bharathv commented on a change in pull request #830: HBASE-23281: Track meta region locations in masters URL: https://github.com/apache/hbase/pull/830#discussion_r348081119
########## File path: hbase-server/src/main/java/org/apache/hadoop/hbase/master/MetaRegionLocationCache.java ########## @@ -0,0 +1,211 @@ +/* + * 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.master; + +import java.util.ArrayList; +import java.util.List; +import java.util.Optional; +import java.util.concurrent.ConcurrentNavigableMap; +import org.apache.hadoop.hbase.HRegionLocation; +import org.apache.hadoop.hbase.exceptions.DeserializationException; +import org.apache.hadoop.hbase.types.CopyOnWriteArrayMap; +import org.apache.hadoop.hbase.util.RetryCounter; +import org.apache.hadoop.hbase.util.RetryCounterFactory; +import org.apache.hadoop.hbase.zookeeper.ZKListener; +import org.apache.hadoop.hbase.zookeeper.ZKUtil; +import org.apache.hadoop.hbase.zookeeper.ZKWatcher; +import org.apache.hadoop.hbase.zookeeper.ZNodePaths; +import org.apache.yetus.audience.InterfaceAudience; +import org.apache.zookeeper.KeeperException; +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; +import org.apache.hadoop.hbase.shaded.protobuf.ProtobufUtil; + +/** + * A cache of meta region location metadata. Registers a listener on ZK to track changes to the + * meta table znodes. Clients are expected to retry if the meta information is stale. This class + * is thread-safe. + */ +@InterfaceAudience.Private +public class MetaRegionLocationCache extends ZKListener { + + private static final Logger LOG = LoggerFactory.getLogger(MetaRegionLocationCache.class); + + // Maximum number of times we retry when ZK operation times out. + private static final int MAX_ZK_META_FETCH_RETRIES = 10; + // Sleep interval ms between ZK operation retries. + private static final int SLEEP_INTERVAL_MS_BETWEEN_RETRIES = 1000; + private final RetryCounterFactory retryCounterFactory = + new RetryCounterFactory(MAX_ZK_META_FETCH_RETRIES, SLEEP_INTERVAL_MS_BETWEEN_RETRIES); + + // Cached meta region locations indexed by replica ID. + // CopyOnWriteArrayMap ensures synchronization during updates and a consistent snapshot during + // client requests. Even though CopyOnWriteArrayMap copies the data structure for every write, + // that should be OK since the size of the list is often small and mutations are not too often + // and we do not need to block client requests while mutations are in progress. + private final CopyOnWriteArrayMap<Integer, HRegionLocation> cachedMetaLocations; + + private enum ZNodeOpType { + INIT, + CREATED, + CHANGED, + DELETED + }; + + MetaRegionLocationCache(ZKWatcher zkWatcher) { + super(zkWatcher); + cachedMetaLocations = new CopyOnWriteArrayMap<>(); + watcher.registerListener(this); + // Populate the initial snapshot of data from meta znodes. + // This is needed because stand-by masters can potentially start after the initial znode + // creation. + populateInitialMetaLocations(); + } + + private void populateInitialMetaLocations() { + RetryCounter retryCounter = retryCounterFactory.create(); + List<String> znodes = null; + do { + try { + znodes = watcher.getMetaReplicaNodes(); + break; + } catch (KeeperException ke) { + LOG.debug("Error populating intial meta locations", ke); + try { + retryCounter.sleepUntilNextRetry(); + } catch (InterruptedException ie) { + LOG.error("Interrupted while populating intial meta locations", ie); + return; + } + if (!retryCounter.shouldRetry()) { + LOG.error("Error populating intial meta locations. Retries exhausted. Last error: ", ke); + break; + } + } + } while (retryCounter.shouldRetry()); + if (znodes == null) { + return; + } + for (String znode: znodes) { + String path = ZNodePaths.joinZNode(watcher.getZNodePaths().baseZNode, znode); + updateMetaLocation(path, ZNodeOpType.INIT); + } + } + + /** + * Gets the HRegionLocation for a given meta replica ID. Renews the watch on the znode for + * future updates. + * @param replicaId ReplicaID of the region. + * @return HRegionLocation for the meta replica. + * @throws KeeperException if there is any issue fetching/parsing the serialized data. + */ + private HRegionLocation getMetaRegionLocation(int replicaId) + throws KeeperException { + RegionState metaRegionState; + try { + byte[] data = ZKUtil.getDataAndWatch(watcher, + watcher.getZNodePaths().getZNodeForReplica(replicaId)); + metaRegionState = ProtobufUtil.parseMetaRegionStateFrom(data, replicaId); + } catch (DeserializationException e) { + throw ZKUtil.convert(e); + } + return new HRegionLocation(metaRegionState.getRegion(), metaRegionState.getServerName()); + } + + private void updateMetaLocation(String path, ZNodeOpType opType) { + if (!isValidMetaZNode(path)) { + return; + } + LOG.debug("Updating meta znode for path {}: {}", path, opType.name()); + int replicaId = watcher.getZNodePaths().getMetaReplicaIdFromPath(path); + RetryCounter retryCounter = retryCounterFactory.create(); + HRegionLocation location = null; + do { + try { + if (opType == ZNodeOpType.DELETED) { + if (!ZKUtil.watchAndCheckExists(watcher, path)) { + // The path does not exist, we've set the watcher and we can break for now. + break; + } + // If it is a transient error and the node appears right away, we fetch the + // latest meta state. + } + location = getMetaRegionLocation(replicaId); + break; + } catch (KeeperException e) { + LOG.debug("Error getting meta location for path {}", path, e); + if (retryCounter.shouldRetry()) { + try { + retryCounter.sleepUntilNextRetry(); + } catch (InterruptedException ie) { + LOG.error("Interrupted while updating meta location for path {}", path, ie); + return; + } + } else { + LOG.error("Error getting meta location for path {}. Retries exhausted.", path, e); + } + } + } while (retryCounter.shouldRetry()); + if (location == null) { + cachedMetaLocations.remove(replicaId); + return; + } + cachedMetaLocations.put(replicaId, location); + } + + /** + * @return List of HRegionLocations for meta replica(s), null if the cache is empty. + */ + public Optional<List<HRegionLocation>> getMetaRegionLocations() { + ConcurrentNavigableMap<Integer, HRegionLocation> snapshot = + cachedMetaLocations.tailMap(cachedMetaLocations.firstKey()); + if (snapshot == null || snapshot.isEmpty()) { Review comment: Done. ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: us...@infra.apache.org With regards, Apache Git Services
