diff --git a/hyracks-dataflow-std/src/main/java/edu/uci/ics/hyracks/dataflow/std/group/ExternalGroupOperatorDescriptor.java b/hyracks-dataflow-std/src/main/java/edu/uci/ics/hyracks/dataflow/std/group/ExternalGroupOperatorDescriptor.java
index 0cc47b8..2483470 100644
--- a/hyracks-dataflow-std/src/main/java/edu/uci/ics/hyracks/dataflow/std/group/ExternalGroupOperatorDescriptor.java
+++ b/hyracks-dataflow-std/src/main/java/edu/uci/ics/hyracks/dataflow/std/group/ExternalGroupOperatorDescriptor.java
@@ -194,7 +194,7 @@
 
                 @Override
                 public void fail() throws HyracksDataException {
-
+                    throw new HyracksDataException("failed");
                 }
 
                 @Override
@@ -316,7 +316,12 @@
                                     gTable.sortFrames();
                                 gTable.flushFrames(writer, false);
                             }
+                            gTable = null;
+                            aggState = null;
+                            System.gc();
                         } else {
+                            aggState = null;
+                            System.gc();
                             runs = new LinkedList<RunFileReader>(runs);
                             inFrames = new ArrayList<ByteBuffer>();
                             outFrame = ctx.allocateFrame();