/**
* Copyright 2011 The Apache Software Foundation
*
* 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.regionserver;
import static org.apache.hadoop.hbase.zookeeper.ZKSplitLog.Counters.*;
import java.io.IOException;
import java.io.InterruptedIOException;
import java.util.List;
import java.util.concurrent.atomic.AtomicLong;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.hbase.master.SplitLogManager;
import org.apache.hadoop.hbase.regionserver.wal.HLogSplitter;
import org.apache.hadoop.hbase.util.CancelableProgressable;
import org.apache.hadoop.hbase.util.FSUtils;
import org.apache.hadoop.hbase.zookeeper.ZKSplitLog;
import org.apache.hadoop.hbase.zookeeper.ZKSplitLog.TaskState;
import org.apache.hadoop.hbase.zookeeper.ZKUtil;
import org.apache.hadoop.hbase.zookeeper.ZooKeeperListener;
import org.apache.hadoop.hbase.zookeeper.ZooKeeperWatcher;
import org.apache.hadoop.util.StringUtils;
import org.apache.zookeeper.AsyncCallback;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.data.Stat;
/**
* This worker is spawned in every regionserver (should we also spawn one in
* the master?). The Worker waits for log splitting tasks to be put up by the
* {@link SplitLogManager} running in the master and races with other workers
* in other serves to acquire those tasks. The coordination is done via
* zookeeper. All the action takes place at /hbase/splitlog znode.
* <p>
* If a worker has successfully moved the task from state UNASSIGNED to
* OWNED then it owns the task. It keeps heart beating the manager by
* periodically moving the task from OWNED to OWNED state. On success it
* moves the task to SUCCESS. On unrecoverable error it moves task state to
* ERR. If it cannot continue but wants the master to retry the task then it
* moves the task state to RESIGNED.
* <p>
* The manager can take a task away from a worker by moving the task from
* OWNED to UNASSIGNED. In the absence of a global lock there is a
* unavoidable race here - a worker might have just finished its task when it
* is stripped of its ownership. Here we rely on the idempotency of the log
* splitting task for correctness
*/
public class SplitLogWorker extends ZooKeeperListener implements Runnable {
private static final Log LOG = LogFactory.getLog(SplitLogWorker.class);
Thread worker;
private final String serverName;
private final TaskExecutor executor;
private long zkretries;
private Object taskReadyLock = new Object();
volatile int taskReadySeq = 0;
private volatile String currentTask = null;
private int currentVersion;
private volatile boolean exitWorker;
private Object grabTaskLock = new Object();
private boolean workerInGrabTask = false;
public SplitLogWorker(ZooKeeperWatcher watcher, Configuration conf,
String serverName, TaskExecutor executor) {
super(watcher);
this.serverName = serverName;
this.executor = executor;
this.zkretries = conf.getLong("hbase.splitlog.zk.retries", 3);
}
public SplitLogWorker(ZooKeeperWatcher watcher, final Configuration conf,
final String serverName) {
this(watcher, conf, serverName, new TaskExecutor () {
@Override
public Status exec(String filename, CancelableProgressable p) {
Path rootdir;
FileSystem fs;
try {
rootdir = FSUtils.getRootDir(conf);
fs = rootdir.getFileSystem(conf);
} catch (IOException e) {
LOG.warn("could not find root dir or fs", e);
return Status.RESIGNED;
}
// TODO have to correctly figure out when log splitting has been
// interrupted or has encountered a transient error and when it has
// encountered a bad non-retry-able persistent error.
try {
String tmpname =
ZKSplitLog.getSplitLogDirTmpComponent(serverName, filename);
if (HLogSplitter.splitLogFileToTemp(rootdir, tmpname,
fs.getFileStatus(new Path(filename)), fs, conf, p) == false) {
return Status.PREEMPTED;
}
} catch (InterruptedIOException iioe) {
LOG.warn("log splitting of " + filename + " interrupted, resigning",
iioe);
return Status.RESIGNED;
} catch (IOException e) {
Throwable cause = e.getCause();
if (cause instanceof InterruptedException) {
LOG.warn("log splitting of " + filename + " interrupted, resigning",
e);
return Status.RESIGNED;
}
LOG.warn("log splitting of " + filename + " failed, returning error",
e);
return Status.ERR;
}
return Status.DONE;
}
});
}
@Override
public void run() {
try {
LOG.info("SplitLogWorker " + this.serverName + " starting");
this.watcher.registerListener(this);
int res;
// wait for master to create the splitLogZnode
res = -1;
while (res == -1) {
try {
res = ZKUtil.checkExists(watcher, watcher.splitLogZNode);
} catch (KeeperException e) {
// ignore
LOG.warn("Exception when checking for " + watcher.splitLogZNode +
" ... retrying", e);
}
if (res == -1) {
try {
LOG.info(watcher.splitLogZNode + " znode does not exist," +
" waiting for master to create one");
Thread.sleep(1000);
} catch (InterruptedException e) {
LOG.debug("Interrupted while waiting for " + watcher.splitLogZNode);
assert exitWorker == true;
}
}
}
taskLoop();
} catch (Throwable t) {
// only a logical error can cause here. Printing it out
// to make debugging easier
LOG.error("unexpected error ", t);
} finally {
LOG.info("SplitLogWorker " + this.serverName + " exiting");
}
}
/**
* Wait for tasks to become available at /hbase/splitlog zknode. Grab a task
* one at a time. This policy puts an upper-limit on the number of
* simultaneous log splitting that could be happening in a cluster.
* <p>
* Synchronization using {@link #task_ready_signal_seq} ensures that it will
* try to grab every task that has been put up
*/
private void taskLoop() {
while (true) {
int seq_start = taskReadySeq;
List<String> paths = getTaskList();
if (paths == null) {
LOG.warn("Could not get tasks, did someone remove " +
this.watcher.splitLogZNode + " ... worker thread exiting.");
return;
}
int offset = (int)(Math.random() * paths.size());
for (int i = 0; i < paths.size(); i ++) {
int idx = (i + offset) % paths.size();
// don't call ZKSplitLog.getNodeName() because that will lead to
// double encoding of the path name
grabTask(ZKUtil.joinZNode(watcher.splitLogZNode, paths.get(idx)));
if (exitWorker == true) {
return;
}
}
synchronized (taskReadyLock) {
while (seq_start == taskReadySeq) {
try {
taskReadyLock.wait();
} catch (InterruptedException e) {
LOG.info("SplitLogWorker interrupted while waiting for task," +
" exiting: " + e.toString());
assert exitWorker == true;
return;
}
}
}
}
}
/**
* try to grab a 'lock' on the task zk node to own and execute the task.
* <p>
* @param path zk node for the task
*/
private void grabTask(String path) {
Stat stat = new Stat();
long t = -1;
byte[] data;
synchronized (grabTaskLock) {
currentTask = path;
workerInGrabTask = true;
if (Thread.interrupted()) {
return;
}
}
try {
try {
if ((data = ZKUtil.getDataNoWatch(this.watcher, path, stat)) == null) {
tot_wkr_failed_to_grab_task_no_data.incrementAndGet();
return;
}
} catch (KeeperException e) {
LOG.warn("Failed to get data for znode " + path, e);
tot_wkr_failed_to_grab_task_exception.incrementAndGet();
return;
}
if (TaskState.TASK_UNASSIGNED.equals(data) == false) {
tot_wkr_failed_to_grab_task_owned.incrementAndGet();
return;
}
currentVersion = stat.getVersion();
if (ownTask(true) == false) {
tot_wkr_failed_to_grab_task_lost_race.incrementAndGet();
return;
}
if (ZKSplitLog.isRescanNode(watcher, currentTask)) {
endTask(TaskState.TASK_DONE, tot_wkr_task_acquired_rescan);
return;
}
LOG.info("worker " + serverName + " acquired task " + path);
tot_wkr_task_acquired.incrementAndGet();
getDataSetWatchAsync();
t = System.currentTimeMillis();
TaskExecutor.Status status;
status = executor.exec(ZKSplitLog.getFileName(currentTask),
new CancelableProgressable() {
@Override
public boolean progress() {
if (ownTask(false) == false) {
LOG.warn("Failed to heartbeat the task" + currentTask);
return false;
}
return true;
}
});
switch (status) {
case DONE:
endTask(TaskState.TASK_DONE, tot_wkr_task_done);
break;
case PREEMPTED:
tot_wkr_preempt_task.incrementAndGet();
LOG.warn("task execution prempted " + path);
break;
case ERR:
if (!exitWorker) {
endTask(TaskState.TASK_ERR, tot_wkr_task_err);
break;
}
// if the RS is exiting then there is probably a tons of stuff
// that can go wrong. Resign instead of signaling error.
//$FALL-THROUGH$
case RESIGNED:
if (exitWorker) {
LOG.info("task execution interrupted because worker is exiting " +
path);
endTask(TaskState.TASK_RESIGNED, tot_wkr_task_resigned);
} else {
tot_wkr_preempt_task.incrementAndGet();
LOG.info("task execution interrupted via zk by manager " +
path);
}
break;
}
} finally {
if (t > 0) {
LOG.info("worker " + serverName + " done with task " + path +
" in " + (System.currentTimeMillis() - t) + "ms");
}
synchronized (grabTaskLock) {
workerInGrabTask = false;
// clear the interrupt from stopTask() otherwise the next task will
// suffer
Thread.interrupted();
}
}
return;
}
/**
* Try to own the task by transitioning the zk node data from UNASSIGNED to
* OWNED.
* <p>
* This method is also used to periodically heartbeat the task progress by
* transitioning the node from OWNED to OWNED.
* <p>
* @return true if task path is successfully locked
*/
private boolean ownTask(boolean isFirstTime) {
try {
Stat stat = this.watcher.getRecoverableZooKeeper().setData(currentTask,
TaskState.TASK_OWNED.get(serverName), currentVersion);
if (stat == null) {
LOG.warn("zk.setData() returned null for path " + currentTask);
tot_wkr_task_heartbeat_failed.incrementAndGet();
return (false);
}
currentVersion = stat.getVersion();
tot_wkr_task_heartbeat.incrementAndGet();
return (true);
} catch (KeeperException e) {
if (!isFirstTime) {
if (e.code().equals(KeeperException.Code.NONODE)) {
LOG.warn("NONODE failed to assert ownership for " + currentTask, e);
} else if (e.code().equals(KeeperException.Code.BADVERSION)) {
LOG.warn("BADVERSION failed to assert ownership for " +
currentTask, e);
} else {
LOG.warn("failed to assert ownership for " + currentTask, e);
}
}
} catch (InterruptedException e1) {
LOG.warn("Interrupted while trying to assert ownership of " +
currentTask + " " + StringUtils.stringifyException(e1));
Thread.currentThread().interrupt();
}
tot_wkr_task_heartbeat_failed.incrementAndGet();
return (false);
}
/**
* endTask() can fail and the only way to recover out of it is for the
* {@link SplitLogManager} to timeout the task node.
* @param ts
* @param ctr
*/
private void endTask(ZKSplitLog.TaskState ts, AtomicLong ctr) {
String path = currentTask;
currentTask = null;
try {
if (ZKUtil.setData(this.watcher, path, ts.get(serverName),
currentVersion)) {
LOG.info("successfully transitioned task " + path +
" to final state " + ts);
ctr.incrementAndGet();
return;
}
LOG.warn("failed to transistion task " + path + " to end state " + ts +
" because of version mismatch ");
} catch (KeeperException.BadVersionException bve) {
LOG.warn("transisition task " + path + " to " + ts +
" failed because of version mismatch", bve);
} catch (KeeperException.NoNodeException e) {
LOG.fatal("logic error - end task " + path + " " + ts +
" failed because task doesn't exist", e);
} catch (KeeperException e) {
LOG.warn("failed to end task, " + path + " " + ts, e);
}
tot_wkr_final_transistion_failed.incrementAndGet();
return;
}
void getDataSetWatchAsync() {
this.watcher.getRecoverableZooKeeper().getZooKeeper().
getData(currentTask, this.watcher,
new GetDataAsyncCallback(), null);
tot_wkr_get_data_queued.incrementAndGet();
}
void getDataSetWatchSuccess(String path, byte[] data) {
synchronized (grabTaskLock) {
if (workerInGrabTask) {
// currentTask can change but that's ok
String taskpath = currentTask;
if (taskpath != null && taskpath.equals(path)) {
// have to compare data. cannot compare version because then there
// will be race with ownTask()
// cannot just check whether the node has been transitioned to
// UNASSIGNED because by the time this worker sets the data watch
// the node might have made two transitions - from owned by this
// worker to unassigned to owned by another worker
if (! TaskState.TASK_OWNED.equals(data, serverName) &&
! TaskState.TASK_DONE.equals(data, serverName) &&
! TaskState.TASK_ERR.equals(data, serverName) &&
! TaskState.TASK_RESIGNED.equals(data, serverName)) {
LOG.info("task " + taskpath + " preempted from " +
serverName + ", current task state and owner=" +
new String(data));
stopTask();
}
}
}
}
}
void getDataSetWatchFailure(String path) {
synchronized (grabTaskLock) {
if (workerInGrabTask) {
// currentTask can change but that's ok
String taskpath = currentTask;
if (taskpath != null && taskpath.equals(path)) {
LOG.info("retrying data watch on " + path);
tot_wkr_get_data_retry.incrementAndGet();
getDataSetWatchAsync();
} else {
// no point setting a watch on the task which this worker is not
// working upon anymore
}
}
}
}
@Override
public void nodeDataChanged(String path) {
// there will be a self generated dataChanged event every time ownTask()
// heartbeats the task znode by upping its version
synchronized (grabTaskLock) {
if (workerInGrabTask) {
// currentTask can change
String taskpath = currentTask;
if (taskpath!= null && taskpath.equals(path)) {
getDataSetWatchAsync();
}
}
}
}
private List<String> getTaskList() {
for (int i = 0; i < zkretries; i++) {
try {
return (ZKUtil.listChildrenAndWatchForNewChildren(this.watcher,
this.watcher.splitLogZNode));
} catch (KeeperException e) {
LOG.warn("Could not get children of znode " +
this.watcher.splitLogZNode, e);
try {
Thread.sleep(1000);
} catch (InterruptedException e1) {
LOG.warn("Interrupted while trying to get task list ...", e1);
Thread.currentThread().interrupt();
return null;
}
}
}
LOG.warn("Tried " + zkretries + " times, still couldn't fetch " +
"children of " + watcher.splitLogZNode + " giving up");
return null;
}
@Override
public void nodeChildrenChanged(String path) {
if(path.equals(watcher.splitLogZNode)) {
LOG.debug("tasks arrived or departed");
synchronized (taskReadyLock) {
taskReadySeq++;
taskReadyLock.notify();
}
}
}
/**
* If the worker is doing a task i.e. splitting a log file then stop the task.
* It doesn't exit the worker thread.
*/
void stopTask() {
LOG.info("Sending interrupt to stop the worker thread");
worker.interrupt(); // TODO interrupt often gets swallowed, do what else?
}
/**
* start the SplitLogWorker thread
*/
public void start() {
worker = new Thread(null, this, "SplitLogWorker-" + serverName);
exitWorker = false;
worker.start();
return;
}
/**
* stop the SplitLogWorker thread
*/
public void stop() {
exitWorker = true;
stopTask();
}
/**
* Asynchronous handler for zk get-data-set-watch on node results.
*/
class GetDataAsyncCallback implements AsyncCallback.DataCallback {
private final Log LOG = LogFactory.getLog(GetDataAsyncCallback.class);
@Override
public void processResult(int rc, String path, Object ctx, byte[] data,
Stat stat) {
tot_wkr_get_data_result.incrementAndGet();
if (rc != 0) {
LOG.warn("getdata rc = " + KeeperException.Code.get(rc) + " " + path);
getDataSetWatchFailure(path);
return;
}
data = watcher.getRecoverableZooKeeper().removeMetaData(data);
getDataSetWatchSuccess(path, data);
return;
}
}
/**
* Objects implementing this interface actually do the task that has been
* acquired by a {@link SplitLogWorker}. Since there isn't a water-tight
* guarantee that two workers will not be executing the same task therefore it
* is better to have workers prepare the task and then have the
* {@link SplitLogManager} commit the work in SplitLogManager.TaskFinisher
*/
static public interface TaskExecutor {
static public enum Status {
DONE(),
ERR(),
RESIGNED(),
PREEMPTED();
}
public Status exec(String name, CancelableProgressable p);
}
}