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From ka...@apache.org
Subject [18/50] [abbrv] hadoop git commit: HADOOP-11828. Implement the Hitchhiker erasure coding algorithm. Contributed by Jack Liu Quan.
Date Mon, 25 Jan 2016 17:25:53 GMT
HADOOP-11828. Implement the Hitchhiker erasure coding algorithm. Contributed by Jack Liu Quan.

Change-Id: If43475ccc2574df60949c947af562722db076251


Project: http://git-wip-us.apache.org/repos/asf/hadoop/repo
Commit: http://git-wip-us.apache.org/repos/asf/hadoop/commit/1bb31fb2
Tree: http://git-wip-us.apache.org/repos/asf/hadoop/tree/1bb31fb2
Diff: http://git-wip-us.apache.org/repos/asf/hadoop/diff/1bb31fb2

Branch: refs/heads/YARN-1011
Commit: 1bb31fb22e6f8e6df8e9ff4e94adf20308b4c743
Parents: 2ac39ca
Author: Zhe Zhang <zhz@apache.org>
Authored: Thu Jan 21 10:30:05 2016 -0800
Committer: Zhe Zhang <zhz@apache.org>
Committed: Thu Jan 21 10:30:05 2016 -0800

----------------------------------------------------------------------
 hadoop-common-project/hadoop-common/CHANGES.txt |   3 +
 .../coder/AbstractErasureDecoder.java           |   2 +-
 .../coder/AbstractHHErasureCodingStep.java      |  49 +++
 .../erasurecode/coder/HHXORErasureDecoder.java  |  95 +++++
 .../coder/HHXORErasureDecodingStep.java         | 349 +++++++++++++++++++
 .../erasurecode/coder/HHXORErasureEncoder.java  |  92 +++++
 .../coder/HHXORErasureEncodingStep.java         | 146 ++++++++
 .../io/erasurecode/coder/util/HHUtil.java       | 216 ++++++++++++
 .../erasurecode/coder/TestErasureCoderBase.java |   4 +-
 .../coder/TestHHErasureCoderBase.java           |  61 ++++
 .../coder/TestHHXORErasureCoder.java            | 120 +++++++
 11 files changed, 1134 insertions(+), 3 deletions(-)
----------------------------------------------------------------------


http://git-wip-us.apache.org/repos/asf/hadoop/blob/1bb31fb2/hadoop-common-project/hadoop-common/CHANGES.txt
----------------------------------------------------------------------
diff --git a/hadoop-common-project/hadoop-common/CHANGES.txt b/hadoop-common-project/hadoop-common/CHANGES.txt
index 19ef66e..e5172d5 100644
--- a/hadoop-common-project/hadoop-common/CHANGES.txt
+++ b/hadoop-common-project/hadoop-common/CHANGES.txt
@@ -262,6 +262,9 @@ Trunk (Unreleased)
     HADOOP-11887. Introduce Intel ISA-L erasure coding library for native
     erasure encoding support (Kai Zheng via Colin P. McCabe)
 
+    HADOOP-11828. Implement the Hitchhiker erasure coding algorithm.
+    (Jack Liuquan via zhz)
+
   BUG FIXES
 
     HADOOP-12617. SPNEGO authentication request to non-default realm gets

http://git-wip-us.apache.org/repos/asf/hadoop/blob/1bb31fb2/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/erasurecode/coder/AbstractErasureDecoder.java
----------------------------------------------------------------------
diff --git a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/erasurecode/coder/AbstractErasureDecoder.java b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/erasurecode/coder/AbstractErasureDecoder.java
index abada3d..d976dd1 100644
--- a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/erasurecode/coder/AbstractErasureDecoder.java
+++ b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/erasurecode/coder/AbstractErasureDecoder.java
@@ -56,7 +56,7 @@ public abstract class AbstractErasureDecoder extends AbstractErasureCoder {
    * We have all the data blocks and parity blocks as input blocks for
    * recovering by default. It's codec specific
    * @param blockGroup
-   * @return
+   * @return input blocks
    */
   protected ECBlock[] getInputBlocks(ECBlockGroup blockGroup) {
     ECBlock[] inputBlocks = new ECBlock[getNumDataUnits() +

http://git-wip-us.apache.org/repos/asf/hadoop/blob/1bb31fb2/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/erasurecode/coder/AbstractHHErasureCodingStep.java
----------------------------------------------------------------------
diff --git a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/erasurecode/coder/AbstractHHErasureCodingStep.java b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/erasurecode/coder/AbstractHHErasureCodingStep.java
new file mode 100644
index 0000000..e577c5d
--- /dev/null
+++ b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/erasurecode/coder/AbstractHHErasureCodingStep.java
@@ -0,0 +1,49 @@
+/**
+ * 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.hadoop.io.erasurecode.coder;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.io.erasurecode.ECBlock;
+
+/**
+ * Abstract class for Hitchhiker common facilities shared by
+ * {@link HHXORErasureEncodingStep}and {@link HHXORErasureDecodingStep}.
+ *
+ * It implements {@link AbstractErasureCodingStep}.
+ */
+@InterfaceAudience.Private
+public abstract class AbstractHHErasureCodingStep
+        extends AbstractErasureCodingStep {
+
+  private static final int SUB_PACKET_SIZE = 2;
+
+  /**
+   * Constructor given input blocks and output blocks.
+   *
+   * @param inputBlocks
+   * @param outputBlocks
+   */
+  public AbstractHHErasureCodingStep(ECBlock[] inputBlocks,
+                                     ECBlock[] outputBlocks) {
+    super(inputBlocks, outputBlocks);
+  }
+
+  protected int getSubPacketSize() {
+    return SUB_PACKET_SIZE;
+  }
+}

http://git-wip-us.apache.org/repos/asf/hadoop/blob/1bb31fb2/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/erasurecode/coder/HHXORErasureDecoder.java
----------------------------------------------------------------------
diff --git a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/erasurecode/coder/HHXORErasureDecoder.java b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/erasurecode/coder/HHXORErasureDecoder.java
new file mode 100644
index 0000000..ac4df16
--- /dev/null
+++ b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/erasurecode/coder/HHXORErasureDecoder.java
@@ -0,0 +1,95 @@
+/**
+ * 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.hadoop.io.erasurecode.coder;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.io.erasurecode.CodecUtil;
+import org.apache.hadoop.io.erasurecode.ECBlock;
+import org.apache.hadoop.io.erasurecode.ECBlockGroup;
+import org.apache.hadoop.io.erasurecode.ECSchema;
+import org.apache.hadoop.io.erasurecode.rawcoder.*;
+
+/**
+ * Hitchhiker is a new erasure coding algorithm developed as a research project
+ * at UC Berkeley by Rashmi Vinayak.
+ * It has been shown to reduce network traffic and disk I/O by 25%-45% during
+ * data reconstruction while retaining the same storage capacity and failure
+ * tolerance capability of RS codes.
+ * The Hitchhiker algorithm is described in K.V.Rashmi, et al.,
+ * "A "Hitchhiker's" Guide to Fast and Efficient Data Reconstruction in
+ * Erasure-coded Data Centers", in ACM SIGCOMM 2014.
+ * This is Hitchhiker-XOR erasure decoder that decodes a block group.
+ */
+@InterfaceAudience.Private
+public class HHXORErasureDecoder extends AbstractErasureDecoder {
+  private RawErasureDecoder rsRawDecoder;
+  private RawErasureEncoder xorRawEncoder;
+
+  public HHXORErasureDecoder(int numDataUnits, int numParityUnits) {
+    super(numDataUnits, numParityUnits);
+  }
+
+  public HHXORErasureDecoder(ECSchema schema) {
+    super(schema);
+  }
+
+  @Override
+  protected ErasureCodingStep prepareDecodingStep(
+          final ECBlockGroup blockGroup) {
+
+    RawErasureDecoder rawDecoder;
+    RawErasureEncoder rawEncoder;
+
+    ECBlock[] inputBlocks = getInputBlocks(blockGroup);
+    ECBlock[] outputBlocks = getOutputBlocks(blockGroup);
+
+    rawDecoder = checkCreateRSRawDecoder();
+    rawEncoder = checkCreateXorRawEncoder();
+
+    return new HHXORErasureDecodingStep(inputBlocks,
+            getErasedIndexes(inputBlocks), outputBlocks, rawDecoder,
+            rawEncoder);
+  }
+
+  private RawErasureDecoder checkCreateRSRawDecoder() {
+    if (rsRawDecoder == null) {
+      rsRawDecoder = CodecUtil.createRSRawDecoder(getConf(),
+              getNumDataUnits(), getNumParityUnits());
+    }
+    return rsRawDecoder;
+  }
+
+  private RawErasureEncoder checkCreateXorRawEncoder() {
+    if (xorRawEncoder == null) {
+      xorRawEncoder = CodecUtil.createXORRawEncoder(getConf(),
+              getNumDataUnits(), getNumParityUnits());
+      xorRawEncoder.setCoderOption(CoderOption.ALLOW_CHANGE_INPUTS, false);
+    }
+    return xorRawEncoder;
+  }
+
+  @Override
+  public void release() {
+    if (rsRawDecoder != null) {
+      rsRawDecoder.release();
+    }
+    if (xorRawEncoder != null) {
+      xorRawEncoder.release();
+    }
+  }
+}

http://git-wip-us.apache.org/repos/asf/hadoop/blob/1bb31fb2/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/erasurecode/coder/HHXORErasureDecodingStep.java
----------------------------------------------------------------------
diff --git a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/erasurecode/coder/HHXORErasureDecodingStep.java b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/erasurecode/coder/HHXORErasureDecodingStep.java
new file mode 100644
index 0000000..6c81836
--- /dev/null
+++ b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/erasurecode/coder/HHXORErasureDecodingStep.java
@@ -0,0 +1,349 @@
+/**
+ * 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.hadoop.io.erasurecode.coder;
+
+import java.nio.ByteBuffer;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.io.erasurecode.ECBlock;
+import org.apache.hadoop.io.erasurecode.ECChunk;
+import org.apache.hadoop.io.erasurecode.coder.util.HHUtil;
+import org.apache.hadoop.io.erasurecode.rawcoder.RawErasureDecoder;
+import org.apache.hadoop.io.erasurecode.rawcoder.RawErasureEncoder;
+
+/**
+ * Hitchhiker-XOR Erasure decoding step, a wrapper of all the necessary
+ * information to perform a decoding step involved in the whole process of
+ * decoding a block group.
+ */
+@InterfaceAudience.Private
+public class HHXORErasureDecodingStep extends AbstractHHErasureCodingStep {
+  private int pbIndex;
+  private int[] piggyBackIndex;
+  private int[] piggyBackFullIndex;
+  private int[] erasedIndexes;
+  private RawErasureDecoder rsRawDecoder;
+  private RawErasureEncoder xorRawEncoder;
+
+  /**
+   * The constructor with all the necessary info.
+   * @param inputBlocks
+   * @param erasedIndexes the indexes of erased blocks in inputBlocks array
+   * @param outputBlocks
+   * @param rawDecoder underlying RS decoder for hitchhiker decoding
+   * @param rawEncoder underlying XOR encoder for hitchhiker decoding
+   */
+  public HHXORErasureDecodingStep(ECBlock[] inputBlocks, int[] erasedIndexes,
+      ECBlock[] outputBlocks, RawErasureDecoder rawDecoder,
+      RawErasureEncoder rawEncoder) {
+    super(inputBlocks, outputBlocks);
+    this.pbIndex = rawDecoder.getNumParityUnits() - 1;
+    this.erasedIndexes = erasedIndexes;
+    this.rsRawDecoder = rawDecoder;
+    this.xorRawEncoder = rawEncoder;
+
+    this.piggyBackIndex = HHUtil.initPiggyBackIndexWithoutPBVec(
+        rawDecoder.getNumDataUnits(), rawDecoder.getNumParityUnits());
+    this.piggyBackFullIndex = HHUtil.initPiggyBackFullIndexVec(
+        rawDecoder.getNumDataUnits(), piggyBackIndex);
+  }
+
+  @Override
+  public void performCoding(ECChunk[] inputChunks, ECChunk[] outputChunks) {
+    if (erasedIndexes.length == 0) {
+      return;
+    }
+
+    ByteBuffer[] inputBuffers = ECChunk.toBuffers(inputChunks);
+    ByteBuffer[] outputBuffers = ECChunk.toBuffers(outputChunks);
+    performCoding(inputBuffers, outputBuffers);
+  }
+
+  private void performCoding(ByteBuffer[] inputs, ByteBuffer[] outputs) {
+    final int numDataUnits = rsRawDecoder.getNumDataUnits();
+    final int numParityUnits = rsRawDecoder.getNumParityUnits();
+    final int numTotalUnits = numDataUnits + numParityUnits;
+    final int subPacketSize = getSubPacketSize();
+
+    ByteBuffer fisrtValidInput = HHUtil.findFirstValidInput(inputs);
+    final int bufSize = fisrtValidInput.remaining();
+
+    if (inputs.length != numTotalUnits * getSubPacketSize()) {
+      throw new IllegalArgumentException("Invalid inputs length");
+    }
+
+    if (outputs.length != erasedIndexes.length * getSubPacketSize()) {
+      throw new IllegalArgumentException("Invalid outputs length");
+    }
+
+    // notes:inputs length = numDataUnits * subPacketizationSize
+    // first numDataUnits length is first sub-stripe,
+    // second numDataUnits length is second sub-stripe
+    ByteBuffer[][] newIn = new ByteBuffer[subPacketSize][numTotalUnits];
+    for (int i = 0; i < subPacketSize; ++i) {
+      for (int j = 0; j < numTotalUnits; ++j) {
+        newIn[i][j] = inputs[i * numTotalUnits + j];
+      }
+    }
+
+    ByteBuffer[][] newOut = new ByteBuffer[subPacketSize][erasedIndexes.length];
+    for (int i = 0; i < subPacketSize; ++i) {
+      for (int j = 0; j < erasedIndexes.length; ++j) {
+        newOut[i][j] = outputs[i * erasedIndexes.length + j];
+      }
+    }
+
+    if (erasedIndexes.length == 1 && erasedIndexes[0] < numDataUnits) {
+      // Only reconstruct one data unit missing
+      doDecodeSingle(newIn, newOut, erasedIndexes[0], bufSize,
+              fisrtValidInput.isDirect());
+    } else {
+      doDecodeMultiAndParity(newIn, newOut, erasedIndexes, bufSize);
+    }
+  }
+
+  private void doDecodeSingle(ByteBuffer[][] inputs, ByteBuffer[][] outputs,
+                              int erasedLocationToFix, int bufSize,
+                              boolean isDirect) {
+    final int numDataUnits = rsRawDecoder.getNumDataUnits();
+    final int numParityUnits = rsRawDecoder.getNumParityUnits();
+    final int subPacketSize = getSubPacketSize();
+
+    int[][] inputPositions = new int[subPacketSize][inputs[0].length];
+    for (int i = 0; i < subPacketSize; ++i) {
+      for (int j = 0; j < inputs[i].length; ++j) {
+        if (inputs[i][j] != null) {
+          inputPositions[i][j] = inputs[i][j].position();
+        }
+      }
+    }
+
+    ByteBuffer[] tempInputs = new ByteBuffer[numDataUnits + numParityUnits];
+    for (int i = 0; i < tempInputs.length; ++i) {
+      tempInputs[i] = inputs[1][i];
+    }
+
+    ByteBuffer[][] tmpOutputs = new ByteBuffer[subPacketSize][numParityUnits];
+    for (int i = 0; i < getSubPacketSize(); ++i) {
+      for (int j = 0; j < erasedIndexes.length; ++j) {
+        tmpOutputs[i][j] = outputs[i][j];
+      }
+
+      for (int m = erasedIndexes.length; m < numParityUnits; ++m) {
+        tmpOutputs[i][m] = HHUtil.allocateByteBuffer(isDirect, bufSize);
+      }
+    }
+
+    // First consider the second subPacket
+    int[] erasedLocation = new int[numParityUnits];
+    erasedLocation[0] = erasedLocationToFix;
+
+    // assign the erased locations based on the locations not read for
+    // second subPacket but from decoding
+    for (int i = 1; i < numParityUnits; i++) {
+      erasedLocation[i] = numDataUnits + i;
+      tempInputs[numDataUnits + i] = null;
+    }
+
+    rsRawDecoder.decode(tempInputs, erasedLocation, tmpOutputs[1]);
+
+    int piggyBackParityIndex = piggyBackFullIndex[erasedLocationToFix];
+    ByteBuffer piggyBack = HHUtil.getPiggyBackForDecode(inputs, tmpOutputs,
+            piggyBackParityIndex, numDataUnits, numParityUnits, pbIndex);
+
+    // Second consider the first subPacket.
+    // get the value of the piggyback associated with the erased location
+    if (isDirect) {
+      // decode the erased value in the first subPacket by using the piggyback
+      int idxToWrite = 0;
+      doDecodeByPiggyBack(inputs[0], tmpOutputs[0][idxToWrite], piggyBack,
+              erasedLocationToFix);
+    } else {
+      ByteBuffer buffer;
+      byte[][][] newInputs = new byte[getSubPacketSize()][inputs[0].length][];
+      int[][] inputOffsets = new int[getSubPacketSize()][inputs[0].length];
+      byte[][][] newOutputs = new byte[getSubPacketSize()][numParityUnits][];
+      int[][] outOffsets = new int[getSubPacketSize()][numParityUnits];
+
+      for (int i = 0; i < getSubPacketSize(); ++i) {
+        for (int j = 0; j < inputs[0].length; ++j) {
+          buffer = inputs[i][j];
+          if (buffer != null) {
+            inputOffsets[i][j] = buffer.arrayOffset() + buffer.position();
+            newInputs[i][j] = buffer.array();
+          }
+        }
+      }
+
+      for (int i = 0; i < getSubPacketSize(); ++i) {
+        for (int j = 0; j < numParityUnits; ++j) {
+          buffer = tmpOutputs[i][j];
+          if (buffer != null) {
+            outOffsets[i][j] = buffer.arrayOffset() + buffer.position();
+            newOutputs[i][j] = buffer.array();
+          }
+        }
+      }
+
+      byte[] newPiggyBack = piggyBack.array();
+
+      // decode the erased value in the first subPacket by using the piggyback
+      int idxToWrite = 0;
+      doDecodeByPiggyBack(newInputs[0], inputOffsets[0],
+              newOutputs[0][idxToWrite], outOffsets[0][idxToWrite],
+              newPiggyBack, erasedLocationToFix, bufSize);
+    }
+
+    for (int i = 0; i < subPacketSize; ++i) {
+      for (int j = 0; j < inputs[i].length; ++j) {
+        if (inputs[i][j] != null) {
+          inputs[i][j].position(inputPositions[i][j] + bufSize);
+        }
+      }
+    }
+  }
+
+  private void doDecodeByPiggyBack(ByteBuffer[] inputs,
+                                   ByteBuffer outputs,
+                                   ByteBuffer piggyBack,
+                                   int erasedLocationToFix) {
+    final int thisPiggyBackSetIdx = piggyBackFullIndex[erasedLocationToFix];
+    final int startIndex = piggyBackIndex[thisPiggyBackSetIdx - 1];
+    final int endIndex = piggyBackIndex[thisPiggyBackSetIdx];
+
+    // recover first sub-stripe data by XOR piggyback
+    int bufSize = piggyBack.remaining();
+    for (int i = piggyBack.position();
+         i < piggyBack.position() + bufSize; i++) {
+      for (int j = startIndex; j < endIndex; j++) {
+        if (inputs[j] != null) {
+          piggyBack.put(i, (byte)
+                  (piggyBack.get(i) ^ inputs[j].get(inputs[j].position() + i)));
+        }
+      }
+      outputs.put(outputs.position() + i, piggyBack.get(i));
+    }
+  }
+
+  private void doDecodeByPiggyBack(byte[][] inputs, int[] inputOffsets,
+                                   byte[] outputs, int outOffset,
+                                   byte[] piggyBack, int erasedLocationToFix,
+                                   int bufSize) {
+    final int thisPiggyBackSetIdx = piggyBackFullIndex[erasedLocationToFix];
+    final int startIndex = piggyBackIndex[thisPiggyBackSetIdx - 1];
+    final int endIndex = piggyBackIndex[thisPiggyBackSetIdx];
+
+    // recover first sub-stripe data by XOR piggyback
+    for (int i = 0; i < bufSize; i++) {
+      for (int j = startIndex; j < endIndex; j++) {
+        if (inputs[j] != null) {
+          piggyBack[i] = (byte) (piggyBack[i] ^ inputs[j][i + inputOffsets[j]]);
+        }
+      }
+      outputs[i + outOffset] = piggyBack[i];
+    }
+  }
+
+  private void doDecodeMultiAndParity(ByteBuffer[][] inputs,
+                                      ByteBuffer[][] outputs,
+                                      int[] erasedLocationToFix, int bufSize) {
+    final int numDataUnits = rsRawDecoder.getNumDataUnits();
+    final int numParityUnits = rsRawDecoder.getNumParityUnits();
+    final int numTotalUnits = numDataUnits + numParityUnits;
+    int[] parityToFixFlag = new int[numTotalUnits];
+
+    for (int i = 0; i < erasedLocationToFix.length; ++i) {
+      if (erasedLocationToFix[i] >= numDataUnits) {
+        parityToFixFlag[erasedLocationToFix[i]] = 1;
+      }
+    }
+
+    int[] inputPositions = new int[inputs[0].length];
+    for (int i = 0; i < inputPositions.length; i++) {
+      if (inputs[0][i] != null) {
+        inputPositions[i] = inputs[0][i].position();
+      }
+    }
+
+    // decoded first sub-stripe
+    rsRawDecoder.decode(inputs[0], erasedLocationToFix, outputs[0]);
+
+    for (int i = 0; i < inputs[0].length; i++) {
+      if (inputs[0][i] != null) {
+        // dataLen bytes consumed
+        inputs[0][i].position(inputPositions[i]);
+      }
+    }
+
+    ByteBuffer[] tempInput = new ByteBuffer[numDataUnits];
+    for (int i = 0; i < numDataUnits; ++i) {
+      tempInput[i] = inputs[0][i];
+//
+//      if (!isDirect && tempInput[i] != null) {
+//        tempInput[i].position(tempInput[i].position() - bufSize);
+//      }
+    }
+
+    for (int i = 0; i < erasedLocationToFix.length; ++i) {
+      if (erasedLocationToFix[i] < numDataUnits) {
+        tempInput[erasedLocationToFix[i]] = outputs[0][i];
+      }
+    }
+
+    ByteBuffer[] piggyBack = HHUtil.getPiggyBacksFromInput(tempInput,
+            piggyBackIndex, numParityUnits, 0, xorRawEncoder);
+
+    for (int j = numDataUnits + 1; j < numTotalUnits; ++j) {
+      if (parityToFixFlag[j] == 0 && inputs[1][j] != null) {
+        // f(b) + f(a1,a2,a3....)
+        for (int k = inputs[1][j].position(),
+             m = piggyBack[j - numDataUnits - 1].position();
+             k < inputs[1][j].limit(); ++k, ++m) {
+          inputs[1][j].put(k, (byte)
+                  (inputs[1][j].get(k) ^
+                          piggyBack[j - numDataUnits - 1].get(m)));
+        }
+      }
+    }
+
+    // decoded second sub-stripe
+    rsRawDecoder.decode(inputs[1], erasedLocationToFix, outputs[1]);
+
+    // parity index = 0, the data have no piggyBack
+    for (int j = 0; j < erasedLocationToFix.length; ++j) {
+      if (erasedLocationToFix[j] < numTotalUnits
+              && erasedLocationToFix[j] > numDataUnits) {
+        int parityIndex = erasedLocationToFix[j] - numDataUnits - 1;
+        for (int k = outputs[1][j].position(),
+             m = piggyBack[parityIndex].position();
+             k < outputs[1][j].limit(); ++k, ++m) {
+          outputs[1][j].put(k, (byte)
+                  (outputs[1][j].get(k) ^ piggyBack[parityIndex].get(m)));
+        }
+      }
+    }
+
+    for (int i = 0; i < inputs[0].length; i++) {
+      if (inputs[0][i] != null) {
+        // dataLen bytes consumed
+        inputs[0][i].position(inputPositions[i] + bufSize);
+      }
+    }
+  }
+
+}

http://git-wip-us.apache.org/repos/asf/hadoop/blob/1bb31fb2/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/erasurecode/coder/HHXORErasureEncoder.java
----------------------------------------------------------------------
diff --git a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/erasurecode/coder/HHXORErasureEncoder.java b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/erasurecode/coder/HHXORErasureEncoder.java
new file mode 100644
index 0000000..f30572f
--- /dev/null
+++ b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/erasurecode/coder/HHXORErasureEncoder.java
@@ -0,0 +1,92 @@
+/**
+ * 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.hadoop.io.erasurecode.coder;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.io.erasurecode.CodecUtil;
+import org.apache.hadoop.io.erasurecode.ECBlock;
+import org.apache.hadoop.io.erasurecode.ECBlockGroup;
+import org.apache.hadoop.io.erasurecode.ECSchema;
+import org.apache.hadoop.io.erasurecode.rawcoder.CoderOption;
+import org.apache.hadoop.io.erasurecode.rawcoder.RawErasureEncoder;
+
+/**
+ * Hitchhiker is a new erasure coding algorithm developed as a research project
+ * at UC Berkeley by Rashmi Vinayak.
+ * It has been shown to reduce network traffic and disk I/O by 25%-45% during
+ * data reconstruction while retaining the same storage capacity and failure
+ * tolerance capability of RS codes.
+ * The Hitchhiker algorithm is described in K.V.Rashmi, et al.,
+ * "A "Hitchhiker's" Guide to Fast and Efficient Data Reconstruction in
+ * Erasure-coded Data Centers", in ACM SIGCOMM 2014.
+ * This is Hitchhiker-XOR erasure encoder that encodes a block group.
+ */
+@InterfaceAudience.Private
+public class HHXORErasureEncoder extends AbstractErasureEncoder {
+  private RawErasureEncoder rsRawEncoder;
+  private RawErasureEncoder xorRawEncoder;
+
+  public HHXORErasureEncoder(int numDataUnits, int numParityUnits) {
+    super(numDataUnits, numParityUnits);
+  }
+
+  public HHXORErasureEncoder(ECSchema schema) {
+    super(schema);
+  }
+
+  @Override
+  protected ErasureCodingStep prepareEncodingStep(
+          final ECBlockGroup blockGroup) {
+
+    RawErasureEncoder rsRawEncoderTmp = checkCreateRSRawEncoder();
+    RawErasureEncoder xorRawEncoderTmp = checkCreateXorRawEncoder();
+
+    ECBlock[] inputBlocks = getInputBlocks(blockGroup);
+
+    return new HHXORErasureEncodingStep(inputBlocks,
+            getOutputBlocks(blockGroup), rsRawEncoderTmp, xorRawEncoderTmp);
+  }
+
+  private RawErasureEncoder checkCreateRSRawEncoder() {
+    if (rsRawEncoder == null) {
+      rsRawEncoder = CodecUtil.createRSRawEncoder(getConf(),
+              getNumDataUnits(), getNumParityUnits());
+    }
+    return rsRawEncoder;
+  }
+
+  private RawErasureEncoder checkCreateXorRawEncoder() {
+    if (xorRawEncoder == null) {
+      xorRawEncoder = CodecUtil.createXORRawEncoder(getConf(),
+              getNumDataUnits(), getNumParityUnits());
+      xorRawEncoder.setCoderOption(CoderOption.ALLOW_CHANGE_INPUTS, false);
+    }
+    return xorRawEncoder;
+  }
+
+  @Override
+  public void release() {
+    if (rsRawEncoder != null) {
+      rsRawEncoder.release();
+    }
+    if (xorRawEncoder != null) {
+      xorRawEncoder.release();
+    }
+  }
+
+}

http://git-wip-us.apache.org/repos/asf/hadoop/blob/1bb31fb2/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/erasurecode/coder/HHXORErasureEncodingStep.java
----------------------------------------------------------------------
diff --git a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/erasurecode/coder/HHXORErasureEncodingStep.java b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/erasurecode/coder/HHXORErasureEncodingStep.java
new file mode 100644
index 0000000..f83ee26
--- /dev/null
+++ b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/erasurecode/coder/HHXORErasureEncodingStep.java
@@ -0,0 +1,146 @@
+/**
+ * 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.hadoop.io.erasurecode.coder;
+
+import java.nio.ByteBuffer;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.io.erasurecode.ECBlock;
+import org.apache.hadoop.io.erasurecode.ECChunk;
+import org.apache.hadoop.io.erasurecode.coder.util.HHUtil;
+import org.apache.hadoop.io.erasurecode.rawcoder.RawErasureEncoder;
+
+/**
+ * Hitchhiker-XOR Erasure encoding step, a wrapper of all the necessary
+ * information to perform an encoding step involved in the whole process of
+ * encoding a block group.
+ */
+@InterfaceAudience.Private
+public class HHXORErasureEncodingStep extends AbstractHHErasureCodingStep {
+  private int[] piggyBackIndex;
+  private RawErasureEncoder rsRawEncoder;
+  private RawErasureEncoder xorRawEncoder;
+
+  /**
+   * The constructor with all the necessary info.
+   *
+   * @param inputBlocks
+   * @param outputBlocks
+   * @param rsRawEncoder  underlying RS encoder for hitchhiker encoding
+   * @param xorRawEncoder underlying XOR encoder for hitchhiker encoding
+   */
+  public HHXORErasureEncodingStep(ECBlock[] inputBlocks, ECBlock[] outputBlocks,
+                                  RawErasureEncoder rsRawEncoder,
+                                  RawErasureEncoder xorRawEncoder) {
+    super(inputBlocks, outputBlocks);
+
+    this.rsRawEncoder = rsRawEncoder;
+    this.xorRawEncoder = xorRawEncoder;
+    piggyBackIndex = HHUtil.initPiggyBackIndexWithoutPBVec(
+            rsRawEncoder.getNumDataUnits(), rsRawEncoder.getNumParityUnits());
+  }
+
+  @Override
+  public void performCoding(ECChunk[] inputChunks, ECChunk[] outputChunks) {
+    ByteBuffer[] inputBuffers = ECChunk.toBuffers(inputChunks);
+    ByteBuffer[] outputBuffers = ECChunk.toBuffers(outputChunks);
+    performCoding(inputBuffers, outputBuffers);
+  }
+
+  private void performCoding(ByteBuffer[] inputs, ByteBuffer[] outputs) {
+    final int numDataUnits = this.rsRawEncoder.getNumDataUnits();
+    final int numParityUnits = this.rsRawEncoder.getNumParityUnits();
+    final int subSPacketSize = getSubPacketSize();
+
+    // inputs length = numDataUnits * subPacketSize
+    if (inputs.length != numDataUnits * subSPacketSize) {
+      throw new IllegalArgumentException("Invalid inputs length");
+    }
+
+    if (outputs.length != numParityUnits * subSPacketSize) {
+      throw new IllegalArgumentException("Invalid outputs length");
+    }
+
+    // first numDataUnits length is first sub-stripe,
+    // second numDataUnits length is second sub-stripe
+    ByteBuffer[][] hhInputs = new ByteBuffer[subSPacketSize][numDataUnits];
+    for (int i = 0; i < subSPacketSize; ++i) {
+      for (int j = 0; j < numDataUnits; ++j) {
+        hhInputs[i][j] = inputs[i * numDataUnits + j];
+      }
+    }
+
+    ByteBuffer[][] hhOutputs = new ByteBuffer[subSPacketSize][numParityUnits];
+    for (int i = 0; i < subSPacketSize; ++i) {
+      for (int j = 0; j < numParityUnits; ++j) {
+        hhOutputs[i][j] = outputs[i * numParityUnits + j];
+      }
+    }
+
+    doEncode(hhInputs, hhOutputs);
+  }
+
+  private void doEncode(ByteBuffer[][] inputs, ByteBuffer[][] outputs) {
+    final int numParityUnits = this.rsRawEncoder.getNumParityUnits();
+
+    // calc piggyBacks using first sub-packet
+    ByteBuffer[] piggyBacks = HHUtil.getPiggyBacksFromInput(inputs[0],
+            piggyBackIndex, numParityUnits, 0, xorRawEncoder);
+
+    // Step1: RS encode each byte-stripe of sub-packets
+    for (int i = 0; i < getSubPacketSize(); ++i) {
+      rsRawEncoder.encode(inputs[i], outputs[i]);
+    }
+
+    // Step2: Adding piggybacks to the parities
+    // Only second sub-packet is added with a piggyback.
+    encodeWithPiggyBacks(piggyBacks, outputs, numParityUnits,
+            inputs[0][0].isDirect());
+  }
+
+  private void encodeWithPiggyBacks(ByteBuffer[] piggyBacks,
+                                    ByteBuffer[][] outputs,
+                                    int numParityUnits,
+                                    boolean bIsDirect) {
+    if (!bIsDirect) {
+      for (int i = 0; i < numParityUnits - 1; i++) {
+        int parityIndex = i + 1;
+        int bufSize = piggyBacks[i].remaining();
+        byte[] newOut = outputs[1][parityIndex].array();
+        int offset = outputs[1][parityIndex].arrayOffset()
+                + outputs[1][parityIndex].position();
+
+        for (int k = offset, j = 0; j < bufSize; k++, j++) {
+          newOut[k] = (byte) (newOut[k] ^ piggyBacks[i].get(j));
+        }
+      }
+      return;
+    }
+
+    for (int i = 0; i < numParityUnits - 1; i++) {
+      int parityIndex = i + 1;
+      for (int k = piggyBacks[i].position(),
+           m = outputs[1][parityIndex].position();
+           k < piggyBacks[i].limit(); k++, m++) {
+        outputs[1][parityIndex].put(m,
+                (byte) (outputs[1][parityIndex].get(m) ^ piggyBacks[i].get(k)));
+      }
+    }
+  }
+
+}

http://git-wip-us.apache.org/repos/asf/hadoop/blob/1bb31fb2/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/erasurecode/coder/util/HHUtil.java
----------------------------------------------------------------------
diff --git a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/erasurecode/coder/util/HHUtil.java b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/erasurecode/coder/util/HHUtil.java
new file mode 100644
index 0000000..cfb567e3
--- /dev/null
+++ b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/erasurecode/coder/util/HHUtil.java
@@ -0,0 +1,216 @@
+/**
+ * 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.hadoop.io.erasurecode.coder.util;
+
+import java.nio.ByteBuffer;
+import org.apache.hadoop.HadoopIllegalArgumentException;
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.io.erasurecode.rawcoder.RawErasureEncoder;
+import org.apache.hadoop.io.erasurecode.rawcoder.util.RSUtil;
+
+/**
+ * Some utilities for Hitchhiker coding.
+ */
+@InterfaceAudience.Private
+public final class HHUtil {
+  private HHUtil() {
+    // No called
+  }
+
+  public static int[] initPiggyBackIndexWithoutPBVec(int numDataUnits,
+                                                     int numParityUnits) {
+    final int piggyBackSize = numDataUnits / (numParityUnits - 1);
+    int[] piggyBackIndex = new int[numParityUnits];
+
+    for (int i = 0; i < numDataUnits; ++i) {
+      if ((i % piggyBackSize) == 0) {
+        piggyBackIndex[i / piggyBackSize] = i;
+      }
+    }
+
+    piggyBackIndex[numParityUnits - 1] = numDataUnits;
+    return piggyBackIndex;
+  }
+
+  public static int[] initPiggyBackFullIndexVec(int numDataUnits,
+                                                int[] piggyBackIndex) {
+    int[] piggyBackFullIndex = new int[numDataUnits];
+
+    for (int i = 1; i < piggyBackIndex.length; ++i) {
+      for (int j = piggyBackIndex[i - 1]; j < piggyBackIndex[i]; ++j) {
+        piggyBackFullIndex[j] = i;
+      }
+    }
+
+    return piggyBackFullIndex;
+  }
+
+  public static ByteBuffer[] getPiggyBacksFromInput(ByteBuffer[] inputs,
+                                                    int[] piggyBackIndex,
+                                                    int numParityUnits,
+                                                    int pgIndex,
+                                                    RawErasureEncoder encoder) {
+    ByteBuffer[] emptyInput = new ByteBuffer[inputs.length];
+    ByteBuffer[] tempInput = new ByteBuffer[inputs.length];
+    int[] inputPositions = new int[inputs.length];
+
+    for (int m = 0; m < inputs.length; ++m) {
+      if (inputs[m] != null) {
+        emptyInput[m] = allocateByteBuffer(inputs[m].isDirect(),
+                inputs[m].remaining());
+      }
+    }
+
+    ByteBuffer[] tempOutput = new ByteBuffer[numParityUnits];
+    for (int m = 0; m < numParityUnits; ++m) {
+      tempOutput[m] = allocateByteBuffer(inputs[m].isDirect(),
+              inputs[0].remaining());
+    }
+
+    ByteBuffer[] piggyBacks = new ByteBuffer[numParityUnits - 1];
+    assert (piggyBackIndex.length >= numParityUnits);
+
+    // using underlying RS code to create piggybacks
+    for (int i = 0; i < numParityUnits - 1; ++i) {
+      for (int k = piggyBackIndex[i]; k < piggyBackIndex[i + 1]; ++k) {
+        tempInput[k] = inputs[k];
+        inputPositions[k] = inputs[k].position();
+      }
+      for (int n = 0; n < emptyInput.length; ++n) {
+        if (tempInput[n] == null) {
+          tempInput[n] = emptyInput[n];
+          inputPositions[n] = emptyInput[n].position();
+        }
+      }
+
+      encoder.encode(tempInput, tempOutput);
+
+      piggyBacks[i] = cloneBufferData(tempOutput[pgIndex]);
+
+      for (int j = 0; j < tempInput.length; j++) {
+        if (tempInput[j] != null) {
+          tempInput[j].position(inputPositions[j]);
+          tempInput[j] = null;
+        }
+      }
+
+      for (int j = 0; j < tempOutput.length; j++) {
+        tempOutput[j].clear();
+      }
+    }
+
+    return piggyBacks;
+  }
+
+  private static ByteBuffer cloneBufferData(ByteBuffer srcBuffer) {
+    ByteBuffer destBuffer;
+    byte[] bytesArr = new byte[srcBuffer.remaining()];
+
+    srcBuffer.mark();
+    srcBuffer.get(bytesArr);
+    srcBuffer.reset();
+
+    if (!srcBuffer.isDirect()) {
+      destBuffer = ByteBuffer.wrap(bytesArr);
+    } else {
+      destBuffer = ByteBuffer.allocateDirect(srcBuffer.remaining());
+      destBuffer.put(bytesArr);
+      destBuffer.flip();
+    }
+
+    return destBuffer;
+  }
+
+  public static ByteBuffer allocateByteBuffer(boolean useDirectBuffer,
+                                              int bufSize) {
+    if (useDirectBuffer) {
+      return ByteBuffer.allocateDirect(bufSize);
+    } else {
+      return ByteBuffer.allocate(bufSize);
+    }
+  }
+
+  public static ByteBuffer getPiggyBackForDecode(ByteBuffer[][] inputs,
+                                                 ByteBuffer[][] outputs,
+                                                 int pbParityIndex,
+                                                 int numDataUnits,
+                                                 int numParityUnits,
+                                                 int pbIndex) {
+    ByteBuffer fisrtValidInput = HHUtil.findFirstValidInput(inputs[0]);
+    int bufSize = fisrtValidInput.remaining();
+
+    ByteBuffer piggybacks = allocateByteBuffer(fisrtValidInput.isDirect(),
+            bufSize);
+
+    // Use piggyBackParityIndex to figure out which parity location has the
+    // associated piggyBack
+    // Obtain the piggyback by subtracting the decoded (second sub-packet
+    // only ) parity value from the actually read parity value
+    if (pbParityIndex < numParityUnits) {
+      // not the last piggybackSet
+      int inputIdx = numDataUnits + pbParityIndex;
+      int inputPos = inputs[1][inputIdx].position();
+      int outputPos = outputs[1][pbParityIndex].position();
+
+      for (int m = 0, k = inputPos, n = outputPos; m < bufSize; k++, m++, n++) {
+        int valueWithPb = 0xFF & inputs[1][inputIdx].get(k);
+        int valueWithoutPb = 0xFF & outputs[1][pbParityIndex].get(n);
+        piggybacks.put(m, (byte) RSUtil.GF.add(valueWithPb, valueWithoutPb));
+      }
+    } else {
+      // last piggybackSet
+      int sum = 0;
+      for (int k = 0; k < bufSize; k++) {
+        sum = 0;
+        for (int i = 1; i < numParityUnits; i++) {
+          int inIdx = numDataUnits + i;
+          int inPos = inputs[1][numDataUnits + i].position();
+          int outPos = outputs[1][i].position();
+
+          sum = RSUtil.GF.add(sum, (0xFF & inputs[1][inIdx].get(inPos + k)));
+          sum = RSUtil.GF.add(sum, (0xFF & outputs[1][i].get(outPos + k)));
+        }
+
+        sum = RSUtil.GF.add(sum,
+                (0xFF & inputs[0][numDataUnits + pbIndex].get(
+                        inputs[0][numDataUnits + pbIndex].position() + k)));
+
+        piggybacks.put(k, (byte) sum);
+      }
+
+    }
+
+    return piggybacks;
+  }
+
+  /**
+   * Find the valid input from all the inputs.
+   * @param inputs input buffers to look for valid input
+   * @return the first valid input
+   */
+  public static <T> T findFirstValidInput(T[] inputs) {
+    for (T input : inputs) {
+      if (input != null) {
+        return input;
+      }
+    }
+
+    throw new HadoopIllegalArgumentException(
+            "Invalid inputs are found, all being null");
+  }
+}

http://git-wip-us.apache.org/repos/asf/hadoop/blob/1bb31fb2/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/io/erasurecode/coder/TestErasureCoderBase.java
----------------------------------------------------------------------
diff --git a/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/io/erasurecode/coder/TestErasureCoderBase.java b/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/io/erasurecode/coder/TestErasureCoderBase.java
index 0584977..261be57 100644
--- a/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/io/erasurecode/coder/TestErasureCoderBase.java
+++ b/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/io/erasurecode/coder/TestErasureCoderBase.java
@@ -41,7 +41,7 @@ public abstract class TestErasureCoderBase extends TestCoderBase {
    * at all for simple.
    */
   protected static class TestBlock extends ECBlock {
-    private ECChunk[] chunks;
+    protected ECChunk[] chunks;
 
     // For simple, just assume the block have the chunks already ready.
     // In practice we need to read/write chunks from/to the block via file IO.
@@ -101,7 +101,7 @@ public abstract class TestErasureCoderBase extends TestCoderBase {
    * This is typically how a coding step should be performed.
    * @param codingStep
    */
-  private void performCodingStep(ErasureCodingStep codingStep) {
+  protected void performCodingStep(ErasureCodingStep codingStep) {
     // Pretend that we're opening these input blocks and output blocks.
     ECBlock[] inputBlocks = codingStep.getInputBlocks();
     ECBlock[] outputBlocks = codingStep.getOutputBlocks();

http://git-wip-us.apache.org/repos/asf/hadoop/blob/1bb31fb2/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/io/erasurecode/coder/TestHHErasureCoderBase.java
----------------------------------------------------------------------
diff --git a/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/io/erasurecode/coder/TestHHErasureCoderBase.java b/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/io/erasurecode/coder/TestHHErasureCoderBase.java
new file mode 100644
index 0000000..5471153
--- /dev/null
+++ b/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/io/erasurecode/coder/TestHHErasureCoderBase.java
@@ -0,0 +1,61 @@
+/**
+ * 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.hadoop.io.erasurecode.coder;
+
+import org.apache.hadoop.io.erasurecode.ECBlock;
+import org.apache.hadoop.io.erasurecode.ECChunk;
+
+
+/**
+ * Erasure coder test base with utilities for hitchhiker.
+ */
+public abstract class TestHHErasureCoderBase extends TestErasureCoderBase{
+  protected int subPacketSize = 2;
+
+  @Override
+  protected void performCodingStep(ErasureCodingStep codingStep) {
+    // Pretend that we're opening these input blocks and output blocks.
+    ECBlock[] inputBlocks = codingStep.getInputBlocks();
+    ECBlock[] outputBlocks = codingStep.getOutputBlocks();
+    // We allocate input and output chunks accordingly.
+    ECChunk[] inputChunks = new ECChunk[inputBlocks.length * subPacketSize];
+    ECChunk[] outputChunks = new ECChunk[outputBlocks.length * subPacketSize];
+
+    for (int i = 0; i < numChunksInBlock; i += subPacketSize) {
+      // Pretend that we're reading input chunks from input blocks.
+      for (int k = 0; k < subPacketSize; ++k) {
+        for (int j = 0; j < inputBlocks.length; ++j) {
+          inputChunks[k * inputBlocks.length + j] = ((TestBlock)
+                  inputBlocks[j]).chunks[i + k];
+        }
+
+        // Pretend that we allocate and will write output results to the blocks.
+        for (int j = 0; j < outputBlocks.length; ++j) {
+          outputChunks[k * outputBlocks.length + j] = allocateOutputChunk();
+          ((TestBlock) outputBlocks[j]).chunks[i + k] =
+                  outputChunks[k * outputBlocks.length + j];
+        }
+      }
+
+      // Given the input chunks and output chunk buffers, just call it !
+      codingStep.performCoding(inputChunks, outputChunks);
+    }
+
+    codingStep.finish();
+  }
+}

http://git-wip-us.apache.org/repos/asf/hadoop/blob/1bb31fb2/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/io/erasurecode/coder/TestHHXORErasureCoder.java
----------------------------------------------------------------------
diff --git a/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/io/erasurecode/coder/TestHHXORErasureCoder.java b/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/io/erasurecode/coder/TestHHXORErasureCoder.java
new file mode 100644
index 0000000..ad346e0
--- /dev/null
+++ b/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/io/erasurecode/coder/TestHHXORErasureCoder.java
@@ -0,0 +1,120 @@
+/**
+ * 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.hadoop.io.erasurecode.coder;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.fs.CommonConfigurationKeys;
+import org.apache.hadoop.io.erasurecode.rawcoder.RSRawErasureCoderFactory;
+import org.junit.Before;
+import org.junit.Test;
+
+public class TestHHXORErasureCoder extends TestHHErasureCoderBase {
+
+  @Before
+  public void setup() {
+    this.encoderClass = HHXORErasureEncoder.class;
+    this.decoderClass = HHXORErasureDecoder.class;
+    this.numChunksInBlock = 10;
+    this.subPacketSize = 2;
+  }
+
+  @Test
+  public void testCodingNoDirectBuffer_10x4_erasing_d0() {
+    prepare(null, 10, 4, new int[]{0}, new int[0]);
+    /**
+     * Doing twice to test if the coders can be repeatedly reused. This matters
+     * as the underlying coding buffers are shared, which may have bugs.
+     */
+    testCoding(false);
+    testCoding(false);
+  }
+
+  @Test
+  public void testCodingDirectBufferWithConf_10x4_erasing_d0() {
+    /**
+     * This tests if the configuration items work or not.
+     */
+    Configuration conf = new Configuration();
+    conf.set(CommonConfigurationKeys.IO_ERASURECODE_CODEC_RS_RAWCODER_KEY,
+        RSRawErasureCoderFactory.class.getCanonicalName());
+    prepare(conf, 10, 4, new int[]{0}, new int[0]);
+
+    testCoding(true);
+    testCoding(true);
+  }
+
+  @Test
+  public void testCodingDirectBuffer_10x4_erasing_p1() {
+    prepare(null, 10, 4, new int[]{}, new int[]{1});
+    testCoding(true);
+    testCoding(true);
+  }
+
+  @Test
+  public void testCodingDirectBuffer_10x4_erasing_d4() {
+    prepare(null, 10, 4, new int[] {4}, new int[] {});
+    testCoding(true);
+    testCoding(true);
+  }
+
+  @Test
+  public void testCodingDirectBuffer_10x4_erasing_d0_p0() {
+    prepare(null, 10, 4, new int[] {0}, new int[] {0});
+    testCoding(true);
+    testCoding(true);
+  }
+
+  @Test
+  public void testCodingBothBuffers_10x4_erasing_d0_p0() {
+    prepare(null, 10, 4, new int[] {0}, new int[] {0});
+
+    /**
+     * Doing in mixed buffer usage model to test if the coders can be repeatedly
+     * reused with different buffer usage model. This matters as the underlying
+     * coding buffers are shared, which may have bugs.
+     */
+    testCoding(true);
+    testCoding(false);
+    testCoding(true);
+    testCoding(false);
+  }
+
+  @Test
+  public void testCodingDirectBuffer_10x4_erasure_of_d2_d4_p0() {
+    prepare(null, 10, 4, new int[] {2, 4}, new int[] {0});
+    testCoding(true);
+  }
+
+  @Test
+  public void testCodingDirectBuffer_10x4_erasing_d0_d1_p0_p1() {
+    prepare(null, 10, 4, new int[] {0, 1}, new int[] {0, 1});
+    testCoding(true);
+  }
+
+//  @Test
+//  public void testCodingNoDirectBuffer_3x3_erasing_d0_p0() {
+//    prepare(null, 3, 3, new int[] {0}, new int[] {0});
+//    testCoding(false);
+//  }
+
+  @Test
+  public void testCodingDirectBuffer_6x3_erasing_d0_p0() {
+    prepare(null, 6, 3, new int[] {0}, new int[] {0});
+    testCoding(true);
+  }
+}


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