org.apache.hadoop.hbase.client.AsyncMetaRegionLocator Maven / Gradle / Ivy
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* 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.client.AsyncRegionLocatorHelper.canUpdateOnError;
import static org.apache.hadoop.hbase.client.AsyncRegionLocatorHelper.createRegionLocations;
import static org.apache.hadoop.hbase.client.AsyncRegionLocatorHelper.isGood;
import static org.apache.hadoop.hbase.client.AsyncRegionLocatorHelper.removeRegionLocation;
import static org.apache.hadoop.hbase.client.AsyncRegionLocatorHelper.replaceRegionLocation;
import static org.apache.hadoop.hbase.util.FutureUtils.addListener;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.atomic.AtomicReference;
import org.apache.hadoop.hbase.HRegionLocation;
import org.apache.hadoop.hbase.RegionLocations;
import org.apache.yetus.audience.InterfaceAudience;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* The asynchronous locator for meta region.
*/
@InterfaceAudience.Private
class AsyncMetaRegionLocator {
private static final Logger LOG = LoggerFactory.getLogger(AsyncMetaRegionLocator.class);
private final AsyncRegistry registry;
private final AtomicReference metaRegionLocations = new AtomicReference<>();
private final AtomicReference> metaRelocateFuture =
new AtomicReference<>();
AsyncMetaRegionLocator(AsyncRegistry registry) {
this.registry = registry;
}
/**
* Get the region locations for meta region. If the location for the given replica is not
* available in the cached locations, then fetch from the HBase cluster.
*
* The replicaId parameter is important. If the region replication config for meta
* region is changed, then the cached region locations may not have the locations for new
* replicas. If we do not check the location for the given replica, we will always return the
* cached region locations and cause an infinite loop.
*/
CompletableFuture getRegionLocations(int replicaId, boolean reload) {
for (;;) {
if (!reload) {
RegionLocations locs = this.metaRegionLocations.get();
if (isGood(locs, replicaId)) {
return CompletableFuture.completedFuture(locs);
}
}
LOG.trace("Meta region location cache is null, try fetching from registry.");
if (metaRelocateFuture.compareAndSet(null, new CompletableFuture<>())) {
LOG.debug("Start fetching meta region location from registry.");
CompletableFuture future = metaRelocateFuture.get();
addListener(registry.getMetaRegionLocation(), (locs, error) -> {
if (error != null) {
LOG.debug("Failed to fetch meta region location from registry", error);
metaRelocateFuture.getAndSet(null).completeExceptionally(error);
return;
}
LOG.debug("The fetched meta region location is {}" + locs);
// Here we update cache before reset future, so it is possible that someone can get a
// stale value. Consider this:
// 1. update cache
// 2. someone clear the cache and relocate again
// 3. the metaRelocateFuture is not null so the old future is used.
// 4. we clear metaRelocateFuture and complete the future in it with the value being
// cleared in step 2.
// But we do not think it is a big deal as it rarely happens, and even if it happens, the
// caller will retry again later, no correctness problems.
this.metaRegionLocations.set(locs);
metaRelocateFuture.set(null);
future.complete(locs);
});
} else {
CompletableFuture future = metaRelocateFuture.get();
if (future != null) {
return future;
}
}
}
}
private HRegionLocation getCacheLocation(HRegionLocation loc) {
RegionLocations locs = metaRegionLocations.get();
return locs != null ? locs.getRegionLocation(loc.getRegion().getReplicaId()) : null;
}
private void addLocationToCache(HRegionLocation loc) {
for (;;) {
int replicaId = loc.getRegion().getReplicaId();
RegionLocations oldLocs = metaRegionLocations.get();
if (oldLocs == null) {
RegionLocations newLocs = createRegionLocations(loc);
if (metaRegionLocations.compareAndSet(null, newLocs)) {
return;
}
}
HRegionLocation oldLoc = oldLocs.getRegionLocation(replicaId);
if (oldLoc != null && (oldLoc.getSeqNum() > loc.getSeqNum() ||
oldLoc.getServerName().equals(loc.getServerName()))) {
return;
}
RegionLocations newLocs = replaceRegionLocation(oldLocs, loc);
if (metaRegionLocations.compareAndSet(oldLocs, newLocs)) {
return;
}
}
}
private void removeLocationFromCache(HRegionLocation loc) {
for (;;) {
RegionLocations oldLocs = metaRegionLocations.get();
if (oldLocs == null) {
return;
}
HRegionLocation oldLoc = oldLocs.getRegionLocation(loc.getRegion().getReplicaId());
if (!canUpdateOnError(loc, oldLoc)) {
return;
}
RegionLocations newLocs = removeRegionLocation(oldLocs, loc.getRegion().getReplicaId());
if (metaRegionLocations.compareAndSet(oldLocs, newLocs)) {
return;
}
}
}
void updateCachedLocationOnError(HRegionLocation loc, Throwable exception) {
AsyncRegionLocatorHelper.updateCachedLocationOnError(loc, exception, this::getCacheLocation,
this::addLocationToCache, this::removeLocationFromCache);
}
void clearCache() {
metaRegionLocations.set(null);
}
}