hadoop HHXORErasureDecoder 源码

haddop HHXORErasureDecoder 代码

文件路径：/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/erasurecode/coder/HHXORErasureDecoder.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.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.ErasureCodeConstants;
import org.apache.hadoop.io.erasurecode.ErasureCoderOptions;
import org.apache.hadoop.io.erasurecode.rawcoder.RawErasureDecoder;
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 decoder that decodes a block group.
 */
@InterfaceAudience.Private
public class HHXORErasureDecoder extends ErasureDecoder {
  private RawErasureDecoder rsRawDecoder;
  private RawErasureEncoder xorRawEncoder;

  public HHXORErasureDecoder(ErasureCoderOptions options) {
    super(options);
  }

  @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.createRawDecoder(getConf(),
              ErasureCodeConstants.RS_CODEC_NAME, getOptions());
    }
    return rsRawDecoder;
  }

  private RawErasureEncoder checkCreateXorRawEncoder() {
    if (xorRawEncoder == null) {
      xorRawEncoder = CodecUtil.createRawEncoder(getConf(),
          ErasureCodeConstants.XOR_CODEC_NAME, getOptions());
    }
    return xorRawEncoder;
  }

  @Override
  public boolean preferDirectBuffer() {
    return false;
  }

  @Override
  public void release() {
    if (rsRawDecoder != null) {
      rsRawDecoder.release();
    }
    if (xorRawEncoder != null) {
      xorRawEncoder.release();
    }
  }
}

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