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/**
*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.hadoop.hbase.master;
import java.util.List;
import java.util.Map;
import edu.umd.cs.findbugs.annotations.Nullable;
import org.apache.hadoop.hbase.classification.InterfaceAudience;
import org.apache.hadoop.hbase.conf.ConfigurationObserver;
import org.apache.hadoop.conf.Configurable;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.hbase.ClusterStatus;
import org.apache.hadoop.hbase.HBaseIOException;
import org.apache.hadoop.hbase.HRegionInfo;
import org.apache.hadoop.hbase.ServerName;
import org.apache.hadoop.hbase.Stoppable;
/**
* Makes decisions about the placement and movement of Regions across
* RegionServers.
*
* Cluster-wide load balancing will occur only when there are no regions in
* transition and according to a fixed period of a time using {@link #balanceCluster(Map)}.
*
*
Inline region placement with {@link #immediateAssignment} can be used when
* the Master needs to handle closed regions that it currently does not have
* a destination set for. This can happen during master failover.
*
*
On cluster startup, bulk assignment can be used to determine
* locations for all Regions in a cluster.
*
*
This classes produces plans for the {@link AssignmentManager} to execute.
*/
@InterfaceAudience.Private
public interface LoadBalancer extends Configurable, Stoppable, ConfigurationObserver {
/**
* Set the current cluster status. This allows a LoadBalancer to map host name to a server
* @param st
*/
void setClusterStatus(ClusterStatus st);
/**
* Set the master service.
* @param masterServices
*/
void setMasterServices(MasterServices masterServices);
/**
* Perform the major balance operation
* @param clusterState
* @return List of plans
*/
List balanceCluster(Map> clusterState) throws HBaseIOException;
/**
* Perform a Round Robin assignment of regions.
* @param regions
* @param servers
* @return Map of servername to regioninfos
*/
Map> roundRobinAssignment(
List regions,
List servers
) throws HBaseIOException;
/**
* Assign regions to the previously hosting region server
* @param regions
* @param servers
* @return List of plans
*/
Map> retainAssignment(
Map regions,
List servers
) throws HBaseIOException;
/**
* Sync assign a region
* @param regions
* @param servers
* @return Map regioninfos to servernames
*/
Map immediateAssignment(
List regions,
List servers
) throws HBaseIOException;
/**
* Get a random region server from the list
* @param regionInfo Region for which this selection is being done.
* @param servers
* @return Servername
*/
ServerName randomAssignment(
HRegionInfo regionInfo, List servers
) throws HBaseIOException;
/**
* Initialize the load balancer. Must be called after setters.
* @throws HBaseIOException
*/
void initialize() throws HBaseIOException;
/**
* Marks the region as online at balancer.
* @param regionInfo
* @param sn
*/
void regionOnline(HRegionInfo regionInfo, ServerName sn);
/**
* Marks the region as offline at balancer.
* @param regionInfo
*/
void regionOffline(HRegionInfo regionInfo);
/*
* Notification that config has changed
* @param conf
*/
void onConfigurationChange(Configuration conf);
}