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HBASE-27458 Use ReadWriteLock for region scanner readpoint map #5068

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Mar 2, 2023
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Original file line number Diff line number Diff line change
Expand Up @@ -396,6 +396,7 @@ public void setRestoredRegion(boolean restoredRegion) {
final ExecutorService rowProcessorExecutor = Executors.newCachedThreadPool();

final ConcurrentHashMap<RegionScanner, Long> scannerReadPoints;
final ReadPointCalculationLock smallestReadPointCalcLock;

/**
* The sequence ID that was enLongAddered when this region was opened.
Expand Down Expand Up @@ -434,19 +435,18 @@ public void setRestoredRegion(boolean restoredRegion) {
* this readPoint, are included in every read operation.
*/
public long getSmallestReadPoint() {
long minimumReadPoint;
// We need to ensure that while we are calculating the smallestReadPoint
// no new RegionScanners can grab a readPoint that we are unaware of.
// We achieve this by synchronizing on the scannerReadPoints object.
synchronized (scannerReadPoints) {
minimumReadPoint = mvcc.getReadPoint();
smallestReadPointCalcLock.lock(ReadPointCalculationLock.LockType.CALCULATION_LOCK);
try {
long minimumReadPoint = mvcc.getReadPoint();
for (Long readPoint : this.scannerReadPoints.values()) {
if (readPoint < minimumReadPoint) {
minimumReadPoint = readPoint;
}
minimumReadPoint = Math.min(minimumReadPoint, readPoint);
}
return minimumReadPoint;
} finally {
smallestReadPointCalcLock.unlock(ReadPointCalculationLock.LockType.CALCULATION_LOCK);
}
return minimumReadPoint;
}

/*
Expand Down Expand Up @@ -811,6 +811,7 @@ public HRegion(final HRegionFileSystem fs, final WAL wal, final Configuration co

setHTableSpecificConf();
this.scannerReadPoints = new ConcurrentHashMap<>();
this.smallestReadPointCalcLock = new ReadPointCalculationLock(conf);

this.busyWaitDuration = conf.getLong("hbase.busy.wait.duration", DEFAULT_BUSY_WAIT_DURATION);
this.maxBusyWaitMultiplier = conf.getInt("hbase.busy.wait.multiplier.max", 2);
Expand Down Expand Up @@ -6990,7 +6991,8 @@ public RegionInfo getRegionInfo() {
// getSmallestReadPoint, before scannerReadPoints is updated.
IsolationLevel isolationLevel = scan.getIsolationLevel();
long mvccReadPoint = PackagePrivateFieldAccessor.getMvccReadPoint(scan);
synchronized (scannerReadPoints) {
region.smallestReadPointCalcLock.lock(ReadPointCalculationLock.LockType.RECORDING_LOCK);
try {
if (mvccReadPoint > 0) {
this.readPt = mvccReadPoint;
} else if (
Expand All @@ -7001,6 +7003,8 @@ public RegionInfo getRegionInfo() {
this.readPt = rsServices.getNonceManager().getMvccFromOperationContext(nonceGroup, nonce);
}
scannerReadPoints.put(this, this.readPt);
} finally {
region.smallestReadPointCalcLock.unlock(ReadPointCalculationLock.LockType.RECORDING_LOCK);
}
initializeScanners(scan, additionalScanners);
}
Expand Down
Original file line number Diff line number Diff line change
@@ -0,0 +1,90 @@
/*
* 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 java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;
import org.apache.hadoop.conf.Configuration;
import org.apache.yetus.audience.InterfaceAudience;

/**
* Lock to manage concurrency between {@link RegionScanner} and
* {@link HRegion#getSmallestReadPoint()}. We need to ensure that while we are calculating the
* smallest read point, no new scanners can modify the scannerReadPoints Map. We used to achieve
* this by synchronizing on the scannerReadPoints object. But this may block the read thread and
* reduce the read performance. Since the scannerReadPoints object is a
* {@link java.util.concurrent.ConcurrentHashMap}, which is thread-safe, so the
* {@link RegionScanner} can record their read points concurrently, what it needs to do is just
* acquiring a shared lock. When we calculate the smallest read point, we need to acquire an
* exclusive lock. This can improve read performance in most scenarios, only not when we have a lot
* of delta operations, like {@link org.apache.hadoop.hbase.client.Append} or
* {@link org.apache.hadoop.hbase.client.Increment}. So we introduce a flag to enable/disable this
* feature.
*/
@InterfaceAudience.Private
public class ReadPointCalculationLock {

public enum LockType {
CALCULATION_LOCK,
RECORDING_LOCK
}

private final boolean useReadWriteLockForReadPoints;
private Lock lock;
private ReadWriteLock readWriteLock;

ReadPointCalculationLock(Configuration conf) {
this.useReadWriteLockForReadPoints =
conf.getBoolean("hbase.region.readpoints.read.write.lock.enable", false);
if (useReadWriteLockForReadPoints) {
readWriteLock = new ReentrantReadWriteLock();
} else {
lock = new ReentrantLock();
}
}

void lock(LockType lockType) {
if (useReadWriteLockForReadPoints) {
assert lock == null;
if (lockType == LockType.CALCULATION_LOCK) {
readWriteLock.writeLock().lock();
} else {
readWriteLock.readLock().lock();
}
} else {
assert readWriteLock == null;
lock.lock();
}
}

void unlock(LockType lockType) {
if (useReadWriteLockForReadPoints) {
assert lock == null;
if (lockType == LockType.CALCULATION_LOCK) {
readWriteLock.writeLock().unlock();
} else {
readWriteLock.readLock().unlock();
}
} else {
assert readWriteLock == null;
lock.unlock();
}
}
}