org.apache.hadoop.hbase.master

Interface LoadBalancer

All Superinterfaces:

ConfigurationObserver, Stoppable

All Known Implementing Classes:

BaseLoadBalancer, FavoredNodeLoadBalancer, SimpleLoadBalancer, StochasticLoadBalancer, TestAssignmentManager.MockedLoadBalancer, TestBaseLoadBalancer.MockBalancer

@InterfaceAudience.Private
public interface LoadBalancer
extends Stoppable, ConfigurationObserver

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 balanceCluster(Map).

Inline region placement with immediateAssignment(java.util.List<org.apache.hadoop.hbase.HRegionInfo>, java.util.List<org.apache.hadoop.hbase.ServerName>) 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 AssignmentManager to execute.

Method Summary

Modifier and Type	Method and Description
List<RegionPlan>	balanceCluster(Map<ServerName,List<HRegionInfo>> clusterState) Perform the major balance operation
Map<HRegionInfo,ServerName>	immediateAssignment(List<HRegionInfo> regions, List<ServerName> servers) Sync assign a region
void	initialize() Initialize the load balancer.
void	onConfigurationChange(Configuration conf) This method would be called by the ConfigurationManager object when the Configuration object is reloaded from disk.
ServerName	randomAssignment(HRegionInfo regionInfo, List<ServerName> servers) Get a random region server from the list
void	regionOffline(HRegionInfo regionInfo) Marks the region as offline at balancer.
void	regionOnline(HRegionInfo regionInfo, ServerName sn) Marks the region as online at balancer.
Map<ServerName,List<HRegionInfo>>	retainAssignment(Map<HRegionInfo,ServerName> regions, List<ServerName> servers) Assign regions to the previously hosting region server
Map<ServerName,List<HRegionInfo>>	roundRobinAssignment(List<HRegionInfo> regions, List<ServerName> servers) Perform a Round Robin assignment of regions.
void	setClusterStatus(ClusterStatus st) Set the current cluster status.
void	setMasterServices(MasterServices masterServices) Set the master service.

Methods inherited from interface org.apache.hadoop.hbase.Stoppable

isStopped, stop

Method Detail

setClusterStatus

void setClusterStatus(ClusterStatus st)

Set the current cluster status. This allows a LoadBalancer to map host name to a server

Parameters:

st -

setMasterServices

void setMasterServices(MasterServices masterServices)

Set the master service.

Parameters:

masterServices -

balanceCluster

List<RegionPlan> balanceCluster(Map<ServerName,List<HRegionInfo>> clusterState)
                         throws HBaseIOException

Perform the major balance operation

Parameters:

clusterState -

Returns:

List of plans

Throws:

HBaseIOException

roundRobinAssignment

Map<ServerName,List<HRegionInfo>> roundRobinAssignment(List<HRegionInfo> regions,
                                                       List<ServerName> servers)
                                                throws HBaseIOException

Perform a Round Robin assignment of regions.

Parameters:

regions -

servers -

Returns:

Map of servername to regioninfos

Throws:

HBaseIOException

retainAssignment

Map<ServerName,List<HRegionInfo>> retainAssignment(Map<HRegionInfo,ServerName> regions,
                                                   List<ServerName> servers)
                                            throws HBaseIOException

Assign regions to the previously hosting region server

Parameters:

regions -

servers -

Returns:

List of plans

Throws:

HBaseIOException

immediateAssignment

Map<HRegionInfo,ServerName> immediateAssignment(List<HRegionInfo> regions,
                                                List<ServerName> servers)
                                         throws HBaseIOException

Sync assign a region

Parameters:

regions -

servers -

Returns:

Map regioninfos to servernames

Throws:

HBaseIOException

randomAssignment

ServerName randomAssignment(HRegionInfo regionInfo,
                            List<ServerName> servers)
                     throws HBaseIOException

Get a random region server from the list

Parameters:

regionInfo - Region for which this selection is being done.

servers -

Returns:

Servername

Throws:

HBaseIOException

initialize

void initialize()
         throws HBaseIOException

Initialize the load balancer. Must be called after setters.

Throws:

HBaseIOException

regionOnline

void regionOnline(HRegionInfo regionInfo,
                  ServerName sn)

Marks the region as online at balancer.

Parameters:

regionInfo -

sn -

regionOffline

void regionOffline(HRegionInfo regionInfo)

Marks the region as offline at balancer.

Parameters:

regionInfo -

onConfigurationChange

void onConfigurationChange(Configuration conf)

Description copied from interface: ConfigurationObserver

This method would be called by the ConfigurationManager object when the Configuration object is reloaded from disk.

Specified by:

onConfigurationChange in interface ConfigurationObserver