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