1 /** 2 * Copyright 2011 The Apache Software Foundation 3 * 4 * Licensed to the Apache Software Foundation (ASF) under one 5 * or more contributor license agreements. See the NOTICE file 6 * distributed with this work for additional information 7 * regarding copyright ownership. The ASF licenses this file 8 * to you under the Apache License, Version 2.0 (the 9 * "License"); you may not use this file except in compliance 10 * with the License. You may obtain a copy of the License at 11 * 12 * http://www.apache.org/licenses/LICENSE-2.0 13 * 14 * Unless required by applicable law or agreed to in writing, software 15 * distributed under the License is distributed on an "AS IS" BASIS, 16 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 17 * See the License for the specific language governing permissions and 18 * limitations under the License. 19 */ 20 package org.apache.hadoop.hbase.master; 21 22 import org.apache.hadoop.conf.Configurable; 23 import org.apache.hadoop.hbase.ClusterStatus; 24 import org.apache.hadoop.hbase.HRegionInfo; 25 import org.apache.hadoop.hbase.ServerName; 26 27 import java.util.List; 28 import java.util.Map; 29 30 /** 31 * Makes decisions about the placement and movement of Regions across 32 * RegionServers. 33 * 34 * <p>Cluster-wide load balancing will occur only when there are no regions in 35 * transition and according to a fixed period of a time using {@link #balanceCluster(Map)}. 36 * 37 * <p>Inline region placement with {@link #immediateAssignment} can be used when 38 * the Master needs to handle closed regions that it currently does not have 39 * a destination set for. This can happen during master failover. 40 * 41 * <p>On cluster startup, bulk assignment can be used to determine 42 * locations for all Regions in a cluster. 43 * 44 * <p>This classes produces plans for the {@link AssignmentManager} to execute. 45 */ 46 public interface LoadBalancer extends Configurable { 47 48 /** 49 * Set the current cluster status. This allows a LoadBalancer to map host name to a server 50 * @param st 51 */ 52 public void setClusterStatus(ClusterStatus st); 53 54 55 /** 56 * Set the master service. 57 * @param masterServices 58 */ 59 public void setMasterServices(MasterServices masterServices); 60 61 /** 62 * Perform the major balance operation 63 * @param clusterState 64 * @return List of plans 65 */ 66 public List<RegionPlan> balanceCluster(Map<ServerName, List<HRegionInfo>> clusterState); 67 68 /** 69 * Perform a Round Robin assignment of regions. 70 * @param regions 71 * @param servers 72 * @return Map of servername to regioninfos 73 */ 74 public Map<ServerName, List<HRegionInfo>> roundRobinAssignment(List<HRegionInfo> regions, List<ServerName> servers); 75 76 /** 77 * Assign regions to the previously hosting region server 78 * @param regions 79 * @param servers 80 * @return List of plans 81 */ 82 public Map<ServerName, List<HRegionInfo>> retainAssignment(Map<HRegionInfo, ServerName> regions, List<ServerName> servers); 83 84 /** 85 * Sync assign a region 86 * @param regions 87 * @param servers 88 * @return Map regioninfos to servernames 89 */ 90 public Map<HRegionInfo, ServerName> immediateAssignment(List<HRegionInfo> regions, List<ServerName> servers); 91 92 /** 93 * Get a random region server from the list 94 * @param servers 95 * @return Servername 96 */ 97 public ServerName randomAssignment(List<ServerName> servers); 98 }