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Posted to issues@hbase.apache.org by GitBox <gi...@apache.org> on 2019/11/14 21:07:15 UTC
[GitHub] [hbase] bharathv commented on a change in pull request #830:
HBASE-23281: Track meta region locations in masters
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_r346545702
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File path: hbase-server/src/main/java/org/apache/hadoop/hbase/master/MetaRegionLocationCache.java
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@@ -0,0 +1,217 @@
+/*
+ * 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.ServerName;
+import org.apache.hadoop.hbase.client.RegionInfoBuilder;
+import org.apache.hadoop.hbase.client.RegionReplicaUtil;
+import org.apache.hadoop.hbase.exceptions.DeserializationException;
+import org.apache.hadoop.hbase.shaded.protobuf.ProtobufUtil;
+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;
+
+/**
+ * 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);
+
+ private final 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.
+ private final CopyOnWriteArrayMap<Integer, HRegionLocation> cachedMetaLocations;
+
+ private enum ZNodeOpType {
+ INIT,
+ CREATED,
+ CHANGED,
+ DELETED
+ };
+
+ 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() {
+ 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 {
+ ServerName serverName = null;
+ try {
+ byte[] data = ZKUtil.getDataAndWatch(watcher,
+ watcher.getZNodePaths().getZNodeForReplica(replicaId));
+ serverName = ProtobufUtil.parseMetaServerNameFrom(data);
+ } catch (DeserializationException e) {
+ throw ZKUtil.convert(e);
+ }
+ return new HRegionLocation(RegionReplicaUtil.getRegionInfoForReplica(
+ RegionInfoBuilder.FIRST_META_REGIONINFO, replicaId), serverName);
+ }
+
+ 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>> getCachedMetaRegionLocations() {
Review comment:
@ndimiduk Switched to Optional for better nullability semantics.
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