hadoop CheckpointCommand 源码
haddop CheckpointCommand 代码
文件路径：/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/protocol/CheckpointCommand.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.hdfs.server.protocol;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.hdfs.server.namenode.CheckpointSignature;
/**
* Checkpoint command.
* <p>
* Returned to the backup node by the name-node as a reply to the
* {@link NamenodeProtocol#startCheckpoint(NamenodeRegistration)}
* request.<br>
* Contains:
* <ul>
* <li>{@link CheckpointSignature} identifying the particular checkpoint</li>
* <li>indicator whether the backup image should be discarded before starting
* the checkpoint</li>
* <li>indicator whether the image should be transfered back to the name-node
* upon completion of the checkpoint.</li>
* </ul>
*/
@InterfaceAudience.Private
@InterfaceStability.Evolving
public class CheckpointCommand extends NamenodeCommand {
private final CheckpointSignature cSig;
private final boolean needToReturnImage;
public CheckpointCommand() {
this(null, false);
}
public CheckpointCommand(CheckpointSignature sig,
boolean needToReturnImg) {
super(NamenodeProtocol.ACT_CHECKPOINT);
this.cSig = sig;
this.needToReturnImage = needToReturnImg;
}
/**
* Checkpoint signature is used to ensure
* that nodes are talking about the same checkpoint.
*/
public CheckpointSignature getSignature() {
return cSig;
}
/**
* Indicates whether the new checkpoint image needs to be transfered
* back to the name-node after the checkpoint is done.
*
* @return true if the checkpoint should be returned back.
*/
public boolean needToReturnImage() {
return needToReturnImage;
}
}
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