hbase-server/src/main/java/org/apache/hadoop/hbase/master/LoadBalancer.java

   1 /**
   2  *
   3  * Licensed to the Apache Software Foundation (ASF) under one
   4  * or more contributor license agreements.  See the NOTICE file
   5  * distributed with this work for additional information
   6  * regarding copyright ownership.  The ASF licenses this file
   7  * to you under the Apache License, Version 2.0 (the
   8  * "License"); you may not use this file except in compliance
   9  * with the License.  You may obtain a copy of the License at
  10  *
  11  *     http://www.apache.org/licenses/LICENSE-2.0
  12  *
  13  * Unless required by applicable law or agreed to in writing, software
  14  * distributed under the License is distributed on an "AS IS" BASIS,
  15  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  16  * See the License for the specific language governing permissions and
  17  * limitations under the License.
  18  */
  19 package org.apache.hadoop.hbase.master;
  20
  21 import edu.umd.cs.findbugs.annotations.Nullable;
  22 import java.io.IOException;
  23 import java.util.List;
  24 import java.util.Map;
  25 import org.apache.hadoop.conf.Configurable;
  26 import org.apache.hadoop.conf.Configuration;
  27 import org.apache.hadoop.hbase.ClusterMetrics;
  28 import org.apache.hadoop.hbase.ServerName;
  29 import org.apache.hadoop.hbase.Stoppable;
  30 import org.apache.hadoop.hbase.TableName;
  31 import org.apache.hadoop.hbase.client.RegionInfo;
  32 import org.apache.hadoop.hbase.conf.ConfigurationObserver;
  33 import org.apache.yetus.audience.InterfaceAudience;
  34
  35 /**
  36  * Makes decisions about the placement and movement of Regions across
  37  * RegionServers.
  38  *
  39  * <p>Cluster-wide load balancing will occur only when there are no regions in
  40  * transition and according to a fixed period of a time using {@link #balanceCluster(Map)}.
  41  *
  42  * <p>On cluster startup, bulk assignment can be used to determine
  43  * locations for all Regions in a cluster.
  44  *
  45  * <p>This class produces plans for the
  46  * {@link org.apache.hadoop.hbase.master.assignment.AssignmentManager}
  47  * to execute.
  48  */
  49 @InterfaceAudience.Private
  50 public interface LoadBalancer extends Configurable, Stoppable, ConfigurationObserver {
  51   /**
  52    * Master can carry regions as of hbase-2.0.0.
  53    * By default, it carries no tables.
  54    * TODO: Add any | system as flags to indicate what it can do.
  55    */
  56   String TABLES_ON_MASTER = "hbase.balancer.tablesOnMaster";
  57
  58   /**
  59    * Master carries system tables.
  60    */
  61   String SYSTEM_TABLES_ON_MASTER = "hbase.balancer.tablesOnMaster.systemTablesOnly";
  62
  63   // Used to signal to the caller that the region(s) cannot be assigned
  64   // We deliberately use 'localhost' so the operation will fail fast
  65   ServerName BOGUS_SERVER_NAME = ServerName.valueOf("localhost,1,1");
  66
  67   /**
  68    * Config for pluggable load balancers.
  69    * @deprecated since 3.0.0, will be removed in 4.0.0. In the new implementation, as the base load
  70    *             balancer will always be the rs group based one, you should just use
  71    *             {@link org.apache.hadoop.hbase.HConstants#HBASE_MASTER_LOADBALANCER_CLASS} to
  72    *             config the per group load balancer.
  73    */
  74   @Deprecated
  75   String HBASE_RSGROUP_LOADBALANCER_CLASS = "hbase.rsgroup.grouploadbalancer.class";
  76   /**
  77    * Set the current cluster status. This allows a LoadBalancer to map host name to a server
  78    */
  79   void setClusterMetrics(ClusterMetrics st);
  80
  81
  82   /**
  83    * Set the master service.
  84    */
  85   void setMasterServices(MasterServices masterServices);
  86
  87   /**
  88    * Perform the major balance operation for cluster, will invoke {@link #balanceTable} to do actual
  89    * balance. Normally not need override this method, except
  90    * {@link org.apache.hadoop.hbase.master.balancer.SimpleLoadBalancer} and
  91    * {@link org.apache.hadoop.hbase.rsgroup.RSGroupBasedLoadBalancer}
  92    * @param loadOfAllTable region load of servers for all table
  93    * @return a list of regions to be moved, including source and destination, or null if cluster is
  94    *         already balanced
  95    */
  96   List<RegionPlan> balanceCluster(Map<TableName,
  97       Map<ServerName, List<RegionInfo>>> loadOfAllTable) throws IOException;
  98
  99   /**
 100    * Perform the major balance operation for table, all class implement of {@link LoadBalancer}
 101    * should override this method
 102    * @param tableName the table to be balanced
 103    * @param loadOfOneTable region load of servers for the specific one table
 104    * @return List of plans
 105    */
 106   List<RegionPlan> balanceTable(TableName tableName,
 107       Map<ServerName, List<RegionInfo>> loadOfOneTable);
 108
 109   /**
 110    * Perform a Round Robin assignment of regions.
 111    * @return Map of servername to regioninfos
 112    */
 113   Map<ServerName, List<RegionInfo>> roundRobinAssignment(List<RegionInfo> regions,
 114       List<ServerName> servers) throws IOException;
 115
 116   /**
 117    * Assign regions to the previously hosting region server
 118    * @return List of plans
 119    */
 120   @Nullable
 121   Map<ServerName, List<RegionInfo>> retainAssignment(Map<RegionInfo, ServerName> regions,
 122       List<ServerName> servers) throws IOException;
 123
 124   /**
 125    * Get a random region server from the list
 126    * @param regionInfo Region for which this selection is being done.
 127    */
 128   ServerName randomAssignment(RegionInfo regionInfo, List<ServerName> servers) throws IOException;
 129
 130   /**
 131    * Initialize the load balancer. Must be called after setters.
 132    */
 133   void initialize() throws IOException;
 134
 135   /**
 136    * Marks the region as online at balancer.
 137    */
 138   void regionOnline(RegionInfo regionInfo, ServerName sn);
 139
 140   /**
 141    * Marks the region as offline at balancer.
 142    */
 143   void regionOffline(RegionInfo regionInfo);
 144
 145   /**
 146    * Notification that config has changed
 147    */
 148   @Override
 149   void onConfigurationChange(Configuration conf);
 150
 151   /**
 152    * If balancer needs to do initialization after Master has started up, lets do that here.
 153    */
 154   void postMasterStartupInitialize();
 155
 156   /*Updates balancer status tag reported to JMX*/
 157   void updateBalancerStatus(boolean status);
 158
 159   /**
 160    * @return true if Master carries regions
 161    */
 162   static boolean isTablesOnMaster(Configuration conf) {
 163     return conf.getBoolean(TABLES_ON_MASTER, false);
 164   }
 165
 166   static boolean isSystemTablesOnlyOnMaster(Configuration conf) {
 167     return conf.getBoolean(SYSTEM_TABLES_ON_MASTER, false);
 168   }
 169
 170   static boolean isMasterCanHostUserRegions(Configuration conf) {
 171     return isTablesOnMaster(conf) && !isSystemTablesOnlyOnMaster(conf);
 172   }
 173 }