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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;
import org.apache.hadoop.hbase.TableName;

/**
 * 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 tableName * @param clusterState * @return List of plans */ List balanceCluster(TableName tableName, Map> clusterState) throws HBaseIOException; /** * 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); /** * If balancer needs to do initialization after Master has started up, lets do that here. */ void postMasterStartupInitialize(); /*Updates balancer status tag reported to JMX*/ void updateBalancerStatus(boolean status); }





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