[FLINK-1285] Make Merge-Join aware of object-reuse setting

This closes #259

flink-runtime/src/main/java/org/apache/flink/runtime/operators/MatchDriver.java

@@ -22,6 +22,7 @@ package org.apache.flink.runtime.operators;
 import org.apache.flink.api.common.ExecutionConfig;
 import org.apache.flink.runtime.operators.hash.NonReusingBuildFirstHashMatchIterator;
 import org.apache.flink.runtime.operators.hash.NonReusingBuildSecondHashMatchIterator;
+import org.apache.flink.runtime.operators.sort.NonReusingMergeMatchIterator;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 import org.apache.flink.api.common.functions.FlatJoinFunction;
@@ -32,7 +33,7 @@ import org.apache.flink.runtime.io.disk.iomanager.IOManager;
 import org.apache.flink.runtime.memorymanager.MemoryManager;
 import org.apache.flink.runtime.operators.hash.ReusingBuildFirstHashMatchIterator;
 import org.apache.flink.runtime.operators.hash.ReusingBuildSecondHashMatchIterator;
-import org.apache.flink.runtime.operators.sort.MergeMatchIterator;
+import org.apache.flink.runtime.operators.sort.ReusingMergeMatchIterator;
 import org.apache.flink.runtime.operators.util.JoinTaskIterator;
 import org.apache.flink.runtime.operators.util.TaskConfig;
 import org.apache.flink.util.Collector;
@@ -125,7 +126,7 @@ public class MatchDriver<IT1, IT2, OT> implements PactDriver<FlatJoinFunction<IT
 		if (this.objectReuseEnabled) {
 			switch (ls) {
 				case MERGE:
-					this.matchIterator = new MergeMatchIterator<IT1, IT2, OT>(in1, in2, serializer1, comparator1, serializer2, comparator2, pairComparatorFactory.createComparator12(comparator1, comparator2), memoryManager, ioManager, numPages, this.taskContext.getOwningNepheleTask());
+					this.matchIterator = new ReusingMergeMatchIterator<IT1, IT2, OT>(in1, in2, serializer1, comparator1, serializer2, comparator2, pairComparatorFactory.createComparator12(comparator1, comparator2), memoryManager, ioManager, numPages, this.taskContext.getOwningNepheleTask());
 
 					break;
 				case HYBRIDHASH_BUILD_FIRST:
@@ -140,7 +141,7 @@ public class MatchDriver<IT1, IT2, OT> implements PactDriver<FlatJoinFunction<IT
 		} else {
 			switch (ls) {
 				case MERGE:
-					this.matchIterator = new MergeMatchIterator<IT1, IT2, OT>(in1, in2, serializer1, comparator1, serializer2, comparator2, pairComparatorFactory.createComparator12(comparator1, comparator2), memoryManager, ioManager, numPages, this.taskContext.getOwningNepheleTask());
+					this.matchIterator = new NonReusingMergeMatchIterator<IT1, IT2, OT>(in1, in2, serializer1, comparator1, serializer2, comparator2, pairComparatorFactory.createComparator12(comparator1, comparator2), memoryManager, ioManager, numPages, this.taskContext.getOwningNepheleTask());
 
 					break;
 				case HYBRIDHASH_BUILD_FIRST:

flink-runtime/src/main/java/org/apache/flink/runtime/operators/resettable/BlockResettableIterator.java → flink-runtime/src/main/java/org/apache/flink/runtime/operators/resettable/NonReusingBlockResettableIterator.java

@@ -36,41 +36,37 @@ import org.apache.flink.runtime.util.ResettableIterator;
  * access to the data in that block.
  * 
  */
-public class BlockResettableIterator<T> extends AbstractBlockResettableIterator<T> implements ResettableIterator<T> {
+public class NonReusingBlockResettableIterator<T> extends AbstractBlockResettableIterator<T> implements ResettableIterator<T> {
 	
-	public static final Logger LOG = LoggerFactory.getLogger(BlockResettableIterator.class);
+	public static final Logger LOG = LoggerFactory.getLogger(NonReusingBlockResettableIterator.class);
 	
 	// ------------------------------------------------------------------------
 	
 	protected Iterator<T> input;
 	
-	private T nextElement;
+	protected T nextElement;
 
-	private final T reuseElement;
+	protected T leftOverElement;
 	
-	private T leftOverElement;
+	protected boolean readPhase;
 	
-	private boolean readPhase;
-	
-	private boolean noMoreBlocks;
+	protected boolean noMoreBlocks;
 	
 	// ------------------------------------------------------------------------
 	
-	public BlockResettableIterator(MemoryManager memoryManager, Iterator<T> input,
-			TypeSerializer<T> serializer, int numPages, AbstractInvokable ownerTask)
+	public NonReusingBlockResettableIterator(MemoryManager memoryManager, Iterator<T> input,
+			TypeSerializer<T> serializer, int numPages,
+			AbstractInvokable ownerTask)
 	throws MemoryAllocationException
 	{
 		this(memoryManager, serializer, numPages, ownerTask);
 		this.input = input;
 	}
 	
-	public BlockResettableIterator(MemoryManager memoryManager,
-			TypeSerializer<T> serializer, int numPages, AbstractInvokable ownerTask)
+	public NonReusingBlockResettableIterator(MemoryManager memoryManager, TypeSerializer<T> serializer, int numPages, AbstractInvokable ownerTask)
 	throws MemoryAllocationException
 	{
 		super(serializer, memoryManager, numPages, ownerTask);
-		
-		this.reuseElement = serializer.createInstance();
 	}
 	
 	// ------------------------------------------------------------------------
@@ -83,8 +79,6 @@ public class BlockResettableIterator<T> extends AbstractBlockResettableIterator<
 		
 		nextBlock();
 	}
-	
-	
 
 	@Override
 	public boolean hasNext() {
@@ -92,7 +86,7 @@ public class BlockResettableIterator<T> extends AbstractBlockResettableIterator<
 			if (this.nextElement == null) {
 				if (this.readPhase) {
 					// read phase, get next element from buffer
-					T tmp = getNextRecord(this.reuseElement);
+					T tmp = getNextRecord();
 					if (tmp != null) {
 						this.nextElement = tmp;
 						return true;

flink-runtime/src/main/java/org/apache/flink/runtime/operators/resettable/ReusingBlockResettableIterator.java

+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+
+package org.apache.flink.runtime.operators.resettable;
+
+import org.apache.flink.api.common.typeutils.TypeSerializer;
+import org.apache.flink.runtime.jobgraph.tasks.AbstractInvokable;
+import org.apache.flink.runtime.memorymanager.MemoryAllocationException;
+import org.apache.flink.runtime.memorymanager.MemoryManager;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.io.IOException;
+import java.util.Iterator;
+
+/**
+ * Implementation of an iterator that fetches a block of data into main memory and offers resettable
+ * access to the data in that block.
+ * 
+ */
+public class ReusingBlockResettableIterator<T> extends NonReusingBlockResettableIterator<T> {
+
+	public static final Logger LOG = LoggerFactory.getLogger(ReusingBlockResettableIterator.class);
+
+	private final T reuseElement;
+
+	// ------------------------------------------------------------------------
+
+	public ReusingBlockResettableIterator(MemoryManager memoryManager, Iterator<T> input,
+			TypeSerializer<T> serializer, int numPages,
+			AbstractInvokable ownerTask)
+	throws MemoryAllocationException
+	{
+		this(memoryManager, serializer, numPages, ownerTask);
+		this.input = input;
+	}
+
+	public ReusingBlockResettableIterator(MemoryManager memoryManager, TypeSerializer<T>
+			serializer, int numPages, AbstractInvokable ownerTask)
+	throws MemoryAllocationException
+	{
+		super(memoryManager, serializer, numPages, ownerTask);
+		
+		this.reuseElement = serializer.createInstance();
+	}
+	
+	// ------------------------------------------------------------------------
+	
+	@Override
+	public boolean hasNext() {
+		try {
+			if (this.nextElement == null) {
+				if (this.readPhase) {
+					// read phase, get next element from buffer
+					T tmp = getNextRecord(this.reuseElement);
+					if (tmp != null) {
+						this.nextElement = tmp;
+						return true;
+					} else {
+						return false;
+					}
+				} else {
+					if (this.input.hasNext()) {
+						final T next = this.input.next();
+						if (writeNextRecord(next)) {
+							this.nextElement = next;
+							return true;
+						} else {
+							this.leftOverElement = next;
+							return false;
+						}
+					} else {
+						this.noMoreBlocks = true;
+						return false;
+					}
+				}
+			} else {
+				return true;
+			}
+		} catch (IOException ioex) {
+			throw new RuntimeException("Error (de)serializing record in block resettable iterator.", ioex);
+		}
+	}
+}

flink-runtime/src/main/java/org/apache/flink/runtime/operators/sort/NonReusingMergeMatchIterator.java

+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.flink.runtime.operators.sort;
+
+import org.apache.flink.api.common.functions.FlatJoinFunction;
+import org.apache.flink.api.common.typeutils.TypeComparator;
+import org.apache.flink.api.common.typeutils.TypePairComparator;
+import org.apache.flink.api.common.typeutils.TypeSerializer;
+import org.apache.flink.core.memory.MemorySegment;
+import org.apache.flink.runtime.io.disk.iomanager.IOManager;
+import org.apache.flink.runtime.jobgraph.tasks.AbstractInvokable;
+import org.apache.flink.runtime.memorymanager.MemoryAllocationException;
+import org.apache.flink.runtime.memorymanager.MemoryManager;
+import org.apache.flink.runtime.operators.resettable.NonReusingBlockResettableIterator;
+import org.apache.flink.runtime.operators.resettable.SpillingResettableIterator;
+import org.apache.flink.runtime.operators.util.JoinTaskIterator;
+import org.apache.flink.runtime.util.NonReusingKeyGroupedIterator;
+import org.apache.flink.util.Collector;
+import org.apache.flink.util.MutableObjectIterator;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.io.IOException;
+import java.util.Iterator;
+import java.util.List;
+
+
+/**
+ * An implementation of the {@link org.apache.flink.runtime.operators.util.JoinTaskIterator} that realizes the
+ * matching through a sort-merge join strategy.
+ */
+public class NonReusingMergeMatchIterator<T1, T2, O> implements JoinTaskIterator<T1, T2, O> {
+
+	/**
+	 * The log used by this iterator to log messages.
+	 */
+	private static final Logger LOG = LoggerFactory.getLogger(NonReusingMergeMatchIterator.class);
+
+	// --------------------------------------------------------------------------------------------
+
+	private TypePairComparator<T1, T2> comp;
+
+	private NonReusingKeyGroupedIterator<T1> iterator1;
+
+	private NonReusingKeyGroupedIterator<T2> iterator2;
+
+	private final TypeSerializer<T1> serializer1;
+
+	private final TypeSerializer<T2> serializer2;
+
+	private final NonReusingBlockResettableIterator<T2> blockIt;				// for N:M cross products with same key
+
+	private final List<MemorySegment> memoryForSpillingIterator;
+
+	private final MemoryManager memoryManager;
+
+	private final IOManager ioManager;
+
+	// --------------------------------------------------------------------------------------------
+
+	public NonReusingMergeMatchIterator(
+			MutableObjectIterator<T1> input1,
+			MutableObjectIterator<T2> input2,
+			TypeSerializer<T1> serializer1, TypeComparator<T1> comparator1,
+			TypeSerializer<T2> serializer2, TypeComparator<T2> comparator2,
+			TypePairComparator<T1, T2> pairComparator,
+			MemoryManager memoryManager,
+			IOManager ioManager,
+			int numMemoryPages,
+			AbstractInvokable parentTask)
+	throws MemoryAllocationException
+	{
+		if (numMemoryPages < 2) {
+			throw new IllegalArgumentException("Merger needs at least 2 memory pages.");
+		}
+
+		this.comp = pairComparator;
+		this.serializer1 = serializer1;
+		this.serializer2 = serializer2;
+
+		this.memoryManager = memoryManager;
+		this.ioManager = ioManager;
+
+		this.iterator1 = new NonReusingKeyGroupedIterator<T1>(input1, this.serializer1, comparator1.duplicate());
+		this.iterator2 = new NonReusingKeyGroupedIterator<T2>(input2, this.serializer2, comparator2.duplicate());
+
+		final int numPagesForSpiller = numMemoryPages > 20 ? 2 : 1;
+		this.blockIt = new NonReusingBlockResettableIterator<T2>(this.memoryManager, this.serializer2,
+			(numMemoryPages - numPagesForSpiller), parentTask);
+		this.memoryForSpillingIterator = memoryManager.allocatePages(parentTask, numPagesForSpiller);
+	}
+
+
+	@Override
+	public void open() throws IOException {}
+
+
+	@Override
+	public void close() {
+		if (this.blockIt != null) {
+			try {
+				this.blockIt.close();
+			}
+			catch (Throwable t) {
+				LOG.error("Error closing block memory iterator: " + t.getMessage(), t);
+			}
+		}
+
+		this.memoryManager.release(this.memoryForSpillingIterator);
+	}
+
+
+	@Override
+	public void abort() {
+		close();
+	}
+
+	/**
+	 * Calls the <code>JoinFunction#match()</code> method for all two key-value pairs that share the same key and come
+	 * from different inputs. The output of the <code>match()</code> method is forwarded.
+	 * <p>
+	 * This method first zig-zags between the two sorted inputs in order to find a common
+	 * key, and then calls the match stub with the cross product of the values.
+	 *
+	 * @throws Exception Forwards all exceptions from the user code and the I/O system.
+	 *
+	 * @see org.apache.flink.runtime.operators.util.JoinTaskIterator#callWithNextKey(org.apache.flink.api.common.functions.FlatJoinFunction, org.apache.flink.util.Collector)
+	 */
+	@Override
+	public boolean callWithNextKey(final FlatJoinFunction<T1, T2, O> matchFunction, final Collector<O> collector)
+	throws Exception
+	{
+		if (!this.iterator1.nextKey() || !this.iterator2.nextKey()) {
+			// consume all remaining keys (hack to prevent remaining inputs during iterations, lets get rid of this soon)
+			while (this.iterator1.nextKey());
+			while (this.iterator2.nextKey());
+			
+			return false;
+		}
+
+		final TypePairComparator<T1, T2> comparator = this.comp;
+		comparator.setReference(this.iterator1.getCurrent());
+		T2 current2 = this.iterator2.getCurrent();
+				
+		// zig zag
+		while (true) {
+			// determine the relation between the (possibly composite) keys
+			final int comp = comparator.compareToReference(current2);
+			
+			if (comp == 0) {
+				break;
+			}
+			
+			if (comp < 0) {
+				if (!this.iterator2.nextKey()) {
+					return false;
+				}
+				current2 = this.iterator2.getCurrent();
+			}
+			else {
+				if (!this.iterator1.nextKey()) {
+					return false;
+				}
+				comparator.setReference(this.iterator1.getCurrent());
+			}
+		}
+		
+		// here, we have a common key! call the match function with the cross product of the
+		// values
+		final NonReusingKeyGroupedIterator<T1>.ValuesIterator values1 = this.iterator1.getValues();
+		final NonReusingKeyGroupedIterator<T2>.ValuesIterator values2 = this.iterator2.getValues();
+		
+		final T1 firstV1 = values1.next();
+		final T2 firstV2 = values2.next();	
+			
+		final boolean v1HasNext = values1.hasNext();
+		final boolean v2HasNext = values2.hasNext();
+
+		// check if one side is already empty
+		// this check could be omitted if we put this in MatchTask.
+		// then we can derive the local strategy (with build side).
+		
+		if (v1HasNext) {
+			if (v2HasNext) {
+				// both sides contain more than one value
+				// TODO: Decide which side to spill and which to block!
+				crossMwithNValues(firstV1, values1, firstV2, values2, matchFunction, collector);
+			} else {
+				crossSecond1withNValues(firstV2, firstV1, values1, matchFunction, collector);
+			}
+		} else {
+			if (v2HasNext) {
+				crossFirst1withNValues(firstV1, firstV2, values2, matchFunction, collector);
+			} else {
+				// both sides contain only one value
+				matchFunction.join(firstV1, firstV2, collector);
+			}
+		}
+		return true;
+	}
+
+	/**
+	 * Crosses a single value from the first input with N values, all sharing a common key.
+	 * Effectively realizes a <i>1:N</i> match (join).
+	 * 
+	 * @param val1 The value form the <i>1</i> side.
+	 * @param firstValN The first of the values from the <i>N</i> side.
+	 * @param valsN Iterator over remaining <i>N</i> side values.
+	 *          
+	 * @throws Exception Forwards all exceptions thrown by the stub.
+	 */
+	private void crossFirst1withNValues(final T1 val1, final T2 firstValN,
+			final Iterator<T2> valsN, final FlatJoinFunction<T1, T2, O> matchFunction, final Collector<O> collector)
+	throws Exception
+	{
+		T1 copy1 = this.serializer1.copy(val1);
+		matchFunction.join(copy1, firstValN, collector);
+		
+		// set copy and match first element
+		boolean more = true;
+		do {
+			final T2 nRec = valsN.next();
+			
+			if (valsN.hasNext()) {
+				copy1 = this.serializer1.copy(val1);
+				matchFunction.join(copy1, nRec, collector);
+			} else {
+				matchFunction.join(val1, nRec, collector);
+				more = false;
+			}
+		}
+		while (more);
+	}
+	
+	/**
+	 * Crosses a single value from the second side with N values, all sharing a common key.
+	 * Effectively realizes a <i>N:1</i> match (join).
+	 * 
+	 * @param val1 The value form the <i>1</i> side.
+	 * @param firstValN The first of the values from the <i>N</i> side.
+	 * @param valsN Iterator over remaining <i>N</i> side values.
+	 *          
+	 * @throws Exception Forwards all exceptions thrown by the stub.
+	 */
+	private void crossSecond1withNValues(T2 val1, T1 firstValN,
+			Iterator<T1> valsN, FlatJoinFunction<T1, T2, O> matchFunction, Collector<O> collector)
+	throws Exception
+	{
+		T2 copy2 = this.serializer2.copy(val1);
+		matchFunction.join(firstValN, copy2, collector);
+		
+		// set copy and match first element
+		boolean more = true;
+		do {
+			final T1 nRec = valsN.next();
+			
+			if (valsN.hasNext()) {
+				copy2 = this.serializer2.copy(val1);
+				matchFunction.join(nRec, copy2, collector);
+			} else {
+				matchFunction.join(nRec, val1, collector);
+				more = false;
+			}
+		}
+		while (more);
+	}
+	
+	/**
+	 * @param firstV1
+	 * @param spillVals
+	 * @param firstV2
+	 * @param blockVals
+	 */
+	private void crossMwithNValues(final T1 firstV1, Iterator<T1> spillVals,
+			final T2 firstV2, final Iterator<T2> blockVals,
+			final FlatJoinFunction<T1, T2, O> matchFunction, final Collector<O> collector)
+	throws Exception
+	{
+		// ==================================================
+		// We have one first (head) element from both inputs (firstV1 and firstV2)
+		// We have an iterator for both inputs.
+		// we make the V1 side the spilling side and the V2 side the blocking side.
+		// In order to get the full cross product without unnecessary spilling, we do the
+		// following:
+		// 1) cross the heads
+		// 2) cross the head of the spilling side against the first block of the blocking side
+		// 3) cross the iterator of the spilling side with the head of the block side
+		// 4) cross the iterator of the spilling side with the first block
+		// ---------------------------------------------------
+		// If the blocking side has more than one block, we really need to make the spilling side fully
+		// resettable. For each further block on the block side, we do:
+		// 5) cross the head of the spilling side with the next block
+		// 6) cross the spilling iterator with the next block.
+		
+		// match the first values first
+		T1 copy1 = this.serializer1.copy(firstV1);
+		T2 blockHeadCopy = this.serializer2.copy(firstV2);
+		T1 spillHeadCopy = null;
+
+
+		// --------------- 1) Cross the heads -------------------
+		matchFunction.join(copy1, firstV2, collector);
+		
+		// for the remaining values, we do a block-nested-loops join
+		SpillingResettableIterator<T1> spillIt = null;
+		
+		try {
+			// create block iterator on the second input
+			this.blockIt.reopen(blockVals);
+			
+			// ------------- 2) cross the head of the spilling side with the first block ------------------
+			while (this.blockIt.hasNext()) {
+				final T2 nextBlockRec = this.blockIt.next();
+				copy1 = this.serializer1.copy(firstV1);
+				matchFunction.join(copy1, nextBlockRec, collector);
+			}
+			this.blockIt.reset();
+			
+			// spilling is required if the blocked input has data beyond the current block.
+			// in that case, create the spilling iterator
+			final Iterator<T1> leftSideIter;
+			final boolean spillingRequired = this.blockIt.hasFurtherInput();
+			if (spillingRequired)
+			{
+				// more data than would fit into one block. we need to wrap the other side in a spilling iterator
+				// create spilling iterator on first input
+				spillIt = new SpillingResettableIterator<T1>(spillVals, this.serializer1,
+						this.memoryManager, this.ioManager, this.memoryForSpillingIterator);
+				leftSideIter = spillIt;
+				spillIt.open();
+				
+				spillHeadCopy = this.serializer1.copy(firstV1);
+			}
+			else {
+				leftSideIter = spillVals;
+			}
+			
+			// cross the values in the v1 iterator against the current block
+			
+			while (leftSideIter.hasNext()) {
+				final T1 nextSpillVal = leftSideIter.next();
+				copy1 = this.serializer1.copy(nextSpillVal);
+				
+				
+				// -------- 3) cross the iterator of the spilling side with the head of the block side --------
+				T2 copy2 = this.serializer2.copy(blockHeadCopy);
+				matchFunction.join(copy1, copy2, collector);
+				
+				// -------- 4) cross the iterator of the spilling side with the first block --------
+				while (this.blockIt.hasNext()) {
+					T2 nextBlockRec = this.blockIt.next();
+					
+					// get instances of key and block value
+					copy1 = this.serializer1.copy(nextSpillVal);
+					matchFunction.join(copy1, nextBlockRec, collector);
+				}
+				// reset block iterator
+				this.blockIt.reset();
+			}
+			
+			// if everything from the block-side fit into a single block, we are done.
+			// note that in this special case, we did not create a spilling iterator at all
+			if (!spillingRequired) {
+				return;
+			}
+			
+			// here we are, because we have more blocks on the block side
+			// loop as long as there are blocks from the blocked input
+			while (this.blockIt.nextBlock())
+			{
+				// rewind the spilling iterator
+				spillIt.reset();
+				
+				// ------------- 5) cross the head of the spilling side with the next block ------------
+				while (this.blockIt.hasNext()) {
+					copy1 = this.serializer1.copy(spillHeadCopy);
+					final T2 nextBlockVal = blockIt.next();
+					matchFunction.join(copy1, nextBlockVal, collector);
+				}
+				this.blockIt.reset();
+				
+				// -------- 6) cross the spilling iterator with the next block. ------------------
+				while (spillIt.hasNext())
+				{
+					// get value from resettable iterator
+					final T1 nextSpillVal = spillIt.next();
+					// cross value with block values
+					while (this.blockIt.hasNext()) {
+						// get instances of key and block value
+						final T2 nextBlockVal = this.blockIt.next();
+						copy1 = this.serializer1.copy(nextSpillVal);
+						matchFunction.join(copy1, nextBlockVal, collector);
+					}
+					
+					// reset block iterator
+					this.blockIt.reset();
+				}
+				// reset v1 iterator
+				spillIt.reset();
+			}
+		}
+		finally {
+			if (spillIt != null) {
+				this.memoryForSpillingIterator.addAll(spillIt.close());
+			}
+		}
+	}
+}

flink-runtime/src/main/java/org/apache/flink/runtime/operators/sort/MergeMatchIterator.java → flink-runtime/src/main/java/org/apache/flink/runtime/operators/sort/ReusingMergeMatchIterator.java

@@ -33,7 +33,7 @@ import org.apache.flink.runtime.io.disk.iomanager.IOManager;
 import org.apache.flink.runtime.jobgraph.tasks.AbstractInvokable;
 import org.apache.flink.runtime.memorymanager.MemoryAllocationException;
 import org.apache.flink.runtime.memorymanager.MemoryManager;
-import org.apache.flink.runtime.operators.resettable.BlockResettableIterator;
+import org.apache.flink.runtime.operators.resettable.NonReusingBlockResettableIterator;
 import org.apache.flink.runtime.operators.resettable.SpillingResettableIterator;
 import org.apache.flink.runtime.operators.util.JoinTaskIterator;
 import org.apache.flink.runtime.util.ReusingKeyGroupedIterator;
@@ -45,12 +45,12 @@ import org.apache.flink.util.MutableObjectIterator;
  * An implementation of the {@link JoinTaskIterator} that realizes the
  * matching through a sort-merge join strategy.
  */
-public class MergeMatchIterator<T1, T2, O> implements JoinTaskIterator<T1, T2, O> {
+public class ReusingMergeMatchIterator<T1, T2, O> implements JoinTaskIterator<T1, T2, O> {
 	
 	/**
 	 * The log used by this iterator to log messages.
 	 */
-	private static final Logger LOG = LoggerFactory.getLogger(MergeMatchIterator.class);
+	private static final Logger LOG = LoggerFactory.getLogger(ReusingMergeMatchIterator.class);
 	
 	// --------------------------------------------------------------------------------------------
 	
@@ -72,7 +72,7 @@ public class MergeMatchIterator<T1, T2, O> implements JoinTaskIterator<T1, T2, O
 	
 	private T2 blockHeadCopy;
 	
-	private final BlockResettableIterator<T2> blockIt;				// for N:M cross products with same key
+	private final NonReusingBlockResettableIterator<T2> blockIt;				// for N:M cross products with same key
 	
 	private final List<MemorySegment> memoryForSpillingIterator;
 	
@@ -82,10 +82,16 @@ public class MergeMatchIterator<T1, T2, O> implements JoinTaskIterator<T1, T2, O
 	
 	// --------------------------------------------------------------------------------------------
 	
-	public MergeMatchIterator(MutableObjectIterator<T1> input1, MutableObjectIterator<T2> input2,
+	public ReusingMergeMatchIterator(
+			MutableObjectIterator<T1> input1,
+			MutableObjectIterator<T2> input2,
 			TypeSerializer<T1> serializer1, TypeComparator<T1> comparator1,
-			TypeSerializer<T2> serializer2, TypeComparator<T2> comparator2, TypePairComparator<T1, T2> pairComparator,
-			MemoryManager memoryManager, IOManager ioManager, int numMemoryPages, AbstractInvokable parentTask)
+			TypeSerializer<T2> serializer2, TypeComparator<T2> comparator2,
+			TypePairComparator<T1, T2> pairComparator,
+			MemoryManager memoryManager,
+			IOManager ioManager,
+			int numMemoryPages,
+			AbstractInvokable parentTask)
 	throws MemoryAllocationException
 	{
 		if (numMemoryPages < 2) {
@@ -108,7 +114,7 @@ public class MergeMatchIterator<T1, T2, O> implements JoinTaskIterator<T1, T2, O
 		this.iterator2 = new ReusingKeyGroupedIterator<T2>(input2, this.serializer2, comparator2.duplicate());
 		
 		final int numPagesForSpiller = numMemoryPages > 20 ? 2 : 1;
-		this.blockIt = new BlockResettableIterator<T2>(this.memoryManager, this.serializer2,
+		this.blockIt = new NonReusingBlockResettableIterator<T2>(this.memoryManager, this.serializer2,
 			(numMemoryPages - numPagesForSpiller), parentTask);
 		this.memoryForSpillingIterator = memoryManager.allocatePages(parentTask, numPagesForSpiller);
 	}

flink-runtime/src/test/java/org/apache/flink/runtime/operators/resettable/BlockResettableIteratorTest.java → flink-runtime/src/test/java/org/apache/flink/runtime/operators/resettable/NonReusingBlockResettableIteratorTest.java

@@ -29,7 +29,6 @@ import org.apache.flink.api.common.typeutils.record.RecordSerializer;
 import org.apache.flink.runtime.jobgraph.tasks.AbstractInvokable;
 import org.apache.flink.runtime.memorymanager.DefaultMemoryManager;
 import org.apache.flink.runtime.memorymanager.MemoryManager;
-import org.apache.flink.runtime.operators.resettable.BlockResettableIterator;
 import org.apache.flink.runtime.operators.testutils.DummyInvokable;
 import org.apache.flink.types.IntValue;
 import org.apache.flink.types.Record;
@@ -38,7 +37,7 @@ import org.junit.Before;
 import org.junit.Test;
 
 
-public class BlockResettableIteratorTest
+public class NonReusingBlockResettableIteratorTest
 {
 	private static final int MEMORY_CAPACITY = 3 * 128 * 1024;
 	
@@ -85,7 +84,7 @@ public class BlockResettableIteratorTest
 	{
 		final AbstractInvokable memOwner = new DummyInvokable();
 		// create the resettable Iterator
-		final BlockResettableIterator<Record> iterator = new BlockResettableIterator<Record>(
+		final NonReusingBlockResettableIterator<Record> iterator = new NonReusingBlockResettableIterator<Record>(
 				this.memman, this.reader, this.serializer, 1, memOwner);
 		// open the iterator
 		iterator.open();
@@ -124,7 +123,7 @@ public class BlockResettableIteratorTest
 	{
 		final AbstractInvokable memOwner = new DummyInvokable();
 		// create the resettable Iterator
-		final BlockResettableIterator<Record> iterator = new BlockResettableIterator<Record>(
+		final NonReusingBlockResettableIterator<Record> iterator = new NonReusingBlockResettableIterator<Record>(
 				this.memman, this.reader, this.serializer, 2, memOwner);
 		// open the iterator
 		iterator.open();
@@ -164,7 +163,7 @@ public class BlockResettableIteratorTest
 	{
 		final AbstractInvokable memOwner = new DummyInvokable();
 		// create the resettable Iterator
-		final BlockResettableIterator<Record> iterator = new BlockResettableIterator<Record>(
+		final NonReusingBlockResettableIterator<Record> iterator = new NonReusingBlockResettableIterator<Record>(
 				this.memman, this.reader, this.serializer, 12, memOwner);
 		// open the iterator
 		iterator.open();

flink-runtime/src/test/java/org/apache/flink/runtime/operators/resettable/ReusingBlockResettableIteratorTest.java

+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+
+package org.apache.flink.runtime.operators.resettable;
+
+import org.apache.flink.api.common.typeutils.TypeSerializer;
+import org.apache.flink.api.common.typeutils.record.RecordSerializer;
+import org.apache.flink.runtime.jobgraph.tasks.AbstractInvokable;
+import org.apache.flink.runtime.memorymanager.DefaultMemoryManager;
+import org.apache.flink.runtime.memorymanager.MemoryManager;
+import org.apache.flink.runtime.operators.testutils.DummyInvokable;
+import org.apache.flink.types.IntValue;
+import org.apache.flink.types.Record;
+import org.junit.After;
+import org.junit.Assert;
+import org.junit.Before;
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.List;
+
+
+public class ReusingBlockResettableIteratorTest
+{
+	private static final int MEMORY_CAPACITY = 3 * 128 * 1024;
+	
+	private static final int NUM_VALUES = 20000;
+	
+	private MemoryManager memman;
+
+	private Iterator<Record> reader;
+
+	private List<Record> objects;
+	
+	private final TypeSerializer<Record> serializer = RecordSerializer.get();
+
+	@Before
+	public void startup() {
+		// set up IO and memory manager
+		this.memman = new DefaultMemoryManager(MEMORY_CAPACITY, 1);
+		
+		// create test objects
+		this.objects = new ArrayList<Record>(20000);
+		for (int i = 0; i < NUM_VALUES; ++i) {
+			this.objects.add(new Record(new IntValue(i)));
+		}
+		
+		// create the reader
+		this.reader = objects.iterator();
+	}
+	
+	@After
+	public void shutdown() {
+		this.objects = null;
+		
+		// check that the memory manager got all segments back
+		if (!this.memman.verifyEmpty()) {
+			Assert.fail("A memory leak has occurred: Not all memory was properly returned to the memory manager.");
+		}
+		
+		this.memman.shutdown();
+		this.memman = null;
+	}
+
+	@Test
+	public void testSerialBlockResettableIterator() throws Exception
+	{
+		final AbstractInvokable memOwner = new DummyInvokable();
+		// create the resettable Iterator
+		final ReusingBlockResettableIterator<Record> iterator = new ReusingBlockResettableIterator<Record>(
+				this.memman, this.reader, this.serializer, 1, memOwner);
+		// open the iterator
+		iterator.open();
+		
+		// now test walking through the iterator
+		int lower = 0;
+		int upper = 0;
+		do {
+			lower = upper;
+			upper = lower;
+			// find the upper bound
+			while (iterator.hasNext()) {
+				Record target = iterator.next();
+				int val = target.getField(0, IntValue.class).getValue();
+				Assert.assertEquals(upper++, val);
+			}
+			// now reset the buffer a few times
+			for (int i = 0; i < 5; ++i) {
+				iterator.reset();
+				int count = 0;
+				while (iterator.hasNext()) {
+					Record target = iterator.next();
+					int val = target.getField(0, IntValue.class).getValue();
+					Assert.assertEquals(lower + (count++), val);
+				}
+				Assert.assertEquals(upper - lower, count);
+			}
+		} while (iterator.nextBlock());
+		Assert.assertEquals(NUM_VALUES, upper);
+		// close the iterator
+		iterator.close();
+	}
+
+	@Test
+	public void testDoubleBufferedBlockResettableIterator() throws Exception
+	{
+		final AbstractInvokable memOwner = new DummyInvokable();
+		// create the resettable Iterator
+		final ReusingBlockResettableIterator<Record> iterator = new ReusingBlockResettableIterator<Record>(
+				this.memman, this.reader, this.serializer, 2, memOwner);
+		// open the iterator
+		iterator.open();
+		
+		// now test walking through the iterator
+		int lower = 0;
+		int upper = 0;
+		do {
+			lower = upper;
+			upper = lower;
+			// find the upper bound
+			while (iterator.hasNext()) {
+				Record target = iterator.next();
+				int val = target.getField(0, IntValue.class).getValue();
+				Assert.assertEquals(upper++, val);
+			}
+			// now reset the buffer a few times
+			for (int i = 0; i < 5; ++i) {
+				iterator.reset();
+				int count = 0;
+				while (iterator.hasNext()) {
+					Record target = iterator.next();
+					int val = target.getField(0, IntValue.class).getValue();
+					Assert.assertEquals(lower + (count++), val);
+				}
+				Assert.assertEquals(upper - lower, count);
+			}
+		} while (iterator.nextBlock());
+		Assert.assertEquals(NUM_VALUES, upper);
+		
+		// close the iterator
+		iterator.close();
+	}
+
+	@Test
+	public void testTwelveFoldBufferedBlockResettableIterator() throws Exception
+	{
+		final AbstractInvokable memOwner = new DummyInvokable();
+		// create the resettable Iterator
+		final ReusingBlockResettableIterator<Record> iterator = new ReusingBlockResettableIterator<Record>(
+				this.memman, this.reader, this.serializer, 12, memOwner);
+		// open the iterator
+		iterator.open();
+		
+		// now test walking through the iterator
+		int lower = 0;
+		int upper = 0;
+		do {
+			lower = upper;
+			upper = lower;
+			// find the upper bound
+			while (iterator.hasNext()) {
+				Record target = iterator.next();
+				int val = target.getField(0, IntValue.class).getValue();
+				Assert.assertEquals(upper++, val);
+			}
+			// now reset the buffer a few times
+			for (int i = 0; i < 5; ++i) {
+				iterator.reset();
+				int count = 0;
+				while (iterator.hasNext()) {
+					Record target = iterator.next();
+					int val = target.getField(0, IntValue.class).getValue();
+					Assert.assertEquals(lower + (count++), val);
+				}
+				Assert.assertEquals(upper - lower, count);
+			}
+		} while (iterator.nextBlock());
+		Assert.assertEquals(NUM_VALUES, upper);
+		
+		// close the iterator
+		iterator.close();
+	}
+
+}

flink-runtime/src/test/java/org/apache/flink/runtime/operators/sort/SortMergeMatchIteratorITCase.java → flink-runtime/src/test/java/org/apache/flink/runtime/operators/sort/NonReusingSortMergeMatchIteratorITCase.java

@@ -37,8 +37,6 @@ import org.apache.flink.runtime.io.disk.iomanager.IOManagerAsync;
 import org.apache.flink.runtime.jobgraph.tasks.AbstractInvokable;
 import org.apache.flink.runtime.memorymanager.DefaultMemoryManager;
 import org.apache.flink.runtime.memorymanager.MemoryManager;
-import org.apache.flink.runtime.operators.sort.MergeIterator;
-import org.apache.flink.runtime.operators.sort.MergeMatchIterator;
 import org.apache.flink.runtime.operators.testutils.DiscardingOutputCollector;
 import org.apache.flink.runtime.operators.testutils.DummyInvokable;
 import org.apache.flink.runtime.operators.testutils.TestData;
@@ -55,7 +53,7 @@ import org.junit.Before;
 import org.junit.Test;
 
 @SuppressWarnings("deprecation")
-public class SortMergeMatchIteratorITCase {
+public class NonReusingSortMergeMatchIteratorITCase {
 	
 	// total memory
 	private static final int MEMORY_SIZE = 1024 * 1024 * 16;
@@ -143,8 +141,8 @@ public class SortMergeMatchIteratorITCase {
 			input2.reset();
 	
 			// compare with iterator values
-			MergeMatchIterator<Record, Record, Record> iterator = 
-				new MergeMatchIterator<Record, Record, Record>(
+			NonReusingMergeMatchIterator<Record, Record, Record> iterator =
+				new NonReusingMergeMatchIterator<Record, Record, Record>(
 					input1, input2, this.serializer1, this.comparator1, this.serializer2, this.comparator2,
 					this.pairComparator, this.memoryManager, this.ioManager, PAGES_FOR_BNLJN, this.parentTask);
 	
@@ -230,8 +228,8 @@ public class SortMergeMatchIteratorITCase {
 			
 			// we create this sort-merge iterator with little memory for the block-nested-loops fall-back to make sure it
 			// needs to spill for the duplicate keys
-			MergeMatchIterator<Record, Record, Record> iterator = 
-				new MergeMatchIterator<Record, Record, Record>(
+			NonReusingMergeMatchIterator<Record, Record, Record> iterator =
+				new NonReusingMergeMatchIterator<Record, Record, Record>(
 					input1, input2, this.serializer1, this.comparator1, this.serializer2, this.comparator2,
 					this.pairComparator, this.memoryManager, this.ioManager, PAGES_FOR_BNLJN, this.parentTask);
 	

flink-runtime/src/test/java/org/apache/flink/runtime/operators/sort/ReusingSortMergeMatchIteratorITCase.java

+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.flink.runtime.operators.sort;
+
+import org.apache.flink.api.common.typeutils.TypeComparator;
+import org.apache.flink.api.common.typeutils.TypePairComparator;
+import org.apache.flink.api.common.typeutils.TypeSerializer;
+import org.apache.flink.api.common.typeutils.record.RecordComparator;
+import org.apache.flink.api.common.typeutils.record.RecordPairComparator;
+import org.apache.flink.api.common.typeutils.record.RecordSerializer;
+import org.apache.flink.api.java.record.functions.JoinFunction;
+import org.apache.flink.runtime.io.disk.iomanager.IOManager;
+import org.apache.flink.runtime.io.disk.iomanager.IOManagerAsync;
+import org.apache.flink.runtime.jobgraph.tasks.AbstractInvokable;
+import org.apache.flink.runtime.memorymanager.DefaultMemoryManager;
+import org.apache.flink.runtime.memorymanager.MemoryManager;
+import org.apache.flink.runtime.operators.testutils.DiscardingOutputCollector;
+import org.apache.flink.runtime.operators.testutils.DummyInvokable;
+import org.apache.flink.runtime.operators.testutils.TestData;
+import org.apache.flink.runtime.operators.testutils.TestData.Generator;
+import org.apache.flink.runtime.operators.testutils.TestData.Generator.KeyMode;
+import org.apache.flink.runtime.operators.testutils.TestData.Generator.ValueMode;
+import org.apache.flink.types.Record;
+import org.apache.flink.types.Value;
+import org.apache.flink.util.Collector;
+import org.apache.flink.util.MutableObjectIterator;
+import org.junit.After;
+import org.junit.Assert;
+import org.junit.Before;
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Map.Entry;
+
+@SuppressWarnings("deprecation")
+public class ReusingSortMergeMatchIteratorITCase {
+
+	// total memory
+	private static final int MEMORY_SIZE = 1024 * 1024 * 16;
+	private static final int PAGES_FOR_BNLJN = 2;
+
+	// the size of the left and right inputs
+	private static final int INPUT_1_SIZE = 20000;
+
+	private static final int INPUT_2_SIZE = 1000;
+
+	// random seeds for the left and right input data generators
+	private static final long SEED1 = 561349061987311L;
+
+	private static final long SEED2 = 231434613412342L;
+
+	// dummy abstract task
+	private final AbstractInvokable parentTask = new DummyInvokable();
+
+	private IOManager ioManager;
+	private MemoryManager memoryManager;
+
+	private TypeSerializer<Record> serializer1;
+	private TypeSerializer<Record> serializer2;
+	private TypeComparator<Record> comparator1;
+	private TypeComparator<Record> comparator2;
+	private TypePairComparator<Record, Record> pairComparator;
+
+
+	@SuppressWarnings("unchecked")
+	@Before
+	public void beforeTest() {
+		this.serializer1 = RecordSerializer.get();
+		this.serializer2 = RecordSerializer.get();
+		this.comparator1 = new RecordComparator(new int[] {0}, new Class[]{TestData.Key.class});
+		this.comparator2 = new RecordComparator(new int[] {0}, new Class[]{TestData.Key.class});
+		this.pairComparator = new RecordPairComparator(new int[] {0}, new int[] {0}, new Class[]{TestData.Key.class});
+
+		this.memoryManager = new DefaultMemoryManager(MEMORY_SIZE, 1);
+		this.ioManager = new IOManagerAsync();
+	}
+
+	@After
+	public void afterTest() {
+		if (this.ioManager != null) {
+			this.ioManager.shutdown();
+			if (!this.ioManager.isProperlyShutDown()) {
+				Assert.fail("I/O manager failed to properly shut down.");
+			}
+			this.ioManager = null;
+		}
+
+		if (this.memoryManager != null) {
+			Assert.assertTrue("Memory Leak: Not all memory has been returned to the memory manager.",
+				this.memoryManager.verifyEmpty());
+			this.memoryManager.shutdown();
+			this.memoryManager = null;
+		}
+	}
+
+
+
+	@Test
+	public void testMerge() {
+		try {
+
+			final Generator generator1 = new Generator(SEED1, 500, 4096, KeyMode.SORTED, ValueMode.RANDOM_LENGTH);
+			final Generator generator2 = new Generator(SEED2, 500, 2048, KeyMode.SORTED, ValueMode.RANDOM_LENGTH);
+
+			final TestData.GeneratorIterator input1 = new TestData.GeneratorIterator(generator1, INPUT_1_SIZE);
+			final TestData.GeneratorIterator input2 = new TestData.GeneratorIterator(generator2, INPUT_2_SIZE);
+
+			// collect expected data
+			final Map<TestData.Key, Collection<Match>> expectedMatchesMap = matchValues(
+				collectData(input1),
+				collectData(input2));
+
+			final JoinFunction matcher = new MatchRemovingMatcher(expectedMatchesMap);
+
+			final Collector<Record> collector = new DiscardingOutputCollector<Record>();
+
+			// reset the generators
+			generator1.reset();
+			generator2.reset();
+			input1.reset();
+			input2.reset();
+
+			// compare with iterator values
+			ReusingMergeMatchIterator<Record, Record, Record> iterator =
+				new ReusingMergeMatchIterator<Record, Record, Record>(
+					input1, input2, this.serializer1, this.comparator1, this.serializer2, this.comparator2,
+					this.pairComparator, this.memoryManager, this.ioManager, PAGES_FOR_BNLJN, this.parentTask);
+
+			iterator.open();
+
+			while (iterator.callWithNextKey(matcher, collector));
+
+			iterator.close();
+
+			// assert that each expected match was seen
+			for (Entry<TestData.Key, Collection<Match>> entry : expectedMatchesMap.entrySet()) {
+				Assert.assertTrue("Collection for key " + entry.getKey() + " is not empty", entry.getValue().isEmpty());
+			}
+		}
+		catch (Exception e) {
+			e.printStackTrace();
+			Assert.fail("An exception occurred during the test: " + e.getMessage());
+		}
+	}
+
+	@Test
+	public void testMergeWithHighNumberOfCommonKeys()
+	{
+		// the size of the left and right inputs
+		final int INPUT_1_SIZE = 200;
+		final int INPUT_2_SIZE = 100;
+
+		final int INPUT_1_DUPLICATES = 10;
+		final int INPUT_2_DUPLICATES = 4000;
+		final int DUPLICATE_KEY = 13;
+
+		try {
+			final Generator generator1 = new Generator(SEED1, 500, 4096, KeyMode.SORTED, ValueMode.RANDOM_LENGTH);
+			final Generator generator2 = new Generator(SEED2, 500, 2048, KeyMode.SORTED, ValueMode.RANDOM_LENGTH);
+			
+			final TestData.GeneratorIterator gen1Iter = new TestData.GeneratorIterator(generator1, INPUT_1_SIZE);
+			final TestData.GeneratorIterator gen2Iter = new TestData.GeneratorIterator(generator2, INPUT_2_SIZE);
+			
+			final TestData.ConstantValueIterator const1Iter = new TestData.ConstantValueIterator(DUPLICATE_KEY, "LEFT String for Duplicate Keys", INPUT_1_DUPLICATES);
+			final TestData.ConstantValueIterator const2Iter = new TestData.ConstantValueIterator(DUPLICATE_KEY, "RIGHT String for Duplicate Keys", INPUT_2_DUPLICATES);
+			
+			final List<MutableObjectIterator<Record>> inList1 = new ArrayList<MutableObjectIterator<Record>>();
+			inList1.add(gen1Iter);
+			inList1.add(const1Iter);
+			
+			final List<MutableObjectIterator<Record>> inList2 = new ArrayList<MutableObjectIterator<Record>>();
+			inList2.add(gen2Iter);
+			inList2.add(const2Iter);
+			
+			MutableObjectIterator<Record> input1 = new MergeIterator<Record>(inList1, serializer1, comparator1.duplicate());
+			MutableObjectIterator<Record> input2 = new MergeIterator<Record>(inList2, serializer2, comparator2.duplicate());
+			
+			// collect expected data
+			final Map<TestData.Key, Collection<Match>> expectedMatchesMap = matchValues(
+				collectData(input1),
+				collectData(input2));
+			
+			// re-create the whole thing for actual processing
+			
+			// reset the generators and iterators
+			generator1.reset();
+			generator2.reset();
+			const1Iter.reset();
+			const2Iter.reset();
+			gen1Iter.reset();
+			gen2Iter.reset();
+			
+			inList1.clear();
+			inList1.add(gen1Iter);
+			inList1.add(const1Iter);
+			
+			inList2.clear();
+			inList2.add(gen2Iter);
+			inList2.add(const2Iter);
+	
+			input1 = new MergeIterator<Record>(inList1, serializer1, comparator1.duplicate());
+			input2 = new MergeIterator<Record>(inList2, serializer2, comparator2.duplicate());
+			
+			final JoinFunction matcher = new MatchRemovingMatcher(expectedMatchesMap);
+			
+			final Collector<Record> collector = new DiscardingOutputCollector<Record>();
+	
+			
+			// we create this sort-merge iterator with little memory for the block-nested-loops fall-back to make sure it
+			// needs to spill for the duplicate keys
+			ReusingMergeMatchIterator<Record, Record, Record> iterator =
+				new ReusingMergeMatchIterator<Record, Record, Record>(
+					input1, input2, this.serializer1, this.comparator1, this.serializer2, this.comparator2,
+					this.pairComparator, this.memoryManager, this.ioManager, PAGES_FOR_BNLJN, this.parentTask);
+	
+			iterator.open();
+			
+			while (iterator.callWithNextKey(matcher, collector));
+			
+			iterator.close();
+	
+			// assert that each expected match was seen
+			for (Entry<TestData.Key, Collection<Match>> entry : expectedMatchesMap.entrySet()) {
+				if (!entry.getValue().isEmpty()) {
+					Assert.fail("Collection for key " + entry.getKey() + " is not empty");
+				}
+			}
+		}
+		catch (Exception e) {
+			e.printStackTrace();
+			Assert.fail("An exception occurred during the test: " + e.getMessage());
+		}
+	}
+	
+	
+	
+	// --------------------------------------------------------------------------------------------
+	//                                    Utilities
+	// --------------------------------------------------------------------------------------------
+
+	private Map<TestData.Key, Collection<Match>> matchValues(
+			Map<TestData.Key, Collection<TestData.Value>> leftMap,
+			Map<TestData.Key, Collection<TestData.Value>> rightMap)
+	{
+		Map<TestData.Key, Collection<Match>> map = new HashMap<TestData.Key, Collection<Match>>();
+
+		for (TestData.Key key : leftMap.keySet()) {
+			Collection<TestData.Value> leftValues = leftMap.get(key);
+			Collection<TestData.Value> rightValues = rightMap.get(key);
+
+			if (rightValues == null) {
+				continue;
+			}
+
+			if (!map.containsKey(key)) {
+				map.put(key, new ArrayList<Match>());
+			}
+
+			Collection<Match> matchedValues = map.get(key);
+
+			for (TestData.Value leftValue : leftValues) {
+				for (TestData.Value rightValue : rightValues) {
+					matchedValues.add(new Match(leftValue, rightValue));
+				}
+			}
+		}
+
+		return map;
+	}
+
+	
+	private Map<TestData.Key, Collection<TestData.Value>> collectData(MutableObjectIterator<Record> iter)
+	throws Exception
+	{
+		Map<TestData.Key, Collection<TestData.Value>> map = new HashMap<TestData.Key, Collection<TestData.Value>>();
+		Record pair = new Record();
+		
+		while ((pair = iter.next(pair)) != null) {
+			TestData.Key key = pair.getField(0, TestData.Key.class);
+			
+			if (!map.containsKey(key)) {
+				map.put(new TestData.Key(key.getKey()), new ArrayList<TestData.Value>());
+			}
+
+			Collection<TestData.Value> values = map.get(key);
+			values.add(new TestData.Value(pair.getField(1, TestData.Value.class).getValue()));
+		}
+
+		return map;
+	}
+
+	/**
+	 * Private class used for storage of the expected matches in a hashmap.
+	 */
+	private static class Match {
+		private final Value left;
+
+		private final Value right;
+
+		public Match(Value left, Value right) {
+			this.left = left;
+			this.right = right;
+		}
+
+		@Override
+		public boolean equals(Object obj) {
+			Match o = (Match) obj;
+			return this.left.equals(o.left) && this.right.equals(o.right);
+		}
+		
+		@Override
+		public int hashCode() {
+			return this.left.hashCode() ^ this.right.hashCode();
+		}
+
+		@Override
+		public String toString() {
+			return left + ", " + right;
+		}
+	}
+	
+	private static final class MatchRemovingMatcher extends JoinFunction {
+		private static final long serialVersionUID = 1L;
+		
+		private final Map<TestData.Key, Collection<Match>> toRemoveFrom;
+		
+		protected MatchRemovingMatcher(Map<TestData.Key, Collection<Match>> map) {
+			this.toRemoveFrom = map;
+		}
+		
+		@Override
+		public void join(Record rec1, Record rec2, Collector<Record> out) throws Exception {
+			TestData.Key key = rec1.getField(0, TestData.Key.class);
+			TestData.Value value1 = rec1.getField(1, TestData.Value.class);
+			TestData.Value value2 = rec2.getField(1, TestData.Value.class);
+			
+			Collection<Match> matches = this.toRemoveFrom.get(key);
+			if (matches == null) {
+				Assert.fail("Match " + key + " - " + value1 + ":" + value2 + " is unexpected.");
+			}
+			
+			boolean contained = matches.remove(new Match(value1, value2));
+			if (!contained) {
+				Assert.fail("Produced match was not contained: " + key + " - " + value1 + ":" + value2);
+			}
+			if (matches.isEmpty()) {
+				this.toRemoveFrom.remove(key);
+			}
+		}
+	}
+}

flink-runtime/src/test/java/org/apache/flink/runtime/operators/util/HashVsSortMiniBenchmark.java

@@ -32,7 +32,7 @@ import org.apache.flink.runtime.memorymanager.DefaultMemoryManager;
 import org.apache.flink.runtime.memorymanager.MemoryManager;
 import org.apache.flink.runtime.operators.hash.ReusingBuildFirstHashMatchIterator;
 import org.apache.flink.runtime.operators.hash.ReusingBuildSecondHashMatchIterator;
-import org.apache.flink.runtime.operators.sort.MergeMatchIterator;
+import org.apache.flink.runtime.operators.sort.ReusingMergeMatchIterator;
 import org.apache.flink.runtime.operators.sort.UnilateralSortMerger;
 import org.apache.flink.runtime.operators.testutils.DiscardingOutputCollector;
 import org.apache.flink.runtime.operators.testutils.DummyInvokable;
@@ -143,8 +143,8 @@ public class HashVsSortMiniBenchmark {
 			final MutableObjectIterator<Record> sortedInput2 = sorter2.getIterator();
 			
 			// compare with iterator values
-			MergeMatchIterator<Record, Record, Record> iterator = 
-				new MergeMatchIterator<Record, Record, Record>(sortedInput1, sortedInput2, 
+			ReusingMergeMatchIterator<Record, Record, Record> iterator =
+				new ReusingMergeMatchIterator<Record, Record, Record>(sortedInput1, sortedInput2,
 						this.serializer1.getSerializer(), this.comparator1, this.serializer2.getSerializer(), this.comparator2, this.pairComparator11,
 						this.memoryManager, this.ioManager, MEMORY_PAGES_FOR_MERGE, this.parentTask);