[GitHub] [hbase] ndimiduk commented on a change in pull request #781: HBASE-18095: Zookeeper-less client connection implementation

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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_r344406342
 
 

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 File path: hbase-server/src/main/java/org/apache/hadoop/hbase/master/MetaRegionLocationCache.java
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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.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) {
 
 Review comment:
   Can be package-private.

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