Deduplicate Empty InternalAggregations (#58386)

Working through a heap dump for an unrelated issue I found that we can easily rack up
tens of MBs of duplicate empty instances in some cases.
I moved to a static constructor to guard against that in all cases.

client/client-benchmark-noop-api-plugin/src/main/java/org/elasticsearch/plugin/noop/action/search/TransportNoopSearchAction.java

@@ -49,7 +49,7 @@ public class TransportNoopSearchAction extends HandledTransportAction<SearchRequ
         listener.onResponse(new SearchResponse(new InternalSearchResponse(
             new SearchHits(
                 new SearchHit[0], new TotalHits(0L, TotalHits.Relation.EQUAL_TO), 0.0f),
-            new InternalAggregations(Collections.emptyList()),
+            InternalAggregations.EMPTY,
             new Suggest(Collections.emptyList()),
             new SearchProfileShardResults(Collections.emptyMap()), false, false, 1),
             "", 1, 1, 0, 0, ShardSearchFailure.EMPTY_ARRAY, SearchResponse.Clusters.EMPTY));

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

@@ -706,7 +706,7 @@ public final class SearchPhaseController {
                         InternalAggregations reduced =
                                 InternalAggregations.topLevelReduce(aggs, aggReduceContextBuilder.forPartialReduction());
                         reducedAggs = aggsBuffer[0] = DelayableWriteable.referencing(reduced)
-                                .asSerialized(InternalAggregations::new, namedWriteableRegistry);
+                                .asSerialized(InternalAggregations::readFrom, namedWriteableRegistry);
                         long previousBufferSize = aggsCurrentBufferSize;
                         aggsMaxBufferSize = Math.max(aggsMaxBufferSize, aggsCurrentBufferSize);
                         aggsCurrentBufferSize = aggsBuffer[0].ramBytesUsed();
@@ -729,7 +729,7 @@ public final class SearchPhaseController {
                 }
                 final int i = index++;
                 if (hasAggs) {
-                    aggsBuffer[i] = querySearchResult.consumeAggs().asSerialized(InternalAggregations::new, namedWriteableRegistry);
+                    aggsBuffer[i] = querySearchResult.consumeAggs().asSerialized(InternalAggregations::readFrom, namedWriteableRegistry);
                     aggsCurrentBufferSize += aggsBuffer[i].ramBytesUsed();
                 }
                 if (hasTopDocs) {

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

@@ -130,7 +130,7 @@ public class AggregationPhase implements SearchPhase {
                 throw new AggregationExecutionException("Failed to build aggregation [" + aggregator.name() + "]", e);
             }
         }
-        context.queryResult().aggregations(new InternalAggregations(aggregations));
+        context.queryResult().aggregations(InternalAggregations.from(aggregations));
 
         // disable aggregations so that they don't run on next pages in case of scrolling
         context.aggregations(null);

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

@@ -259,7 +259,7 @@ public abstract class AggregatorBase extends Aggregator {
         for (Aggregator aggregator : subAggregators) {
             aggs.add(aggregator.buildEmptyAggregation());
         }
-        return new InternalAggregations(aggs);
+        return InternalAggregations.from(aggs);
     }
 
     @Override

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

@@ -56,12 +56,19 @@ public final class InternalAggregations extends Aggregations implements Writeabl
     /**
      * Constructs a new aggregation.
      */
-    public InternalAggregations(List<InternalAggregation> aggregations) {
+    private InternalAggregations(List<InternalAggregation> aggregations) {
         super(aggregations);
     }
 
-    public InternalAggregations(StreamInput in) throws IOException {
+    public static InternalAggregations from(List<InternalAggregation> aggregations) {
-        super(in.readList(stream -> in.readNamedWriteable(InternalAggregation.class)));
+        if (aggregations.isEmpty()) {
+            return EMPTY;
+        }
+        return new InternalAggregations(aggregations);
+    }
+
+    public static InternalAggregations readFrom(StreamInput in) throws IOException {
+        return from(in.readList(stream -> in.readNamedWriteable(InternalAggregation.class)));
     }
 
     @Override
@@ -117,10 +124,10 @@ public final class InternalAggregations extends Aggregations implements Writeabl
 
             for (PipelineAggregator pipelineAggregator : context.pipelineTreeRoot().aggregators()) {
                 SiblingPipelineAggregator sib = (SiblingPipelineAggregator) pipelineAggregator;
-                InternalAggregation newAgg = sib.doReduce(new InternalAggregations(reducedInternalAggs), context);
+                InternalAggregation newAgg = sib.doReduce(from(reducedInternalAggs), context);
                 reducedInternalAggs.add(newAgg);
             }
-            return new InternalAggregations(reducedInternalAggs);
+            return from(reducedInternalAggs);
         }
         return reduced;
     }
@@ -157,6 +164,6 @@ public final class InternalAggregations extends Aggregations implements Writeabl
             reducedAggregations.add(first.reduce(aggregations, context));
         }
 
-        return new InternalAggregations(reducedAggregations);
+        return from(reducedAggregations);
     }
 }

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

@@ -192,7 +192,7 @@ public abstract class InternalMultiBucketAggregation<A extends InternalMultiBuck
                 PipelineTree subTree = pipelineTree.subTree(agg.getName());
                 aggs.add(((InternalAggregation)agg).reducePipelines((InternalAggregation)agg, reduceContext, subTree));
             }
-            reducedBuckets.add(createBucket(new InternalAggregations(aggs), bucket));
+            reducedBuckets.add(createBucket(InternalAggregations.from(aggs), bucket));
         }
         return reducedBuckets;
     }

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

@@ -178,7 +178,7 @@ public abstract class BucketsAggregator extends AggregatorBase {
                 slice[i] = aggregations[i][ord];
             }
             final int thisOrd = ord;
-            result[ord] = new InternalAggregations(new AbstractList<InternalAggregation>() {
+            result[ord] = InternalAggregations.from(new AbstractList<InternalAggregation>() {
                 @Override
                 public InternalAggregation get(int index) {
                     return aggregations[index][thisOrd];
@@ -353,17 +353,6 @@ public abstract class BucketsAggregator extends AggregatorBase {
         InternalAggregation build(long owninigBucketOrd, List<B> buckets);
     }
 
-    /**
-     * Utility method to build empty aggregations of the sub aggregators.
-     */
-    protected final InternalAggregations bucketEmptyAggregations() {
-        final InternalAggregation[] aggregations = new InternalAggregation[subAggregators.length];
-        for (int i = 0; i < subAggregators.length; i++) {
-            aggregations[i] = subAggregators[i].buildEmptyAggregation();
-        }
-        return new InternalAggregations(Arrays.asList(aggregations));
-    }
-
     @Override
     public final void close() {
         try (Releasable releasable = docCounts) {

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

@@ -64,7 +64,7 @@ public abstract class InternalSingleBucketAggregation extends InternalAggregatio
     protected InternalSingleBucketAggregation(StreamInput in) throws IOException {
         super(in);
         docCount = in.readVLong();
-        aggregations = new InternalAggregations(in);
+        aggregations = InternalAggregations.readFrom(in);
     }
 
     @Override
@@ -128,7 +128,7 @@ public abstract class InternalSingleBucketAggregation extends InternalAggregatio
                 PipelineTree subTree = pipelineTree.subTree(agg.getName());
                 aggs.add(((InternalAggregation)agg).reducePipelines((InternalAggregation)agg, reduceContext, subTree));
             }
-            InternalAggregations reducedSubAggs = new InternalAggregations(aggs);
+            InternalAggregations reducedSubAggs = InternalAggregations.from(aggs);
             reduced = create(reducedSubAggs);
         }
         return super.reducePipelines(reduced, reduceContext, pipelineTree);

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

@@ -56,7 +56,7 @@ public class InternalAdjacencyMatrix
         public InternalBucket(StreamInput in) throws IOException {
             key = in.readOptionalString();
             docCount = in.readVLong();
-            aggregations = new InternalAggregations(in);
+            aggregations = InternalAggregations.readFrom(in);
         }
 
         @Override

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

@@ -286,7 +286,7 @@ public class InternalComposite
         InternalBucket(StreamInput in, List<String> sourceNames, List<DocValueFormat> formats, int[] reverseMuls) throws IOException {
             this.key = new CompositeKey(in);
             this.docCount = in.readVLong();
-            this.aggregations = new InternalAggregations(in);
+            this.aggregations = InternalAggregations.readFrom(in);
             this.reverseMuls = reverseMuls;
             this.sourceNames = sourceNames;
             this.formats = formats;

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

@@ -56,7 +56,7 @@ public class InternalFilters extends InternalMultiBucketAggregation<InternalFilt
             this.keyed = keyed;
             key = in.readOptionalString();
             docCount = in.readVLong();
-            aggregations = new InternalAggregations(in);
+            aggregations = InternalAggregations.readFrom(in);
         }
 
         @Override

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

@@ -50,7 +50,7 @@ public abstract class InternalGeoGridBucket<B extends InternalGeoGridBucket>
     public InternalGeoGridBucket(StreamInput in) throws IOException {
         hashAsLong = in.readLong();
         docCount = in.readVLong();
-        aggregations = new InternalAggregations(in);
+        aggregations = InternalAggregations.readFrom(in);
     }
 
     @Override

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

@@ -72,7 +72,7 @@ public final class InternalAutoDateHistogram extends
             this.format = format;
             key = in.readLong();
             docCount = in.readVLong();
-            aggregations = new InternalAggregations(in);
+            aggregations = InternalAggregations.readFrom(in);
         }
 
         @Override
@@ -163,7 +163,7 @@ public final class InternalAutoDateHistogram extends
                 roundingInfos[i] = new RoundingInfo(in);
             }
             roundingIdx = in.readVInt();
-            emptySubAggregations = new InternalAggregations(in);
+            emptySubAggregations = InternalAggregations.readFrom(in);
         }
 
         void writeTo(StreamOutput out) throws IOException {

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

@@ -76,7 +76,7 @@ public final class InternalDateHistogram extends InternalMultiBucketAggregation<
             this.keyed = keyed;
             key = in.readLong();
             docCount = in.readVLong();
-            aggregations = new InternalAggregations(in);
+            aggregations = InternalAggregations.readFrom(in);
         }
 
         @Override
@@ -174,7 +174,7 @@ public final class InternalDateHistogram extends InternalMultiBucketAggregation<
 
         EmptyBucketInfo(StreamInput in) throws IOException {
             rounding = Rounding.read(in);
-            subAggregations = new InternalAggregations(in);
+            subAggregations = InternalAggregations.readFrom(in);
             bounds = in.readOptionalWriteable(ExtendedBounds::new);
         }
 

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

@@ -72,7 +72,7 @@ public final class InternalHistogram extends InternalMultiBucketAggregation<Inte
             this.keyed = keyed;
             key = in.readDouble();
             docCount = in.readVLong();
-            aggregations = new InternalAggregations(in);
+            aggregations = InternalAggregations.readFrom(in);
         }
 
         @Override
@@ -166,7 +166,7 @@ public final class InternalHistogram extends InternalMultiBucketAggregation<Inte
         }
 
         EmptyBucketInfo(StreamInput in) throws IOException {
-            this(in.readDouble(), in.readDouble(), in.readDouble(), in.readDouble(), new InternalAggregations(in));
+            this(in.readDouble(), in.readDouble(), in.readDouble(), in.readDouble(), InternalAggregations.readFrom(in));
         }
 
         public void writeTo(StreamOutput out) throws IOException {

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

@@ -77,7 +77,7 @@ public final class InternalBinaryRange
             BytesRef from = in.readBoolean() ? in.readBytesRef() : null;
             BytesRef to = in.readBoolean() ? in.readBytesRef() : null;
             long docCount = in.readLong();
-            InternalAggregations aggregations = new InternalAggregations(in);
+            InternalAggregations aggregations = InternalAggregations.readFrom(in);
 
             return new Bucket(format, keyed, key, from, to, docCount, aggregations);
         }

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

@@ -37,7 +37,7 @@ public class InternalDateRange extends InternalRange<InternalDateRange.Bucket, I
 
         public Bucket(String key, double from, double to, long docCount, List<InternalAggregation> aggregations, boolean keyed,
                 DocValueFormat formatter) {
-            super(key, from, to, docCount, new InternalAggregations(aggregations), keyed, formatter);
+            super(key, from, to, docCount, InternalAggregations.from(aggregations), keyed, formatter);
         }
 
         public Bucket(String key, double from, double to, long docCount, InternalAggregations aggregations, boolean keyed,

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

@@ -20,7 +20,6 @@ package org.elasticsearch.search.aggregations.bucket.range;
 
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.search.DocValueFormat;
-import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.search.aggregations.InternalAggregations;
 import org.elasticsearch.search.aggregations.support.CoreValuesSourceType;
 import org.elasticsearch.search.aggregations.support.ValueType;
@@ -35,10 +34,6 @@ public class InternalGeoDistance extends InternalRange<InternalGeoDistance.Bucke
 
     static class Bucket extends InternalRange.Bucket {
 
-        Bucket(String key, double from, double to, long docCount, List<InternalAggregation> aggregations, boolean keyed) {
-            this(key, from, to, docCount, new InternalAggregations(aggregations), keyed);
-        }
-
         Bucket(String key, double from, double to, long docCount, InternalAggregations aggregations, boolean keyed) {
             super(key, from, to, docCount, aggregations, keyed, DocValueFormat.RAW);
         }

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

@@ -241,7 +241,7 @@ public class InternalRange<B extends InternalRange.Bucket, R extends InternalRan
         for (int i = 0; i < size; i++) {
             String key = in.readString();
             ranges.add(getFactory().createBucket(key, in.readDouble(), in.readDouble(), in.readVLong(),
-                    new InternalAggregations(in), keyed, format));
+                    InternalAggregations.readFrom(in), keyed, format));
         }
         this.ranges = ranges;
     }

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

@@ -68,7 +68,7 @@ public abstract class InternalRareTerms<A extends InternalRareTerms<A, B>, B ext
         protected Bucket(StreamInput in, DocValueFormat formatter) throws IOException {
             this.format = formatter;
             docCount = in.readVLong();
-            aggregations = new InternalAggregations(in);
+            aggregations = InternalAggregations.readFrom(in);
         }
 
         @Override

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

@@ -84,7 +84,7 @@ public abstract class InternalTerms<A extends InternalTerms<A, B>, B extends Int
             if (showDocCountError) {
                 docCountError = in.readLong();
             }
-            aggregations = new InternalAggregations(in);
+            aggregations = InternalAggregations.readFrom(in);
         }
 
         @Override

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

@@ -53,7 +53,7 @@ public class SignificantLongTerms extends InternalMappedSignificantTerms<Signifi
             supersetDf = in.readVLong();
             term = in.readLong();
             score = in.readDouble();
-            aggregations = new InternalAggregations(in);
+            aggregations = InternalAggregations.readFrom(in);
         }
 
         @Override

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

@@ -57,7 +57,7 @@ public class SignificantStringTerms extends InternalMappedSignificantTerms<Signi
             subsetDf = in.readVLong();
             supersetDf = in.readVLong();
             score = in.readDouble();
-            aggregations = new InternalAggregations(in);
+            aggregations = InternalAggregations.readFrom(in);
         }
 
         @Override

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

@@ -89,7 +89,7 @@ public class BucketScriptPipelineAggregator extends PipelineAggregator {
 
                     InternalSimpleValue simpleValue = new InternalSimpleValue(name(), returned.doubleValue(), formatter, metadata());
                     aggs.add(simpleValue);
-                    InternalMultiBucketAggregation.InternalBucket newBucket = originalAgg.createBucket(new InternalAggregations(aggs),
+                    InternalMultiBucketAggregation.InternalBucket newBucket = originalAgg.createBucket(InternalAggregations.from(aggs),
                         bucket);
                     newBuckets.add(newBucket);
                 }

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

@@ -66,7 +66,7 @@ public class CumulativeSumPipelineAggregator extends PipelineAggregator {
                 .map((p) -> (InternalAggregation) p)
                 .collect(Collectors.toList());
             aggs.add(new InternalSimpleValue(name(), sum, formatter, metadata()));
-            Bucket newBucket = factory.createBucket(factory.getKey(bucket), bucket.getDocCount(), new InternalAggregations(aggs));
+            Bucket newBucket = factory.createBucket(factory.getKey(bucket), bucket.getDocCount(), InternalAggregations.from(aggs));
             newBuckets.add(newBucket);
         }
         return factory.createAggregation(newBuckets);

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

@@ -73,7 +73,7 @@ public class DerivativePipelineAggregator extends PipelineAggregator {
                     return (InternalAggregation) p;
                 }).collect(Collectors.toList());
                 aggs.add(new InternalDerivative(name(), gradient, xDiff, formatter, metadata()));
-                Bucket newBucket = factory.createBucket(factory.getKey(bucket), bucket.getDocCount(), new InternalAggregations(aggs));
+                Bucket newBucket = factory.createBucket(factory.getKey(bucket), bucket.getDocCount(), InternalAggregations.from(aggs));
                 newBuckets.add(newBucket);
             } else {
                 newBuckets.add(bucket);

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

@@ -122,7 +122,7 @@ public class MovFnPipelineAggregator extends PipelineAggregator {
                     .map(InternalAggregation.class::cast)
                     .collect(Collectors.toList());
                 aggs.add(new InternalSimpleValue(name(), movavg, formatter, metadata()));
-                newBucket = factory.createBucket(factory.getKey(bucket), bucket.getDocCount(), new InternalAggregations(aggs));
+                newBucket = factory.createBucket(factory.getKey(bucket), bucket.getDocCount(), InternalAggregations.from(aggs));
                 index++;
             }
             newBuckets.add(newBucket);

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

@@ -89,7 +89,7 @@ public class SerialDiffPipelineAggregator extends PipelineAggregator {
                 List<InternalAggregation> aggs = StreamSupport.stream(bucket.getAggregations().spliterator(), false).map(
                         (p) -> (InternalAggregation) p).collect(Collectors.toList());
                 aggs.add(new InternalSimpleValue(name(), diff, formatter, metadata()));
-                newBucket = factory.createBucket(factory.getKey(bucket), bucket.getDocCount(), new InternalAggregations(aggs));
+                newBucket = factory.createBucket(factory.getKey(bucket), bucket.getDocCount(), InternalAggregations.from(aggs));
             }
 
             newBuckets.add(newBucket);

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

@@ -37,7 +37,7 @@ public abstract class SiblingPipelineAggregator extends PipelineAggregator {
         return aggregation.copyWithRewritenBuckets(aggregations -> {
             List<InternalAggregation> aggs = aggregations.copyResults();
             aggs.add(doReduce(aggregations, reduceContext));
-            return new InternalAggregations(aggs);
+            return InternalAggregations.from(aggs);
         });
     }
 

server/src/main/java/org/elasticsearch/search/internal/InternalSearchResponse.java

@@ -52,7 +52,7 @@ public class InternalSearchResponse extends SearchResponseSections implements Wr
     public InternalSearchResponse(StreamInput in) throws IOException {
         super(
                 new SearchHits(in),
-                in.readBoolean() ? new InternalAggregations(in) : null,
+                in.readBoolean() ? InternalAggregations.readFrom(in) : null,
                 in.readBoolean() ? new Suggest(in) : null,
                 in.readBoolean(),
                 in.readOptionalBoolean(),

server/src/main/java/org/elasticsearch/search/query/QuerySearchResult.java

@@ -316,7 +316,7 @@ public final class QuerySearchResult extends SearchPhaseResult {
         }
         setTopDocs(readTopDocs(in));
         if (hasAggs = in.readBoolean()) {
-            aggregations = DelayableWriteable.delayed(InternalAggregations::new, in);
+            aggregations = DelayableWriteable.delayed(InternalAggregations::readFrom, in);
         }
         if (in.readBoolean()) {
             suggest = new Suggest(in);

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

@@ -396,7 +396,7 @@ public class SearchPhaseControllerTests extends ESTestCase {
             new SearchShardTarget("node", new ShardId("a", "b", 0), null, OriginalIndices.NONE));
         result.topDocs(new TopDocsAndMaxScore(new TopDocs(new TotalHits(0, TotalHits.Relation.EQUAL_TO), new ScoreDoc[0]), Float.NaN),
             new DocValueFormat[0]);
-        InternalAggregations aggs = new InternalAggregations(singletonList(new InternalMax("test", 1.0D, DocValueFormat.RAW, emptyMap())));
+        InternalAggregations aggs = InternalAggregations.from(singletonList(new InternalMax("test", 1.0D, DocValueFormat.RAW, emptyMap())));
         result.aggregations(aggs);
         result.setShardIndex(0);
         consumer.consumeResult(result);
@@ -405,7 +405,7 @@ public class SearchPhaseControllerTests extends ESTestCase {
             new SearchShardTarget("node", new ShardId("a", "b", 0), null, OriginalIndices.NONE));
         result.topDocs(new TopDocsAndMaxScore(new TopDocs(new TotalHits(0, TotalHits.Relation.EQUAL_TO), new ScoreDoc[0]), Float.NaN),
             new DocValueFormat[0]);
-        aggs = new InternalAggregations(singletonList(new InternalMax("test", 3.0D, DocValueFormat.RAW, emptyMap())));
+        aggs = InternalAggregations.from(singletonList(new InternalMax("test", 3.0D, DocValueFormat.RAW, emptyMap())));
         result.aggregations(aggs);
         result.setShardIndex(2);
         consumer.consumeResult(result);
@@ -414,7 +414,7 @@ public class SearchPhaseControllerTests extends ESTestCase {
             new SearchShardTarget("node", new ShardId("a", "b", 0), null, OriginalIndices.NONE));
         result.topDocs(new TopDocsAndMaxScore(new TopDocs(new TotalHits(0, TotalHits.Relation.EQUAL_TO), new ScoreDoc[0]), Float.NaN),
             new DocValueFormat[0]);
-        aggs = new InternalAggregations(singletonList(new InternalMax("test", 2.0D, DocValueFormat.RAW, emptyMap())));
+        aggs = InternalAggregations.from(singletonList(new InternalMax("test", 2.0D, DocValueFormat.RAW, emptyMap())));
         result.aggregations(aggs);
         result.setShardIndex(1);
         consumer.consumeResult(result);
@@ -483,7 +483,7 @@ public class SearchPhaseControllerTests extends ESTestCase {
                 result.topDocs(new TopDocsAndMaxScore(
                     new TopDocs(new TotalHits(1, TotalHits.Relation.EQUAL_TO), new ScoreDoc[] {new ScoreDoc(0, number)}), number),
                     new DocValueFormat[0]);
-                InternalAggregations aggs = new InternalAggregations(Collections.singletonList(new InternalMax("test", (double) number,
+                InternalAggregations aggs = InternalAggregations.from(Collections.singletonList(new InternalMax("test", (double) number,
                     DocValueFormat.RAW, Collections.emptyMap())));
                 result.aggregations(aggs);
                 result.setShardIndex(id);
@@ -526,7 +526,7 @@ public class SearchPhaseControllerTests extends ESTestCase {
                 new SearchShardTarget("node", new ShardId("a", "b", i), null, OriginalIndices.NONE));
             result.topDocs(new TopDocsAndMaxScore(new TopDocs(new TotalHits(1, TotalHits.Relation.EQUAL_TO), new ScoreDoc[0]), number),
                     new DocValueFormat[0]);
-            InternalAggregations aggs = new InternalAggregations(Collections.singletonList(new InternalMax("test", (double) number,
+            InternalAggregations aggs = InternalAggregations.from(Collections.singletonList(new InternalMax("test", (double) number,
                 DocValueFormat.RAW, Collections.emptyMap())));
             result.aggregations(aggs);
             result.setShardIndex(i);
@@ -878,7 +878,7 @@ public class SearchPhaseControllerTests extends ESTestCase {
                     result.topDocs(new TopDocsAndMaxScore(
                             new TopDocs(new TotalHits(1, TotalHits.Relation.EQUAL_TO), new ScoreDoc[]{new ScoreDoc(0, number)}), number),
                         new DocValueFormat[0]);
-                    InternalAggregations aggs = new InternalAggregations(Collections.singletonList(
+                    InternalAggregations aggs = InternalAggregations.from(Collections.singletonList(
                         new InternalMax("test", (double) number, DocValueFormat.RAW, Collections.emptyMap())));
                     result.aggregations(aggs);
                     result.setShardIndex(id);

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

@@ -370,7 +370,7 @@ public class SearchResponseMergerTests extends ESTestCase {
             InternalDateRange.Bucket bucket = factory.createBucket("bucket", 0, 10000, count, InternalAggregations.EMPTY,
                 false, DocValueFormat.RAW);
             InternalDateRange range = factory.create(rangeAggName, singletonList(bucket), DocValueFormat.RAW, false, emptyMap());
-            InternalAggregations aggs = new InternalAggregations(Arrays.asList(range, max));
+            InternalAggregations aggs = InternalAggregations.from(Arrays.asList(range, max));
             SearchHits searchHits = new SearchHits(new SearchHit[0], null, Float.NaN);
             InternalSearchResponse internalSearchResponse = new InternalSearchResponse(searchHits, aggs, null, null, false, null, 1);
             SearchResponse searchResponse = new SearchResponse(internalSearchResponse, null, 1, 1, 0, randomLong(),

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

@@ -298,6 +298,6 @@ public class AggregationsTests extends ESTestCase {
             }
             aggs.add(testCase.createTestInstance());
         }
-        return new InternalAggregations(aggs);
+        return InternalAggregations.from(aggs);
     }
 }

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

@@ -59,7 +59,7 @@ public class InternalAggregationsTests extends ESTestCase {
     public void testNonFinalReduceTopLevelPipelineAggs()  {
         InternalAggregation terms = new StringTerms("name", BucketOrder.key(true),
             10, 1, Collections.emptyMap(), DocValueFormat.RAW, 25, false, 10, Collections.emptyList(), 0);
-        List<InternalAggregations> aggs = singletonList(new InternalAggregations(Collections.singletonList(terms)));
+        List<InternalAggregations> aggs = singletonList(InternalAggregations.from(Collections.singletonList(terms)));
         InternalAggregations reducedAggs = InternalAggregations.topLevelReduce(aggs, maxBucketReduceContext().forPartialReduction());
         assertEquals(1, reducedAggs.aggregations.size());
     }
@@ -68,7 +68,7 @@ public class InternalAggregationsTests extends ESTestCase {
         InternalAggregation terms = new StringTerms("name", BucketOrder.key(true),
             10, 1, Collections.emptyMap(), DocValueFormat.RAW, 25, false, 10, Collections.emptyList(), 0);
 
-        InternalAggregations aggs = new InternalAggregations(Collections.singletonList(terms));
+        InternalAggregations aggs = InternalAggregations.from(Collections.singletonList(terms));
         InternalAggregations reducedAggs = InternalAggregations.topLevelReduce(Collections.singletonList(aggs),
                 maxBucketReduceContext().forFinalReduction());
         assertEquals(2, reducedAggs.aggregations.size());
@@ -98,7 +98,7 @@ public class InternalAggregationsTests extends ESTestCase {
             InternalSimpleValueTests simpleValueTests = new InternalSimpleValueTests();
             aggsList.add(simpleValueTests.createTestInstance());
         }
-        return new InternalAggregations(aggsList);
+        return InternalAggregations.from(aggsList);
     }
 
     public void testSerialization() throws Exception {
@@ -113,7 +113,7 @@ public class InternalAggregationsTests extends ESTestCase {
             aggregations.writeTo(out);
             try (StreamInput in = new NamedWriteableAwareStreamInput(StreamInput.wrap(out.bytes().toBytesRef().bytes), registry)) {
                 in.setVersion(version);
-                InternalAggregations deserialized = new InternalAggregations(in);
+                InternalAggregations deserialized = InternalAggregations.readFrom(in);
                 assertEquals(aggregations.aggregations, deserialized.aggregations);
                 if (iteration < 2) {
                     writeToAndReadFrom(deserialized, iteration + 1);

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

@@ -42,7 +42,7 @@ public class InternalMultiBucketAggregationTests extends ESTestCase {
         AggregationPath path = AggregationPath.parse("the_avg");
         List<LongTerms.Bucket> buckets = new ArrayList<>();
         InternalAggregation agg = new InternalAvg("the_avg", 2, 1, DocValueFormat.RAW, Collections.emptyMap());
-        InternalAggregations internalAggregations = new InternalAggregations(Collections.singletonList(agg));
+        InternalAggregations internalAggregations = InternalAggregations.from(Collections.singletonList(agg));
 
         LongTerms.Bucket bucket = new LongTerms.Bucket(1, 1, internalAggregations, false, 0, DocValueFormat.RAW);
         buckets.add(bucket);
@@ -55,7 +55,7 @@ public class InternalMultiBucketAggregationTests extends ESTestCase {
         AggregationPath path = AggregationPath.parse("the_avg.value");
         List<LongTerms.Bucket> buckets = new ArrayList<>();
         InternalAggregation agg = new InternalAvg("the_avg", 2, 1, DocValueFormat.RAW, Collections.emptyMap());
-        InternalAggregations internalAggregations = new InternalAggregations(Collections.singletonList(agg));
+        InternalAggregations internalAggregations = InternalAggregations.from(Collections.singletonList(agg));
 
         LongTerms.Bucket bucket = new LongTerms.Bucket(1, 1, internalAggregations, false, 0, DocValueFormat.RAW);
         buckets.add(bucket);
@@ -68,7 +68,7 @@ public class InternalMultiBucketAggregationTests extends ESTestCase {
         AggregationPath path = AggregationPath.parse("foo.value");
         List<LongTerms.Bucket> buckets = new ArrayList<>();
         InternalAggregation agg = new InternalAvg("the_avg", 2, 1, DocValueFormat.RAW, Collections.emptyMap());
-        InternalAggregations internalAggregations = new InternalAggregations(Collections.singletonList(agg));
+        InternalAggregations internalAggregations = InternalAggregations.from(Collections.singletonList(agg));
 
         LongTerms.Bucket bucket = new LongTerms.Bucket(1, 1, internalAggregations, false, 0, DocValueFormat.RAW);
         buckets.add(bucket);
@@ -82,7 +82,7 @@ public class InternalMultiBucketAggregationTests extends ESTestCase {
         AggregationPath path = AggregationPath.parse("the_avg.unknown");
         List<LongTerms.Bucket> buckets = new ArrayList<>();
         InternalAggregation agg = new InternalAvg("the_avg", 2, 1, DocValueFormat.RAW, Collections.emptyMap());
-        InternalAggregations internalAggregations = new InternalAggregations(Collections.singletonList(agg));
+        InternalAggregations internalAggregations = InternalAggregations.from(Collections.singletonList(agg));
 
         LongTerms.Bucket bucket = new LongTerms.Bucket(1, 1, internalAggregations, false, 0, DocValueFormat.RAW);
         buckets.add(bucket);
@@ -96,7 +96,7 @@ public class InternalMultiBucketAggregationTests extends ESTestCase {
         AggregationPath path = AggregationPath.parse("_bucket_count");
         List<LongTerms.Bucket> buckets = new ArrayList<>();
         InternalAggregation agg = new InternalAvg("the_avg", 2, 1, DocValueFormat.RAW, Collections.emptyMap());
-        InternalAggregations internalAggregations = new InternalAggregations(Collections.singletonList(agg));
+        InternalAggregations internalAggregations = InternalAggregations.from(Collections.singletonList(agg));
 
         LongTerms.Bucket bucket = new LongTerms.Bucket(1, 1, internalAggregations, false, 0, DocValueFormat.RAW);
         buckets.add(bucket);
@@ -109,7 +109,7 @@ public class InternalMultiBucketAggregationTests extends ESTestCase {
         AggregationPath path = AggregationPath.parse("_count");
         List<LongTerms.Bucket> buckets = new ArrayList<>();
         InternalAggregation agg = new InternalAvg("the_avg", 2, 1, DocValueFormat.RAW, Collections.emptyMap());
-        InternalAggregations internalAggregations = new InternalAggregations(Collections.singletonList(agg));
+        InternalAggregations internalAggregations = InternalAggregations.from(Collections.singletonList(agg));
 
         LongTerms.Bucket bucket = new LongTerms.Bucket(1, 1, internalAggregations, false, 0, DocValueFormat.RAW);
         buckets.add(bucket);
@@ -122,7 +122,7 @@ public class InternalMultiBucketAggregationTests extends ESTestCase {
         AggregationPath path = AggregationPath.parse("_key");
         List<LongTerms.Bucket> buckets = new ArrayList<>();
         InternalAggregation agg = new InternalAvg("the_avg", 2, 1, DocValueFormat.RAW, Collections.emptyMap());
-        InternalAggregations internalAggregations = new InternalAggregations(Collections.singletonList(agg));
+        InternalAggregations internalAggregations = InternalAggregations.from(Collections.singletonList(agg));
 
         LongTerms.Bucket bucket = new LongTerms.Bucket(19, 1, internalAggregations, false, 0, DocValueFormat.RAW);
         buckets.add(bucket);
@@ -136,14 +136,14 @@ public class InternalMultiBucketAggregationTests extends ESTestCase {
 
         List<LongTerms.Bucket> buckets = new ArrayList<>();
         InternalAggregation agg = new InternalAvg("the_avg", 2, 1, DocValueFormat.RAW, Collections.emptyMap());
-        InternalAggregations internalStringAggs = new InternalAggregations(Collections.singletonList(agg));
+        InternalAggregations internalStringAggs = InternalAggregations.from(Collections.singletonList(agg));
         List<StringTerms.Bucket> stringBuckets = Collections.singletonList(new StringTerms.Bucket(
             new BytesRef("foo".getBytes(StandardCharsets.UTF_8), 0, "foo".getBytes(StandardCharsets.UTF_8).length), 1,
             internalStringAggs, false, 0, DocValueFormat.RAW));
 
         InternalTerms termsAgg = new StringTerms("string_terms", BucketOrder.count(false), 1, 0,
             Collections.emptyMap(), DocValueFormat.RAW, 1, false, 0, stringBuckets, 0);
-        InternalAggregations internalAggregations = new InternalAggregations(Collections.singletonList(termsAgg));
+        InternalAggregations internalAggregations = InternalAggregations.from(Collections.singletonList(termsAgg));
         LongTerms.Bucket bucket = new LongTerms.Bucket(19, 1, internalAggregations, false, 0, DocValueFormat.RAW);
         buckets.add(bucket);
 
@@ -156,14 +156,14 @@ public class InternalMultiBucketAggregationTests extends ESTestCase {
 
         List<LongTerms.Bucket> buckets = new ArrayList<>();
         InternalAggregation agg = new InternalAvg("the_avg", 2, 1, DocValueFormat.RAW, Collections.emptyMap());
-        InternalAggregations internalStringAggs = new InternalAggregations(Collections.singletonList(agg));
+        InternalAggregations internalStringAggs = InternalAggregations.from(Collections.singletonList(agg));
         List<StringTerms.Bucket> stringBuckets = Collections.singletonList(new StringTerms.Bucket(
             new BytesRef("foo".getBytes(StandardCharsets.UTF_8), 0, "foo".getBytes(StandardCharsets.UTF_8).length), 1,
             internalStringAggs, false, 0, DocValueFormat.RAW));
 
         InternalTerms termsAgg = new StringTerms("string_terms", BucketOrder.count(false), 1, 0,
             Collections.emptyMap(), DocValueFormat.RAW, 1, false, 0, stringBuckets, 0);
-        InternalAggregations internalAggregations = new InternalAggregations(Collections.singletonList(termsAgg));
+        InternalAggregations internalAggregations = InternalAggregations.from(Collections.singletonList(termsAgg));
         LongTerms.Bucket bucket = new LongTerms.Bucket(19, 1, internalAggregations, false, 0, DocValueFormat.RAW);
         buckets.add(bucket);
 

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

@@ -64,7 +64,7 @@ public class InternalFilterTests extends InternalSingleBucketAggregationTestCase
         InternalFilter dummy = createTestInstance();
         InternalFilter inner = createTestInstance();
 
-        InternalAggregations sub = new InternalAggregations(List.of(inner));
+        InternalAggregations sub = InternalAggregations.from(List.of(inner));
         InternalFilter test = createTestInstance("test", randomNonNegativeLong(), sub, emptyMap());
         PipelineAggregator mockPipeline = new PipelineAggregator(null, null, null) {
             @Override

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

@@ -131,7 +131,7 @@ public class InternalFiltersTests extends InternalMultiBucketAggregationTestCase
         InternalFilters dummy = createTestInstance();
         InternalFilters inner = createTestInstance();
 
-        InternalAggregations sub = new InternalAggregations(List.of(inner));
+        InternalAggregations sub = InternalAggregations.from(List.of(inner));
         InternalFilters test = createTestInstance("test", emptyMap(), sub);
         PipelineAggregator mockPipeline = new PipelineAggregator(null, null, null) {
             @Override

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

@@ -37,14 +37,12 @@ import java.time.ZoneOffset;
 import java.time.ZonedDateTime;
 import java.util.ArrayList;
 import java.util.Arrays;
-import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.TreeMap;
 import java.util.concurrent.TimeUnit;
 
-import static java.util.Collections.emptyList;
 import static java.util.Collections.emptyMap;
 import static java.util.stream.Collectors.toList;
 import static org.hamcrest.Matchers.empty;
@@ -73,8 +71,7 @@ public class InternalAutoDateHistogramTests extends InternalMultiBucketAggregati
             long key = startingDate + (intervalMillis * i);
             buckets.add(i, new InternalAutoDateHistogram.Bucket(key, randomIntBetween(1, 100), format, aggregations));
         }
-        InternalAggregations subAggregations = new InternalAggregations(Collections.emptyList());
+        BucketInfo bucketInfo = new BucketInfo(roundingInfos, roundingIndex, InternalAggregations.EMPTY);
-        BucketInfo bucketInfo = new BucketInfo(roundingInfos, roundingIndex, subAggregations);
         return new InternalAutoDateHistogram(name, buckets, targetBuckets, bucketInfo, format, metadata, 1);
     }
 
@@ -360,7 +357,7 @@ public class InternalAutoDateHistogramTests extends InternalMultiBucketAggregati
 
         ReduceTestBuilder bucket(String key, long docCount) {
             buckets.add(new InternalAutoDateHistogram.Bucket(
-                utcMillis(key), docCount, FORMAT, new InternalAggregations(emptyList())));
+                utcMillis(key), docCount, FORMAT, InternalAggregations.EMPTY));
             return this;
         }
 
@@ -376,7 +373,7 @@ public class InternalAutoDateHistogramTests extends InternalMultiBucketAggregati
             assertThat("rounding [" + whichRounding + "] should be in " + Arrays.toString(roundings), roundingIdx, greaterThan(-1));
             assertTrue(Arrays.toString(roundings[roundingIdx].innerIntervals) + " must contain " + innerInterval,
                     Arrays.binarySearch(roundings[roundingIdx].innerIntervals, innerInterval) >= 0);
-            BucketInfo bucketInfo = new BucketInfo(roundings, roundingIdx, new InternalAggregations(emptyList()));
+            BucketInfo bucketInfo = new BucketInfo(roundings, roundingIdx, InternalAggregations.EMPTY);
             results.add(new InternalAutoDateHistogram("test", new ArrayList<>(buckets), targetBuckets, bucketInfo,
                     FORMAT, emptyMap(), innerInterval));
             buckets.clear();

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

@@ -62,7 +62,7 @@ public abstract class InternalSingleBucketAggregationTestCase<T extends Internal
             if (hasInternalMin) {
                 aggs.add(new InternalMin("min", randomDouble(), randomNumericDocValueFormat(), emptyMap()));
             }
-            return new InternalAggregations(aggs);
+            return InternalAggregations.from(aggs);
         };
     }
 
@@ -93,7 +93,7 @@ public abstract class InternalSingleBucketAggregationTestCase<T extends Internal
             List<InternalAggregation> aggs = new ArrayList<>();
             aggs.add(new InternalMax("new_max", randomDouble(), randomNumericDocValueFormat(), emptyMap()));
             aggs.add(new InternalMin("new_min", randomDouble(), randomNumericDocValueFormat(), emptyMap()));
-            aggregations = new InternalAggregations(aggs);
+            aggregations = InternalAggregations.from(aggs);
             break;
         case 3:
         default:

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

@@ -78,7 +78,7 @@ public abstract class InternalMultiBucketAggregationTestCase<T extends InternalA
                 for (int i = 0; i < numAggregations; i++) {
                     aggs.add(createTestInstance(randomAlphaOfLength(5), emptyMap(), InternalAggregations.EMPTY));
                 }
-                return new InternalAggregations(aggs);
+                return InternalAggregations.from(aggs);
             };
         }
     }

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

@@ -62,7 +62,7 @@ public class CumulativeCardinalityPipelineAggregator extends PipelineAggregator
                     .map((p) -> (InternalAggregation) p)
                     .collect(Collectors.toList());
                 aggs.add(new InternalSimpleLongValue(name(), cardinality, formatter, metadata()));
-                Bucket newBucket = factory.createBucket(factory.getKey(bucket), bucket.getDocCount(), new InternalAggregations(aggs));
+                Bucket newBucket = factory.createBucket(factory.getKey(bucket), bucket.getDocCount(), InternalAggregations.from(aggs));
                 newBuckets.add(newBucket);
             }
             return factory.createAggregation(newBuckets);

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

@@ -106,7 +106,7 @@ public class MovingPercentilesPipelineAggregator extends PipelineAggregator {
                     .map((p) -> (InternalAggregation) p)
                     .collect(Collectors.toList());
                 aggs.add(new InternalTDigestPercentiles(name(), config.keys, state, config.keyed, config.formatter, metadata()));
-                newBucket = factory.createBucket(factory.getKey(bucket), bucket.getDocCount(), new InternalAggregations(aggs));
+                newBucket = factory.createBucket(factory.getKey(bucket), bucket.getDocCount(), InternalAggregations.from(aggs));
             }
             newBuckets.add(newBucket);
             index++;
@@ -152,7 +152,7 @@ public class MovingPercentilesPipelineAggregator extends PipelineAggregator {
                     .map((p) -> (InternalAggregation) p)
                     .collect(Collectors.toList());
                 aggs.add(new InternalHDRPercentiles(name(), config.keys, state, config.keyed, config.formatter, metadata()));
-                newBucket = factory.createBucket(factory.getKey(bucket), bucket.getDocCount(), new InternalAggregations(aggs));
+                newBucket = factory.createBucket(factory.getKey(bucket), bucket.getDocCount(), InternalAggregations.from(aggs));
             }
             newBuckets.add(newBucket);
             index++;

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

@@ -67,7 +67,7 @@ public class NormalizePipelineAggregator extends PipelineAggregator {
                 .map((p) -> (InternalAggregation) p)
                 .collect(Collectors.toList());
             aggs.add(new InternalSimpleValue(name(), normalizedBucketValue, formatter, metadata()));
-            InternalMultiBucketAggregation.InternalBucket newBucket = originalAgg.createBucket(new InternalAggregations(aggs), bucket);
+            InternalMultiBucketAggregation.InternalBucket newBucket = originalAgg.createBucket(InternalAggregations.from(aggs), bucket);
             newBuckets.add(newBucket);
         }
 

x-pack/plugin/rollup/src/main/java/org/elasticsearch/xpack/rollup/RollupResponseTranslator.java

@@ -5,8 +5,6 @@
  */
 package org.elasticsearch.xpack.rollup;
 
-import org.apache.logging.log4j.LogManager;
-import org.apache.logging.log4j.Logger;
 import org.apache.lucene.util.BytesRef;
 import org.elasticsearch.ResourceNotFoundException;
 import org.elasticsearch.action.search.MultiSearchResponse;
@@ -41,7 +39,6 @@ import org.elasticsearch.xpack.core.rollup.RollupField;
 import java.nio.charset.StandardCharsets;
 import java.util.ArrayList;
 import java.util.Arrays;
-import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -57,8 +54,6 @@ import java.util.stream.Collectors;
  */
 public class RollupResponseTranslator {
 
-    private static final Logger logger = LogManager.getLogger(RollupResponseTranslator.class);
-
     /**
      * Verifies a live-only search response.  Essentially just checks for failure then returns
      * the response since we have no work to do
@@ -272,7 +267,7 @@ public class RollupResponseTranslator {
         // The combination process returns a tree that is identical to the non-rolled
         // which means we can use aggregation's reduce method to combine, just as if
         // it was a result from another shard
-        InternalAggregations currentTree = new InternalAggregations(Collections.emptyList());
+        InternalAggregations currentTree = InternalAggregations.EMPTY;
         InternalAggregation.ReduceContext finalReduceContext = InternalAggregation.ReduceContext.forFinalReduction(
                 reduceContext.bigArrays(), reduceContext.scriptService(), b -> {}, PipelineTree.EMPTY);
         for (SearchResponse rolledResponse : rolledResponses) {
@@ -291,7 +286,7 @@ public class RollupResponseTranslator {
 
             // Iteratively merge in each new set of unrolled aggs, so that we can identify/fix overlapping doc_counts
             // in the next round of unrolling
-            InternalAggregations finalUnrolledAggs = new InternalAggregations(unrolledAggs);
+            InternalAggregations finalUnrolledAggs = InternalAggregations.from(unrolledAggs);
             currentTree = InternalAggregations.reduce(Arrays.asList(currentTree, finalUnrolledAggs), finalReduceContext);
         }
 
@@ -505,7 +500,7 @@ public class RollupResponseTranslator {
      */
     private static InternalAggregations unrollSubAggsFromMulti(InternalBucket bucket, InternalBucket original, InternalBucket currentTree) {
         // Iterate over the subAggs in each bucket
-        return new InternalAggregations(bucket.getAggregations()
+        return InternalAggregations.from(bucket.getAggregations()
                 .asList().stream()
                 // Avoid any rollup count metrics, as that's not a true "sub-agg" but rather agg
                 // added by the rollup for accounting purposes (e.g. doc_count)

x-pack/plugin/rollup/src/test/java/org/elasticsearch/xpack/rollup/RollupResponseTranslationTests.java

@@ -162,11 +162,11 @@ public class RollupResponseTranslationTests extends AggregatorTestCase {
         when(count.getType()).thenReturn(SumAggregationBuilder.NAME);
         subaggs.add(count);
 
-        when(filter.getAggregations()).thenReturn(new InternalAggregations(subaggs));
+        when(filter.getAggregations()).thenReturn(InternalAggregations.from(subaggs));
         when(filter.getName()).thenReturn("filter_foo");
         aggTree.add(filter);
 
-        Aggregations mockAggsWithout = new InternalAggregations(aggTree);
+        Aggregations mockAggsWithout = InternalAggregations.from(aggTree);
         when(responseWithout.getAggregations()).thenReturn(mockAggsWithout);
 
         MultiSearchResponse.Item[] msearch = new MultiSearchResponse.Item[]{
@@ -186,8 +186,7 @@ public class RollupResponseTranslationTests extends AggregatorTestCase {
         SearchResponse responseWithout = mock(SearchResponse.class);
         when(responseWithout.getTook()).thenReturn(new TimeValue(100));
 
-        Aggregations mockAggsWithout = new InternalAggregations(Collections.emptyList());
+        when(responseWithout.getAggregations()).thenReturn(InternalAggregations.EMPTY);
-        when(responseWithout.getAggregations()).thenReturn(mockAggsWithout);
 
         MultiSearchResponse.Item[] msearch = new MultiSearchResponse.Item[]{
                 new MultiSearchResponse.Item(responseWithout, null)};
@@ -258,11 +257,11 @@ public class RollupResponseTranslationTests extends AggregatorTestCase {
         when(count.getType()).thenReturn(SumAggregationBuilder.NAME);
         subaggs.add(count);
 
-        when(filter.getAggregations()).thenReturn(new InternalAggregations(subaggs));
+        when(filter.getAggregations()).thenReturn(InternalAggregations.from(subaggs));
         when(filter.getName()).thenReturn("filter_foo");
         aggTree.add(filter);
 
-        Aggregations mockAggs = new InternalAggregations(aggTree);
+        Aggregations mockAggs = InternalAggregations.from(aggTree);
         when(response.getAggregations()).thenReturn(mockAggs);
         MultiSearchResponse.Item item = new MultiSearchResponse.Item(response, null);
 
@@ -298,7 +297,7 @@ public class RollupResponseTranslationTests extends AggregatorTestCase {
         InternalMax protoMax = mock(InternalMax.class);
         when(protoMax.getName()).thenReturn("foo");
         protoAggTree.add(protoMax);
-        Aggregations protoMockAggs = new InternalAggregations(protoAggTree);
+        Aggregations protoMockAggs = InternalAggregations.from(protoAggTree);
         when(protoResponse.getAggregations()).thenReturn(protoMockAggs);
         MultiSearchResponse.Item unrolledResponse = new MultiSearchResponse.Item(protoResponse, null);
 
@@ -307,7 +306,7 @@ public class RollupResponseTranslationTests extends AggregatorTestCase {
         InternalMax max = mock(InternalMax.class);
         when(max.getName()).thenReturn("bizzbuzz");
         aggTreeWithoutFilter.add(max);
-        Aggregations mockAggsWithout = new InternalAggregations(aggTreeWithoutFilter);
+        Aggregations mockAggsWithout = InternalAggregations.from(aggTreeWithoutFilter);
         when(responseWithout.getAggregations()).thenReturn(mockAggsWithout);
         MultiSearchResponse.Item rolledResponse = new MultiSearchResponse.Item(responseWithout, null);
 
@@ -328,7 +327,7 @@ public class RollupResponseTranslationTests extends AggregatorTestCase {
         InternalMax protoMax = mock(InternalMax.class);
         when(protoMax.getName()).thenReturn("foo");
         protoAggTree.add(protoMax);
-        Aggregations protoMockAggs = new InternalAggregations(protoAggTree);
+        Aggregations protoMockAggs = InternalAggregations.from(protoAggTree);
         when(protoResponse.getAggregations()).thenReturn(protoMockAggs);
         MultiSearchResponse.Item unrolledResponse = new MultiSearchResponse.Item(protoResponse, null);
 
@@ -336,7 +335,7 @@ public class RollupResponseTranslationTests extends AggregatorTestCase {
         List<InternalAggregation> aggTreeWithoutFilter = new ArrayList<>(1);
         InternalMax max = new InternalMax("filter_foo", 0, DocValueFormat.RAW, null);
         aggTreeWithoutFilter.add(max);
-        Aggregations mockAggsWithout = new InternalAggregations(aggTreeWithoutFilter);
+        Aggregations mockAggsWithout = InternalAggregations.from(aggTreeWithoutFilter);
         when(responseWithout.getAggregations()).thenReturn(mockAggsWithout);
         MultiSearchResponse.Item rolledResponse = new MultiSearchResponse.Item(responseWithout, null);
 
@@ -358,7 +357,7 @@ public class RollupResponseTranslationTests extends AggregatorTestCase {
         List<InternalAggregation> protoAggTree = new ArrayList<>(1);
         InternalAvg internalAvg = new InternalAvg("foo", 10, 2, DocValueFormat.RAW, null);
         protoAggTree.add(internalAvg);
-        Aggregations protoMockAggs = new InternalAggregations(protoAggTree);
+        Aggregations protoMockAggs = InternalAggregations.from(protoAggTree);
         when(protoResponse.getAggregations()).thenReturn(protoMockAggs);
         MultiSearchResponse.Item unrolledResponse = new MultiSearchResponse.Item(protoResponse, null);
 
@@ -386,11 +385,11 @@ public class RollupResponseTranslationTests extends AggregatorTestCase {
         when(count.getType()).thenReturn(SumAggregationBuilder.NAME);
         subaggs.add(count);
 
-        when(filter.getAggregations()).thenReturn(new InternalAggregations(subaggs));
+        when(filter.getAggregations()).thenReturn(InternalAggregations.from(subaggs));
         when(filter.getName()).thenReturn("filter_foo");
         aggTree.add(filter);
 
-        Aggregations mockAggsWithout = new InternalAggregations(aggTree);
+        Aggregations mockAggsWithout = InternalAggregations.from(aggTree);
         when(responseWithout.getAggregations()).thenReturn(mockAggsWithout);
         MultiSearchResponse.Item rolledResponse = new MultiSearchResponse.Item(responseWithout, null);
 
@@ -495,11 +494,11 @@ public class RollupResponseTranslationTests extends AggregatorTestCase {
         // TODO SearchResponse.Clusters is not public, using null for now.  Should fix upstream.
         MultiSearchResponse.Item unrolledItem = new MultiSearchResponse.Item(new SearchResponse(
                 new InternalSearchResponse(null,
-                        new InternalAggregations(Collections.singletonList(responses.get(0))), null, null, false, false, 1),
+                        InternalAggregations.from(Collections.singletonList(responses.get(0))), null, null, false, false, 1),
                         null, 1, 1, 0, 10, null, null), null);
         MultiSearchResponse.Item rolledItem = new MultiSearchResponse.Item(new SearchResponse(
                 new InternalSearchResponse(null,
-                        new InternalAggregations(Collections.singletonList(responses.get(1))), null, null, false, false, 1),
+                        InternalAggregations.from(Collections.singletonList(responses.get(1))), null, null, false, false, 1),
                         null, 1, 1, 0, 10, null, null), null);
 
         MultiSearchResponse.Item[] msearch = new MultiSearchResponse.Item[]{unrolledItem, rolledItem};

x-pack/plugin/rollup/src/test/java/org/elasticsearch/xpack/rollup/action/SearchActionTests.java

@@ -652,11 +652,11 @@ public class SearchActionTests extends ESTestCase {
         when(count.getType()).thenReturn(SumAggregationBuilder.NAME);
         subaggs.add(count);
 
-        when(filter.getAggregations()).thenReturn(new InternalAggregations(subaggs));
+        when(filter.getAggregations()).thenReturn(InternalAggregations.from(subaggs));
         when(filter.getName()).thenReturn("filter_foo");
         aggTree.add(filter);
 
-        Aggregations mockAggs = new InternalAggregations(aggTree);
+        Aggregations mockAggs = InternalAggregations.from(aggTree);
         when(response.getAggregations()).thenReturn(mockAggs);
         MultiSearchResponse.Item item = new MultiSearchResponse.Item(response, null);
         MultiSearchResponse msearchResponse = new MultiSearchResponse(new MultiSearchResponse.Item[]{item}, 1);
@@ -736,7 +736,7 @@ public class SearchActionTests extends ESTestCase {
         List<InternalAggregation> protoAggTree = new ArrayList<>(1);
         InternalAvg internalAvg = new InternalAvg("foo", 10, 2, DocValueFormat.RAW, null);
         protoAggTree.add(internalAvg);
-        Aggregations protoMockAggs = new InternalAggregations(protoAggTree);
+        Aggregations protoMockAggs = InternalAggregations.from(protoAggTree);
         when(protoResponse.getAggregations()).thenReturn(protoMockAggs);
         MultiSearchResponse.Item unrolledResponse = new MultiSearchResponse.Item(protoResponse, null);
 
@@ -764,11 +764,11 @@ public class SearchActionTests extends ESTestCase {
         when(count.getType()).thenReturn(SumAggregationBuilder.NAME);
         subaggs.add(count);
 
-        when(filter.getAggregations()).thenReturn(new InternalAggregations(subaggs));
+        when(filter.getAggregations()).thenReturn(InternalAggregations.from(subaggs));
         when(filter.getName()).thenReturn("filter_foo");
         aggTree.add(filter);
 
-        Aggregations mockAggsWithout = new InternalAggregations(aggTree);
+        Aggregations mockAggsWithout = InternalAggregations.from(aggTree);
         when(responseWithout.getAggregations()).thenReturn(mockAggsWithout);
         MultiSearchResponse.Item rolledResponse = new MultiSearchResponse.Item(responseWithout, null);
 

x-pack/plugin/rollup/src/test/java/org/elasticsearch/xpack/rollup/job/RollupIndexerStateTests.java

@@ -622,7 +622,7 @@ public class RollupIndexerStateTests extends ESTestCase {
 
                         @Override
                         public Aggregations getAggregations() {
-                            return new InternalAggregations(Collections.emptyList());
+                            return InternalAggregations.EMPTY;
                         }
 
                         @Override
@@ -735,7 +735,7 @@ public class RollupIndexerStateTests extends ESTestCase {
 
                         @Override
                         public Aggregations getAggregations() {
-                            return new InternalAggregations(Collections.emptyList());
+                            return InternalAggregations.EMPTY;
                         }
 
                         @Override
@@ -892,7 +892,7 @@ public class RollupIndexerStateTests extends ESTestCase {
 
                         @Override
                         public Aggregations getAggregations() {
-                            return new InternalAggregations(Collections.emptyList());
+                            return InternalAggregations.EMPTY;
                         }
 
                         @Override