StochasticLoadBalancer (Apache HBase 1.1.7 API)

java.lang.Object
- org.apache.hadoop.hbase.master.balancer.BaseLoadBalancer
- - org.apache.hadoop.hbase.master.balancer.StochasticLoadBalancer

All Implemented Interfaces:

org.apache.hadoop.conf.Configurable, 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()

Constructors
Constructor and Description
`StochasticLoadBalancer()`

Method Summary

Methods
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(org.apache.hadoop.conf.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(org.apache.hadoop.conf.Configuration conf)`
`void`	`setMasterServices(MasterServices masterServices)` Set the master service.
`protected void`	`setSlop(org.apache.hadoop.conf.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(org.apache.hadoop.conf.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(org.apache.hadoop.conf.Configuration conf)
```
    Specified by:
    
    setConf in interface org.apache.hadoop.conf.Configurable
    
    Overrides:
    
    setConf in class BaseLoadBalancer
  - setSlop
```
protected void setSlop(org.apache.hadoop.conf.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.

Class StochasticLoadBalancer

Nested Class Summary

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

Field Summary

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

Constructor Summary

Method Summary

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

Methods inherited from class java.lang.Object

Field Detail

STEPS_PER_REGION_KEY

MAX_STEPS_KEY

MAX_RUNNING_TIME_KEY

KEEP_REGION_LOADS

Constructor Detail

StochasticLoadBalancer

Method Detail

onConfigurationChange

setConf

setSlop

setClusterStatus

setMasterServices

areSomeRegionReplicasColocated

balanceCluster

initCosts

updateCostsWithAction

computeCost