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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.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  import org.apache.hadoop.hbase.Stoppable;
31  
32  /**
33   * Makes decisions about the placement and movement of Regions across
34   * RegionServers.
35   *
36   * <p>Cluster-wide load balancing will occur only when there are no regions in
37   * transition and according to a fixed period of a time using {@link #balanceCluster(Map)}.
38   *
39   * <p>Inline region placement with {@link #immediateAssignment} can be used when
40   * the Master needs to handle closed regions that it currently does not have
41   * a destination set for.  This can happen during master failover.
42   *
43   * <p>On cluster startup, bulk assignment can be used to determine
44   * locations for all Regions in a cluster.
45   *
46   * <p>This classes produces plans for the {@link AssignmentManager} to execute.
47   */
48  @InterfaceAudience.Private
49  public interface LoadBalancer extends Configurable, Stoppable {
50  
51    /**
52     * Set the current cluster status.  This allows a LoadBalancer to map host name to a server
53     * @param st
54     */
55    void setClusterStatus(ClusterStatus st);
56  
57  
58    /**
59     * Set the master service.
60     * @param masterServices
61     */
62    void setMasterServices(MasterServices masterServices);
63  
64    /**
65     * Perform the major balance operation
66     * @param clusterState
67     * @return List of plans
68     */
69    List<RegionPlan> balanceCluster(Map<ServerName,
70        List<HRegionInfo>> clusterState) throws HBaseIOException;
71  
72    /**
73     * Perform a Round Robin assignment of regions.
74     * @param regions
75     * @param servers
76     * @return Map of servername to regioninfos
77     */
78    Map<ServerName, List<HRegionInfo>> roundRobinAssignment(
79      List<HRegionInfo> regions,
80      List<ServerName> servers
81    ) throws HBaseIOException;
82  
83    /**
84     * Assign regions to the previously hosting region server
85     * @param regions
86     * @param servers
87     * @return List of plans
88     */
89    Map<ServerName, List<HRegionInfo>> retainAssignment(
90      Map<HRegionInfo, ServerName> regions,
91      List<ServerName> servers
92    ) throws HBaseIOException;
93  
94    /**
95     * Sync assign a region
96     * @param regions
97     * @param servers
98      * @return Map regioninfos to servernames
99     */
100   Map<HRegionInfo, ServerName> immediateAssignment(
101     List<HRegionInfo> regions,
102     List<ServerName> servers
103   ) throws HBaseIOException;
104 
105   /**
106    * Get a random region server from the list
107    * @param regionInfo Region for which this selection is being done.
108    * @param servers
109    * @return Servername
110    */
111   ServerName randomAssignment(
112     HRegionInfo regionInfo, List<ServerName> servers
113   ) throws HBaseIOException;
114 
115   /**
116    * Initialize the load balancer. Must be called after setters.
117    * @throws HBaseIOException
118    */
119   void initialize() throws HBaseIOException;
120 
121   /**
122    * Marks the region as online at balancer.
123    * @param regionInfo
124    * @param sn
125    */
126   void regionOnline(HRegionInfo regionInfo, ServerName sn);
127 
128   /**
129    * Marks the region as offline at balancer.
130    * @param regionInfo
131    */
132   void regionOffline(HRegionInfo regionInfo);
133 }