Package org.apache.accumulo.core.spi.fs

Class PreferredVolumeChooser

java.lang.Object

org.apache.accumulo.core.spi.fs.RandomVolumeChooser

org.apache.accumulo.core.spi.fs.PreferredVolumeChooser

All Implemented Interfaces:

VolumeChooser

Direct Known Subclasses:

SpaceAwareVolumeChooser

public class PreferredVolumeChooser
extends RandomVolumeChooser

A RandomVolumeChooser that selects preferred volumes to use from the provided volume options. Preferred Volumes are set on either the per-table, per-scope, or default configuration level. Configuration details are overridden based on the top-down "Default","Site","System" scopes.

Defaults to selecting a volume at random from the provided volume options.

Property Details:

Preferred volumes can be set on a per-table basis via the custom property volume.preferred.

This property should contain a comma separated list of Volume URIs. Since this is a custom property, it can be accessed under the prefix table.custom.
The volume.preferred property can be set at various configuration levels depending on the scope. Note: Both the property name and the format of its value are specific to this particular implementation.

Scope Property Lookups and Defaults locations

Scope	Property Value Lookup	Default Property Lookup
Scope.DEFAULT	general.custom.volume.preferred.default	Throws RuntimeException if not set
Scope.INIT	general.custom.volume.preferred.init	general.custom.volume.preferred.default
Scope.LOGGER	general.custom.volume.preferred.logger	general.custom.volume.preferred.default
Scope.TABLE	table.custom.volume.preferred	general.custom.volume.preferred.default

Examples of expected usage:

• Separate metadata table and write ahead logs from general data location.

   
   // Set list of volumes
   instance.volumes=hdfs://namenode_A/accumulo,hdfs://namenode_B/general
   // Enable the preferred volume chooser
   general.volume.chooser=org.apache.accumulo.core.spi.fs.PreferredVolumeChooser
   // Set default preferred volume
   general.custom.volume.preferred.default=hdfs://namenode_B/general
   // Set write-ahead log preferred volume
   general.custom.volume.preferred.logger=hdfs://namenode_A/accumulo
   // Initialize and start accumulo
   // Once accumulo is up, open the shell and configure the metadata table to use a preferred volume
   config -t accumulo.metadata -s table.custom.volume.preferred=hdfs://namenode_A/accumulo
   
   

• Allow general data to use all volumes, but limit a specific table to a preferred volume

   
   // Set list of volumes
   instance.volumes=hdfs://namenode/accumulo,hdfs://namenode/accumulo_select
   // Enable the preferred volume chooser
   general.volume.chooser=org.apache.accumulo.core.spi.fs.PreferredVolumeChooser
   // Set default preferred volumes
   general.custom.volume.preferred.default=hdfs://namenode/accumulo,hdfs://namenode/accumulo_select
   // Initialize and start accumulo
   // Once accumulo is up, open the shell and configure the metadata table to use a preferred volume
   config -t accumulo.metadata -s table.custom.volume.preferred=hdfs://namenode/accumulo_select
   
   

Since:

2.1.0

Constructor Summary

Constructors

Constructor	Description
PreferredVolumeChooser()

Method Summary

Modifier and Type	Method	Description
Set<String>	choosable(VolumeChooserEnvironment env, Set<String> options)	Returns the subset of volumes that match the defined preferred volumes value
String	choose(VolumeChooserEnvironment env, Set<String> options)	Selects a volume at random from the provided set of volumes.

Methods inherited from class java.lang.Object

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

Constructor Detail

PreferredVolumeChooser

public PreferredVolumeChooser()

Method Detail

choose

public String choose(VolumeChooserEnvironment env,
                     Set<String> options)

Description copied from class: RandomVolumeChooser

Selects a volume at random from the provided set of volumes. The environment scope is not utilized.

Specified by:

choose in interface VolumeChooser

Overrides:

choose in class RandomVolumeChooser

Parameters:

env - the server environment provided by the calling framework

options - the list of volumes to choose from

Returns:

a volume from the list of volume options

choosable

public Set<String> choosable(VolumeChooserEnvironment env,
                             Set<String> options)

Returns the subset of volumes that match the defined preferred volumes value

Specified by:

choosable in interface VolumeChooser

Overrides:

choosable in class RandomVolumeChooser

Parameters:

env - the server environment provided by the calling framework

options - the subset of volumes to choose from

Returns:

an array of preferred volumes that are a subset of Property.INSTANCE_VOLUMES