultiTerms extends AbstractInternalTerms<InternalMultiTerms
     }
 
     @Override
-    public InternalAggregation reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalAggregation reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         return reduce(aggregations, reduceContext, needsPromotionToDouble(aggregations));
     }
 

x-pack/plugin/analytics/src/main/java/org/elasticsearch/xpack/analytics/normalize/NormalizePipelineAggregator.java

@@ -8,8 +8,8 @@
 package org.elasticsearch.xpack.analytics.normalize;
 
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
-import org.elasticsearch.search.aggregations.InternalAggregation.ReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregations;
 import org.elasticsearch.search.aggregations.InternalMultiBucketAggregation;
 import org.elasticsearch.search.aggregations.pipeline.BucketHelpers.GapPolicy;
@@ -43,7 +43,7 @@ public class NormalizePipelineAggregator extends PipelineAggregator {
     }
 
     @Override
-    public InternalAggregation reduce(InternalAggregation aggregation, ReduceContext reduceContext) {
+    public InternalAggregation reduce(InternalAggregation aggregation, AggregationReduceContext reduceContext) {
         @SuppressWarnings("unchecked")
         InternalMultiBucketAggregation<?, InternalMultiBucketAggregation.InternalBucket> originalAgg = (InternalMultiBucketAggregation<
             ?,

x-pack/plugin/analytics/src/main/java/org/elasticsearch/xpack/analytics/rate/InternalRate.java

@@ -9,6 +9,7 @@ package org.elasticsearch.xpack.analytics.rate;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.search.aggregations.metrics.CompensatedSum;
 import org.elasticsearch.search.aggregations.metrics.InternalNumericMetricsAggregation;
@@ -68,7 +69,7 @@ public class InternalRate extends InternalNumericMetricsAggregation.SingleValue
     }
 
     @Override
-    public InternalRate reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalRate reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         // Compute the sum of double values with Kahan summation algorithm which is more
         // accurate than naive summation.
         CompensatedSum kahanSummation = new CompensatedSum(0, 0);

x-pack/plugin/analytics/src/main/java/org/elasticsearch/xpack/analytics/stringstats/InternalStringStats.java

@@ -9,6 +9,7 @@ package org.elasticsearch.xpack.analytics.stringstats;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.search.aggregations.metrics.CompensatedSum;
 import org.elasticsearch.xcontent.ParseField;
@@ -200,7 +201,7 @@ public class InternalStringStats extends InternalAggregation {
 
     @Override
     @SuppressWarnings("HiddenField")
-    public InternalStringStats reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalStringStats reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         long count = 0;
         long totalLength = 0;
         int minLength = Integer.MAX_VALUE;

x-pack/plugin/analytics/src/main/java/org/elasticsearch/xpack/analytics/topmetrics/InternalTopMetrics.java

@@ -12,6 +12,7 @@ import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.io.stream.Writeable;
 import org.elasticsearch.core.Nullable;
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.search.aggregations.metrics.InternalMultiValueAggregation;
 import org.elasticsearch.search.sort.SortOrder;
@@ -109,7 +110,7 @@ public class InternalTopMetrics extends InternalMultiValueAggregation {
     }
 
     @Override
-    public InternalTopMetrics reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalTopMetrics reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         if (false == isMapped()) {
             return this;
         }

x-pack/plugin/analytics/src/main/java/org/elasticsearch/xpack/analytics/ttest/InternalTTest.java

@@ -10,6 +10,7 @@ package org.elasticsearch.xpack.analytics.ttest;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.search.aggregations.metrics.InternalNumericMetricsAggregation;
 import org.elasticsearch.xcontent.XContentBuilder;
@@ -55,7 +56,7 @@ public class InternalTTest extends InternalNumericMetricsAggregation.SingleValue
     }
 
     @Override
-    public InternalTTest reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalTTest reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         TTestState reduced = state.reduce(aggregations.stream().map(a -> ((InternalTTest) a).state));
         return new InternalTTest(name, reduced, format, getMetadata());
     }

x-pack/plugin/analytics/src/test/java/org/elasticsearch/xpack/analytics/multiterms/InternalMultiTermsTests.java

@@ -18,11 +18,10 @@ import org.elasticsearch.plugins.SearchPlugin;
 import org.elasticsearch.script.ScriptService;
 import org.elasticsearch.search.DocValueFormat;
 import org.elasticsearch.search.aggregations.Aggregation;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.BucketOrder;
-import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.search.aggregations.InternalAggregations;
 import org.elasticsearch.search.aggregations.ParsedAggregation;
-import org.elasticsearch.search.aggregations.pipeline.PipelineAggregator;
 import org.elasticsearch.test.InternalAggregationTestCase;
 import org.elasticsearch.xcontent.NamedXContentRegistry;
 import org.elasticsearch.xcontent.ParseField;
@@ -371,12 +370,7 @@ public class InternalMultiTermsTests extends InternalAggregationTestCase<Interna
             keyConverters2,
             null
         );
-        InternalAggregation.ReduceContext context = InternalAggregation.ReduceContext.forPartialReduction(
+        AggregationReduceContext context = new AggregationReduceContext.ForPartial(bigArrays, mockScriptService, () -> false);
-            bigArrays,
-            mockScriptService,
-            () -> PipelineAggregator.PipelineTree.EMPTY,
-            () -> false
-        );
 
         InternalMultiTerms result = (InternalMultiTerms) terms1.reduce(List.of(terms1, terms2), context);
         assertThat(result.buckets, hasSize(3));

x-pack/plugin/async-search/src/main/java/org/elasticsearch/xpack/search/AsyncSearchTask.java

@@ -23,7 +23,7 @@ import org.elasticsearch.action.search.ShardSearchFailure;
 import org.elasticsearch.client.Client;
 import org.elasticsearch.core.TimeValue;
 import org.elasticsearch.search.SearchShardTarget;
-import org.elasticsearch.search.aggregations.InternalAggregation;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregations;
 import org.elasticsearch.tasks.TaskId;
 import org.elasticsearch.tasks.TaskManager;
@@ -53,7 +53,7 @@ final class AsyncSearchTask extends SearchTask implements AsyncTask {
     private final AsyncExecutionId searchId;
     private final Client client;
     private final ThreadPool threadPool;
-    private final Supplier<InternalAggregation.ReduceContext> aggReduceContextSupplier;
+    private final Supplier<AggregationReduceContext> aggReduceContextSupplier;
     private final Listener progressListener;
 
     private final Map<String, String> originHeaders;
@@ -95,7 +95,7 @@ final class AsyncSearchTask extends SearchTask implements AsyncTask {
         AsyncExecutionId searchId,
         Client client,
         ThreadPool threadPool,
-        Function<Supplier<Boolean>, Supplier<InternalAggregation.ReduceContext>> aggReduceContextSupplierFactory
+        Function<Supplier<Boolean>, Supplier<AggregationReduceContext>> aggReduceContextSupplierFactory
     ) {
         super(id, type, action, () -> "async_search{" + descriptionSupplier.get() + "}", parentTaskId, taskHeaders);
         this.expirationTimeMillis = getStartTime() + keepAlive.getMillis();

x-pack/plugin/async-search/src/main/java/org/elasticsearch/xpack/search/TransportSubmitAsyncSearchAction.java

@@ -23,7 +23,7 @@ import org.elasticsearch.common.util.BigArrays;
 import org.elasticsearch.common.util.concurrent.ThreadContext;
 import org.elasticsearch.core.TimeValue;
 import org.elasticsearch.search.SearchService;
-import org.elasticsearch.search.aggregations.InternalAggregation;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.tasks.Task;
 import org.elasticsearch.tasks.TaskId;
 import org.elasticsearch.transport.TransportService;
@@ -44,7 +44,7 @@ import static org.elasticsearch.xpack.core.ClientHelper.ASYNC_SEARCH_ORIGIN;
 
 public class TransportSubmitAsyncSearchAction extends HandledTransportAction<SubmitAsyncSearchRequest, AsyncSearchResponse> {
     private final NodeClient nodeClient;
-    private final BiFunction<Supplier<Boolean>, SearchRequest, InternalAggregation.ReduceContext> requestToAggReduceContextBuilder;
+    private final BiFunction<Supplier<Boolean>, SearchRequest, AggregationReduceContext> requestToAggReduceContextBuilder;
     private final TransportSearchAction searchAction;
     private final ThreadContext threadContext;
     private final AsyncTaskIndexService<AsyncSearchResponse> store;
@@ -149,8 +149,8 @@ public class TransportSubmitAsyncSearchAction extends HandledTransportAction<Sub
             @Override
             public AsyncSearchTask createTask(long id, String type, String action, TaskId parentTaskId, Map<String, String> taskHeaders) {
                 AsyncExecutionId searchId = new AsyncExecutionId(docID, new TaskId(nodeClient.getLocalNodeId(), id));
-                Function<Supplier<Boolean>, Supplier<InternalAggregation.ReduceContext>> aggReduceContextSupplierFactory = (
+                Function<Supplier<Boolean>, Supplier<AggregationReduceContext>> aggReduceContextSupplierFactory =
-                    isCancelled) -> () -> requestToAggReduceContextBuilder.apply(isCancelled, request.getSearchRequest());
+                    isCancelled -> () -> requestToAggReduceContextBuilder.apply(isCancelled, request.getSearchRequest());
                 return new AsyncSearchTask(
                     id,
                     type,

x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/aggs/categorization/InternalCategorizationAggregation.java

@@ -14,6 +14,7 @@ import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.io.stream.Writeable;
 import org.elasticsearch.common.util.BytesRefHash;
 import org.elasticsearch.search.aggregations.AggregationExecutionException;
+import org.elasticsearch.search.aggregations.AggregationReduceContext;
 import org.elasticsearch.search.aggregations.Aggregations;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.search.aggregations.InternalAggregations;
@@ -53,7 +54,7 @@ public class InternalCategorizationAggregation extends InternalMultiBucketAggreg
             return docCount;
         }
 
-        public Bucket reduce(BucketKey bucketKey, ReduceContext reduceContext) {
+        public Bucket reduce(BucketKey bucketKey, AggregationReduceContext reduceContext) {
             List<InternalAggregations> innerAggs = new ArrayList<>(toReduce.size());
             long totalDocCount = 0;
             for (Bucket bucket : toReduce) {
@@ -335,7 +336,7 @@ public class InternalCategorizationAggregation extends InternalMultiBucketAggreg
     }
 
     @Override
-    protected Bucket reduceBucket(List<Bucket> buckets, ReduceContext context) {
+    protected Bucket reduceBucket(List<Bucket> buckets, AggregationReduceContext context) {
         throw new IllegalArgumentException("For optimization purposes, typical bucket path is not supported");
     }
 
@@ -350,7 +351,7 @@ public class InternalCategorizationAggregation extends InternalMultiBucketAggreg
     }
 
     @Override
-    public InternalAggregation reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
+    public InternalAggregation reduce(List<InternalAggregation> aggregations, AggregationReduceContext reduceContext) {
         try (CategorizationBytesRefHash hash = new CategorizationBytesRefHash(new BytesRefHash(1L, reduceContext.bigArrays()))) {
             CategorizationTokenTree categorizationTokenTree = new CategorizationTokenTree(
                 maxUniqueTokens,