org.apache.hadoop.hbase.master.balancer

Class StochasticLoadBalancer

java.lang.Object

org.apache.hadoop.hbase.master.balancer.BaseLoadBalancer

org.apache.hadoop.hbase.master.balancer.StochasticLoadBalancer

All Implemented Interfaces:

ConfigurationObserver, LoadBalancer, Stoppable

@InterfaceAudience.LimitedPrivate(value="Configuration")
public class StochasticLoadBalancer
extends BaseLoadBalancer

This is a best effort load balancer. Given a Cost function F(C) => x It will randomly try and mutate the cluster to Cprime. If F(Cprime) < F(C) then the new cluster state becomes the plan. It includes costs functions to compute the cost of:

• Region Load
• Table Load
• Data Locality
• Memstore Sizes
• Storefile Sizes

Every cost function returns a number between 0 and 1 inclusive; where 0 is the lowest cost best solution, and 1 is the highest possible cost and the worst solution. The computed costs are scaled by their respective multipliers:

• hbase.master.balancer.stochastic.regionLoadCost
• hbase.master.balancer.stochastic.moveCost
• hbase.master.balancer.stochastic.tableLoadCost
• hbase.master.balancer.stochastic.localityCost
• hbase.master.balancer.stochastic.memstoreSizeCost
• hbase.master.balancer.stochastic.storefileSizeCost

In addition to the above configurations, the balancer can be tuned by the following configuration values:

• hbase.master.balancer.stochastic.maxMoveRegions which controls what the max number of regions that can be moved in a single invocation of this balancer.
• hbase.master.balancer.stochastic.stepsPerRegion is the coefficient by which the number of regions is multiplied to try and get the number of times the balancer will mutate all servers.
• hbase.master.balancer.stochastic.maxSteps which controls the maximum number of times that the balancer will try and mutate all the servers. The balancer will use the minimum of this value and the above computation.

This balancer is best used with hbase.master.loadbalance.bytable set to false so that the balancer gets the full picture of all loads on the cluster.

Nested Class Summary

Nested classes/interfaces inherited from class org.apache.hadoop.hbase.master.balancer.BaseLoadBalancer

BaseLoadBalancer.Cluster

Field Summary

Fields

Modifier and Type	Field and Description
protected static String	KEEP_REGION_LOADS
protected static String	MAX_RUNNING_TIME_KEY
protected static String	MAX_STEPS_KEY
protected static String	STEPS_PER_REGION_KEY

Fields inherited from class org.apache.hadoop.hbase.master.balancer.BaseLoadBalancer

clusterStatus, config, masterServerName, metricsBalancer, rackManager, regionFinder, services, slop, TABLES_ON_MASTER, tablesOnMaster

Constructor Summary

Constructors

Constructor and Description
StochasticLoadBalancer()

Method Summary

Modifier and Type	Method and Description
protected boolean	areSomeRegionReplicasColocated(BaseLoadBalancer.Cluster c) Subclasses should implement this to return true if the cluster has nodes that hosts multiple replicas for the same region, or, if there are multiple racks and the same rack hosts replicas of the same region
List<RegionPlan>	balanceCluster(Map<ServerName,List<HRegionInfo>> clusterState) Given the cluster state this will try and approach an optimal balance.
protected double	computeCost(BaseLoadBalancer.Cluster cluster, double previousCost) This is the main cost function.
protected void	initCosts(BaseLoadBalancer.Cluster cluster)
void	onConfigurationChange(Configuration conf) This method would be called by the ConfigurationManager object when the Configuration object is reloaded from disk.
void	setClusterStatus(ClusterStatus st) Set the current cluster status.
void	setConf(Configuration conf)
void	setMasterServices(MasterServices masterServices) Set the master service.
protected void	setSlop(Configuration conf)
protected void	updateCostsWithAction(BaseLoadBalancer.Cluster cluster, BaseLoadBalancer.Cluster.Action action)

Methods inherited from class org.apache.hadoop.hbase.master.balancer.BaseLoadBalancer

assignMasterRegions, balanceMasterRegions, createCluster, getConf, getRegionAssignmentsByServer, getTablesOnMaster, immediateAssignment, initialize, isStopped, needsBalance, randomAssignment, regionOffline, regionOnline, retainAssignment, roundRobinAssignment, setRackManager, shouldBeOnMaster, stop, tablesOnMaster

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

STEPS_PER_REGION_KEY

protected static final String STEPS_PER_REGION_KEY

See Also:

Constant Field Values

MAX_STEPS_KEY

protected static final String MAX_STEPS_KEY

See Also:

Constant Field Values

MAX_RUNNING_TIME_KEY

protected static final String MAX_RUNNING_TIME_KEY

See Also:

Constant Field Values

KEEP_REGION_LOADS

protected static final String KEEP_REGION_LOADS

See Also:

Constant Field Values

Constructor Detail

StochasticLoadBalancer

public StochasticLoadBalancer()

Method Detail

onConfigurationChange

public 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

Specified by:

onConfigurationChange in interface LoadBalancer

Overrides:

onConfigurationChange in class BaseLoadBalancer

setConf

public void setConf(Configuration conf)

Overrides:

setConf in class BaseLoadBalancer

setSlop

protected void setSlop(Configuration conf)

Overrides:

setSlop in class BaseLoadBalancer

setClusterStatus

public void setClusterStatus(ClusterStatus st)

Description copied from interface: LoadBalancer

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

Specified by:

setClusterStatus in interface LoadBalancer

Overrides:

setClusterStatus in class BaseLoadBalancer

setMasterServices

public void setMasterServices(MasterServices masterServices)

Description copied from interface: LoadBalancer

Set the master service.

Specified by:

setMasterServices in interface LoadBalancer

Overrides:

setMasterServices in class BaseLoadBalancer

areSomeRegionReplicasColocated

protected boolean areSomeRegionReplicasColocated(BaseLoadBalancer.Cluster c)

Description copied from class: BaseLoadBalancer

Subclasses should implement this to return true if the cluster has nodes that hosts multiple replicas for the same region, or, if there are multiple racks and the same rack hosts replicas of the same region

Overrides:

areSomeRegionReplicasColocated in class BaseLoadBalancer

Parameters:

c - Cluster information

Returns:

whether region replicas are currently co-located

balanceCluster

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

Given the cluster state this will try and approach an optimal balance. This should always approach the optimal state given enough steps.

Returns:

List of plans

initCosts

protected void initCosts(BaseLoadBalancer.Cluster cluster)

updateCostsWithAction

protected void updateCostsWithAction(BaseLoadBalancer.Cluster cluster,
                                     BaseLoadBalancer.Cluster.Action action)

computeCost

protected double computeCost(BaseLoadBalancer.Cluster cluster,
                             double previousCost)

This is the main cost function. It will compute a cost associated with a proposed cluster state. All different costs will be combined with their multipliers to produce a double cost.

Parameters:

cluster - The state of the cluster

previousCost - the previous cost. This is used as an early out.

Returns:

a double of a cost associated with the proposed cluster state. This cost is an aggregate of all individual cost functions.