/**
* 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.client;
import static org.apache.hadoop.hbase.util.CollectionUtils.computeIfAbsent;
import com.google.common.annotations.VisibleForTesting;
import java.io.IOException;
import java.util.Map.Entry;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import org.apache.commons.lang.mutable.MutableBoolean;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.hbase.HConstants;
import org.apache.hadoop.hbase.ServerName;
import org.apache.hadoop.hbase.classification.InterfaceAudience;
import org.apache.hadoop.hbase.exceptions.ClientExceptionsUtil;
import org.apache.hadoop.hbase.exceptions.PreemptiveFastFailException;
import org.apache.hadoop.hbase.ipc.CallTimeoutException;
import org.apache.hadoop.hbase.util.EnvironmentEdgeManager;
import org.apache.hadoop.ipc.RemoteException;
/**
* The concrete {@link RetryingCallerInterceptor} class that implements the preemptive fast fail
* feature.
* <p>
* The motivation is as follows : In case where a large number of clients try and talk to a
* particular region server in hbase, if the region server goes down due to network problems, we
* might end up in a scenario where the clients would go into a state where they all start to retry.
* This behavior will set off many of the threads in pretty much the same path and they all would be
* sleeping giving rise to a state where the client either needs to create more threads to send new
* requests to other hbase machines or block because the client cannot create anymore threads.
* <p>
* In most cases the clients might prefer to have a bound on the number of threads that are created
* in order to send requests to hbase. This would mostly result in the client thread starvation.
* <p>
* To circumvent this problem, the approach that is being taken here under is to let 1 of the many
* threads who are trying to contact the regionserver with connection problems and let the other
* threads get a {@link PreemptiveFastFailException} so that they can move on and take other
* requests.
* <p>
* This would give the client more flexibility on the kind of action he would want to take in cases
* where the regionserver is down. He can either discard the requests and send a nack upstream
* faster or have an application level retry or buffer the requests up so as to send them down to
* hbase later.
*/
@InterfaceAudience.Private
class PreemptiveFastFailInterceptor extends RetryingCallerInterceptor {
private static final Log LOG = LogFactory
.getLog(PreemptiveFastFailInterceptor.class);
// amount of time to wait before we consider a server to be in fast fail
// mode
protected final long fastFailThresholdMilliSec;
// Keeps track of failures when we cannot talk to a server. Helps in
// fast failing clients if the server is down for a long time.
protected final ConcurrentMap<ServerName, FailureInfo> repeatedFailuresMap = new ConcurrentHashMap<>();
// We populate repeatedFailuresMap every time there is a failure. So, to
// keep it from growing unbounded, we garbage collect the failure information
// every cleanupInterval.
protected final long failureMapCleanupIntervalMilliSec;
protected volatile long lastFailureMapCleanupTimeMilliSec;
// clear failure Info. Used to clean out all entries.
// A safety valve, in case the client does not exit the
// fast fail mode for any reason.
private long fastFailClearingTimeMilliSec;
private final ThreadLocal<MutableBoolean> threadRetryingInFastFailMode = new ThreadLocal<>();
public PreemptiveFastFailInterceptor(Configuration conf) {
this.fastFailThresholdMilliSec = conf.getLong(
HConstants.HBASE_CLIENT_FAST_FAIL_THREASHOLD_MS,
HConstants.HBASE_CLIENT_FAST_FAIL_THREASHOLD_MS_DEFAULT);
this.failureMapCleanupIntervalMilliSec = conf.getLong(
HConstants.HBASE_CLIENT_FAST_FAIL_CLEANUP_MS_DURATION_MS,
HConstants.HBASE_CLIENT_FAST_FAIL_CLEANUP_DURATION_MS_DEFAULT);
lastFailureMapCleanupTimeMilliSec = EnvironmentEdgeManager.currentTime();
}
public void intercept(FastFailInterceptorContext context)
throws PreemptiveFastFailException {
context.setFailureInfo(repeatedFailuresMap.get(context.getServer()));
if (inFastFailMode(context.getServer()) && !currentThreadInFastFailMode()) {
// In Fast-fail mode, all but one thread will fast fail. Check
// if we are that one chosen thread.
context.setRetryDespiteFastFailMode(shouldRetryInspiteOfFastFail(context
.getFailureInfo()));
if (!context.isRetryDespiteFastFailMode()) { // we don't have to retry
LOG.debug("Throwing PFFE : " + context.getFailureInfo() + " tries : "
+ context.getTries());
throw new PreemptiveFastFailException(
context.getFailureInfo().numConsecutiveFailures.get(),
context.getFailureInfo().timeOfFirstFailureMilliSec,
context.getFailureInfo().timeOfLatestAttemptMilliSec, context.getServer(),
context.getGuaranteedClientSideOnly().isTrue());
}
}
context.setDidTry(true);
}
public void handleFailure(FastFailInterceptorContext context,
Throwable t) throws IOException {
handleThrowable(t, context.getServer(),
context.getCouldNotCommunicateWithServer(),
context.getGuaranteedClientSideOnly());
}
public void updateFailureInfo(FastFailInterceptorContext context) {
updateFailureInfoForServer(context.getServer(), context.getFailureInfo(),
context.didTry(), context.getCouldNotCommunicateWithServer()
.booleanValue(), context.isRetryDespiteFastFailMode());
}
/**
* Handles failures encountered when communicating with a server.
*
* Updates the FailureInfo in repeatedFailuresMap to reflect the failure.
* Throws RepeatedConnectException if the client is in Fast fail mode.
*
* @param serverName
* @param t
* - the throwable to be handled.
* @throws PreemptiveFastFailException
*/
@VisibleForTesting
protected void handleFailureToServer(ServerName serverName, Throwable t) {
if (serverName == null || t == null) {
return;
}
long currentTime = EnvironmentEdgeManager.currentTime();
FailureInfo fInfo =
computeIfAbsent(repeatedFailuresMap, serverName, () -> new FailureInfo(currentTime));
fInfo.timeOfLatestAttemptMilliSec = currentTime;
fInfo.numConsecutiveFailures.incrementAndGet();
}
public void handleThrowable(Throwable t1, ServerName serverName,
MutableBoolean couldNotCommunicateWithServer,
MutableBoolean guaranteedClientSideOnly) throws IOException {
Throwable t2 = ClientExceptionsUtil.translatePFFE(t1);
boolean isLocalException = !(t2 instanceof RemoteException);
if ((isLocalException && ClientExceptionsUtil.isConnectionException(t2))) {
couldNotCommunicateWithServer.setValue(true);
guaranteedClientSideOnly.setValue(!(t2 instanceof CallTimeoutException));
handleFailureToServer(serverName, t2);
}
}
/**
* Occasionally cleans up unused information in repeatedFailuresMap.
*
* repeatedFailuresMap stores the failure information for all remote hosts
* that had failures. In order to avoid these from growing indefinitely,
* occassionallyCleanupFailureInformation() will clear these up once every
* cleanupInterval ms.
*/
protected void occasionallyCleanupFailureInformation() {
long now = System.currentTimeMillis();
if (!(now > lastFailureMapCleanupTimeMilliSec
+ failureMapCleanupIntervalMilliSec))
return;
// remove entries that haven't been attempted in a while
// No synchronization needed. It is okay if multiple threads try to
// remove the entry again and again from a concurrent hash map.
StringBuilder sb = new StringBuilder();
for (Entry<ServerName, FailureInfo> entry : repeatedFailuresMap.entrySet()) {
if (now > entry.getValue().timeOfLatestAttemptMilliSec
+ failureMapCleanupIntervalMilliSec) { // no recent failures
repeatedFailuresMap.remove(entry.getKey());
} else if (now > entry.getValue().timeOfFirstFailureMilliSec
+ this.fastFailClearingTimeMilliSec) { // been failing for a long
// time
LOG.error(entry.getKey()
+ " been failing for a long time. clearing out."
+ entry.getValue().toString());
repeatedFailuresMap.remove(entry.getKey());
} else {
sb.append(entry.getKey().toString()).append(" failing ")
.append(entry.getValue().toString()).append("\n");
}
}
if (sb.length() > 0) {
LOG.warn("Preemptive failure enabled for : " + sb.toString());
}
lastFailureMapCleanupTimeMilliSec = now;
}
/**
* Checks to see if we are in the Fast fail mode for requests to the server.
*
* If a client is unable to contact a server for more than
* fastFailThresholdMilliSec the client will get into fast fail mode.
*
* @param server
* @return true if the client is in fast fail mode for the server.
*/
private boolean inFastFailMode(ServerName server) {
FailureInfo fInfo = repeatedFailuresMap.get(server);
// if fInfo is null --> The server is considered good.
// If the server is bad, wait long enough to believe that the server is
// down.
return (fInfo != null &&
EnvironmentEdgeManager.currentTime() >
(fInfo.timeOfFirstFailureMilliSec + this.fastFailThresholdMilliSec));
}
/**
* Checks to see if the current thread is already in FastFail mode for *some*
* server.
*
* @return true, if the thread is already in FF mode.
*/
private boolean currentThreadInFastFailMode() {
return (this.threadRetryingInFastFailMode.get() != null && (this.threadRetryingInFastFailMode
.get().booleanValue() == true));
}
/**
* Check to see if the client should try to connnect to the server, inspite of
* knowing that it is in the fast fail mode.
*
* The idea here is that we want just one client thread to be actively trying
* to reconnect, while all the other threads trying to reach the server will
* short circuit.
*
* @param fInfo
* @return true if the client should try to connect to the server.
*/
protected boolean shouldRetryInspiteOfFastFail(FailureInfo fInfo) {
// We believe that the server is down, But, we want to have just one
// client
// actively trying to connect. If we are the chosen one, we will retry
// and not throw an exception.
if (fInfo != null
&& fInfo.exclusivelyRetringInspiteOfFastFail.compareAndSet(false, true)) {
MutableBoolean threadAlreadyInFF = this.threadRetryingInFastFailMode
.get();
if (threadAlreadyInFF == null) {
threadAlreadyInFF = new MutableBoolean();
this.threadRetryingInFastFailMode.set(threadAlreadyInFF);
}
threadAlreadyInFF.setValue(true);
return true;
} else {
return false;
}
}
/**
*
* This function updates the Failure info for a particular server after the
* attempt to
*
* @param server
* @param fInfo
* @param couldNotCommunicate
* @param retryDespiteFastFailMode
*/
private void updateFailureInfoForServer(ServerName server,
FailureInfo fInfo, boolean didTry, boolean couldNotCommunicate,
boolean retryDespiteFastFailMode) {
if (server == null || fInfo == null || didTry == false)
return;
// If we were able to connect to the server, reset the failure
// information.
if (couldNotCommunicate == false) {
LOG.info("Clearing out PFFE for server " + server);
repeatedFailuresMap.remove(server);
} else {
// update time of last attempt
long currentTime = System.currentTimeMillis();
fInfo.timeOfLatestAttemptMilliSec = currentTime;
// Release the lock if we were retrying inspite of FastFail
if (retryDespiteFastFailMode) {
fInfo.exclusivelyRetringInspiteOfFastFail.set(false);
threadRetryingInFastFailMode.get().setValue(false);
}
}
occasionallyCleanupFailureInformation();
}
@Override
public void intercept(RetryingCallerInterceptorContext context)
throws PreemptiveFastFailException {
if (context instanceof FastFailInterceptorContext) {
intercept((FastFailInterceptorContext) context);
}
}
@Override
public void handleFailure(RetryingCallerInterceptorContext context,
Throwable t) throws IOException {
if (context instanceof FastFailInterceptorContext) {
handleFailure((FastFailInterceptorContext) context, t);
}
}
@Override
public void updateFailureInfo(RetryingCallerInterceptorContext context) {
if (context instanceof FastFailInterceptorContext) {
updateFailureInfo((FastFailInterceptorContext) context);
}
}
@Override
public RetryingCallerInterceptorContext createEmptyContext() {
return new FastFailInterceptorContext();
}
protected boolean isServerInFailureMap(ServerName serverName) {
return this.repeatedFailuresMap.containsKey(serverName);
}
@Override
public String toString() {
return "PreemptiveFastFailInterceptor";
}
}