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.HRegionInfo; 28 import org.apache.hadoop.hbase.ServerName; 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 @InterfaceAudience.Public 47 public interface LoadBalancer extends Configurable { 48 49 /** 50 * Set the current cluster status. This allows a LoadBalancer to map host name to a server 51 * @param st 52 */ 53 public void setClusterStatus(ClusterStatus st); 54 55 56 /** 57 * Set the master service. 58 * @param masterServices 59 */ 60 public void setMasterServices(MasterServices masterServices); 61 62 /** 63 * Perform the major balance operation 64 * @param clusterState 65 * @return List of plans 66 */ 67 public List<RegionPlan> balanceCluster(Map<ServerName, List<HRegionInfo>> clusterState); 68 69 /** 70 * Perform a Round Robin assignment of regions. 71 * @param regions 72 * @param servers 73 * @return Map of servername to regioninfos 74 */ 75 public Map<ServerName, List<HRegionInfo>> roundRobinAssignment(List<HRegionInfo> regions, List<ServerName> servers); 76 77 /** 78 * Assign regions to the previously hosting region server 79 * @param regions 80 * @param servers 81 * @return List of plans 82 */ 83 public Map<ServerName, List<HRegionInfo>> retainAssignment(Map<HRegionInfo, ServerName> regions, List<ServerName> servers); 84 85 /** 86 * Sync assign a region 87 * @param regions 88 * @param servers 89 * @return Map regioninfos to servernames 90 */ 91 public Map<HRegionInfo, ServerName> immediateAssignment(List<HRegionInfo> regions, List<ServerName> servers); 92 93 /** 94 * Get a random region server from the list 95 * @param regionInfo Region for which this selection is being done. 96 * @param servers 97 * @return Servername 98 */ 99 public ServerName randomAssignment(HRegionInfo regionInfo, 100 List<ServerName> servers); 101 }