com.tinkerpop.gremlin.process.graph.step.sideEffect.mapreduce

Class GroupCountMapReduce

java.lang.Object

com.tinkerpop.gremlin.process.graph.step.sideEffect.mapreduce.GroupCountMapReduce

All Implemented Interfaces:

MapReduce<java.lang.Object,java.lang.Long,java.lang.Object,java.lang.Long,java.util.Map<java.lang.Object,java.lang.Long>>, java.lang.Cloneable

public final class GroupCountMapReduce
extends java.lang.Object
implements MapReduce<java.lang.Object,java.lang.Long,java.lang.Object,java.lang.Long,java.util.Map<java.lang.Object,java.lang.Long>>

Author:

Marko A. Rodriguez (http://markorodriguez.com)

Nested Class Summary

Nested classes/interfaces inherited from interface com.tinkerpop.gremlin.process.computer.MapReduce

MapReduce.MapEmitter<K,V>, MapReduce.NullObject, MapReduce.ReduceEmitter<OK,OV>, MapReduce.Stage

Field Summary

Fields

Modifier and Type	Field and Description
static java.lang.String	GROUP_COUNT_STEP_SIDE_EFFECT_KEY

Fields inherited from interface com.tinkerpop.gremlin.process.computer.MapReduce

MAP_REDUCE

Constructor Summary

Constructors

Constructor and Description
GroupCountMapReduce(GroupCountStep step)

Method Summary

Modifier and Type	Method and Description
GroupCountMapReduce	clone() When multiple workers on a single machine need MapReduce instances, it is possible to use clone.
void	combine(java.lang.Object key, java.util.Iterator<java.lang.Long> values, MapReduce.ReduceEmitter<java.lang.Object,java.lang.Long> emitter) The combine() method is logically executed at all "machines" in parallel.
boolean	doStage(MapReduce.Stage stage) A MapReduce job can be map-only, map-reduce-only, or map-combine-reduce.
boolean	equals(java.lang.Object object)
java.util.Map<java.lang.Object,java.lang.Long>	generateFinalResult(java.util.Iterator<KeyValue<java.lang.Object,java.lang.Long>> keyValues) The key/value pairs emitted by reduce() (or map() in a map-only job) can be iterated to generate a local JVM Java object.
java.lang.String	getMemoryKey() The results of the MapReduce job are associated with a memory-key to ultimately be stored in Memory.
int	hashCode()
void	loadState(org.apache.commons.configuration.Configuration configuration) When it is necessary to load the state of a MapReduce job, this method is called.
void	map(Vertex vertex, MapReduce.MapEmitter<java.lang.Object,java.lang.Long> emitter) The map() method is logically executed at all vertices in the graph in parallel.
void	reduce(java.lang.Object key, java.util.Iterator<java.lang.Long> values, MapReduce.ReduceEmitter<java.lang.Object,java.lang.Long> emitter) The reduce() method is logically on the "machine" the respective key hashes to.
void	storeState(org.apache.commons.configuration.Configuration configuration) When it is necessary to store the state of a MapReduce job, this method is called.
java.lang.String	toString()

Methods inherited from class java.lang.Object

finalize, getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface com.tinkerpop.gremlin.process.computer.MapReduce

addResultToMemory, createMapReduce, getMapKeySort, getReduceKeySort

Field Detail

GROUP_COUNT_STEP_SIDE_EFFECT_KEY

public static final java.lang.String GROUP_COUNT_STEP_SIDE_EFFECT_KEY

See Also:

Constant Field Values

Constructor Detail

GroupCountMapReduce

public GroupCountMapReduce(GroupCountStep step)

Method Detail

storeState

public void storeState(org.apache.commons.configuration.Configuration configuration)

Description copied from interface: MapReduce

When it is necessary to store the state of a MapReduce job, this method is called. This is typically required when the MapReduce job needs to be serialized to another machine. Note that what is stored is simply the instance state, not any processed data.

Specified by:

storeState in interface MapReduce<java.lang.Object,java.lang.Long,java.lang.Object,java.lang.Long,java.util.Map<java.lang.Object,java.lang.Long>>

Parameters:

configuration - the configuration to store the state of the MapReduce job in.

loadState

public void loadState(org.apache.commons.configuration.Configuration configuration)

Description copied from interface: MapReduce

When it is necessary to load the state of a MapReduce job, this method is called. This is typically required when the MapReduce job needs to be serialized to another machine. Note that what is loaded is simply the instance state, not any processed data.

It is important that the state loaded from loadState() is identical to any state created from a constructor. For those GraphComputers that do not need to use Configurations to migrate state between JVMs, the constructor will only be used.

Specified by:

loadState in interface MapReduce<java.lang.Object,java.lang.Long,java.lang.Object,java.lang.Long,java.util.Map<java.lang.Object,java.lang.Long>>

Parameters:

configuration - the configuration to load the state of the MapReduce job from.

doStage

public boolean doStage(MapReduce.Stage stage)

Description copied from interface: MapReduce

A MapReduce job can be map-only, map-reduce-only, or map-combine-reduce. Before executing the particular stage, this method is called to determine if the respective stage is defined. This method should return true if the respective stage as a non-default method implementation.

Specified by:

doStage in interface MapReduce<java.lang.Object,java.lang.Long,java.lang.Object,java.lang.Long,java.util.Map<java.lang.Object,java.lang.Long>>

Parameters:

stage - the stage to check for definition.

Returns:

whether that stage should be executed.

map

public void map(Vertex vertex,
                MapReduce.MapEmitter<java.lang.Object,java.lang.Long> emitter)

Description copied from interface: MapReduce

The map() method is logically executed at all vertices in the graph in parallel. The map() method emits key/value pairs given some analysis of the data in the vertices (and/or its incident edges).

Specified by:

map in interface MapReduce<java.lang.Object,java.lang.Long,java.lang.Object,java.lang.Long,java.util.Map<java.lang.Object,java.lang.Long>>

Parameters:

vertex - the current vertex being map() processed.

emitter - the component that allows for key/value pairs to be emitted to the next stage.

reduce

public void reduce(java.lang.Object key,
                   java.util.Iterator<java.lang.Long> values,
                   MapReduce.ReduceEmitter<java.lang.Object,java.lang.Long> emitter)

Description copied from interface: MapReduce

The reduce() method is logically on the "machine" the respective key hashes to. The reduce() method combines all the values associated with the key and emits key/value pairs.

Specified by:

reduce in interface MapReduce<java.lang.Object,java.lang.Long,java.lang.Object,java.lang.Long,java.util.Map<java.lang.Object,java.lang.Long>>

Parameters:

key - the key that has aggregated values

values - the aggregated values associated with the key

emitter - the component that allows for key/value pairs to be emitted as the final result.

combine

public void combine(java.lang.Object key,
                    java.util.Iterator<java.lang.Long> values,
                    MapReduce.ReduceEmitter<java.lang.Object,java.lang.Long> emitter)

Description copied from interface: MapReduce

The combine() method is logically executed at all "machines" in parallel. The combine() method pre-combines the values for a key prior to propagation over the wire. The combine() method must emit the same key/value pairs as the reduce() method. If there is a combine() implementation, there must be a reduce() implementation. If the MapReduce implementation is single machine, it can skip executing this method as reduce() is sufficient.

Specified by:

combine in interface MapReduce<java.lang.Object,java.lang.Long,java.lang.Object,java.lang.Long,java.util.Map<java.lang.Object,java.lang.Long>>

Parameters:

key - the key that has aggregated values

values - the aggregated values associated with the key

emitter - the component that allows for key/value pairs to be emitted to the reduce stage.

generateFinalResult

public java.util.Map<java.lang.Object,java.lang.Long> generateFinalResult(java.util.Iterator<KeyValue<java.lang.Object,java.lang.Long>> keyValues)

Description copied from interface: MapReduce

The key/value pairs emitted by reduce() (or map() in a map-only job) can be iterated to generate a local JVM Java object.

Specified by:

generateFinalResult in interface MapReduce<java.lang.Object,java.lang.Long,java.lang.Object,java.lang.Long,java.util.Map<java.lang.Object,java.lang.Long>>

Parameters:

keyValues - the key/value pairs that were emitted from reduce() (or map() in a map-only job)

Returns:

the resultant object formed from the emitted key/values.

getMemoryKey

public java.lang.String getMemoryKey()

Description copied from interface: MapReduce

The results of the MapReduce job are associated with a memory-key to ultimately be stored in Memory.

Specified by:

getMemoryKey in interface MapReduce<java.lang.Object,java.lang.Long,java.lang.Object,java.lang.Long,java.util.Map<java.lang.Object,java.lang.Long>>

Returns:

the memory key of the generated result object.

hashCode

public int hashCode()

Overrides:

hashCode in class java.lang.Object

equals

public boolean equals(java.lang.Object object)

Overrides:

equals in class java.lang.Object

toString

public java.lang.String toString()

Overrides:

toString in class java.lang.Object

clone

public GroupCountMapReduce clone()
                          throws java.lang.CloneNotSupportedException

Description copied from interface: MapReduce

When multiple workers on a single machine need MapReduce instances, it is possible to use clone. This will provide a speedier way of generating instances, over the MapReduce.storeState(org.apache.commons.configuration.Configuration) and MapReduce.loadState(org.apache.commons.configuration.Configuration) model. The default implementation simply returns the object as it assumes that the MapReduce instance is a stateless singleton.

Specified by:

clone in interface MapReduce<java.lang.Object,java.lang.Long,java.lang.Object,java.lang.Long,java.util.Map<java.lang.Object,java.lang.Long>>

Overrides:

clone in class java.lang.Object

Returns:

A clone of the MapReduce object

Throws:

java.lang.CloneNotSupportedException