001/*
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018package org.apache.hadoop.hbase.master;
019
020import edu.umd.cs.findbugs.annotations.NonNull;
021import java.io.IOException;
022import java.util.List;
023import java.util.Map;
024import org.apache.hadoop.conf.Configuration;
025import org.apache.hadoop.hbase.ClusterMetrics;
026import org.apache.hadoop.hbase.HBaseIOException;
027import org.apache.hadoop.hbase.ServerName;
028import org.apache.hadoop.hbase.Stoppable;
029import org.apache.hadoop.hbase.TableName;
030import org.apache.hadoop.hbase.client.RegionInfo;
031import org.apache.hadoop.hbase.conf.ConfigurationObserver;
032import org.apache.yetus.audience.InterfaceAudience;
033
034/**
035 * Makes decisions about the placement and movement of Regions across RegionServers.
036 * <p/>
037 * Cluster-wide load balancing will occur only when there are no regions in transition and according
038 * to a fixed period of a time using {@link #balanceCluster(Map)}.
039 * <p/>
040 * On cluster startup, bulk assignment can be used to determine locations for all Regions in a
041 * cluster.
042 * <p/>
043 * This class produces plans for the {@code AssignmentManager} to execute.
044 * <p/>
045 * About locking:
046 * <ul>
047 * <li>We will first call {@link #setMasterServices(MasterServices)} and then {@link #initialize()}
048 * to initialize the balancer, and before calling {@link #initialize()}, we will never call any
049 * methods of this balancer. So these two methods do not need to be synchronized.</li>
050 * <li>The {@link #balanceCluster(Map)} method will use the {@link ClusterMetrics} which is set by
051 * {@link #updateClusterMetrics(ClusterMetrics)}, and also lots of configurations, which could be
052 * changed by {@link #onConfigurationChange(Configuration)}, so the easier way is to make these
053 * three methods synchronized. And since there will be only one balancing thread, this will not
054 * impact performance too much.</li>
055 * <li>The {@link #roundRobinAssignment(List, List)}, {@link #retainAssignment(Map, List)} and
056 * {@link #randomAssignment(RegionInfo, List)} could be called from multiple threads concurrently,
057 * so these three methods should not be synchronized, the implementation classes need to make sure
058 * that they are thread safe.</li>
059 * </ul>
060 */
061@InterfaceAudience.Private
062public interface LoadBalancer extends Stoppable, ConfigurationObserver {
063  /**
064   * Master can carry regions as of hbase-2.0.0. By default, it carries no tables. TODO: Add any |
065   * system as flags to indicate what it can do.
066   * @deprecated since 2.4.0, will be removed in 3.0.0.
067   * @see <a href="https://issues.apache.org/jira/browse/HBASE-15549">HBASE-15549</a>
068   */
069  @Deprecated
070  String TABLES_ON_MASTER = "hbase.balancer.tablesOnMaster";
071
072  /**
073   * Master carries system tables.
074   * @deprecated since 2.4.0, will be removed in 3.0.0.
075   * @see <a href="https://issues.apache.org/jira/browse/HBASE-15549">HBASE-15549</a>
076   */
077  @Deprecated
078  String SYSTEM_TABLES_ON_MASTER = "hbase.balancer.tablesOnMaster.systemTablesOnly";
079
080  // Used to signal to the caller that the region(s) cannot be assigned
081  // We deliberately use 'localhost' so the operation will fail fast
082  ServerName BOGUS_SERVER_NAME = ServerName.valueOf("localhost,1,1");
083
084  /**
085   * Set the current cluster status. This allows a LoadBalancer to map host name to a server
086   */
087  void updateClusterMetrics(ClusterMetrics metrics);
088
089  /**
090   * Set the master service. n
091   */
092  void setMasterServices(MasterServices masterServices);
093
094  /**
095   * Perform the major balance operation for cluster.
096   * @param loadOfAllTable region load of servers for all table
097   * @return a list of regions to be moved, including source and destination, or null if cluster is
098   *         already balanced
099   */
100  List<RegionPlan> balanceCluster(Map<TableName, Map<ServerName, List<RegionInfo>>> loadOfAllTable)
101    throws IOException;
102
103  /**
104   * Perform a Round Robin assignment of regions. nn * @return Map of servername to regioninfos
105   */
106  @NonNull
107  Map<ServerName, List<RegionInfo>> roundRobinAssignment(List<RegionInfo> regions,
108    List<ServerName> servers) throws HBaseIOException;
109
110  /**
111   * Assign regions to the previously hosting region server nn * @return List of plans
112   */
113  @NonNull
114  Map<ServerName, List<RegionInfo>> retainAssignment(Map<RegionInfo, ServerName> regions,
115    List<ServerName> servers) throws HBaseIOException;
116
117  /**
118   * Get a random region server from the list
119   * @param regionInfo Region for which this selection is being done. nn
120   */
121  ServerName randomAssignment(RegionInfo regionInfo, List<ServerName> servers)
122    throws HBaseIOException;
123
124  /**
125   * Initialize the load balancer. Must be called after setters. n
126   */
127  void initialize() throws HBaseIOException;
128
129  /**
130   * Marks the region as online at balancer. nn
131   */
132  void regionOnline(RegionInfo regionInfo, ServerName sn);
133
134  /**
135   * Marks the region as offline at balancer. n
136   */
137  void regionOffline(RegionInfo regionInfo);
138
139  /*
140   * Notification that config has changed n
141   */
142  @Override
143  void onConfigurationChange(Configuration conf);
144
145  /**
146   * If balancer needs to do initialization after Master has started up, lets do that here.
147   */
148  void postMasterStartupInitialize();
149
150  /* Updates balancer status tag reported to JMX */
151  void updateBalancerStatus(boolean status);
152
153  /**
154   * In some scenarios, Balancer needs to update internal status or information according to the
155   * current tables load
156   * @param loadOfAllTable region load of servers for all table
157   */
158  default void
159    updateBalancerLoadInfo(Map<TableName, Map<ServerName, List<RegionInfo>>> loadOfAllTable) {
160  }
161
162  /**
163   * @return true if Master carries regions
164   * @deprecated since 2.4.0, will be removed in 3.0.0.
165   * @see <a href="https://issues.apache.org/jira/browse/HBASE-15549">HBASE-15549</a>
166   */
167  @Deprecated
168  static boolean isTablesOnMaster(Configuration conf) {
169    return conf.getBoolean(TABLES_ON_MASTER, false);
170  }
171
172  /**
173   * @deprecated since 2.4.0, will be removed in 3.0.0.
174   * @see <a href="https://issues.apache.org/jira/browse/HBASE-15549">HBASE-15549</a>
175   */
176  @Deprecated
177  static boolean isSystemTablesOnlyOnMaster(Configuration conf) {
178    return conf.getBoolean(SYSTEM_TABLES_ON_MASTER, false);
179  }
180
181  /**
182   * @deprecated since 2.4.0, will be removed in 3.0.0.
183   * @see <a href="https://issues.apache.org/jira/browse/HBASE-15549">HBASE-15549</a>
184   */
185  @Deprecated
186  static boolean isMasterCanHostUserRegions(Configuration conf) {
187    return isTablesOnMaster(conf) && !isSystemTablesOnlyOnMaster(conf);
188  }
189}