diff --git a/buildSrc/src/main/resources/checkstyle_suppressions.xml b/buildSrc/src/main/resources/checkstyle_suppressions.xml
index 54f148894da..309fd865a22 100644
--- a/buildSrc/src/main/resources/checkstyle_suppressions.xml
+++ b/buildSrc/src/main/resources/checkstyle_suppressions.xml
@@ -157,7 +157,6 @@
   <suppress files="core[/\\]src[/\\]main[/\\]java[/\\]org[/\\]elasticsearch[/\\]action[/\\]ingest[/\\]SimulatePipelineRequestBuilder.java" checks="LineLength" />
   <suppress files="core[/\\]src[/\\]main[/\\]java[/\\]org[/\\]elasticsearch[/\\]action[/\\]ingest[/\\]SimulatePipelineTransportAction.java" checks="LineLength" />
   <suppress files="core[/\\]src[/\\]main[/\\]java[/\\]org[/\\]elasticsearch[/\\]action[/\\]search[/\\]MultiSearchRequestBuilder.java" checks="LineLength" />
-  <suppress files="core[/\\]src[/\\]main[/\\]java[/\\]org[/\\]elasticsearch[/\\]action[/\\]search[/\\]SearchResponse.java" checks="LineLength" />
   <suppress files="core[/\\]src[/\\]main[/\\]java[/\\]org[/\\]elasticsearch[/\\]action[/\\]search[/\\]ShardSearchFailure.java" checks="LineLength" />
   <suppress files="core[/\\]src[/\\]main[/\\]java[/\\]org[/\\]elasticsearch[/\\]action[/\\]search[/\\]TransportClearScrollAction.java" checks="LineLength" />
   <suppress files="core[/\\]src[/\\]main[/\\]java[/\\]org[/\\]elasticsearch[/\\]action[/\\]search[/\\]TransportMultiSearchAction.java" checks="LineLength" />
diff --git a/client/client-benchmark-noop-api-plugin/src/main/java/org/elasticsearch/plugin/noop/action/search/TransportNoopSearchAction.java b/client/client-benchmark-noop-api-plugin/src/main/java/org/elasticsearch/plugin/noop/action/search/TransportNoopSearchAction.java
index 1e09e890a0b..77e7cdab937 100644
--- a/client/client-benchmark-noop-api-plugin/src/main/java/org/elasticsearch/plugin/noop/action/search/TransportNoopSearchAction.java
+++ b/client/client-benchmark-noop-api-plugin/src/main/java/org/elasticsearch/plugin/noop/action/search/TransportNoopSearchAction.java
@@ -53,6 +53,6 @@ public class TransportNoopSearchAction extends HandledTransportAction<SearchRequ
                 new SearchHit[0], 0L, 0.0f),
             new InternalAggregations(Collections.emptyList()),
             new Suggest(Collections.emptyList()),
-            new SearchProfileShardResults(Collections.emptyMap()), false, false), "", 1, 1, 0, new ShardSearchFailure[0]));
+            new SearchProfileShardResults(Collections.emptyMap()), false, false, 1), "", 1, 1, 0, new ShardSearchFailure[0]));
     }
 }
diff --git a/core/src/main/java/org/elasticsearch/action/search/SearchPhaseController.java b/core/src/main/java/org/elasticsearch/action/search/SearchPhaseController.java
index fe39e741426..eb30df1b699 100644
--- a/core/src/main/java/org/elasticsearch/action/search/SearchPhaseController.java
+++ b/core/src/main/java/org/elasticsearch/action/search/SearchPhaseController.java
@@ -465,7 +465,7 @@ public class SearchPhaseController extends AbstractComponent {
      * @param queryResults a list of non-null query shard results
      */
     public final ReducedQueryPhase reducedQueryPhase(List<? extends AtomicArray.Entry<? extends QuerySearchResultProvider>> queryResults) {
-        return reducedQueryPhase(queryResults, null);
+        return reducedQueryPhase(queryResults, null, 0);
     }
 
     /**
@@ -473,18 +473,22 @@ public class SearchPhaseController extends AbstractComponent {
      * @param queryResults a list of non-null query shard results
      * @param bufferdAggs a list of pre-collected / buffered aggregations. if this list is non-null all aggregations have been consumed
      *                    from all non-null query results.
+     * @param numReducePhases the number of non-final reduce phases applied to the query results.
      * @see QuerySearchResult#consumeAggs()
      * @see QuerySearchResult#consumeProfileResult()
      */
     private ReducedQueryPhase reducedQueryPhase(List<? extends AtomicArray.Entry<? extends QuerySearchResultProvider>> queryResults,
-                                                     List<InternalAggregations> bufferdAggs) {
+                                                     List<InternalAggregations> bufferdAggs, int numReducePhases) {
+        assert numReducePhases >= 0 : "num reduce phases must be >= 0 but was: " + numReducePhases;
+        numReducePhases++; // increment for this phase
         long totalHits = 0;
         long fetchHits = 0;
         float maxScore = Float.NEGATIVE_INFINITY;
         boolean timedOut = false;
         Boolean terminatedEarly = null;
         if (queryResults.isEmpty()) { // early terminate we have nothing to reduce
-            return new ReducedQueryPhase(totalHits, fetchHits, maxScore, timedOut, terminatedEarly, null, null, null, null);
+            return new ReducedQueryPhase(totalHits, fetchHits, maxScore, timedOut, terminatedEarly, null, null, null, null,
+                numReducePhases);
         }
         final QuerySearchResult firstResult = queryResults.get(0).value.queryResult();
         final boolean hasSuggest = firstResult.suggest() != null;
@@ -493,6 +497,7 @@ public class SearchPhaseController extends AbstractComponent {
         final List<InternalAggregations> aggregationsList;
         if (bufferdAggs != null) {
             consumeAggs = false;
+            assert numReducePhases > 1 : "num reduce phases must be > 1 but was: " + numReducePhases;
             // we already have results from intermediate reduces and just need to perform the final reduce
             assert firstResult.hasAggs() : "firstResult has no aggs but we got non null buffered aggs?";
             aggregationsList = bufferdAggs;
@@ -548,7 +553,7 @@ public class SearchPhaseController extends AbstractComponent {
             firstResult.pipelineAggregators(), reduceContext);
         final SearchProfileShardResults shardResults = profileResults.isEmpty() ? null : new SearchProfileShardResults(profileResults);
         return new ReducedQueryPhase(totalHits, fetchHits, maxScore, timedOut, terminatedEarly, firstResult, suggest, aggregations,
-            shardResults);
+            shardResults, numReducePhases);
     }
 
 
@@ -597,10 +602,15 @@ public class SearchPhaseController extends AbstractComponent {
         final InternalAggregations aggregations;
         // the reduced profile results
         final SearchProfileShardResults shardResults;
+        // the number of reduces phases
+        final int numReducePhases;
 
         ReducedQueryPhase(long totalHits, long fetchHits, float maxScore, boolean timedOut, Boolean terminatedEarly,
                                  QuerySearchResult oneResult, Suggest suggest, InternalAggregations aggregations,
-                                 SearchProfileShardResults shardResults) {
+                                 SearchProfileShardResults shardResults, int numReducePhases) {
+            if (numReducePhases <= 0) {
+                throw new IllegalArgumentException("at least one reduce phase must have been applied but was: " + numReducePhases);
+            }
             this.totalHits = totalHits;
             this.fetchHits = fetchHits;
             if (Float.isInfinite(maxScore)) {
@@ -614,6 +624,7 @@ public class SearchPhaseController extends AbstractComponent {
             this.suggest = suggest;
             this.aggregations = aggregations;
             this.shardResults = shardResults;
+            this.numReducePhases = numReducePhases;
         }
 
         /**
@@ -621,7 +632,7 @@ public class SearchPhaseController extends AbstractComponent {
          * @see #merge(boolean, ScoreDoc[], ReducedQueryPhase, AtomicArray)
          */
         public InternalSearchResponse buildResponse(SearchHits hits) {
-            return new InternalSearchResponse(hits, aggregations, suggest, shardResults, timedOut, terminatedEarly);
+            return new InternalSearchResponse(hits, aggregations, suggest, shardResults, timedOut, terminatedEarly, numReducePhases);
         }
 
         /**
@@ -643,6 +654,7 @@ public class SearchPhaseController extends AbstractComponent {
         private final InternalAggregations[] buffer;
         private int index;
         private final SearchPhaseController controller;
+        private int numReducePhases = 0;
 
         /**
          * Creates a new {@link QueryPhaseResultConsumer}
@@ -677,6 +689,7 @@ public class SearchPhaseController extends AbstractComponent {
             if (index == buffer.length) {
                 InternalAggregations reducedAggs = controller.reduceAggsIncrementally(Arrays.asList(buffer));
                 Arrays.fill(buffer, null);
+                numReducePhases++;
                 buffer[0] = reducedAggs;
                 index = 1;
             }
@@ -690,7 +703,7 @@ public class SearchPhaseController extends AbstractComponent {
 
         @Override
         public ReducedQueryPhase reduce() {
-            return controller.reducedQueryPhase(results.asList(), getRemaining());
+            return controller.reducedQueryPhase(results.asList(), getRemaining(), numReducePhases);
         }
 
         /**
@@ -699,6 +712,8 @@ public class SearchPhaseController extends AbstractComponent {
         int getNumBuffered() {
             return index;
         }
+
+        int getNumReducePhases() { return numReducePhases; }
     }
 
     /**
@@ -707,9 +722,9 @@ public class SearchPhaseController extends AbstractComponent {
     InitialSearchPhase.SearchPhaseResults<QuerySearchResultProvider> newSearchPhaseResults(SearchRequest request, int numShards) {
         SearchSourceBuilder source = request.source();
         if (source != null && source.aggregations() != null) {
-            if (request.getReduceUpTo() < numShards) {
+            if (request.getBatchedReduceSize() < numShards) {
                 // only use this if there are aggs and if there are more shards than we should reduce at once
-                return new QueryPhaseResultConsumer(this, numShards, request.getReduceUpTo());
+                return new QueryPhaseResultConsumer(this, numShards, request.getBatchedReduceSize());
             }
         }
         return new InitialSearchPhase.SearchPhaseResults(numShards) {
diff --git a/core/src/main/java/org/elasticsearch/action/search/SearchRequest.java b/core/src/main/java/org/elasticsearch/action/search/SearchRequest.java
index 0c1189d1d69..6e2701ad417 100644
--- a/core/src/main/java/org/elasticsearch/action/search/SearchRequest.java
+++ b/core/src/main/java/org/elasticsearch/action/search/SearchRequest.java
@@ -71,7 +71,7 @@ public final class SearchRequest extends ActionRequest implements IndicesRequest
 
     private Scroll scroll;
 
-    private int reduceUpTo = 512;
+    private int batchedReduceSize = 512;
 
     private String[] types = Strings.EMPTY_ARRAY;
 
@@ -281,19 +281,19 @@ public final class SearchRequest extends ActionRequest implements IndicesRequest
      * Sets the number of shard results that should be reduced at once on the coordinating node. This value should be used as a protection
      * mechanism to reduce the memory overhead per search request if the potential number of shards in the request can be large.
      */
-    public void setReduceUpTo(int reduceUpTo) {
-        if (reduceUpTo <= 1) {
-            throw new IllegalArgumentException("reduceUpTo must be >= 2");
+    public void setBatchedReduceSize(int batchedReduceSize) {
+        if (batchedReduceSize <= 1) {
+            throw new IllegalArgumentException("batchedReduceSize must be >= 2");
         }
-        this.reduceUpTo = reduceUpTo;
+        this.batchedReduceSize = batchedReduceSize;
     }
 
     /**
      * Returns the number of shard results that should be reduced at once on the coordinating node. This value should be used as a
      * protection mechanism to reduce the memory overhead per search request if the potential number of shards in the request can be large.
      */
-    public int getReduceUpTo() {
-        return reduceUpTo;
+    public int getBatchedReduceSize() {
+        return batchedReduceSize;
     }
 
     /**
@@ -343,7 +343,7 @@ public final class SearchRequest extends ActionRequest implements IndicesRequest
         indicesOptions = IndicesOptions.readIndicesOptions(in);
         requestCache = in.readOptionalBoolean();
         if (in.getVersion().onOrAfter(Version.V_6_0_0_alpha1_UNRELEASED)) {
-            reduceUpTo = in.readVInt();
+            batchedReduceSize = in.readVInt();
         }
     }
 
@@ -363,7 +363,7 @@ public final class SearchRequest extends ActionRequest implements IndicesRequest
         indicesOptions.writeIndicesOptions(out);
         out.writeOptionalBoolean(requestCache);
         if (out.getVersion().onOrAfter(Version.V_6_0_0_alpha1_UNRELEASED)) {
-            out.writeVInt(reduceUpTo);
+            out.writeVInt(batchedReduceSize);
         }
     }
 
diff --git a/core/src/main/java/org/elasticsearch/action/search/SearchRequestBuilder.java b/core/src/main/java/org/elasticsearch/action/search/SearchRequestBuilder.java
index c6c5e0fbf3d..ffe2c1b20c5 100644
--- a/core/src/main/java/org/elasticsearch/action/search/SearchRequestBuilder.java
+++ b/core/src/main/java/org/elasticsearch/action/search/SearchRequestBuilder.java
@@ -524,8 +524,12 @@ public class SearchRequestBuilder extends ActionRequestBuilder<SearchRequest, Se
         return request.source();
     }
 
-    public SearchRequestBuilder setReduceUpTo(int reduceUpTo) {
-        this.request.setReduceUpTo(reduceUpTo);
+    /**
+     * Sets the number of shard results that should be reduced at once on the coordinating node. This value should be used as a protection
+     * mechanism to reduce the memory overhead per search request if the potential number of shards in the request can be large.
+     */
+    public SearchRequestBuilder setBatchedReduceSize(int batchedReduceSize) {
+        this.request.setBatchedReduceSize(batchedReduceSize);
         return this;
     }
 }
diff --git a/core/src/main/java/org/elasticsearch/action/search/SearchResponse.java b/core/src/main/java/org/elasticsearch/action/search/SearchResponse.java
index 4b8ba5e64b6..54d8eab99e7 100644
--- a/core/src/main/java/org/elasticsearch/action/search/SearchResponse.java
+++ b/core/src/main/java/org/elasticsearch/action/search/SearchResponse.java
@@ -61,7 +61,8 @@ public class SearchResponse extends ActionResponse implements StatusToXContentOb
     public SearchResponse() {
     }
 
-    public SearchResponse(InternalSearchResponse internalResponse, String scrollId, int totalShards, int successfulShards, long tookInMillis, ShardSearchFailure[] shardFailures) {
+    public SearchResponse(InternalSearchResponse internalResponse, String scrollId, int totalShards, int successfulShards,
+                          long tookInMillis, ShardSearchFailure[] shardFailures) {
         this.internalResponse = internalResponse;
         this.scrollId = scrollId;
         this.totalShards = totalShards;
@@ -106,6 +107,13 @@ public class SearchResponse extends ActionResponse implements StatusToXContentOb
         return internalResponse.terminatedEarly();
     }
 
+    /**
+     * Returns the number of reduce phases applied to obtain this search response
+     */
+    public int getNumReducePhases() {
+        return internalResponse.getNumReducePhases();
+    }
+
     /**
      * How long the search took.
      */
@@ -172,13 +180,6 @@ public class SearchResponse extends ActionResponse implements StatusToXContentOb
         return internalResponse.profile();
     }
 
-    static final class Fields {
-        static final String _SCROLL_ID = "_scroll_id";
-        static final String TOOK = "took";
-        static final String TIMED_OUT = "timed_out";
-        static final String TERMINATED_EARLY = "terminated_early";
-    }
-
     @Override
     public XContentBuilder toXContent(XContentBuilder builder, Params params) throws IOException {
         builder.startObject();
@@ -189,14 +190,18 @@ public class SearchResponse extends ActionResponse implements StatusToXContentOb
 
     public XContentBuilder innerToXContent(XContentBuilder builder, Params params) throws IOException {
         if (scrollId != null) {
-            builder.field(Fields._SCROLL_ID, scrollId);
+            builder.field("_scroll_id", scrollId);
         }
-        builder.field(Fields.TOOK, tookInMillis);
-        builder.field(Fields.TIMED_OUT, isTimedOut());
+        builder.field("took", tookInMillis);
+        builder.field("timed_out", isTimedOut());
         if (isTerminatedEarly() != null) {
-            builder.field(Fields.TERMINATED_EARLY, isTerminatedEarly());
+            builder.field("terminated_early", isTerminatedEarly());
         }
-        RestActions.buildBroadcastShardsHeader(builder, params, getTotalShards(), getSuccessfulShards(), getFailedShards(), getShardFailures());
+        if (getNumReducePhases() != 1) {
+            builder.field("num_reduce_phases", getNumReducePhases());
+        }
+        RestActions.buildBroadcastShardsHeader(builder, params, getTotalShards(), getSuccessfulShards(), getFailedShards(),
+            getShardFailures());
         internalResponse.toXContent(builder, params);
         return builder;
     }
diff --git a/core/src/main/java/org/elasticsearch/rest/action/search/RestSearchAction.java b/core/src/main/java/org/elasticsearch/rest/action/search/RestSearchAction.java
index bf8308202b7..89e2f23861c 100644
--- a/core/src/main/java/org/elasticsearch/rest/action/search/RestSearchAction.java
+++ b/core/src/main/java/org/elasticsearch/rest/action/search/RestSearchAction.java
@@ -20,7 +20,6 @@
 package org.elasticsearch.rest.action.search;
 
 import org.elasticsearch.action.search.SearchRequest;
-import org.elasticsearch.action.search.SearchType;
 import org.elasticsearch.action.support.IndicesOptions;
 import org.elasticsearch.client.node.NodeClient;
 import org.elasticsearch.common.Strings;
@@ -94,6 +93,9 @@ public class RestSearchAction extends BaseRestHandler {
             searchRequest.source().parseXContent(context);
         }
 
+        final int batchedReduceSize = request.paramAsInt("batched_reduce_size", searchRequest.getBatchedReduceSize());
+        searchRequest.setBatchedReduceSize(batchedReduceSize);
+
         // do not allow 'query_and_fetch' or 'dfs_query_and_fetch' search types
         // from the REST layer. these modes are an internal optimization and should
         // not be specified explicitly by the user.
diff --git a/core/src/main/java/org/elasticsearch/search/internal/InternalSearchResponse.java b/core/src/main/java/org/elasticsearch/search/internal/InternalSearchResponse.java
index d396d14e983..998b99a68da 100644
--- a/core/src/main/java/org/elasticsearch/search/internal/InternalSearchResponse.java
+++ b/core/src/main/java/org/elasticsearch/search/internal/InternalSearchResponse.java
@@ -19,6 +19,7 @@
 
 package org.elasticsearch.search.internal;
 
+import org.elasticsearch.Version;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.io.stream.Streamable;
@@ -38,7 +39,7 @@ import java.util.Map;
 public class InternalSearchResponse implements Streamable, ToXContent {
 
     public static InternalSearchResponse empty() {
-        return new InternalSearchResponse(SearchHits.empty(), null, null, null, false, null);
+        return new InternalSearchResponse(SearchHits.empty(), null, null, null, false, null, 1);
     }
 
     private SearchHits hits;
@@ -53,17 +54,21 @@ public class InternalSearchResponse implements Streamable, ToXContent {
 
     private Boolean terminatedEarly = null;
 
+    private int numReducePhases = 1;
+
     private InternalSearchResponse() {
     }
 
     public InternalSearchResponse(SearchHits hits, InternalAggregations aggregations, Suggest suggest,
-                                  SearchProfileShardResults profileResults, boolean timedOut, Boolean terminatedEarly) {
+                                  SearchProfileShardResults profileResults, boolean timedOut, Boolean terminatedEarly,
+                                  int numReducePhases) {
         this.hits = hits;
         this.aggregations = aggregations;
         this.suggest = suggest;
         this.profileResults = profileResults;
         this.timedOut = timedOut;
         this.terminatedEarly = terminatedEarly;
+        this.numReducePhases = numReducePhases;
     }
 
     public boolean timedOut() {
@@ -86,6 +91,13 @@ public class InternalSearchResponse implements Streamable, ToXContent {
         return suggest;
     }
 
+    /**
+     * Returns the number of reduce phases applied to obtain this search response
+     */
+    public int getNumReducePhases() {
+        return numReducePhases;
+    }
+
     /**
      * Returns the profile results for this search response (including all shards).
      * An empty map is returned if profiling was not enabled
@@ -132,6 +144,11 @@ public class InternalSearchResponse implements Streamable, ToXContent {
         timedOut = in.readBoolean();
         terminatedEarly = in.readOptionalBoolean();
         profileResults = in.readOptionalWriteable(SearchProfileShardResults::new);
+        if (in.getVersion().onOrAfter(Version.V_6_0_0_alpha1_UNRELEASED)) {
+            numReducePhases = in.readVInt();
+        } else {
+            numReducePhases = 1;
+        }
     }
 
     @Override
@@ -152,5 +169,8 @@ public class InternalSearchResponse implements Streamable, ToXContent {
         out.writeBoolean(timedOut);
         out.writeOptionalBoolean(terminatedEarly);
         out.writeOptionalWriteable(profileResults);
+        if (out.getVersion().onOrAfter(Version.V_6_0_0_alpha1_UNRELEASED)) {
+            out.writeVInt(numReducePhases);
+        }
     }
 }
diff --git a/core/src/test/java/org/elasticsearch/action/bulk/byscroll/AsyncBulkByScrollActionTests.java b/core/src/test/java/org/elasticsearch/action/bulk/byscroll/AsyncBulkByScrollActionTests.java
index 92ce5040e37..1fafd847a3f 100644
--- a/core/src/test/java/org/elasticsearch/action/bulk/byscroll/AsyncBulkByScrollActionTests.java
+++ b/core/src/test/java/org/elasticsearch/action/bulk/byscroll/AsyncBulkByScrollActionTests.java
@@ -446,7 +446,7 @@ public class AsyncBulkByScrollActionTests extends ESTestCase {
         // Now we can simulate a response and check the delay that we used for the task
         SearchHit hit = new SearchHit(0, "id", new Text("type"), emptyMap());
         SearchHits hits = new SearchHits(new SearchHit[] { hit }, 0, 0);
-        InternalSearchResponse internalResponse = new InternalSearchResponse(hits, null, null, null, false, false);
+        InternalSearchResponse internalResponse = new InternalSearchResponse(hits, null, null, null, false, false, 1);
         SearchResponse searchResponse = new SearchResponse(internalResponse, scrollId(), 5, 4, randomLong(), null);
 
         if (randomBoolean()) {
diff --git a/core/src/test/java/org/elasticsearch/action/search/ExpandSearchPhaseTests.java b/core/src/test/java/org/elasticsearch/action/search/ExpandSearchPhaseTests.java
index 0ac452e62bd..20e295561bb 100644
--- a/core/src/test/java/org/elasticsearch/action/search/ExpandSearchPhaseTests.java
+++ b/core/src/test/java/org/elasticsearch/action/search/ExpandSearchPhaseTests.java
@@ -79,7 +79,7 @@ public class ExpandSearchPhaseTests extends ESTestCase {
 
 
                     InternalSearchResponse internalSearchResponse = new InternalSearchResponse(collapsedHits,
-                        null, null, null, false, null);
+                        null, null, null, false, null, 1);
                     SearchResponse response = mockSearchPhaseContext.buildSearchResponse(internalSearchResponse, null);
                     listener.onResponse(new MultiSearchResponse(new MultiSearchResponse.Item[]{
                         new MultiSearchResponse.Item(response, null)
@@ -91,7 +91,7 @@ public class ExpandSearchPhaseTests extends ESTestCase {
             SearchHits hits = new SearchHits(new SearchHit[]{new SearchHit(1, "ID", new Text("type"),
                 Collections.singletonMap("someField", new SearchHitField("someField", Collections.singletonList(collapseValue))))},
                 1, 1.0F);
-            InternalSearchResponse internalSearchResponse = new InternalSearchResponse(hits, null, null, null, false, null);
+            InternalSearchResponse internalSearchResponse = new InternalSearchResponse(hits, null, null, null, false, null, 1);
             SearchResponse response = mockSearchPhaseContext.buildSearchResponse(internalSearchResponse, null);
             AtomicReference<SearchResponse> reference = new AtomicReference<>();
             ExpandSearchPhase phase = new ExpandSearchPhase(mockSearchPhaseContext, response, r ->
@@ -132,7 +132,7 @@ public class ExpandSearchPhaseTests extends ESTestCase {
             void sendExecuteMultiSearch(MultiSearchRequest request, SearchTask task, ActionListener<MultiSearchResponse> listener) {
                 assertTrue(executedMultiSearch.compareAndSet(false, true));
                 InternalSearchResponse internalSearchResponse = new InternalSearchResponse(collapsedHits,
-                    null, null, null, false, null);
+                    null, null, null, false, null, 1);
                 SearchResponse response = mockSearchPhaseContext.buildSearchResponse(internalSearchResponse, null);
                 listener.onResponse(new MultiSearchResponse(new MultiSearchResponse.Item[]{
                     new MultiSearchResponse.Item(null, new RuntimeException("boom")),
@@ -146,7 +146,7 @@ public class ExpandSearchPhaseTests extends ESTestCase {
             new SearchHit(2, "ID2", new Text("type"),
                 Collections.singletonMap("someField", new SearchHitField("someField", Collections.singletonList(collapseValue))))}, 1,
             1.0F);
-        InternalSearchResponse internalSearchResponse = new InternalSearchResponse(hits, null, null, null, false, null);
+        InternalSearchResponse internalSearchResponse = new InternalSearchResponse(hits, null, null, null, false, null, 1);
         SearchResponse response = mockSearchPhaseContext.buildSearchResponse(internalSearchResponse, null);
         AtomicReference<SearchResponse> reference = new AtomicReference<>();
         ExpandSearchPhase phase = new ExpandSearchPhase(mockSearchPhaseContext, response, r ->
@@ -180,7 +180,7 @@ public class ExpandSearchPhaseTests extends ESTestCase {
             Collections.singletonMap("someField", new SearchHitField("someField", Collections.singletonList(null)))),
             new SearchHit(2, "ID2", new Text("type"),
                 Collections.singletonMap("someField", new SearchHitField("someField", Collections.singletonList(null))))}, 1, 1.0F);
-        InternalSearchResponse internalSearchResponse = new InternalSearchResponse(hits, null, null, null, false, null);
+        InternalSearchResponse internalSearchResponse = new InternalSearchResponse(hits, null, null, null, false, null, 1);
         SearchResponse response = mockSearchPhaseContext.buildSearchResponse(internalSearchResponse, null);
         AtomicReference<SearchResponse> reference = new AtomicReference<>();
         ExpandSearchPhase phase = new ExpandSearchPhase(mockSearchPhaseContext, response, r ->
diff --git a/core/src/test/java/org/elasticsearch/action/search/SearchPhaseControllerTests.java b/core/src/test/java/org/elasticsearch/action/search/SearchPhaseControllerTests.java
index 21d5b6aee90..5270fd59ce9 100644
--- a/core/src/test/java/org/elasticsearch/action/search/SearchPhaseControllerTests.java
+++ b/core/src/test/java/org/elasticsearch/action/search/SearchPhaseControllerTests.java
@@ -29,10 +29,8 @@ import org.elasticsearch.index.Index;
 import org.elasticsearch.search.DocValueFormat;
 import org.elasticsearch.search.SearchShardTarget;
 import org.elasticsearch.search.aggregations.AggregationBuilders;
-import org.elasticsearch.search.aggregations.Aggregations;
 import org.elasticsearch.search.aggregations.InternalAggregations;
 import org.elasticsearch.search.aggregations.metrics.max.InternalMax;
-import org.elasticsearch.search.aggregations.metrics.sum.InternalSum;
 import org.elasticsearch.search.builder.SearchSourceBuilder;
 import org.elasticsearch.search.fetch.FetchSearchResult;
 import org.elasticsearch.search.SearchHit;
@@ -245,7 +243,7 @@ public class SearchPhaseControllerTests extends ESTestCase {
         int bufferSize = randomIntBetween(2, 3);
         SearchRequest request = new SearchRequest();
         request.source(new SearchSourceBuilder().aggregation(AggregationBuilders.avg("foo")));
-        request.setReduceUpTo(bufferSize);
+        request.setBatchedReduceSize(bufferSize);
         InitialSearchPhase.SearchPhaseResults<QuerySearchResultProvider> consumer = searchPhaseController.newSearchPhaseResults(request, 3);
         QuerySearchResult result = new QuerySearchResult(0, new SearchShardTarget("node", new Index("a", "b"), 0));
         result.topDocs(new TopDocs(0, new ScoreDoc[0], 0.0F), new DocValueFormat[0]);
@@ -267,15 +265,18 @@ public class SearchPhaseControllerTests extends ESTestCase {
             Collections.emptyList(), Collections.emptyMap())));
         result.aggregations(aggs);
         consumer.consumeResult(1, result);
-
+        int numTotalReducePhases = 1;
         if (bufferSize == 2) {
             assertThat(consumer, instanceOf(SearchPhaseController.QueryPhaseResultConsumer.class));
+            assertEquals(1, ((SearchPhaseController.QueryPhaseResultConsumer)consumer).getNumReducePhases());
             assertEquals(2, ((SearchPhaseController.QueryPhaseResultConsumer)consumer).getNumBuffered());
+            numTotalReducePhases++;
         } else {
             assertThat(consumer, not(instanceOf(SearchPhaseController.QueryPhaseResultConsumer.class)));
         }
 
         SearchPhaseController.ReducedQueryPhase reduce = consumer.reduce();
+        assertEquals(numTotalReducePhases, reduce.numReducePhases);
         InternalMax max = (InternalMax) reduce.aggregations.asList().get(0);
         assertEquals(3.0D, max.getValue(), 0.0D);
     }
@@ -286,7 +287,7 @@ public class SearchPhaseControllerTests extends ESTestCase {
 
         SearchRequest request = new SearchRequest();
         request.source(new SearchSourceBuilder().aggregation(AggregationBuilders.avg("foo")));
-        request.setReduceUpTo(bufferSize);
+        request.setBatchedReduceSize(bufferSize);
         InitialSearchPhase.SearchPhaseResults<QuerySearchResultProvider> consumer =
             searchPhaseController.newSearchPhaseResults(request, expectedNumResults);
         AtomicInteger max = new AtomicInteger();
@@ -322,7 +323,7 @@ public class SearchPhaseControllerTests extends ESTestCase {
             if ((hasAggs = randomBoolean())) {
                 request.source(new SearchSourceBuilder().aggregation(AggregationBuilders.avg("foo")));
             }
-            request.setReduceUpTo(bufferSize);
+            request.setBatchedReduceSize(bufferSize);
             InitialSearchPhase.SearchPhaseResults<QuerySearchResultProvider> consumer
                 = searchPhaseController.newSearchPhaseResults(request, expectedNumResults);
             if (hasAggs && expectedNumResults > bufferSize) {
diff --git a/core/src/test/java/org/elasticsearch/search/aggregations/bucket/TermsDocCountErrorIT.java b/core/src/test/java/org/elasticsearch/search/aggregations/bucket/TermsDocCountErrorIT.java
index a7173dc4c22..3f2163f25d9 100644
--- a/core/src/test/java/org/elasticsearch/search/aggregations/bucket/TermsDocCountErrorIT.java
+++ b/core/src/test/java/org/elasticsearch/search/aggregations/bucket/TermsDocCountErrorIT.java
@@ -38,7 +38,6 @@ import org.elasticsearch.test.client.RandomizingClient;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.List;
-import java.util.function.Function;
 
 import static org.elasticsearch.common.xcontent.XContentFactory.jsonBuilder;
 import static org.elasticsearch.search.aggregations.AggregationBuilders.sum;
@@ -88,7 +87,7 @@ public class TermsDocCountErrorIT extends ESIntegTestCase {
                  */
                 @Override
                 public SearchRequestBuilder prepareSearch(String... indices) {
-                    return this.in.prepareSearch(indices).setReduceUpTo(512);
+                    return this.in.prepareSearch(indices).setBatchedReduceSize(512);
                 }
             };
         }
diff --git a/rest-api-spec/src/main/resources/rest-api-spec/api/search.json b/rest-api-spec/src/main/resources/rest-api-spec/api/search.json
index 328383e1639..dc5fda57439 100644
--- a/rest-api-spec/src/main/resources/rest-api-spec/api/search.json
+++ b/rest-api-spec/src/main/resources/rest-api-spec/api/search.json
@@ -158,6 +158,11 @@
         "request_cache": {
           "type" : "boolean",
           "description" : "Specify if request cache should be used for this request or not, defaults to index level setting"
+        },
+        "batched_reduce_size" : {
+          "type" : "number",
+          "description" : "The number of shard results that should be reduced at once on the coordinating node. This value should be used as a protection mechanism to reduce the memory overhead per search request if the potential number of shards in the request can be large.",
+          "default" : 512
         }
       }
     },
diff --git a/rest-api-spec/src/main/resources/rest-api-spec/test/search/120_batch_reduce_size.yaml b/rest-api-spec/src/main/resources/rest-api-spec/test/search/120_batch_reduce_size.yaml
new file mode 100644
index 00000000000..4c2054c2964
--- /dev/null
+++ b/rest-api-spec/src/main/resources/rest-api-spec/test/search/120_batch_reduce_size.yaml
@@ -0,0 +1,70 @@
+setup:
+  - do:
+      indices.create:
+          index: test_1
+          body:
+            settings:
+              number_of_shards: 5
+              number_of_replicas: 0
+            mappings:
+              test:
+                properties:
+                  str:
+                     type: keyword
+
+---
+"batched_reduce_size lower limit":
+  - skip:
+      version: " - 5.99.99"
+      reason:  this was added in 6.0.0
+  - do:
+      catch:      /batchedReduceSize must be >= 2/
+      search:
+        index: test_1
+        batched_reduce_size: 1
+
+
+---
+"batched_reduce_size 2 with 5 shards":
+  - skip:
+      version: " - 5.99.99"
+      reason:  this was added in 6.0.0
+  - do:
+      index:
+        index: test_1
+        type: test
+        id: 1
+        body: { "str" : "abc" }
+
+  - do:
+      index:
+        index: test_1
+        type: test
+        id: 2
+        body: { "str": "abc" }
+
+  - do:
+      index:
+        index: test_1
+        type: test
+        id: 3
+        body: { "str": "bcd" }
+  - do:
+      indices.refresh: {}
+
+  - do:
+      search:
+        batched_reduce_size: 2
+        body: { "size" : 0, "aggs" : { "str_terms" : { "terms" : { "field" : "str" } } } }
+
+  - match: { num_reduce_phases: 4 }
+  - match: { hits.total: 3 }
+  - length: { aggregations.str_terms.buckets: 2 }
+  - match: { aggregations.str_terms.buckets.0.key: "abc" }
+  - is_false: aggregations.str_terms.buckets.0.key_as_string
+  - match: { aggregations.str_terms.buckets.0.doc_count: 2 }
+  - match: { aggregations.str_terms.buckets.1.key: "bcd" }
+  - is_false: aggregations.str_terms.buckets.1.key_as_string
+  - match: { aggregations.str_terms.buckets.1.doc_count: 1 }
+
+
diff --git a/test/framework/src/main/java/org/elasticsearch/test/client/RandomizingClient.java b/test/framework/src/main/java/org/elasticsearch/test/client/RandomizingClient.java
index 77fb115c5f7..a7d9a72e6b7 100644
--- a/test/framework/src/main/java/org/elasticsearch/test/client/RandomizingClient.java
+++ b/test/framework/src/main/java/org/elasticsearch/test/client/RandomizingClient.java
@@ -36,7 +36,7 @@ public class RandomizingClient extends FilterClient {
 
     private final SearchType defaultSearchType;
     private final String defaultPreference;
-    private final int reduceUpTo;
+    private final int batchedReduceSize;
 
 
     public RandomizingClient(Client client, Random random) {
@@ -54,13 +54,14 @@ public class RandomizingClient extends FilterClient {
         } else {
             defaultPreference = null;
         }
-        this.reduceUpTo = 2 + random.nextInt(10);
+        this.batchedReduceSize = 2 + random.nextInt(10);
 
     }
 
     @Override
     public SearchRequestBuilder prepareSearch(String... indices) {
-        return in.prepareSearch(indices).setSearchType(defaultSearchType).setPreference(defaultPreference).setReduceUpTo(reduceUpTo);
+        return in.prepareSearch(indices).setSearchType(defaultSearchType).setPreference(defaultPreference)
+            .setBatchedReduceSize(batchedReduceSize);
     }
 
     @Override