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 co.cask.tephra.persist; import org.apache.hadoop.conf.Configuration; import org.apache.hadoop.fs.FileSystem; import org.apache.hadoop.fs.Path; import org.apache.hadoop.hdfs.DistributedFileSystem; import org.apache.hadoop.hdfs.server.namenode.LeaseExpiredException; import org.slf4j.Logger; import org.slf4j.LoggerFactory; import java.io.FileNotFoundException; import java.io.IOException; import java.io.InterruptedIOException; import java.lang.reflect.Method; /** * Utility for handling HDFS file lease recovery. This is a copy-n-paste fork of * {@link org.apache.hadoop.hbase.util.FSHDFSUtils} from the latest HBase 0.94 version (as of 0.94.12), * which contains some additional fixes not present in our current HBase dependency version -- * mainly checking the return value of the {@code DistributedFileSystem.recoverLease()} call to verify that * recovery succeeded. */ public class HDFSUtil { private static final Logger LOG = LoggerFactory.getLogger(HDFSUtil.class); /** * Recover the lease from HDFS, retrying multiple times. */ public void recoverFileLease(final FileSystem fs, final Path p, Configuration conf) throws IOException { // lease recovery not needed for local file system case. if (!(fs instanceof DistributedFileSystem)) { return; } recoverDFSFileLease((DistributedFileSystem) fs, p, conf); } /* * Run the dfs recover lease. recoverLease is asynchronous. It returns: * -false when it starts the lease recovery (i.e. lease recovery not *yet* done) * - true when the lease recovery has succeeded or the file is closed. * But, we have to be careful. Each time we call recoverLease, it starts the recover lease * process over from the beginning. We could put ourselves in a situation where we are * doing nothing but starting a recovery, interrupting it to start again, and so on. * The findings over in HBASE-8354 have it that the namenode will try to recover the lease * on the file's primary node. If all is well, it should return near immediately. But, * as is common, it is the very primary node that has crashed and so the namenode will be * stuck waiting on a socket timeout before it will ask another datanode to start the * recovery. It does not help if we call recoverLease in the meantime and in particular, * subsequent to the socket timeout, a recoverLease invocation will cause us to start * over from square one (possibly waiting on socket timeout against primary node). So, * in the below, we do the following: * 1. Call recoverLease. * 2. If it returns true, break. * 3. If it returns false, wait a few seconds and then call it again. * 4. If it returns true, break. * 5. If it returns false, wait for what we think the datanode socket timeout is * (configurable) and then try again. * 6. If it returns true, break. * 7. If it returns false, repeat starting at step 5. above. * * If HDFS-4525 is available, call it every second and we might be able to exit early. */ boolean recoverDFSFileLease(final DistributedFileSystem dfs, final Path p, final Configuration conf) throws IOException { LOG.info("Recovering lease on dfs file " + p); long startWaiting = System.currentTimeMillis(); // Default is 15 minutes. It's huge, but the idea is that if we have a major issue, HDFS // usually needs 10 minutes before marking the nodes as dead. So we're putting ourselves // beyond that limit 'to be safe'. long recoveryTimeout = conf.getInt("hbase.lease.recovery.timeout", 900000) + startWaiting; // This setting should be what the cluster dfs heartbeat is set to. long firstPause = conf.getInt("hbase.lease.recovery.first.pause", 3000); // This should be set to how long it'll take for us to timeout against primary datanode if it // is dead. We set it to 61 seconds, 1 second than the default READ_TIMEOUT in HDFS, the // default value for DFS_CLIENT_SOCKET_TIMEOUT_KEY. long subsequentPause = conf.getInt("hbase.lease.recovery.dfs.timeout", 61 * 1000); Method isFileClosedMeth = null; // whether we need to look for isFileClosed method boolean findIsFileClosedMeth = true; boolean recovered = false; // We break the loop if we succeed the lease recovery, timeout, or we throw an exception. for (int nbAttempt = 0; !recovered; nbAttempt++) { recovered = recoverLease(dfs, nbAttempt, p, startWaiting); if (recovered || checkIfTimedout(conf, recoveryTimeout, nbAttempt, p, startWaiting)) { break; } try { // On the first time through wait the short 'firstPause'. if (nbAttempt == 0) { Thread.sleep(firstPause); } else { // Cycle here until subsequentPause elapses. While spinning, check isFileClosed if // available (should be in hadoop 2.0.5... not in hadoop 1 though. long localStartWaiting = System.currentTimeMillis(); while ((System.currentTimeMillis() - localStartWaiting) < subsequentPause) { Thread.sleep(conf.getInt("hbase.lease.recovery.pause", 1000)); if (findIsFileClosedMeth) { try { isFileClosedMeth = dfs.getClass().getMethod("isFileClosed", new Class[] { Path.class }); } catch (NoSuchMethodException nsme) { LOG.debug("isFileClosed not available"); } finally { findIsFileClosedMeth = false; } } if (isFileClosedMeth != null && isFileClosed(dfs, isFileClosedMeth, p)) { recovered = true; break; } } } } catch (InterruptedException ie) { InterruptedIOException iioe = new InterruptedIOException(); iioe.initCause(ie); throw iioe; } } return recovered; } boolean checkIfTimedout(final Configuration conf, final long recoveryTimeout, final int nbAttempt, final Path p, final long startWaiting) { if (recoveryTimeout < System.currentTimeMillis()) { LOG.warn("Cannot recoverLease after trying for " + conf.getInt("hbase.lease.recovery.timeout", 900000) + "ms (hbase.lease.recovery.timeout); continuing, but may be DATALOSS!!!; " + getLogMessageDetail(nbAttempt, p, startWaiting)); return true; } return false; } /** * Try to recover the lease. * @param dfs The filesystem instance. * @param nbAttempt Count number of this attempt. * @param p Path of the file to recover. * @param startWaiting Timestamp of when we started attempting to recover the file lease. * @return True if dfs#recoverLease came by true. * @throws java.io.FileNotFoundException */ boolean recoverLease(final DistributedFileSystem dfs, final int nbAttempt, final Path p, final long startWaiting) throws FileNotFoundException { boolean recovered = false; try { recovered = dfs.recoverLease(p); LOG.info("recoverLease=" + recovered + ", " + getLogMessageDetail(nbAttempt, p, startWaiting)); } catch (IOException e) { if (e instanceof LeaseExpiredException && e.getMessage().contains("File does not exist")) { // This exception comes out instead of FNFE, fix it throw new FileNotFoundException("The given file wasn't found at " + p); } else if (e instanceof FileNotFoundException) { throw (FileNotFoundException) e; } LOG.warn(getLogMessageDetail(nbAttempt, p, startWaiting), e); } return recovered; } /** * @param nbAttempt Attempt number for the lease recovery. * @param p Path of the file to recover. * @param startWaiting Timestamp of when we started attempting to recover the file lease. * @return Detail to append to any log message around lease recovering. */ private String getLogMessageDetail(final int nbAttempt, final Path p, final long startWaiting) { return "attempt=" + nbAttempt + " on file=" + p + " after " + (System.currentTimeMillis() - startWaiting) + "ms"; } /** * Call HDFS-4525 isFileClosed if it is available. * @param dfs Filesystem instance to use. * @param m Method instance to call. * @param p Path of the file to check is closed. * @return True if file is closed. */ private boolean isFileClosed(final DistributedFileSystem dfs, final Method m, final Path p) { try { return (Boolean) m.invoke(dfs, p); } catch (SecurityException e) { LOG.warn("No access", e); } catch (Exception e) { LOG.warn("Failed invocation for " + p.toString(), e); } return false; } }