org.apache.tinkerpop.gremlin.process.traversal.step.map

Class GroupStep.GroupMapReduce<K,V,R>

java.lang.Object

org.apache.tinkerpop.gremlin.process.traversal.step.map.GroupStep.GroupMapReduce<K,V,R>

All Implemented Interfaces:

Cloneable, MapReduce<K,Collection<V>,K,R,Map<K,R>>

Enclosing class:

GroupStep<S,K,V,R>

public static final class GroupStep.GroupMapReduce<K,V,R>
extends Object
implements MapReduce<K,Collection<V>,K,R,Map<K,R>>

Nested Class Summary

Nested classes/interfaces inherited from interface org.apache.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 String	GROUP_BY_STEP_STEP_ID

Fields inherited from interface org.apache.tinkerpop.gremlin.process.computer.MapReduce

MAP_REDUCE

Constructor Summary

Constructors

Constructor and Description
GroupMapReduce(GroupStep<?,K,V,R> step)

Method Summary

Modifier and Type	Method and Description
GroupStep.GroupMapReduce<K,V,R>	clone() When multiple workers on a single machine need MapReduce instances, it is possible to use clone.
boolean	doStage(MapReduce.Stage stage) A MapReduce job can be map-only, map-reduce-only, or map-combine-reduce.
Map<K,R>	generateFinalResult(Iterator<KeyValue<K,R>> 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.
String	getMemoryKey() The results of the MapReduce job are associated with a memory-key to ultimately be stored in Memory.
void	loadState(Graph graph, Configuration configuration) When it is necessary to load the state of a MapReduce job, this method is called.
void	map(Vertex vertex, MapReduce.MapEmitter<K,Collection<V>> emitter) The map() method is logically executed at all vertices in the graph in parallel.
void	reduce(K key, Iterator<Collection<V>> values, MapReduce.ReduceEmitter<K,R> emitter) The reduce() method is logically on the "machine" the respective key hashes to.
void	storeState(Configuration configuration) When it is necessary to store the state of a MapReduce job, this method is called.
String	toString()

Methods inherited from class java.lang.Object

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

Methods inherited from interface org.apache.tinkerpop.gremlin.process.computer.MapReduce

addResultToMemory, combine, createMapReduce, getMapKeySort, getReduceKeySort, workerEnd, workerStart

Field Detail

GROUP_BY_STEP_STEP_ID

public static final String GROUP_BY_STEP_STEP_ID

See Also:

Constant Field Values

Constructor Detail

GroupMapReduce

public GroupMapReduce(GroupStep<?,K,V,R> step)

Method Detail

storeState

public void storeState(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<K,Collection<V>,K,R,Map<K,R>>

Parameters:

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

loadState

public void loadState(Graph graph,
                      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<K,Collection<V>,K,R,Map<K,R>>

Parameters:

graph - the graph the MapReduce job will run against

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<K,Collection<V>,K,R,Map<K,R>>

Parameters:

stage - the stage to check for definition.

Returns:

whether that stage should be executed.

map

public void map(Vertex vertex,
                MapReduce.MapEmitter<K,Collection<V>> 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<K,Collection<V>,K,R,Map<K,R>>

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(K key,
                   Iterator<Collection<V>> values,
                   MapReduce.ReduceEmitter<K,R> 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<K,Collection<V>,K,R,Map<K,R>>

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.

generateFinalResult

public Map<K,R> generateFinalResult(Iterator<KeyValue<K,R>> 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<K,Collection<V>,K,R,Map<K,R>>

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 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<K,Collection<V>,K,R,Map<K,R>>

Returns:

the memory key of the generated result object.

clone

public GroupStep.GroupMapReduce<K,V,R> clone()

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(Configuration) and MapReduce.loadState(org.apache.tinkerpop.gremlin.structure.Graph, 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<K,Collection<V>,K,R,Map<K,R>>

Overrides:

clone in class Object

Returns:

A clone of the MapReduce object

toString

public String toString()

Overrides:

toString in class Object