ndimiduk commented on a change in pull request #781: HBASE-18095: Zookeeper-less client connection implementation URL: https://github.com/apache/hbase/pull/781#discussion_r344420633
########## File path: hbase-server/src/main/java/org/apache/hadoop/hbase/master/MetaRegionLocationCache.java ########## @@ -0,0 +1,185 @@ +/** + * 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 org.apache.hadoop.hbase.MetaRegionsNotAvailableException; +import org.apache.hadoop.hbase.shaded.protobuf.generated.HBaseProtos; +import org.apache.hadoop.hbase.shaded.protobuf.ProtobufUtil; + +import org.apache.hadoop.hbase.HRegionLocation; +import org.apache.hadoop.hbase.types.CopyOnWriteArrayMap; +import org.apache.hadoop.hbase.zookeeper.MetaTableLocator; +import org.apache.hadoop.hbase.zookeeper.ZKListener; +import org.apache.hadoop.hbase.zookeeper.ZKWatcher; +import org.apache.hadoop.hbase.zookeeper.ZNodePaths; +import org.apache.hbase.thirdparty.com.google.common.annotations.VisibleForTesting; +import org.apache.yetus.audience.InterfaceAudience; +import org.apache.zookeeper.KeeperException; +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +import java.util.ArrayList; +import java.util.List; +import java.util.concurrent.ConcurrentNavigableMap; + +/** + * A cache of meta region location metadata. This cache is used to serve 'GetMetaLocations' RPCs + * from clients. 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. Should this be configurable? + private static final int MAX_ZK_META_FETCH_RETRIES = 10; + + private ZKWatcher watcher; + // 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. + CopyOnWriteArrayMap<Integer, HRegionLocation> cachedMetaLocations; + + private enum ZNodeOpType { + INIT, + CREATED, + CHANGED, + DELETED + }; + + public MetaRegionLocationCache(ZKWatcher zkWatcher) { + super(zkWatcher); + watcher = 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() { + int retries = 0; + while (retries++ < MAX_ZK_META_FETCH_RETRIES) { + try { + List<String> znodes = watcher.getMetaReplicaNodes(); + for (String znode: znodes) { + String path = ZNodePaths.joinZNode(watcher.getZNodePaths().baseZNode, znode); + updateMetaLocation(path, ZNodeOpType.INIT); + } + break; + } catch (KeeperException.OperationTimeoutException e) { + LOG.warn("Timed out connecting to ZK cluster", e); + + } catch (KeeperException e) { + LOG.warn("Error populating initial meta locations", e); + break; + } + } + } + + private void updateMetaLocation(String path, ZNodeOpType opType) { + if (!isValidMetaZNode(path)) { + return; + } + LOG.info("Meta znode for path {}: {}", path, opType.name()); + int replicaId = watcher.getZNodePaths().getMetaReplicaIdFromPath(path); + if (opType == ZNodeOpType.DELETED) { + cachedMetaLocations.remove(replicaId); + return; + } + RegionState state = null; + int retries = 0; + while (retries++ < MAX_ZK_META_FETCH_RETRIES) { + try { + state = MetaTableLocator.getMetaRegionState(watcher, replicaId); + break; + } catch (KeeperException.OperationTimeoutException oe) { + // LOG and retry. + LOG.warn("Timed out fetching meta location information for path {}", path, oe); + } catch (KeeperException e) { + LOG.error("Error getting meta location for path {}", path, e); + break; + } + } + if (state == null) { + cachedMetaLocations.put(replicaId, null); + return; + } + cachedMetaLocations.put( + replicaId, new HRegionLocation(state.getRegion(), state.getServerName())); + } + + /** + * Converts the current cache snapshot into a GetMetaLocations() RPC return payload. + * @return Protobuf serialized list of cached meta HRegionLocations + * @throws MetaRegionsNotAvailableException if the cache is not populated. + */ + public List<HBaseProtos.RegionLocation> getCachedMetaRegionLocations() + throws MetaRegionsNotAvailableException { + ConcurrentNavigableMap<Integer, HRegionLocation> snapshot = + cachedMetaLocations.tailMap(cachedMetaLocations.firstKey(), true); + if (snapshot == null || snapshot.isEmpty()) { + // This could be possible if the master has not successfully initialized yet or meta region + // is stuck in some weird state. + throw new MetaRegionsNotAvailableException("Meta cache is empty"); + } + List<HBaseProtos.RegionLocation> result = new ArrayList<>(); + // Handle missing replicas, if any? + snapshot.values().stream().forEach( Review comment: `snapshot.values().forEach(...)` works here. ---------------------------------------------------------------- This is an automated message from the Apache Git Service. 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