Package org.apache.storm.grouping

Class PartialKeyGrouping

java.lang.Object

org.apache.storm.grouping.PartialKeyGrouping

All Implemented Interfaces:

Serializable, CustomStreamGrouping

public class PartialKeyGrouping
extends Object
implements CustomStreamGrouping, Serializable

A variation on FieldGrouping. This grouping operates on a partitioning of the incoming tuples (like a FieldGrouping), but it can send Tuples from a given partition to multiple downstream tasks.

Given a total pool of target tasks, this grouping will always send Tuples with a given key to one member of a subset of those tasks. Each key is assigned a subset of tasks. Each tuple is then sent to one task from that subset.

Notes: - the default TaskSelector ensures each task gets as close to a balanced number of Tuples as possible - the default AssignmentCreator hashes the key and produces an assignment of two tasks

See Also:

• Serialized Form

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static interface	PartialKeyGrouping.AssignmentCreator	This interface is responsible for choosing a subset of the target tasks to use for a given key.
static class	PartialKeyGrouping.BalancedTargetSelector	A basic implementation of target selection.
static class	PartialKeyGrouping.RandomTwoTaskAssignmentCreator	This implementation of AssignmentCreator chooses two arbitrary tasks.
static interface	PartialKeyGrouping.TargetSelector	This interface chooses one element from a task assignment to send a specific Tuple to.

Constructor Summary

Constructors

Constructor	Description
PartialKeyGrouping()
PartialKeyGrouping(Fields fields)
PartialKeyGrouping(Fields fields, PartialKeyGrouping.AssignmentCreator assignmentCreator)
PartialKeyGrouping(Fields fields, PartialKeyGrouping.AssignmentCreator assignmentCreator, PartialKeyGrouping.TargetSelector targetSelector)

Method Summary

Modifier and Type	Method	Description
List<Integer>	chooseTasks(int taskId, List<Object> values)	This function implements a custom stream grouping.
void	prepare(WorkerTopologyContext context, GlobalStreamId stream, List<Integer> targetTasks)	Tells the stream grouping at runtime the tasks in the target bolt.

Methods inherited from class java.lang.Object

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

Constructor Details

PartialKeyGrouping

public PartialKeyGrouping()

PartialKeyGrouping

public PartialKeyGrouping(Fields fields)

PartialKeyGrouping

public PartialKeyGrouping(Fields fields,
 PartialKeyGrouping.AssignmentCreator assignmentCreator)

PartialKeyGrouping

public PartialKeyGrouping(Fields fields,
 PartialKeyGrouping.AssignmentCreator assignmentCreator,
 PartialKeyGrouping.TargetSelector targetSelector)

Method Details

prepare

public void prepare(WorkerTopologyContext context,
 GlobalStreamId stream,
 List<Integer> targetTasks)

Description copied from interface: CustomStreamGrouping

Tells the stream grouping at runtime the tasks in the target bolt. This information should be used in chooseTasks to determine the target tasks.

It also tells the grouping the metadata on the stream this grouping will be used on.

Specified by:

prepare in interface CustomStreamGrouping

chooseTasks

public List<Integer> chooseTasks(int taskId,
 List<Object> values)

Description copied from interface: CustomStreamGrouping

This function implements a custom stream grouping. It takes in as input the number of tasks in the target bolt in prepare and returns the tasks to send the tuples to.

Specified by:

chooseTasks in interface CustomStreamGrouping

values - the values to group on