cascading.cascade
Class Cascade

java.lang.Object
  cascading.cascade.Cascade

All Implemented Interfaces:

Runnable

public class Cascade
extends Object
implements Runnable

A Cascade is an assembly of Flow instances that share or depend on equivalent Tap instances and are executed as a single group. The most common case is where one Flow instance depends on a Tap created by a second Flow instance. This dependency chain can continue as practical.

Note Flow instances that have no shared dependencies will be executed in parallel.

Additionally, a Cascade allows for incremental builds of complex data processing processes. If a given source Tap is newer than a subsequent sink Tap in the assembly, the connecting Flow(s) will be executed when the Cascade executed. If all the targets (sinks) are up to date, the Cascade exits immediately and does nothing.

The concept of 'stale' is pluggable, see the FlowSkipStrategy class.

When a Cascade starts up, if first verifies which Flow instances have stale sinks, if the sinks are not stale, the method Flow.deleteSinksIfNotUpdate() is called. Before appends were supported (logically) the Cascade deleted all the sinks in a Flow.

The new consequence of this is if the Cascade fails, but does complete a Flow that appended or updated data, re-running the Cascade (and the successful append/update Flow) will re-update data to the source. Some systems may be idempotent and may not have any side-effects. So plan accordingly.

See Also:

Flow, FlowSkipStrategy

Nested Class Summary

protected class

Cascade.CascadeJob Class CascadeJob manages Flow execution in the current Cascade instance.

Method Summary

void	complete() Method complete begins the current Cascade process if method start() was not previously called.
List<Flow>	findFlows(String regex) Method findFlows returns a List of flows whos names match the given regex pattern.
Collection<Flow>	findFlowsSinkingTo(String identifier) Method findFlowsSinkingTo returns all Flow instances that writes to a sink with the given identifier.
Collection<Flow>	findFlowsSourcingFrom(String identifier) Method findFlowsSourcingFrom returns all Flow instances that reads from a source with the given identifier.
CascadeStats	getCascadeStats() Method getCascadeStats returns the cascadeStats of this Cascade object.
List<Flow>	getFlows() Method getFlows returns the flows managed by this Cascade object.
FlowSkipStrategy	getFlowSkipStrategy() Method getFlowSkipStrategy returns the current FlowSkipStrategy used by this Flow.
String	getID() Method getID returns the ID of this Cascade object.
int	getMaxConcurrentFlows(Map<Object,Object> properties)
String	getName() Method getName returns the name of this Cascade object.
Collection<Flow>	getPredecessorFlows(Flow flow) Method getPredecessorFlows returns a Collection of all the Flow instances that will be executed before the given Flow instance.
Collection<Flow>	getSuccessorFlows(Flow flow) Method getSuccessorFlows returns a Collection of all the Flow instances that will be executed after the given Flow instance.
static void	printBanner()
protected void	printElementGraph(String filename, org.jgrapht.graph.SimpleDirectedGraph<String,Flow.FlowHolder> graph)
void	run() Method run implements the Runnable run method.
FlowSkipStrategy	setFlowSkipStrategy(FlowSkipStrategy flowSkipStrategy) Method setFlowSkipStrategy sets a new FlowSkipStrategy, the current strategy, if any, is returned.
static void	setMaxConcurrentFlows(Map<Object,Object> properties, int numConcurrentFlows) Method setMaxConcurrentFlows sets the maximum number of Flows that a Cascade can run concurrently.
void	start() Method start begins the current Cascade process.
void	stop()
String	toString()
void	writeDOT(String filename) Method writeDOT writes this element graph to a DOT file for easy visualization and debugging.

Methods inherited from class java.lang.Object

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

Method Detail

setMaxConcurrentFlows

public static void setMaxConcurrentFlows(Map<Object,Object> properties,
                                         int numConcurrentFlows)

Method setMaxConcurrentFlows sets the maximum number of Flows that a Cascade can run concurrently.

By default a Cascade will attempt to run all give Flow instances at the same time. But there are occasions where limiting the number for flows helps manages resources.

Parameters:

properties - of type Map

numConcurrentFlows - of type int

getMaxConcurrentFlows

public int getMaxConcurrentFlows(Map<Object,Object> properties)

getName

public String getName()

Method getName returns the name of this Cascade object.

Returns:

the name (type String) of this Cascade object.

getID

public String getID()

Method getID returns the ID of this Cascade object.

The ID value is a long HEX String used to identify this instance globally. Subsequent Cascade instances created with identical paramers will not return the same ID.

Returns:

the ID (type String) of this Cascade object.

getCascadeStats

public CascadeStats getCascadeStats()

Method getCascadeStats returns the cascadeStats of this Cascade object.

Returns:

the cascadeStats (type CascadeStats) of this Cascade object.

getFlows

public List<Flow> getFlows()

Method getFlows returns the flows managed by this Cascade object. The returned Flow instances will be in topological order.

Returns:

the flows (type Collection) of this Cascade object.

findFlows

public List<Flow> findFlows(String regex)

Method findFlows returns a List of flows whos names match the given regex pattern.

Parameters:

regex - of type String

Returns:

List

getSuccessorFlows

public Collection<Flow> getSuccessorFlows(Flow flow)

Method getSuccessorFlows returns a Collection of all the Flow instances that will be executed after the given Flow instance.

Parameters:

flow - of type Flow

Returns:

Collection

getPredecessorFlows

public Collection<Flow> getPredecessorFlows(Flow flow)

Method getPredecessorFlows returns a Collection of all the Flow instances that will be executed before the given Flow instance.

Parameters:

flow - of type Flow

Returns:

Collection

findFlowsSourcingFrom

public Collection<Flow> findFlowsSourcingFrom(String identifier)

Method findFlowsSourcingFrom returns all Flow instances that reads from a source with the given identifier.

Parameters:

identifier - of type String

Returns:

Collection

findFlowsSinkingTo

public Collection<Flow> findFlowsSinkingTo(String identifier)

Method findFlowsSinkingTo returns all Flow instances that writes to a sink with the given identifier.

Parameters:

identifier - of type String

Returns:

Collection

getFlowSkipStrategy

public FlowSkipStrategy getFlowSkipStrategy()

Method getFlowSkipStrategy returns the current FlowSkipStrategy used by this Flow.

Returns:

FlowSkipStrategy

setFlowSkipStrategy

public FlowSkipStrategy setFlowSkipStrategy(FlowSkipStrategy flowSkipStrategy)

Method setFlowSkipStrategy sets a new FlowSkipStrategy, the current strategy, if any, is returned. If a strategy is given, it will be used as the strategy for all Flow instances managed by this Cascade instance. To revert back to consulting the strategies associated with each Flow instance, re-set this value to null, its default value.

FlowSkipStrategy instances define when a Flow instance should be skipped. The default strategy is FlowSkipIfSinkStale and is inherited from the Flow instance in question. An alternative strategy would be FlowSkipIfSinkExists.

A FlowSkipStrategy will not be consulted when executing a Flow directly through start()

Parameters:

flowSkipStrategy - of type FlowSkipStrategy

Returns:

FlowSkipStrategy

start

public void start()

Method start begins the current Cascade process. It returns immediately. See method complete() to block until the Cascade completes.

complete

public void complete()

Method complete begins the current Cascade process if method start() was not previously called. This method blocks until the process completes.

Throws:

RuntimeException - wrapping any exception thrown internally.

run

public void run()

Method run implements the Runnable run method.

Specified by:

run in interface Runnable

stop

public void stop()

writeDOT

public void writeDOT(String filename)

Method writeDOT writes this element graph to a DOT file for easy visualization and debugging.

Parameters:

filename - of type String

printElementGraph

protected void printElementGraph(String filename,
                                 org.jgrapht.graph.SimpleDirectedGraph<String,Flow.FlowHolder> graph)

toString

public String toString()

Overrides:

toString in class Object

printBanner

public static void printBanner()