/**
* 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 java.io.IOException;
import java.io.InterruptedIOException;
import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import java.util.concurrent.Callable;
import java.util.concurrent.CancellationException;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicBoolean;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.hbase.HRegionInfo;
import org.apache.hadoop.hbase.RegionLocations;
import org.apache.hadoop.hbase.TableName;
import org.apache.hadoop.hbase.util.BoundedCompletionService;
import org.apache.hadoop.hbase.util.Pair;
/**
* This class has the logic for handling scanners for regions with and without replicas.
* 1. A scan is attempted on the default (primary) region
* 2. The scanner sends all the RPCs to the default region until it is done, or, there
* is a timeout on the default (a timeout of zero is disallowed).
* 3. If there is a timeout in (2) above, scanner(s) is opened on the non-default replica(s)
* 4. The results from the first successful scanner are taken, and it is stored which server
* returned the results.
* 5. The next RPCs are done on the above stored server until it is done or there is a timeout,
* in which case, the other replicas are queried (as in (3) above).
*
*/
@InterfaceAudience.Private
class ScannerCallableWithReplicas implements RetryingCallable<Result[]> {
private final Log LOG = LogFactory.getLog(this.getClass());
volatile ScannerCallable currentScannerCallable;
AtomicBoolean replicaSwitched = new AtomicBoolean(false);
final ClusterConnection cConnection;
protected final ExecutorService pool;
protected final int timeBeforeReplicas;
private final Scan scan;
private final int retries;
private Result lastResult;
private final RpcRetryingCaller<Result[]> caller;
private final TableName tableName;
private Configuration conf;
private int scannerTimeout;
private Set<ScannerCallable> outstandingCallables = new HashSet<ScannerCallable>();
public ScannerCallableWithReplicas (TableName tableName, ClusterConnection cConnection,
ScannerCallable baseCallable, ExecutorService pool, int timeBeforeReplicas, Scan scan,
int retries, int scannerTimeout, int caching, Configuration conf,
RpcRetryingCaller<Result []> caller) {
this.currentScannerCallable = baseCallable;
this.cConnection = cConnection;
this.pool = pool;
if (timeBeforeReplicas < 0) {
throw new IllegalArgumentException("Invalid value of operation timeout on the primary");
}
this.timeBeforeReplicas = timeBeforeReplicas;
this.scan = scan;
this.retries = retries;
this.tableName = tableName;
this.conf = conf;
this.scannerTimeout = scannerTimeout;
this.caller = caller;
}
public void setClose() {
currentScannerCallable.setClose();
}
public void setCaching(int caching) {
currentScannerCallable.setCaching(caching);
}
public int getCaching() {
return currentScannerCallable.getCaching();
}
public HRegionInfo getHRegionInfo() {
return currentScannerCallable.getHRegionInfo();
}
@Override
public Result [] call(int timeout) throws IOException {
// If the active replica callable was closed somewhere, invoke the RPC to
// really close it. In the case of regular scanners, this applies. We make couple
// of RPCs to a RegionServer, and when that region is exhausted, we set
// the closed flag. Then an RPC is required to actually close the scanner.
if (currentScannerCallable != null && currentScannerCallable.closed) {
// For closing we target that exact scanner (and not do replica fallback like in
// the case of normal reads)
if (LOG.isTraceEnabled()) {
LOG.trace("Closing scanner id=" + currentScannerCallable.scannerId);
}
Result[] r = currentScannerCallable.call(timeout);
currentScannerCallable = null;
return r;
}
// We need to do the following:
//1. When a scan goes out to a certain replica (default or not), we need to
// continue to hit that until there is a failure. So store the last successfully invoked
// replica
//2. We should close the "losing" scanners (scanners other than the ones we hear back
// from first)
//
RegionLocations rl = RpcRetryingCallerWithReadReplicas.getRegionLocations(true,
RegionReplicaUtil.DEFAULT_REPLICA_ID, cConnection, tableName,
currentScannerCallable.getRow());
// allocate a boundedcompletion pool of some multiple of number of replicas.
// We want to accomodate some RPCs for redundant replica scans (but are still in progress)
BoundedCompletionService<Pair<Result[], ScannerCallable>> cs =
new BoundedCompletionService<Pair<Result[], ScannerCallable>>(pool, rl.size() * 5);
List<ExecutionException> exceptions = null;
int submitted = 0, completed = 0;
AtomicBoolean done = new AtomicBoolean(false);
replicaSwitched.set(false);
// submit call for the primary replica.
submitted += addCallsForCurrentReplica(cs, rl);
try {
// wait for the timeout to see whether the primary responds back
Future<Pair<Result[], ScannerCallable>> f = cs.poll(timeBeforeReplicas,
TimeUnit.MICROSECONDS); // Yes, microseconds
if (f != null) {
Pair<Result[], ScannerCallable> r = f.get();
if (r != null && r.getSecond() != null) {
updateCurrentlyServingReplica(r.getSecond(), r.getFirst(), done, pool);
}
return r == null ? null : r.getFirst(); //great we got a response
}
} catch (ExecutionException e) {
// the primary call failed with RetriesExhaustedException or DoNotRetryIOException
// but the secondaries might still succeed. Continue on the replica RPCs.
exceptions = new ArrayList<ExecutionException>(rl.size());
exceptions.add(e);
completed++;
} catch (CancellationException e) {
throw new InterruptedIOException(e.getMessage());
} catch (InterruptedException e) {
throw new InterruptedIOException(e.getMessage());
}
// submit call for the all of the secondaries at once
// TODO: this may be an overkill for large region replication
submitted += addCallsForOtherReplicas(cs, rl, 0, rl.size() - 1);
try {
while (completed < submitted) {
try {
Future<Pair<Result[], ScannerCallable>> f = cs.take();
Pair<Result[], ScannerCallable> r = f.get();
if (r != null && r.getSecond() != null) {
updateCurrentlyServingReplica(r.getSecond(), r.getFirst(), done, pool);
}
return r == null ? null : r.getFirst(); // great we got an answer
} catch (ExecutionException e) {
// if not cancel or interrupt, wait until all RPC's are done
// one of the tasks failed. Save the exception for later.
if (exceptions == null) exceptions = new ArrayList<ExecutionException>(rl.size());
exceptions.add(e);
completed++;
}
}
} catch (CancellationException e) {
throw new InterruptedIOException(e.getMessage());
} catch (InterruptedException e) {
throw new InterruptedIOException(e.getMessage());
} finally {
// We get there because we were interrupted or because one or more of the
// calls succeeded or failed. In all case, we stop all our tasks.
cs.cancelAll(true);
}
if (exceptions != null && !exceptions.isEmpty()) {
RpcRetryingCallerWithReadReplicas.throwEnrichedException(exceptions.get(0),
retries); // just rethrow the first exception for now.
}
return null; // unreachable
}
private void updateCurrentlyServingReplica(ScannerCallable scanner, Result[] result,
AtomicBoolean done, ExecutorService pool) {
if (done.compareAndSet(false, true)) {
if (currentScannerCallable != scanner) replicaSwitched.set(true);
currentScannerCallable = scanner;
// store where to start the replica scanner from if we need to.
if (result != null && result.length != 0) this.lastResult = result[result.length - 1];
if (LOG.isTraceEnabled()) {
LOG.trace("Setting current scanner as id=" + currentScannerCallable.scannerId +
" associated with replica=" + currentScannerCallable.getHRegionInfo().getReplicaId());
}
// close all outstanding replica scanners but the one we heard back from
outstandingCallables.remove(scanner);
for (ScannerCallable s : outstandingCallables) {
if (LOG.isTraceEnabled()) {
LOG.trace("Closing scanner id=" + s.scannerId +
", replica=" + s.getHRegionInfo().getRegionId() +
" because slow and replica=" +
this.currentScannerCallable.getHRegionInfo().getReplicaId() + " succeeded");
}
// Submit the "close" to the pool since this might take time, and we don't
// want to wait for the "close" to happen yet. The "wait" will happen when
// the table is closed (when the awaitTermination of the underlying pool is called)
s.setClose();
RetryingRPC r = new RetryingRPC(s);
pool.submit(r);
}
// now clear outstandingCallables since we scheduled a close for all the contained scanners
outstandingCallables.clear();
}
}
/**
* When a scanner switches in the middle of scanning (the 'next' call fails
* for example), the upper layer {@link ClientScanner} needs to know
* @return
*/
public boolean switchedToADifferentReplica() {
return replicaSwitched.get();
}
private int addCallsForCurrentReplica(
BoundedCompletionService<Pair<Result[], ScannerCallable>> cs, RegionLocations rl) {
RetryingRPC retryingOnReplica = new RetryingRPC(currentScannerCallable);
outstandingCallables.add(currentScannerCallable);
cs.submit(retryingOnReplica);
return 1;
}
private int addCallsForOtherReplicas(
BoundedCompletionService<Pair<Result[], ScannerCallable>> cs, RegionLocations rl, int min,
int max) {
if (scan.getConsistency() == Consistency.STRONG) {
return 0; // not scheduling on other replicas for strong consistency
}
for (int id = min; id <= max; id++) {
if (currentScannerCallable.getHRegionInfo().getReplicaId() == id) {
continue; //this was already scheduled earlier
}
ScannerCallable s = currentScannerCallable.getScannerCallableForReplica(id);
if (this.lastResult != null) {
s.getScan().setStartRow(this.lastResult.getRow());
}
outstandingCallables.add(s);
RetryingRPC retryingOnReplica = new RetryingRPC(s);
cs.submit(retryingOnReplica);
}
return max - min + 1;
}
class RetryingRPC implements Callable<Pair<Result[], ScannerCallable>> {
final ScannerCallable callable;
RetryingRPC(ScannerCallable callable) {
this.callable = callable;
}
@Override
public Pair<Result[], ScannerCallable> call() throws IOException {
// For the Consistency.STRONG (default case), we reuse the caller
// to keep compatibility with what is done in the past
// For the Consistency.TIMELINE case, we can't reuse the caller
// since we could be making parallel RPCs (caller.callWithRetries is synchronized
// and we can't invoke it multiple times at the same time)
RpcRetryingCaller<Result[]> caller = ScannerCallableWithReplicas.this.caller;
if (scan.getConsistency() == Consistency.TIMELINE) {
caller = new RpcRetryingCallerFactory(ScannerCallableWithReplicas.this.conf).
<Result[]>newCaller();
}
Result[] res = caller.callWithRetries(callable, scannerTimeout);
return new Pair<Result[], ScannerCallable>(res, callable);
}
}
@Override
public void prepare(boolean reload) throws IOException {
}
@Override
public void throwable(Throwable t, boolean retrying) {
currentScannerCallable.throwable(t, retrying);
}
@Override
public String getExceptionMessageAdditionalDetail() {
return currentScannerCallable.getExceptionMessageAdditionalDetail();
}
@Override
public long sleep(long pause, int tries) {
return currentScannerCallable.sleep(pause, tries);
}
}