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

Class GroupCountSideEffectStep.GroupCountSideEffectMapReduce<E>

java.lang.Object

org.apache.tinkerpop.gremlin.process.computer.util.StaticMapReduce<E,Long,E,Long,Map<E,Long>>

org.apache.tinkerpop.gremlin.process.traversal.step.sideEffect.GroupCountSideEffectStep.GroupCountSideEffectMapReduce<E>

All Implemented Interfaces:

Cloneable, MapReduce<E,Long,E,Long,Map<E,Long>>

Enclosing class:

GroupCountSideEffectStep<S,E>

public static final class GroupCountSideEffectStep.GroupCountSideEffectMapReduce<E>
extends StaticMapReduce<E,Long,E,Long,Map<E,Long>>

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_COUNT_SIDE_EFFECT_STEP_SIDE_EFFECT_KEY

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

MAP_REDUCE

Constructor Summary

Constructors

Constructor and Description
GroupCountSideEffectMapReduce(GroupCountSideEffectStep step)

Method Summary

Modifier and Type	Method and Description
void	combine(E key, Iterator<Long> values, MapReduce.ReduceEmitter<E,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.
Map<E,Long>	generateFinalResult(Iterator<KeyValue<E,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.
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<E,Long> emitter) The map() method is logically executed at all vertices in the graph in parallel.
void	reduce(E key, Iterator<Long> values, MapReduce.ReduceEmitter<E,Long> 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.

Methods inherited from class org.apache.tinkerpop.gremlin.process.computer.util.StaticMapReduce

clone, equals, hashCode, toString

Methods inherited from class java.lang.Object

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

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

addResultToMemory, createMapReduce, getMapKeySort, getReduceKeySort, workerEnd, workerStart

Field Detail

GROUP_COUNT_SIDE_EFFECT_STEP_SIDE_EFFECT_KEY

public static final String GROUP_COUNT_SIDE_EFFECT_STEP_SIDE_EFFECT_KEY

See Also:

Constant Field Values

Constructor Detail

GroupCountSideEffectMapReduce

public GroupCountSideEffectMapReduce(GroupCountSideEffectStep 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<E,Long,E,Long,Map<E,Long>>

Overrides:

storeState in class StaticMapReduce<E,Long,E,Long,Map<E,Long>>

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.

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.

Parameters:

stage - the stage to check for definition.

Returns:

whether that stage should be executed.

map

public void map(Vertex vertex,
                MapReduce.MapEmitter<E,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).

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(E key,
                   Iterator<Long> values,
                   MapReduce.ReduceEmitter<E,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.

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(E key,
                    Iterator<Long> values,
                    MapReduce.ReduceEmitter<E,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.

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 Map<E,Long> generateFinalResult(Iterator<KeyValue<E,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.

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.

Returns:

the memory key of the generated result object.