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.hbase.classification.InterfaceAudience;
25 import org.apache.hadoop.hbase.conf.ConfigurationObserver;
26 import org.apache.hadoop.conf.Configurable;
27 import org.apache.hadoop.conf.Configuration;
28 import org.apache.hadoop.hbase.ClusterStatus;
29 import org.apache.hadoop.hbase.HBaseIOException;
30 import org.apache.hadoop.hbase.HRegionInfo;
31 import org.apache.hadoop.hbase.ServerName;
32 import org.apache.hadoop.hbase.Stoppable;
33 import org.apache.hadoop.hbase.TableName;
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>Inline region placement with {@link #immediateAssignment} can be used when
43 * the Master needs to handle closed regions that it currently does not have
44 * a destination set for. This can happen during master failover.
45 *
46 * <p>On cluster startup, bulk assignment can be used to determine
47 * locations for all Regions in a cluster.
48 *
49 * <p>This classes produces plans for the {@link AssignmentManager} to execute.
50 */
51 @InterfaceAudience.Private
52 public interface LoadBalancer extends Configurable, Stoppable, ConfigurationObserver {
53
54 //used to signal to the caller that the region(s) cannot be assigned
55 ServerName BOGUS_SERVER_NAME = ServerName.parseServerName("localhost,1,1");
56
57 /**
58 * Set the current cluster status. This allows a LoadBalancer to map host name to a server
59 * @param st
60 */
61 void setClusterStatus(ClusterStatus st);
62
63
64 /**
65 * Set the master service.
66 * @param masterServices
67 */
68 void setMasterServices(MasterServices masterServices);
69
70 /**
71 * Perform the major balance operation
72 * @param tableName
73 * @param clusterState
74 * @return List of plans
75 */
76 List<RegionPlan> balanceCluster(TableName tableName, Map<ServerName,
77 List<HRegionInfo>> clusterState) throws HBaseIOException;
78
79 /**
80 * Perform the major balance operation
81 * @param clusterState
82 * @return List of plans
83 */
84 List<RegionPlan> balanceCluster(Map<ServerName,
85 List<HRegionInfo>> clusterState) throws HBaseIOException;
86
87 /**
88 * Perform a Round Robin assignment of regions.
89 * @param regions
90 * @param servers
91 * @return Map of servername to regioninfos
92 */
93 Map<ServerName, List<HRegionInfo>> roundRobinAssignment(
94 List<HRegionInfo> regions,
95 List<ServerName> servers
96 ) throws HBaseIOException;
97
98 /**
99 * Assign regions to the previously hosting region server
100 * @param regions
101 * @param servers
102 * @return List of plans
103 */
104 Map<ServerName, List<HRegionInfo>> retainAssignment(
105 Map<HRegionInfo, ServerName> regions,
106 List<ServerName> servers
107 ) throws HBaseIOException;
108
109 /**
110 * Sync assign a region
111 * @param regions
112 * @param servers
113 * @return Map regioninfos to servernames
114 */
115 Map<HRegionInfo, ServerName> immediateAssignment(
116 List<HRegionInfo> regions,
117 List<ServerName> servers
118 ) throws HBaseIOException;
119
120 /**
121 * Get a random region server from the list
122 * @param regionInfo Region for which this selection is being done.
123 * @param servers
124 * @return Servername
125 */
126 ServerName randomAssignment(
127 HRegionInfo regionInfo, List<ServerName> servers
128 ) throws HBaseIOException;
129
130 /**
131 * Initialize the load balancer. Must be called after setters.
132 * @throws HBaseIOException
133 */
134 void initialize() throws HBaseIOException;
135
136 /**
137 * Marks the region as online at balancer.
138 * @param regionInfo
139 * @param sn
140 */
141 void regionOnline(HRegionInfo regionInfo, ServerName sn);
142
143 /**
144 * Marks the region as offline at balancer.
145 * @param regionInfo
146 */
147 void regionOffline(HRegionInfo regionInfo);
148
149 /*
150 * Notification that config has changed
151 * @param conf
152 */
153 void onConfigurationChange(Configuration conf);
154 }