huaxiangsun commented on a change in pull request #2584: URL: https://github.com/apache/hbase/pull/2584#discussion_r513778939
########## File path: hbase-client/src/main/java/org/apache/hadoop/hbase/client/CatalogReplicaLoadBalanceReplicaSimpleSelector.java ########## @@ -0,0 +1,273 @@ +/** + * 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.ConnectionUtils.isEmptyStopRow; +import static org.apache.hadoop.hbase.util.Bytes.BYTES_COMPARATOR; +import static org.apache.hadoop.hbase.util.ConcurrentMapUtils.computeIfAbsent; +import java.io.IOException; +import java.util.Iterator; +import java.util.Map; +import java.util.concurrent.ConcurrentHashMap; +import java.util.concurrent.ConcurrentMap; +import java.util.concurrent.ConcurrentNavigableMap; +import java.util.concurrent.ConcurrentSkipListMap; +import java.util.concurrent.ThreadLocalRandom; +import org.apache.commons.lang3.builder.ToStringBuilder; +import org.apache.hadoop.hbase.HRegionLocation; +import org.apache.hadoop.hbase.ScheduledChore; +import org.apache.hadoop.hbase.Stoppable; +import org.apache.hadoop.hbase.TableName; +import org.apache.hadoop.hbase.util.Bytes; +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +/** + * CatalogReplicaLoadBalanceReplicaSimpleSelector implements a simple catalog replica load balancing + * algorithm. It maintains a stale location cache for each table. Whenever client looks up location, + * it first check if the row is the stale location cache. If yes, the location from + * catalog replica is stale, it will go to the primary region to look up update-to-date location; + * otherwise, it will randomly pick up a replica region for lookup. When clients receive + * RegionNotServedException from region servers, it will add these region locations to the stale + * location cache. The stale cache will be cleaned up periodically by a chore. + * + * It follows a simple algorithm to choose a replica to go: + * + * 1. If there is no stale location entry for rows it looks up, it will randomly + * pick a replica region to do lookup. + * 2. If the location from the replica region is stale, client gets RegionNotServedException + * from region server, in this case, it will create StaleLocationCacheEntry in + * CatalogReplicaLoadBalanceReplicaSimpleSelector. + * 3. When client tries to do location lookup, it checks StaleLocationCache first for rows it + * tries to lookup, if entry exists, it will go with primary meta region to do lookup; + * otherwise, it will follow step 1. + * 4. A chore will periodically run to clean up cache entries in the StaleLocationCache. + */ +class CatalogReplicaLoadBalanceReplicaSimpleSelector implements + CatalogReplicaLoadBalanceReplicaSelector { + private static final Logger LOG = + LoggerFactory.getLogger(CatalogReplicaLoadBalanceReplicaSimpleSelector.class); + private final long STALE_CACHE_TIMEOUT_IN_MILLISECONDS = 3000; // 3 seconds + private final int STALE_CACHE_CLEAN_CHORE_INTERVAL = 1500; // 1.5 seconds + + /** + * StaleLocationCacheEntry is the entry when a stale location is reported by an client. + */ + private static final class StaleLocationCacheEntry { + // replica id where the stale location comes from. + private int fromReplicaId; + + // timestamp in milliseconds + private long timestamp; + + private byte[] endKey; + + StaleLocationCacheEntry(final int metaReplicaId, final byte[] endKey) { + this.fromReplicaId = metaReplicaId; + this.endKey = endKey; + timestamp = System.currentTimeMillis(); + } + + public byte[] getEndKey() { + return this.endKey; + } + + public int getFromReplicaId() { + return this.fromReplicaId; + } + public long getTimestamp() { + return this.timestamp; + } + + @Override + public String toString() { + return new ToStringBuilder(this) + .append("endKey", endKey) + .append("fromReplicaId", fromReplicaId) + .append("timestamp", timestamp) + .toString(); + } + } + + private static final class StaleTableCache { + private final ConcurrentNavigableMap<byte[], StaleLocationCacheEntry> cache = + new ConcurrentSkipListMap<>(BYTES_COMPARATOR); + } + + private final ConcurrentMap<TableName, StaleTableCache> staleCache; + private int numOfReplicas; + private final AsyncConnectionImpl conn; + private TableName tableName; + + CatalogReplicaLoadBalanceReplicaSimpleSelector(TableName tableName, AsyncConnectionImpl conn) { + staleCache = new ConcurrentHashMap<>(); + this.conn = conn; + this.tableName = tableName; + + // This numOfReplicas is going to be lazy initialized. + this.numOfReplicas = -1; + // Start connection's chore service in case. + this.conn.startChoreService(); + this.conn.getChoreService().scheduleChore(getCacheCleanupChore(this)); + } + + /** + * When a client runs into RegionNotServingException, it will call this method to + * update Selector's internal state. + * @param loc the location which causes exception. + * @param fromReplicaId the replica id where the stale location comes from. + */ + public void notifyOnError(HRegionLocation loc, int fromReplicaId) { + StaleTableCache tableCache = + computeIfAbsent(staleCache, loc.getRegion().getTable(), StaleTableCache::new); + byte[] startKey = loc.getRegion().getStartKey(); + tableCache.cache.putIfAbsent(startKey, + new StaleLocationCacheEntry(fromReplicaId, loc.getRegion().getEndKey())); + LOG.debug("Add entry to stale cache for table {} with startKey {}, {}", Review comment: It may not happen if the entry exists in the cache, so will leave it as it is. ---------------------------------------------------------------- This is an automated message from the Apache Git Service. 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