hbase-server/src/main/java/org/apache/hadoop/hbase/ZNodeClearer.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.hbase;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.hbase.zookeeper.MasterAddressTracker;
import org.apache.hadoop.hbase.zookeeper.ZKWatcher;
import org.apache.yetus.audience.InterfaceAudience;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * <p>
 * Contains a set of methods for the collaboration between the start/stop scripts and the servers.
 * It allows to delete immediately the znode when the master or the regions server crashes. The
 * region server / master writes a specific file when it starts / becomes main master. When they end
 * properly, they delete the file.
 * </p>
 * <p>
 * In the script, we check for the existence of these files when the program ends. If they still
 * exist we conclude that the server crashed, likely without deleting their znode. To have a faster
 * recovery we delete immediately the znode.
 * </p>
 * <p>
 * The strategy depends on the server type. For a region server we store the znode path in the file,
 * and use it to delete it. for a master, as the znode path constant whatever the server, we check
 * its content to make sure that the backup server is not now in charge.
 * </p>
 */
@InterfaceAudience.Private
public final class ZNodeClearer {
  private static final Logger LOG = LoggerFactory.getLogger(ZNodeClearer.class);

  private ZNodeClearer() {
  }

  /**
   * Logs the errors without failing on exception.
   */
  public static void writeMyEphemeralNodeOnDisk(String fileContent) {
    String fileName = ZNodeClearer.getMyEphemeralNodeFileName();
    if (fileName == null) {
      LOG.warn("Environment variable HBASE_ZNODE_FILE not set; znodes will not be cleared "
        + "on crash by start scripts (Longer MTTR!)");
      return;
    }

    FileWriter fstream;
    try {
      fstream = new FileWriter(fileName);
    } catch (IOException e) {
      LOG.warn("Can't write znode file " + fileName, e);
      return;
    }

    BufferedWriter out = new BufferedWriter(fstream);

    try {
      try {
        out.write(fileContent + "\n");
      } finally {
        try {
          out.close();
        } finally {
          fstream.close();
        }
      }
    } catch (IOException e) {
      LOG.warn("Can't write znode file " + fileName, e);
    }
  }

  /**
   * read the content of znode file, expects a single line.
   */
  public static String readMyEphemeralNodeOnDisk() throws IOException {
    String fileName = getMyEphemeralNodeFileName();
    if (fileName == null) {
      throw new FileNotFoundException("No filename; set environment variable HBASE_ZNODE_FILE");
    }
    FileReader znodeFile = new FileReader(fileName);
    BufferedReader br = null;
    try {
      br = new BufferedReader(znodeFile);
      String file_content = br.readLine();
      return file_content;
    } finally {
      if (br != null) br.close();
    }
  }

  /**
   * Get the name of the file used to store the znode contents
   */
  public static String getMyEphemeralNodeFileName() {
    return System.getenv().get("HBASE_ZNODE_FILE");
  }

  /**
   * delete the znode file
   */
  public static void deleteMyEphemeralNodeOnDisk() {
    String fileName = getMyEphemeralNodeFileName();

    if (fileName != null) {
      new File(fileName).delete();
    }
  }

  /**
   * See HBASE-14861. We are extracting master ServerName from rsZnodePath example:
   * "/hbase/rs/server.example.com,16020,1448266496481"
   * @param rsZnodePath from HBASE_ZNODE_FILE
   * @return String representation of ServerName or null if fails
   */

  public static String parseMasterServerName(String rsZnodePath) {
    String masterServerName = null;
    try {
      String[] rsZnodeParts = rsZnodePath.split("/");
      masterServerName = rsZnodeParts[rsZnodeParts.length - 1];
    } catch (IndexOutOfBoundsException e) {
      LOG.warn("String " + rsZnodePath + " has wrong format", e);
    }
    return masterServerName;
  }

  /**
   * Delete the master znode if its content (ServerName string) is the same as the one in the znode
   * file. (env: HBASE_ZNODE_FILE). I case of master-rs colloaction we extract ServerName string
   * from rsZnode path.(HBASE-14861)
   * @return true on successful deletion, false otherwise.
   */
  public static boolean clear(Configuration conf) {
    Configuration tempConf = new Configuration(conf);
    tempConf.setInt("zookeeper.recovery.retry", 0);

    ZKWatcher zkw;
    try {
      zkw = new ZKWatcher(tempConf, "clean znode for master", new Abortable() {
        @Override
        public void abort(String why, Throwable e) {
        }

        @Override
        public boolean isAborted() {
          return false;
        }
      });
    } catch (IOException e) {
      LOG.warn("Can't connect to zookeeper to read the master znode", e);
      return false;
    }

    String znodeFileContent;
    try {
      znodeFileContent = ZNodeClearer.readMyEphemeralNodeOnDisk();
      return MasterAddressTracker.deleteIfEquals(zkw, znodeFileContent);
    } catch (FileNotFoundException fnfe) {
      // If no file, just keep going -- return success.
      LOG.warn("Can't find the znode file; presume non-fatal", fnfe);
      return true;
    } catch (IOException e) {
      LOG.warn("Can't read the content of the znode file", e);
      return false;
    } finally {
      zkw.close();
    }
  }
}