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
34 /**
35 * Makes decisions about the placement and movement of Regions across
36 * RegionServers.
37 *
38 * <p>Cluster-wide load balancing will occur only when there are no regions in
39 * transition and according to a fixed period of a time using {@link #balanceCluster(Map)}.
40 *
41 * <p>Inline region placement with {@link #immediateAssignment} can be used when
42 * the Master needs to handle closed regions that it currently does not have
43 * a destination set for. This can happen during master failover.
44 *
45 * <p>On cluster startup, bulk assignment can be used to determine
46 * locations for all Regions in a cluster.
47 *
48 * <p>This classes produces plans for the {@link AssignmentManager} to execute.
49 */
50 @InterfaceAudience.Private
51 public interface LoadBalancer extends Configurable, Stoppable, ConfigurationObserver {
52
53 /**
54 * Set the current cluster status. This allows a LoadBalancer to map host name to a server
55 * @param st
56 */
57 void setClusterStatus(ClusterStatus st);
58
59
60 /**
61 * Set the master service.
62 * @param masterServices
63 */
64 void setMasterServices(MasterServices masterServices);
65
66 /**
67 * Perform the major balance operation
68 * @param clusterState
69 * @return List of plans
70 */
71 List<RegionPlan> balanceCluster(Map<ServerName,
72 List<HRegionInfo>> clusterState) throws HBaseIOException;
73
74 /**
75 * Perform a Round Robin assignment of regions.
76 * @param regions
77 * @param servers
78 * @return Map of servername to regioninfos
79 */
80 Map<ServerName, List<HRegionInfo>> roundRobinAssignment(
81 List<HRegionInfo> regions,
82 List<ServerName> servers
83 ) throws HBaseIOException;
84
85 /**
86 * Assign regions to the previously hosting region server
87 * @param regions
88 * @param servers
89 * @return List of plans
90 */
91 Map<ServerName, List<HRegionInfo>> retainAssignment(
92 Map<HRegionInfo, ServerName> regions,
93 List<ServerName> servers
94 ) throws HBaseIOException;
95
96 /**
97 * Sync assign a region
98 * @param regions
99 * @param servers
100 * @return Map regioninfos to servernames
101 */
102 Map<HRegionInfo, ServerName> immediateAssignment(
103 List<HRegionInfo> regions,
104 List<ServerName> servers
105 ) throws HBaseIOException;
106
107 /**
108 * Get a random region server from the list
109 * @param regionInfo Region for which this selection is being done.
110 * @param servers
111 * @return Servername
112 */
113 ServerName randomAssignment(
114 HRegionInfo regionInfo, List<ServerName> servers
115 ) throws HBaseIOException;
116
117 /**
118 * Initialize the load balancer. Must be called after setters.
119 * @throws HBaseIOException
120 */
121 void initialize() throws HBaseIOException;
122
123 /**
124 * Marks the region as online at balancer.
125 * @param regionInfo
126 * @param sn
127 */
128 void regionOnline(HRegionInfo regionInfo, ServerName sn);
129
130 /**
131 * Marks the region as offline at balancer.
132 * @param regionInfo
133 */
134 void regionOffline(HRegionInfo regionInfo);
135
136 /*
137 * Notification that config has changed
138 * @param conf
139 */
140 void onConfigurationChange(Configuration conf);
141 }