org.apache.tinkerpop.gremlin.process.computer.traversal

Class TraversalVertexProgram

java.lang.Object

org.apache.tinkerpop.gremlin.process.computer.traversal.TraversalVertexProgram

All Implemented Interfaces:

Cloneable, VertexProgram<TraverserSet<Object>>

public final class TraversalVertexProgram
extends Object
implements VertexProgram<TraverserSet<Object>>

TraversalVertexProgram enables the evaluation of a Traversal on a GraphComputer. At the start of the computation, each Vertex (or Edge) is assigned a single Traverser. For each traverser that is local to the vertex, the vertex looks up its current location in the traversal and processes that step. If the outputted traverser of the step references a local structure on the vertex (e.g. the vertex, an incident edge, its properties, or an arbitrary object), then the vertex continues to compute the next traverser. If the traverser references another location in the graph, then the traverser is sent to that location in the graph via a message. The messages of TraversalVertexProgram are traversers. This continues until all traversers in the computation have halted.

Author:

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

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	TraversalVertexProgram.Builder

Nested classes/interfaces inherited from interface org.apache.tinkerpop.gremlin.process.computer.VertexProgram

VertexProgram.Features

Field Summary

Fields

Modifier and Type	Field and Description
static String	ACTIVE_TRAVERSERS
static String	HALTED_TRAVERSERS
protected static String	MUTATED_MEMORY_KEYS
static String	TRAVERSAL

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

VERTEX_PROGRAM

Method Summary

Modifier and Type	Method and Description
static TraversalVertexProgram.Builder	build()
TraversalVertexProgram	clone() When multiple workers on a single machine need VertexProgram instances, it is possible to use clone.
void	execute(Vertex vertex, Messenger<TraverserSet<Object>> messenger, Memory memory) This method denotes the main body of the computation and is executed on each vertex in the graph.
VertexProgram.Features	getFeatures()
Set<MapReduce>	getMapReducers() The set of MapReduce jobs that are associated with the VertexProgram.
Set<MemoryComputeKey>	getMemoryComputeKeys() The Memory keys that will be used during the computation.
Optional<MessageCombiner<TraverserSet<Object>>>	getMessageCombiner() Combine the messages in route to a particular vertex.
Set<MessageScope>	getMessageScopes(Memory memory) This method returns all the MessageScope possibilities for a particular iteration of the vertex program.
GraphComputer.Persist	getPreferredPersist()
GraphComputer.ResultGraph	getPreferredResultGraph()
PureTraversal<?,?>	getTraversal() Get the PureTraversal associated with the current instance of the TraversalVertexProgram.
Set<VertexComputeKey>	getVertexComputeKeys() The Element properties that will be mutated during the computation.
static <R> TraverserSet<R>	loadHaltedTraversers(Configuration configuration)
void	loadState(Graph graph, Configuration configuration) When it is necessary to load the state of the VertexProgram, this method is called.
void	setup(Memory memory) The method is called at the beginning of the computation.
static <R> void	storeHaltedTraversers(Configuration configuration, TraverserSet<R> haltedTraversers)
void	storeState(Configuration configuration) When it is necessary to store the state of the VertexProgram, this method is called.
boolean	terminate(Memory memory) The method is called at the end of each iteration to determine if the computation is complete.
String	toString()
void	workerIterationEnd(Memory memory) This method is called at the end of each iteration of each "computational chunk." The set of vertices in the graph are typically not processed with full parallelism.
void	workerIterationStart(Memory memory) This method is called at the start of each iteration of each "computational chunk." The set of vertices in the graph are typically not processed with full parallelism.

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.VertexProgram

createVertexProgram, getTraverserRequirements

Field Detail

TRAVERSAL

public static final String TRAVERSAL

See Also:

Constant Field Values

HALTED_TRAVERSERS

public static final String HALTED_TRAVERSERS

See Also:

Constant Field Values

ACTIVE_TRAVERSERS

public static final String ACTIVE_TRAVERSERS

See Also:

Constant Field Values

MUTATED_MEMORY_KEYS

protected static final String MUTATED_MEMORY_KEYS

See Also:

Constant Field Values

Method Detail

getTraversal

public PureTraversal<?,?> getTraversal()

Get the PureTraversal associated with the current instance of the TraversalVertexProgram.

Returns:

the pure traversal of the instantiated program

loadHaltedTraversers

public static <R> TraverserSet<R> loadHaltedTraversers(Configuration configuration)

storeHaltedTraversers

public static <R> void storeHaltedTraversers(Configuration configuration,
                                             TraverserSet<R> haltedTraversers)

loadState

public void loadState(Graph graph,
                      Configuration configuration)

Description copied from interface: VertexProgram

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

Specified by:

loadState in interface VertexProgram<TraverserSet<Object>>

Parameters:

graph - the graph that the VertexProgram will run against

configuration - the configuration to load the state of the VertexProgram from.

storeState

public void storeState(Configuration configuration)

Description copied from interface: VertexProgram

When it is necessary to store the state of the VertexProgram, this method is called. This is typically required when the VertexProgram needs to be serialized to another machine. Note that what is stored is simply the instance/configuration state, not any processed data. The default implementation provided simply stores the VertexProgram class name for reflective reconstruction. It is typically a good idea to VertexProgram.super.storeState().

Specified by:

storeState in interface VertexProgram<TraverserSet<Object>>

Parameters:

configuration - the configuration to store the state of the VertexProgram in.

setup

public void setup(Memory memory)

Description copied from interface: VertexProgram

The method is called at the beginning of the computation. The method is global to the GraphComputer and as such, is not called for each vertex. During this stage, the Memory should be initialized to to its "start state."

Specified by:

setup in interface VertexProgram<TraverserSet<Object>>

Parameters:

memory - The global memory of the GraphComputer

getMessageScopes

public Set<MessageScope> getMessageScopes(Memory memory)

Description copied from interface: VertexProgram

This method returns all the MessageScope possibilities for a particular iteration of the vertex program. The returned messages scopes are the scopes that will be used to send messages during the stated iteration. It is not a requirement that all stated messages scopes be used, just that it is possible that they be used during the iteration.

Specified by:

getMessageScopes in interface VertexProgram<TraverserSet<Object>>

Parameters:

memory - an immutable form of the Memory

Returns:

all possible message scopes during said vertex program iteration

execute

public void execute(Vertex vertex,
                    Messenger<TraverserSet<Object>> messenger,
                    Memory memory)

Description copied from interface: VertexProgram

This method denotes the main body of the computation and is executed on each vertex in the graph. This method is logically executed in parallel on all vertices in the graph. When the Memory is read, it is according to the aggregated state yielded in the previous iteration. When the Memory is written, the data will be aggregated at the end of the iteration for reading in the next iteration.

Specified by:

execute in interface VertexProgram<TraverserSet<Object>>

Parameters:

vertex - the Vertex to execute the VertexProgram on

messenger - the messenger that moves data between vertices

memory - the shared state between all vertices in the computation

terminate

public boolean terminate(Memory memory)

Description copied from interface: VertexProgram

The method is called at the end of each iteration to determine if the computation is complete. The method is global to the GraphComputer and as such, is not called for each Vertex. The Memory maintains the aggregated data from the last execute() iteration.

Specified by:

terminate in interface VertexProgram<TraverserSet<Object>>

Parameters:

memory - The global memory of the GraphComputer

Returns:

whether or not to halt the computation

workerIterationStart

public void workerIterationStart(Memory memory)

Description copied from interface: VertexProgram

This method is called at the start of each iteration of each "computational chunk." The set of vertices in the graph are typically not processed with full parallelism. The vertex set is split into subsets and a worker is assigned to call the VertexProgram.execute(org.apache.tinkerpop.gremlin.structure.Vertex, org.apache.tinkerpop.gremlin.process.computer.Messenger<M>, org.apache.tinkerpop.gremlin.process.computer.Memory) method. The default implementation is a no-op.

Specified by:

workerIterationStart in interface VertexProgram<TraverserSet<Object>>

Parameters:

memory - The memory at the start of the iteration.

workerIterationEnd

public void workerIterationEnd(Memory memory)

Description copied from interface: VertexProgram

This method is called at the end of each iteration of each "computational chunk." The set of vertices in the graph are typically not processed with full parallelism. The vertex set is split into subsets and a worker is assigned to call the VertexProgram.execute(org.apache.tinkerpop.gremlin.structure.Vertex, org.apache.tinkerpop.gremlin.process.computer.Messenger<M>, org.apache.tinkerpop.gremlin.process.computer.Memory) method. The default implementation is a no-op.

Specified by:

workerIterationEnd in interface VertexProgram<TraverserSet<Object>>

Parameters:

memory - The memory at the end of the iteration.

getVertexComputeKeys

public Set<VertexComputeKey> getVertexComputeKeys()

Description copied from interface: VertexProgram

The Element properties that will be mutated during the computation. All properties in the graph are readable, but only the keys specified here are writable. The default is an empty set.

Specified by:

getVertexComputeKeys in interface VertexProgram<TraverserSet<Object>>

Returns:

the set of element keys that will be mutated during the vertex program's execution

getMemoryComputeKeys

public Set<MemoryComputeKey> getMemoryComputeKeys()

Description copied from interface: VertexProgram

The Memory keys that will be used during the computation. These are the only keys that can be read or written throughout the life of the GraphComputer. The default is an empty set.

Specified by:

getMemoryComputeKeys in interface VertexProgram<TraverserSet<Object>>

Returns:

the set of memory keys that will be read/written

getMapReducers

public Set<MapReduce> getMapReducers()

Description copied from interface: VertexProgram

The set of MapReduce jobs that are associated with the VertexProgram. This is not necessarily the exhaustive list over the life of the GraphComputer. If MapReduce jobs are declared by GraphComputer.mapReduce(), they are not contained in this set. The default is an empty set.

Specified by:

getMapReducers in interface VertexProgram<TraverserSet<Object>>

Returns:

the set of MapReduce jobs associated with this VertexProgram

getMessageCombiner

public Optional<MessageCombiner<TraverserSet<Object>>> getMessageCombiner()

Description copied from interface: VertexProgram

Combine the messages in route to a particular vertex. Useful to reduce the amount of data transmitted over the wire. For example, instead of sending two objects that will ultimately be merged at the vertex destination, merge/combine into one and send that object. If no message combiner is provider, then no messages will be combined. Furthermore, it is not guaranteed the all messages in route to the vertex will be combined and thus, combiner-state should not be used. The result of the vertex program algorithm should be the same regardless of whether message combining is executed or not.

Specified by:

getMessageCombiner in interface VertexProgram<TraverserSet<Object>>

Returns:

A optional denoting whether or not their is a message combine associated with the vertex program.

clone

public TraversalVertexProgram clone()

Description copied from interface: VertexProgram

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

Specified by:

clone in interface VertexProgram<TraverserSet<Object>>

Overrides:

clone in class Object

Returns:

A clone of the VertexProgram object

getPreferredResultGraph

public GraphComputer.ResultGraph getPreferredResultGraph()

Specified by:

getPreferredResultGraph in interface VertexProgram<TraverserSet<Object>>

getPreferredPersist

public GraphComputer.Persist getPreferredPersist()

Specified by:

getPreferredPersist in interface VertexProgram<TraverserSet<Object>>

toString

public String toString()

Overrides:

toString in class Object

getFeatures

public VertexProgram.Features getFeatures()

Specified by:

getFeatures in interface VertexProgram<TraverserSet<Object>>

build

public static TraversalVertexProgram.Builder build()