org.apache.hadoop.io.erasurecode.coder.XORErasureDecoder Maven / Gradle / Ivy
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* 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;
/**
* Xor erasure decoder that decodes a block group.
*
* It implements {@link ErasureCoder}.
*/
@InterfaceAudience.Private
public class XORErasureDecoder extends ErasureDecoder {
public XORErasureDecoder(ErasureCoderOptions options) {
super(options);
}
@Override
protected ErasureCodingStep prepareDecodingStep(
final ECBlockGroup blockGroup) {
RawErasureDecoder rawDecoder = CodecUtil.createRawDecoder(getConf(),
ErasureCodeConstants.XOR_CODEC_NAME, getOptions());
ECBlock[] inputBlocks = getInputBlocks(blockGroup);
return new ErasureDecodingStep(inputBlocks,
getErasedIndexes(inputBlocks),
getOutputBlocks(blockGroup), rawDecoder);
}
/**
* Which blocks were erased ? For XOR it's simple we only allow and return one
* erased block, either data or parity.
* @param blockGroup
* @return output blocks to recover
*/
@Override
protected ECBlock[] getOutputBlocks(ECBlockGroup blockGroup) {
/**
* If more than one blocks (either data or parity) erased, then it's not
* edible to recover. We don't have the check here since it will be done
* by upper level: ErasreCoder call can be avoid if not possible to recover
* at all.
*/
int erasedNum = getNumErasedBlocks(blockGroup);
ECBlock[] outputBlocks = new ECBlock[erasedNum];
int idx = 0;
for (int i = 0; i < getNumParityUnits(); i++) {
if (blockGroup.getParityBlocks()[i].isErased()) {
outputBlocks[idx++] = blockGroup.getParityBlocks()[i];
}
}
for (int i = 0; i < getNumDataUnits(); i++) {
if (blockGroup.getDataBlocks()[i].isErased()) {
outputBlocks[idx++] = blockGroup.getDataBlocks()[i];
}
}
return outputBlocks;
}
}