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 java.util.List; 22 import java.util.Map; 23 24 import org.apache.hadoop.classification.InterfaceAudience; 25 import org.apache.hadoop.conf.Configurable; 26 import org.apache.hadoop.hbase.ClusterStatus; 27 import org.apache.hadoop.hbase.HBaseIOException; 28 import org.apache.hadoop.hbase.HRegionInfo; 29 import org.apache.hadoop.hbase.ServerName; 30 import org.apache.hadoop.hbase.Stoppable; 31 32 /** 33 * Makes decisions about the placement and movement of Regions across 34 * RegionServers. 35 * 36 * <p>Cluster-wide load balancing will occur only when there are no regions in 37 * transition and according to a fixed period of a time using {@link #balanceCluster(Map)}. 38 * 39 * <p>Inline region placement with {@link #immediateAssignment} can be used when 40 * the Master needs to handle closed regions that it currently does not have 41 * a destination set for. This can happen during master failover. 42 * 43 * <p>On cluster startup, bulk assignment can be used to determine 44 * locations for all Regions in a cluster. 45 * 46 * <p>This classes produces plans for the {@link AssignmentManager} to execute. 47 */ 48 @InterfaceAudience.Private 49 public interface LoadBalancer extends Configurable, Stoppable { 50 51 /** 52 * Set the current cluster status. This allows a LoadBalancer to map host name to a server 53 * @param st 54 */ 55 void setClusterStatus(ClusterStatus st); 56 57 58 /** 59 * Set the master service. 60 * @param masterServices 61 */ 62 void setMasterServices(MasterServices masterServices); 63 64 /** 65 * Perform the major balance operation 66 * @param clusterState 67 * @return List of plans 68 */ 69 List<RegionPlan> balanceCluster(Map<ServerName, 70 List<HRegionInfo>> clusterState) throws HBaseIOException; 71 72 /** 73 * Perform a Round Robin assignment of regions. 74 * @param regions 75 * @param servers 76 * @return Map of servername to regioninfos 77 */ 78 Map<ServerName, List<HRegionInfo>> roundRobinAssignment( 79 List<HRegionInfo> regions, 80 List<ServerName> servers 81 ) throws HBaseIOException; 82 83 /** 84 * Assign regions to the previously hosting region server 85 * @param regions 86 * @param servers 87 * @return List of plans 88 */ 89 Map<ServerName, List<HRegionInfo>> retainAssignment( 90 Map<HRegionInfo, ServerName> regions, 91 List<ServerName> servers 92 ) throws HBaseIOException; 93 94 /** 95 * Sync assign a region 96 * @param regions 97 * @param servers 98 * @return Map regioninfos to servernames 99 */ 100 Map<HRegionInfo, ServerName> immediateAssignment( 101 List<HRegionInfo> regions, 102 List<ServerName> servers 103 ) throws HBaseIOException; 104 105 /** 106 * Get a random region server from the list 107 * @param regionInfo Region for which this selection is being done. 108 * @param servers 109 * @return Servername 110 */ 111 ServerName randomAssignment( 112 HRegionInfo regionInfo, List<ServerName> servers 113 ) throws HBaseIOException; 114 115 /** 116 * Initialize the load balancer. Must be called after setters. 117 * @throws HBaseIOException 118 */ 119 void initialize() throws HBaseIOException; 120 121 /** 122 * Marks the region as online at balancer. 123 * @param regionInfo 124 * @param sn 125 */ 126 void regionOnline(HRegionInfo regionInfo, ServerName sn); 127 128 /** 129 * Marks the region as offline at balancer. 130 * @param regionInfo 131 */ 132 void regionOffline(HRegionInfo regionInfo); 133 }