Java tutorial
/** * 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 java.io.IOException; import org.apache.hadoop.classification.InterfaceAudience; import org.apache.hadoop.hdfs.DFSConfigKeys; import org.apache.hadoop.hdfs.protocol.DatanodeInfo; import org.apache.hadoop.hdfs.security.token.block.ExportedBlockKeys; import org.apache.hadoop.hdfs.server.namenode.CheckpointSignature; import org.apache.hadoop.io.retry.AtMostOnce; import org.apache.hadoop.io.retry.Idempotent; import org.apache.hadoop.security.KerberosInfo; /***************************************************************************** * Protocol that a secondary NameNode uses to communicate with the NameNode. * Also used by external storage policy satisfier. It's used to get part of the * name node state *****************************************************************************/ @KerberosInfo(serverPrincipal = DFSConfigKeys.DFS_NAMENODE_KERBEROS_PRINCIPAL_KEY) @InterfaceAudience.Private public interface NamenodeProtocol { /** * Until version 6L, this class served as both * the client interface to the NN AND the RPC protocol used to * communicate with the NN. * * This class is used by both the DFSClient and the * NN server side to insulate from the protocol serialization. * * If you are adding/changing NN's interface then you need to * change both this class and ALSO related protocol buffer * wire protocol definition in NamenodeProtocol.proto. * * For more details on protocol buffer wire protocol, please see * .../org/apache/hadoop/hdfs/protocolPB/overview.html * * 6: Switch to txid-based file naming for image and edits */ public static final long versionID = 6L; // Error codes passed by errorReport(). final static int NOTIFY = 0; final static int FATAL = 1; public final static int ACT_UNKNOWN = 0; // unknown action public final static int ACT_SHUTDOWN = 50; // shutdown node public final static int ACT_CHECKPOINT = 51; // do checkpoint /** * Get a list of blocks belonging to <code>datanode</code> * whose total size equals <code>size</code>. * * @see org.apache.hadoop.hdfs.server.balancer.Balancer * @param datanode a data node * @param size requested size * @param minBlockSize each block should be of this minimum Block Size * @return a list of blocks & their locations * @throws IOException if size is less than or equal to 0 or datanode does not exist */ @Idempotent BlocksWithLocations getBlocks(DatanodeInfo datanode, long size, long minBlockSize) throws IOException; /** * Get the current block keys * * @return ExportedBlockKeys containing current block keys * @throws IOException */ @Idempotent public ExportedBlockKeys getBlockKeys() throws IOException; /** * @return The most recent transaction ID that has been synced to * persistent storage, or applied from persistent storage in the * case of a non-active node. * @throws IOException */ @Idempotent public long getTransactionID() throws IOException; /** * Get the transaction ID of the most recent checkpoint. */ @Idempotent public long getMostRecentCheckpointTxId() throws IOException; /** * Closes the current edit log and opens a new one. The * call fails if the file system is in SafeMode. * @throws IOException * @return a unique token to identify this transaction. */ @Idempotent public CheckpointSignature rollEditLog() throws IOException; /** * Request name-node version and storage information. * * @return {@link NamespaceInfo} identifying versions and storage information * of the name-node * @throws IOException */ @Idempotent public NamespaceInfo versionRequest() throws IOException; /** * Report to the active name-node an error occurred on a subordinate node. * Depending on the error code the active node may decide to unregister the * reporting node. * * @param registration requesting node. * @param errorCode indicates the error * @param msg free text description of the error * @throws IOException */ @Idempotent public void errorReport(NamenodeRegistration registration, int errorCode, String msg) throws IOException; /** * Register a subordinate name-node like backup node. * * @return {@link NamenodeRegistration} of the node, * which this node has just registered with. */ @Idempotent public NamenodeRegistration registerSubordinateNamenode(NamenodeRegistration registration) throws IOException; /** * A request to the active name-node to start a checkpoint. * The name-node should decide whether to admit it or reject. * The name-node also decides what should be done with the backup node * image before and after the checkpoint. * * @see CheckpointCommand * @see NamenodeCommand * @see #ACT_SHUTDOWN * * @param registration the requesting node * @return {@link CheckpointCommand} if checkpoint is allowed. * @throws IOException */ @AtMostOnce public NamenodeCommand startCheckpoint(NamenodeRegistration registration) throws IOException; /** * A request to the active name-node to finalize * previously started checkpoint. * * @param registration the requesting node * @param sig {@code CheckpointSignature} which identifies the checkpoint. * @throws IOException */ @AtMostOnce public void endCheckpoint(NamenodeRegistration registration, CheckpointSignature sig) throws IOException; /** * Return a structure containing details about all edit logs * available to be fetched from the NameNode. * @param sinceTxId return only logs that contain transactions >= sinceTxId */ @Idempotent public RemoteEditLogManifest getEditLogManifest(long sinceTxId) throws IOException; /** * @return Whether the NameNode is in upgrade state (false) or not (true) */ @Idempotent public boolean isUpgradeFinalized() throws IOException; /** * return whether the Namenode is rolling upgrade in progress (true) or * not (false). * @return * @throws IOException */ @Idempotent boolean isRollingUpgrade() throws IOException; /** * @return Gets the next available sps path, otherwise null. This API used * by External SPS. */ @AtMostOnce Long getNextSPSPath() throws IOException; }