diff --git a/processing/src/main/java/io/druid/query/QueryToolChest.java b/processing/src/main/java/io/druid/query/QueryToolChest.java
index bf5483f01c5..250c7baa695 100644
--- a/processing/src/main/java/io/druid/query/QueryToolChest.java
+++ b/processing/src/main/java/io/druid/query/QueryToolChest.java
@@ -42,10 +42,11 @@ public abstract class QueryToolChest<ResultType, QueryType extends Query<ResultT
    * This method doesn't belong here, but it's here for now just to make it work.
    *
    * @param seqOfSequences
+   * @param ordered whether the seqOfSequences is ordered or not.
    *
    * @return
    */
-  public abstract Sequence<ResultType> mergeSequences(Sequence<Sequence<ResultType>> seqOfSequences);
+  public abstract Sequence<ResultType> mergeSequences(Sequence<Sequence<ResultType>> seqOfSequences, boolean ordered);
 
   public abstract ServiceMetricEvent.Builder makeMetricBuilder(QueryType query);
 
@@ -80,6 +81,4 @@ public abstract class QueryToolChest<ResultType, QueryType extends Query<ResultT
   {
     return segments;
   }
-
-  public abstract Ordering<ResultType> getOrdering();
 }
diff --git a/processing/src/main/java/io/druid/query/UnionQueryRunner.java b/processing/src/main/java/io/druid/query/UnionQueryRunner.java
index 727f8d3c4d2..1954937094c 100644
--- a/processing/src/main/java/io/druid/query/UnionQueryRunner.java
+++ b/processing/src/main/java/io/druid/query/UnionQueryRunner.java
@@ -46,8 +46,7 @@ public class UnionQueryRunner<T> implements QueryRunner<T>
   {
     DataSource dataSource = query.getDataSource();
     if (dataSource instanceof UnionDataSource) {
-      return new MergeSequence<T>(
-          toolChest.getOrdering(),
+      return toolChest.mergeSequences(
           Sequences.simple(
               Lists.transform(
                   ((UnionDataSource) dataSource).getDataSources(),
@@ -62,7 +61,8 @@ public class UnionQueryRunner<T> implements QueryRunner<T>
                     }
                   }
               )
-          )
+          ),
+          false
       );
     } else {
       return baseRunner.run(query);
diff --git a/processing/src/main/java/io/druid/query/groupby/GroupByQueryQueryToolChest.java b/processing/src/main/java/io/druid/query/groupby/GroupByQueryQueryToolChest.java
index 96e70957888..ef7c7e8708c 100644
--- a/processing/src/main/java/io/druid/query/groupby/GroupByQueryQueryToolChest.java
+++ b/processing/src/main/java/io/druid/query/groupby/GroupByQueryQueryToolChest.java
@@ -191,13 +191,16 @@ public class GroupByQueryQueryToolChest extends QueryToolChest<Row, GroupByQuery
 
 
   @Override
-  public Sequence<Row> mergeSequences(Sequence<Sequence<Row>> seqOfSequences)
+  public Sequence<Row> mergeSequences(Sequence<Sequence<Row>> seqOfSequences, boolean ordered)
   {
-    return new OrderedMergeSequence<>(getOrdering(), seqOfSequences);
+    if (ordered) {
+      return new OrderedMergeSequence<>(getOrdering(), seqOfSequences);
+    } else {
+      return new MergeSequence<>(getOrdering(), seqOfSequences);
+    }
   }
 
-  @Override
-  public Ordering<Row> getOrdering()
+  private  Ordering<Row> getOrdering()
   {
     return Ordering.<Row>natural().nullsFirst();
   }
diff --git a/processing/src/main/java/io/druid/query/metadata/SegmentMetadataQueryQueryToolChest.java b/processing/src/main/java/io/druid/query/metadata/SegmentMetadataQueryQueryToolChest.java
index d7b41f86d9f..6ab91ca9596 100644
--- a/processing/src/main/java/io/druid/query/metadata/SegmentMetadataQueryQueryToolChest.java
+++ b/processing/src/main/java/io/druid/query/metadata/SegmentMetadataQueryQueryToolChest.java
@@ -144,9 +144,13 @@ public class SegmentMetadataQueryQueryToolChest extends QueryToolChest<SegmentAn
   }
 
   @Override
-  public Sequence<SegmentAnalysis> mergeSequences(Sequence<Sequence<SegmentAnalysis>> seqOfSequences)
+  public Sequence<SegmentAnalysis> mergeSequences(Sequence<Sequence<SegmentAnalysis>> seqOfSequences, boolean ordered)
   {
-    return new OrderedMergeSequence<SegmentAnalysis>(getOrdering(), seqOfSequences);
+    if (ordered) {
+      return new OrderedMergeSequence<>(getOrdering(), seqOfSequences);
+    } else {
+      return new MergeSequence<>(getOrdering(), seqOfSequences);
+    }
   }
 
   @Override
@@ -234,8 +238,7 @@ public class SegmentMetadataQueryQueryToolChest extends QueryToolChest<SegmentAn
     };
   }
 
-  @Override
-  public Ordering<SegmentAnalysis> getOrdering()
+  private Ordering<SegmentAnalysis> getOrdering()
   {
     return new Ordering<SegmentAnalysis>()
     {
diff --git a/processing/src/main/java/io/druid/query/search/SearchQueryQueryToolChest.java b/processing/src/main/java/io/druid/query/search/SearchQueryQueryToolChest.java
index e24239f8896..c7bf9f52c3e 100644
--- a/processing/src/main/java/io/druid/query/search/SearchQueryQueryToolChest.java
+++ b/processing/src/main/java/io/druid/query/search/SearchQueryQueryToolChest.java
@@ -109,9 +109,16 @@ public class SearchQueryQueryToolChest extends QueryToolChest<Result<SearchResul
   }
 
   @Override
-  public Sequence<Result<SearchResultValue>> mergeSequences(Sequence<Sequence<Result<SearchResultValue>>> seqOfSequences)
+  public Sequence<Result<SearchResultValue>> mergeSequences(
+      Sequence<Sequence<Result<SearchResultValue>>> seqOfSequences,
+      boolean ordered
+  )
   {
-    return new OrderedMergeSequence<Result<SearchResultValue>>(getOrdering(), seqOfSequences);
+    if (ordered) {
+      return new OrderedMergeSequence<>(getOrdering(), seqOfSequences);
+    } else {
+      return new MergeSequence<>(getOrdering(), seqOfSequences);
+    }
   }
 
   @Override
diff --git a/processing/src/main/java/io/druid/query/select/SelectQueryQueryToolChest.java b/processing/src/main/java/io/druid/query/select/SelectQueryQueryToolChest.java
index 95480302336..79297ca9ebe 100644
--- a/processing/src/main/java/io/druid/query/select/SelectQueryQueryToolChest.java
+++ b/processing/src/main/java/io/druid/query/select/SelectQueryQueryToolChest.java
@@ -111,9 +111,16 @@ public class SelectQueryQueryToolChest extends QueryToolChest<Result<SelectResul
   }
 
   @Override
-  public Sequence<Result<SelectResultValue>> mergeSequences(Sequence<Sequence<Result<SelectResultValue>>> seqOfSequences)
+  public Sequence<Result<SelectResultValue>> mergeSequences(
+      Sequence<Sequence<Result<SelectResultValue>>> seqOfSequences,
+      boolean ordered
+  )
   {
-    return new OrderedMergeSequence<Result<SelectResultValue>>(getOrdering(), seqOfSequences);
+    if (ordered) {
+      return new OrderedMergeSequence<>(getOrdering(), seqOfSequences);
+    } else {
+      return new MergeSequence<>(getOrdering(), seqOfSequences);
+    }
   }
 
   @Override
diff --git a/processing/src/main/java/io/druid/query/timeboundary/TimeBoundaryQueryQueryToolChest.java b/processing/src/main/java/io/druid/query/timeboundary/TimeBoundaryQueryQueryToolChest.java
index 088ec0b6eb8..c3bbd88bcca 100644
--- a/processing/src/main/java/io/druid/query/timeboundary/TimeBoundaryQueryQueryToolChest.java
+++ b/processing/src/main/java/io/druid/query/timeboundary/TimeBoundaryQueryQueryToolChest.java
@@ -109,9 +109,16 @@ public class TimeBoundaryQueryQueryToolChest
   }
 
   @Override
-  public Sequence<Result<TimeBoundaryResultValue>> mergeSequences(Sequence<Sequence<Result<TimeBoundaryResultValue>>> seqOfSequences)
+  public Sequence<Result<TimeBoundaryResultValue>> mergeSequences(
+      Sequence<Sequence<Result<TimeBoundaryResultValue>>> seqOfSequences,
+      boolean ordered
+  )
   {
-    return new OrderedMergeSequence<>(getOrdering(), seqOfSequences);
+    if (ordered) {
+      return new OrderedMergeSequence<>(getOrdering(), seqOfSequences);
+    } else {
+      return new MergeSequence<>(getOrdering(), seqOfSequences);
+    }
   }
 
   @Override
diff --git a/processing/src/main/java/io/druid/query/timeseries/TimeseriesQueryQueryToolChest.java b/processing/src/main/java/io/druid/query/timeseries/TimeseriesQueryQueryToolChest.java
index e7c7e0849b5..5c1b15e0b96 100644
--- a/processing/src/main/java/io/druid/query/timeseries/TimeseriesQueryQueryToolChest.java
+++ b/processing/src/main/java/io/druid/query/timeseries/TimeseriesQueryQueryToolChest.java
@@ -110,9 +110,16 @@ public class TimeseriesQueryQueryToolChest extends QueryToolChest<Result<Timeser
   }
 
   @Override
-  public Sequence<Result<TimeseriesResultValue>> mergeSequences(Sequence<Sequence<Result<TimeseriesResultValue>>> seqOfSequences)
+  public Sequence<Result<TimeseriesResultValue>> mergeSequences(
+      Sequence<Sequence<Result<TimeseriesResultValue>>> seqOfSequences,
+      boolean ordered
+  )
   {
-    return new OrderedMergeSequence<Result<TimeseriesResultValue>>(getOrdering(), seqOfSequences);
+    if (ordered) {
+      return new OrderedMergeSequence<>(getOrdering(), seqOfSequences);
+    } else {
+      return new MergeSequence<>(getOrdering(), seqOfSequences);
+    }
   }
 
   @Override
diff --git a/processing/src/main/java/io/druid/query/topn/TopNQueryQueryToolChest.java b/processing/src/main/java/io/druid/query/topn/TopNQueryQueryToolChest.java
index ab1faebf67e..7e60209f987 100644
--- a/processing/src/main/java/io/druid/query/topn/TopNQueryQueryToolChest.java
+++ b/processing/src/main/java/io/druid/query/topn/TopNQueryQueryToolChest.java
@@ -126,9 +126,16 @@ public class TopNQueryQueryToolChest extends QueryToolChest<Result<TopNResultVal
   }
 
   @Override
-  public Sequence<Result<TopNResultValue>> mergeSequences(Sequence<Sequence<Result<TopNResultValue>>> seqOfSequences)
+  public Sequence<Result<TopNResultValue>> mergeSequences(
+      Sequence<Sequence<Result<TopNResultValue>>> seqOfSequences,
+      boolean ordered
+  )
   {
-    return new OrderedMergeSequence<Result<TopNResultValue>>(getOrdering(), seqOfSequences);
+    if (ordered) {
+      return new OrderedMergeSequence<>(getOrdering(), seqOfSequences);
+    } else {
+      return new MergeSequence<>(getOrdering(), seqOfSequences);
+    }
   }
 
   @Override
diff --git a/server/src/main/java/io/druid/client/CachingClusteredClient.java b/server/src/main/java/io/druid/client/CachingClusteredClient.java
index d0135eb7f4a..11f2e09681c 100644
--- a/server/src/main/java/io/druid/client/CachingClusteredClient.java
+++ b/server/src/main/java/io/druid/client/CachingClusteredClient.java
@@ -265,7 +265,7 @@ public class CachingClusteredClient<T> implements QueryRunner<T>
                 Iterables.transform(listOfSequences, Pair.<DateTime, Sequence<T>>rhsFn())
             );
             if (strategy == null) {
-              return toolChest.mergeSequences(seq);
+              return toolChest.mergeSequences(seq, true);
             } else {
               return strategy.mergeSequences(seq);
             }
@@ -383,7 +383,8 @@ public class CachingClusteredClient<T> implements QueryRunner<T>
                             );
                           }
                         }
-                    )
+                    ),
+                    true
                 );
               }
 
diff --git a/server/src/test/java/io/druid/server/coordination/ServerManagerTest.java b/server/src/test/java/io/druid/server/coordination/ServerManagerTest.java
index 1148a107752..10580482e98 100644
--- a/server/src/test/java/io/druid/server/coordination/ServerManagerTest.java
+++ b/server/src/test/java/io/druid/server/coordination/ServerManagerTest.java
@@ -567,7 +567,7 @@ public class ServerManagerTest
     }
 
     @Override
-    public Sequence<T> mergeSequences(Sequence<Sequence<T>> seqOfSequences)
+    public Sequence<T> mergeSequences(Sequence<Sequence<T>> seqOfSequences, boolean ordered)
     {
       return new ConcatSequence<T>(seqOfSequences);
     }
@@ -591,12 +591,6 @@ public class ServerManagerTest
       {
       };
     }
-
-    @Override
-    public Ordering<T> getOrdering()
-    {
-      return null;
-    }
   }
 
   private static class SegmentForTesting implements Segment