HBASE-5926 Delete the master znode after a master crash

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1340200 13f79535-47bb-0310-9956-ffa450edef68

src/main/java/org/apache/hadoop/hbase/ZNodeClearer.java

@@ -0,0 +1,152 @@
+/**
+ * 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 org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.hbase.zookeeper.MasterAddressTracker;
+import org.apache.hadoop.hbase.zookeeper.ZooKeeperWatcher;
+
+import java.io.BufferedReader;
+import java.io.BufferedWriter;
+import java.io.File;
+import java.io.FileReader;
+import java.io.FileWriter;
+import java.io.IOException;
+
+/**
+ * <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>
+ */
+public class ZNodeClearer {
+  public static final Log LOG = LogFactory.getLog(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("No filename given to save the znode used, it won't be saved " +
+          "(Environment variable HBASE_ZNODE_FILE is not set).");
+      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 IOException("No filename");
+    }
+    FileReader znodeFile = new FileReader(fileName);
+    BufferedReader br = new BufferedReader(znodeFile);
+    String file_content = br.readLine();
+    br.close();
+    return file_content;
+  }
+
+  /**
+   * 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();
+    }
+  }
+
+  /**
+   * Delete the master znode if its content (ServerName string) is the same
+   *  as the one in the znode file. (env: HBASE_ZNODE_FILE).
+   * @return true on successful deletion, false otherwise.
+   */
+  public static boolean clear(Configuration conf) {
+    Configuration tempConf = new Configuration(conf);
+    tempConf.setInt("zookeeper.recovery.retry", 0);
+
+    ZooKeeperWatcher zkw;
+    try {
+      zkw = new ZooKeeperWatcher(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();
+    } catch (IOException e) {
+      LOG.warn("Can't read the content of the znode file", e);
+      return false;
+    }
+
+    return MasterAddressTracker.deleteIfEquals(zkw, znodeFileContent);
+  }
+}