[GitHub] [hbase] ddupg commented on a change in pull request #2397: HBASE-24999 Master manages ReplicationServers

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ddupg commented on a change in pull request #2397:
URL: https://github.com/apache/hbase/pull/2397#discussion_r491778751



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File path: hbase-server/src/main/java/org/apache/hadoop/hbase/master/ReplicationServerManager.java
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@@ -0,0 +1,208 @@
+/*
+ * 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.Collections;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.ConcurrentNavigableMap;
+import java.util.concurrent.ConcurrentSkipListMap;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.hbase.ScheduledChore;
+import org.apache.hadoop.hbase.ServerMetrics;
+import org.apache.hadoop.hbase.ServerName;
+import org.apache.yetus.audience.InterfaceAudience;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * The ServerManager class manages info about replication servers.
+ * <p>
+ * Maintains lists of online and dead servers.
+ * <p>
+ * Servers are distinguished in two different ways.  A given server has a
+ * location, specified by hostname and port, and of which there can only be one
+ * online at any given time.  A server instance is specified by the location
+ * (hostname and port) as well as the startcode (timestamp from when the server
+ * was started).  This is used to differentiate a restarted instance of a given
+ * server from the original instance.
+ * <p>
+ * If a sever is known not to be running any more, it is called dead. The dead
+ * server needs to be handled by a ServerShutdownHandler.  If the handler is not
+ * enabled yet, the server can't be handled right away so it is queued up.
+ * After the handler is enabled, the server will be submitted to a handler to handle.
+ * However, the handler may be just partially enabled.  If so,
+ * the server cannot be fully processed, and be queued up for further processing.
+ * A server is fully processed only after the handler is fully enabled
+ * and has completed the handling.
+ */
+@InterfaceAudience.Private
+public class ReplicationServerManager {
+
+  private static final Logger LOG = LoggerFactory.getLogger(ReplicationServerManager.class);
+
+  public static final String ONLINE_SERVER_REFRESH_INTERVAL =
+      "hbase.master.replication.server.refresh.interval";
+  public static final int ONLINE_SERVER_REFRESH_INTERVAL_DEFAULT = 60 * 1000; // 1 mins
+
+  private final MasterServices master;
+
+  /** Map of registered servers to their current load */
+  private final ConcurrentNavigableMap<ServerName, ServerMetrics> onlineServers =
+    new ConcurrentSkipListMap<>();
+
+  private OnlineServerRefresher onlineServerRefresher;
+  private int refreshPeriod;
+
+  /**
+   * Constructor.
+   */
+  public ReplicationServerManager(final MasterServices master) {
+    this.master = master;
+  }
+
+  /**
+   * start chore in ServerManager
+   */
+  public void startChore() {
+    Configuration conf = master.getConfiguration();
+    refreshPeriod = conf.getInt(ONLINE_SERVER_REFRESH_INTERVAL,
+        ONLINE_SERVER_REFRESH_INTERVAL_DEFAULT);
+    onlineServerRefresher = new OnlineServerRefresher("ReplicationServerRefresher", refreshPeriod);
+    master.getChoreService().scheduleChore(onlineServerRefresher);
+  }
+
+  /**
+   * Stop the ServerManager.
+   */
+  public void stop() {
+    if (onlineServerRefresher != null) {
+      onlineServerRefresher.cancel();
+    }
+  }
+
+  public void serverReport(ServerName sn, ServerMetrics sl) {
+    if (null == this.onlineServers.replace(sn, sl)) {
+      if (!checkAndRecordNewServer(sn, sl)) {
+        LOG.info("ReplicationServerReport ignored, could not record the server: {}", sn);
+      }
+    }
+  }
+
+  /**
+   * Check is a server of same host and port already exists,
+   * if not, or the existed one got a smaller start code, record it.
+   *
+   * @param serverName the server to check and record
+   * @param sl the server load on the server
+   * @return true if the server is recorded, otherwise, false
+   */
+  boolean checkAndRecordNewServer(final ServerName serverName, final ServerMetrics sl) {
+    ServerName existingServer = null;
+    synchronized (this.onlineServers) {
+      existingServer = findServerWithSameHostnamePortWithLock(serverName);
+      if (existingServer != null && (existingServer.getStartcode() > serverName.getStartcode())) {
+        LOG.info("ReplicationServer serverName={} rejected; we already have {} registered with "
+          + "same hostname and port", serverName, existingServer);
+        return false;
+      }
+      recordNewServerWithLock(serverName, sl);
+      // Note that we assume that same ts means same server, and don't expire in that case.
+      if (existingServer != null && (existingServer.getStartcode() < serverName.getStartcode())) {
+        LOG.info("Triggering server recovery; existingServer {} looks stale, new server: {}",
+            existingServer, serverName);
+        expireServerWithLock(existingServer);
+      }
+    }
+    return true;
+  }
+
+  /**
+   * Assumes onlineServers is locked.
+   * @return ServerName with matching hostname and port.
+   */
+  private ServerName findServerWithSameHostnamePortWithLock(final ServerName serverName) {

Review comment:
       Just keep same style with ServerManager. It means that `onlineServers` must be locked to access this method.




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