Package org.apache.hadoop.hbase.master

Interface LoadBalancer

All Superinterfaces:

ConfigurationObserver, Stoppable

All Known Implementing Classes:

BaseLoadBalancer, CacheAwareLoadBalancer, FavoredNodeLoadBalancer, FavoredStochasticBalancer, MaintenanceLoadBalancer, RSGroupBasedLoadBalancer, SimpleLoadBalancer, StochasticLoadBalancer

@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).

On cluster startup, bulk assignment can be used to determine locations for all Regions in a cluster.

This class produces plans for the AssignmentManager to execute.

About locking:

• We will first call setClusterInfoProvider(ClusterInfoProvider) and then initialize() to initialize the balancer, and before calling initialize(), we will never call any methods of this balancer. So these two methods do not need to be synchronized.
• The balanceCluster(Map) method will use the ClusterMetrics which is set by updateClusterMetrics(ClusterMetrics), and also lots of configurations, which could be changed by onConfigurationChange(Configuration), so the easier way is to make these three methods synchronized. And since there will be only one balancing thread, this will not impact performance too much.
• The roundRobinAssignment(List, List), retainAssignment(Map, List) and randomAssignment(RegionInfo, List) could be called from multiple threads concurrently, so these three methods should not be synchronized, the implementation classes need to make sure that they are thread safe.

Field Summary

Fields

Modifier and Type	Field	Description
static final ServerName	BOGUS_SERVER_NAME
static final String	HBASE_RSGROUP_LOADBALANCER_CLASS	Deprecated. since 3.0.0, will be removed in 4.0.0.

Method Summary

Modifier and Type	Method	Description
List<RegionPlan>	balanceCluster(Map<TableName,Map<ServerName,List<RegionInfo>>> loadOfAllTable)	Perform the major balance operation for cluster.
void	initialize()	Initialize the load balancer.
void	onConfigurationChange(org.apache.hadoop.conf.Configuration conf)	Notification that config has changed
void	postMasterStartupInitialize()	If balancer needs to do initialization after Master has started up, lets do that here.
ServerName	randomAssignment(RegionInfo regionInfo, List<ServerName> servers)	Get a random region server from the list
void	regionOffline(RegionInfo regionInfo)	Marks the region as offline at balancer.
void	regionOnline(RegionInfo regionInfo, ServerName sn)	Marks the region as online at balancer.
Map<ServerName,List<RegionInfo>>	retainAssignment(Map<RegionInfo,ServerName> regions, List<ServerName> servers)	Assign regions to the previously hosting region server
Map<ServerName,List<RegionInfo>>	roundRobinAssignment(List<RegionInfo> regions, List<ServerName> servers)	Perform a Round Robin assignment of regions.
void	setClusterInfoProvider(ClusterInfoProvider provider)	Set the cluster info provider.
default void	updateBalancerLoadInfo(Map<TableName,Map<ServerName,List<RegionInfo>>> loadOfAllTable)	In some scenarios, Balancer needs to update internal status or information according to the current tables load
void	updateBalancerStatus(boolean status)
void	updateClusterMetrics(ClusterMetrics metrics)	Set the current cluster status.

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

isStopped, stop

Field Details

BOGUS_SERVER_NAME

static final ServerName BOGUS_SERVER_NAME

HBASE_RSGROUP_LOADBALANCER_CLASS

@Deprecated
static final String HBASE_RSGROUP_LOADBALANCER_CLASS

Deprecated.

since 3.0.0, will be removed in 4.0.0. In the new implementation, as the base load balancer will always be the rs group based one, you should just use HConstants.HBASE_MASTER_LOADBALANCER_CLASS to config the per group load balancer.

Config for pluggable load balancers.

See Also:

• Constant Field Values

Method Details

updateClusterMetrics

void updateClusterMetrics(ClusterMetrics metrics)

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

setClusterInfoProvider

void setClusterInfoProvider(ClusterInfoProvider provider)

Set the cluster info provider. Usually it is just a wrapper of master.

balanceCluster

List<RegionPlan> balanceCluster(Map<TableName,Map<ServerName,List<RegionInfo>>> loadOfAllTable)
                         throws IOException

Perform the major balance operation for cluster.

Parameters:

loadOfAllTable - region load of servers for all table

Returns:

a list of regions to be moved, including source and destination, or null if cluster is already balanced

Throws:

IOException

roundRobinAssignment

@NonNull
Map<ServerName,List<RegionInfo>> roundRobinAssignment(List<RegionInfo> regions,
 List<ServerName> servers)
                                               throws IOException

Perform a Round Robin assignment of regions.

Returns:

Map of servername to regioninfos

Throws:

IOException

retainAssignment

@NonNull
Map<ServerName,List<RegionInfo>> retainAssignment(Map<RegionInfo,ServerName> regions,
 List<ServerName> servers)
                                           throws IOException

Assign regions to the previously hosting region server

Returns:

List of plans

Throws:

IOException

randomAssignment

ServerName randomAssignment(RegionInfo regionInfo,
 List<ServerName> servers)
                     throws IOException

Get a random region server from the list

Parameters:

regionInfo - Region for which this selection is being done.

Throws:

IOException

initialize

void initialize()
         throws IOException

Initialize the load balancer. Must be called after setters.

Throws:

IOException

regionOnline

void regionOnline(RegionInfo regionInfo,
 ServerName sn)

Marks the region as online at balancer.

regionOffline

void regionOffline(RegionInfo regionInfo)

Marks the region as offline at balancer.

onConfigurationChange

void onConfigurationChange(org.apache.hadoop.conf.Configuration conf)

Notification that config has changed

Specified by:

onConfigurationChange in interface ConfigurationObserver

postMasterStartupInitialize

void postMasterStartupInitialize()

If balancer needs to do initialization after Master has started up, lets do that here.

updateBalancerStatus

void updateBalancerStatus(boolean status)

updateBalancerLoadInfo

default void updateBalancerLoadInfo(Map<TableName,Map<ServerName,List<RegionInfo>>> loadOfAllTable)

In some scenarios, Balancer needs to update internal status or information according to the current tables load

Parameters:

loadOfAllTable - region load of servers for all table