datanodeprotocol.java

来自「Hadoop是一个用于运行应用程序在大型集群的廉价硬件设备上的框架。Hadoop」· Java 代码 · 共 69 行

/**
 * Copyright 2005 The Apache Software Foundation
 *
 * Licensed 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.dfs;

import java.io.*;

/**********************************************************************
 * Protocol that a DFS datanode uses to communicate with the NameNode.
 * It's used to upload current load information and block reports.
 *
 * The only way a NameNode can communicate with a DataNode is by
 * returning values from these functions.
 *
 * @author Michael Cafarella
 **********************************************************************/
interface DatanodeProtocol {
    /**
     * sendHeartbeat() tells the NameNode that the DataNode is still
     * alive and well.  Includes some status info, too.
     */
    public void sendHeartbeat(String sender, long capacity, long remaining) throws IOException;

    /**
     * blockReport() tells the NameNode about all the locally-stored blocks.
     * The NameNode returns an array of Blocks that have become obsolete
     * and should be deleted.  This function is meant to upload *all*
     * the locally-stored blocks.  It's invoked upon startup and then
     * infrequently afterwards.
     */
    public Block[] blockReport(String sender, Block blocks[]) throws IOException;
    
    /**
     * blockReceived() allows the DataNode to tell the NameNode about
     * recently-received block data.  For example, whenever client code
     * writes a new Block here, or another DataNode copies a Block to
     * this DataNode, it will call blockReceived().
     */
    public void blockReceived(String sender, Block blocks[]) throws IOException;

    /**
     * errorReport() tells the NameNode about something that has gone
     * awry.  Useful for debugging.
     */
    public void errorReport(String sender, String msg) throws IOException;

    /**
     * The DataNode periodically calls getBlockwork().  It includes a
     * small amount of status information, but mainly gives the NameNode
     * a chance to return a "BlockCommand" object.  A BlockCommand tells
     * the DataNode to invalidate local block(s), or to copy them to other 
     * DataNodes, etc.
     */
    public BlockCommand getBlockwork(String sender, int xmitsInProgress) throws IOException;
}