diff --git a/processing/src/main/java/io/druid/query/groupby/epinephelinae/ConcurrentGrouper.java b/processing/src/main/java/io/druid/query/groupby/epinephelinae/ConcurrentGrouper.java
index 46edd1f917d..6e47ebaa2e2 100644
--- a/processing/src/main/java/io/druid/query/groupby/epinephelinae/ConcurrentGrouper.java
+++ b/processing/src/main/java/io/druid/query/groupby/epinephelinae/ConcurrentGrouper.java
@@ -139,8 +139,9 @@ public class ConcurrentGrouper<KeyType> implements Grouper<KeyType>
         getCombiningFactories(aggregatorFactories),
         combineKeySerdeFactory,
         executor,
+        sortHasNonGroupingFields,
         concurrencyHint,
-        sortHasNonGroupingFields
+        priority
     );
     this.maxDictionarySizeForCombiner = combineKeySerdeFactory.getMaxDictionarySize();
   }
diff --git a/processing/src/main/java/io/druid/query/groupby/epinephelinae/ParallelCombiner.java b/processing/src/main/java/io/druid/query/groupby/epinephelinae/ParallelCombiner.java
index ad3326d7ba4..e14de0bc997 100644
--- a/processing/src/main/java/io/druid/query/groupby/epinephelinae/ParallelCombiner.java
+++ b/processing/src/main/java/io/druid/query/groupby/epinephelinae/ParallelCombiner.java
@@ -31,6 +31,7 @@ import io.druid.java.util.common.ISE;
 import io.druid.java.util.common.Pair;
 import io.druid.java.util.common.io.Closer;
 import io.druid.java.util.common.parsers.CloseableIterator;
+import io.druid.query.AbstractPrioritizedCallable;
 import io.druid.query.QueryInterruptedException;
 import io.druid.query.aggregation.AggregatorFactory;
 import io.druid.query.dimension.DimensionSpec;
@@ -71,14 +72,16 @@ public class ParallelCombiner<KeyType>
   private final ListeningExecutorService executor;
   private final Comparator<Entry<KeyType>> keyObjComparator;
   private final int concurrencyHint;
+  private final int priority;
 
   public ParallelCombiner(
       Supplier<ResourceHolder<ByteBuffer>> combineBufferSupplier,
       AggregatorFactory[] combiningFactories,
       KeySerdeFactory<KeyType> combineKeySerdeFactory,
       ListeningExecutorService executor,
+      boolean sortHasNonGroupingFields,
       int concurrencyHint,
-      boolean sortHasNonGroupingFields
+      int priority
   )
   {
     this.combineBufferSupplier = combineBufferSupplier;
@@ -87,6 +90,7 @@ public class ParallelCombiner<KeyType>
     this.executor = executor;
     this.keyObjComparator = combineKeySerdeFactory.objectComparator(sortHasNonGroupingFields);;
     this.concurrencyHint = concurrencyHint;
+    this.priority = priority;
   }
 
   /**
@@ -322,29 +326,37 @@ public class ParallelCombiner<KeyType>
         combiningFactories
     );
 
-    final ListenableFuture future = executor.submit(() -> {
-      grouper.init();
+    final ListenableFuture future = executor.submit(
+        new AbstractPrioritizedCallable<Void>(priority)
+        {
+          @Override
+          public Void call() throws Exception
+          {
+            grouper.init();
 
-      try (
-          CloseableIterator<Entry<KeyType>> mergedIterator = CloseableIterators.mergeSorted(
-              iterators,
-              keyObjComparator
-          )
-      ) {
-        while (mergedIterator.hasNext()) {
-          final Entry<KeyType> next = mergedIterator.next();
+            try (
+                CloseableIterator<Entry<KeyType>> mergedIterator = CloseableIterators.mergeSorted(
+                    iterators,
+                    keyObjComparator
+                )
+            ) {
+              while (mergedIterator.hasNext()) {
+                final Entry<KeyType> next = mergedIterator.next();
 
-          settableColumnSelectorFactory.set(next.values);
-          grouper.aggregate(next.key); // grouper always returns ok or throws an exception
-          settableColumnSelectorFactory.set(null);
+                settableColumnSelectorFactory.set(next.values);
+                grouper.aggregate(next.key); // grouper always returns ok or throws an exception
+                settableColumnSelectorFactory.set(null);
+              }
+            }
+            catch (IOException e) {
+              throw Throwables.propagate(e);
+            }
+
+            grouper.finish();
+            return null;
+          }
         }
-      }
-      catch (IOException e) {
-        throw Throwables.propagate(e);
-      }
-
-      grouper.finish();
-    });
+    );
 
     return new Pair<>(grouper.iterator(), future);
   }
diff --git a/processing/src/test/java/io/druid/query/groupby/epinephelinae/ParallelCombinerTest.java b/processing/src/test/java/io/druid/query/groupby/epinephelinae/ParallelCombinerTest.java
index 5c1ec778ca8..0fe75d822cc 100644
--- a/processing/src/test/java/io/druid/query/groupby/epinephelinae/ParallelCombinerTest.java
+++ b/processing/src/test/java/io/druid/query/groupby/epinephelinae/ParallelCombinerTest.java
@@ -113,8 +113,9 @@ public class ParallelCombinerTest
         new AggregatorFactory[]{new CountAggregatorFactory("cnt").getCombiningFactory()},
         ConcurrentGrouperTest.KEY_SERDE_FACTORY,
         MoreExecutors.listeningDecorator(SERVICE),
+        false,
         THREAD_NUM,
-        false
+        0
     );
 
     final int numRows = 1000;