org.apache.beam.sdk.transforms

Class PeriodicSequence.OutputRangeTracker

java.lang.Object

org.apache.beam.sdk.transforms.splittabledofn.RestrictionTracker<OffsetRange,java.lang.Long>

org.apache.beam.sdk.transforms.PeriodicSequence.OutputRangeTracker

All Implemented Interfaces:

RestrictionTracker.HasProgress

Enclosing class:

PeriodicSequence

@Experimental(value=SPLITTABLE_DO_FN)
public static class PeriodicSequence.OutputRangeTracker
extends RestrictionTracker<OffsetRange,java.lang.Long>
implements RestrictionTracker.HasProgress

Nested Class Summary

Nested classes/interfaces inherited from class org.apache.beam.sdk.transforms.splittabledofn.RestrictionTracker

RestrictionTracker.HasProgress, RestrictionTracker.Progress

Constructor Summary

Constructors

Constructor and Description
OutputRangeTracker(OffsetRange range)

Method Summary

Modifier and Type	Method and Description
void	checkDone() Called by the runner after DoFn.ProcessElement returns.
OffsetRange	currentRestriction() Returns a restriction accurately describing the full range of work the current DoFn.ProcessElement call will do, including already completed work.
RestrictionTracker.Progress	getProgress() A representation for the amount of known completed and known remaining work.
java.lang.String	toString()
boolean	tryClaim(java.lang.Long i) Attempts to claim the block of work in the current restriction identified by the given position.
SplitResult<OffsetRange>	trySplit(double fractionOfRemainder) Splits current restriction based on fractionOfRemainder.

Methods inherited from class java.lang.Object

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

Constructor Detail

OutputRangeTracker

public OutputRangeTracker(OffsetRange range)

Method Detail

currentRestriction

public OffsetRange currentRestriction()

Description copied from class: RestrictionTracker

Returns a restriction accurately describing the full range of work the current DoFn.ProcessElement call will do, including already completed work.

Specified by:

currentRestriction in class RestrictionTracker<OffsetRange,java.lang.Long>

trySplit

public SplitResult<OffsetRange> trySplit(double fractionOfRemainder)

Description copied from class: RestrictionTracker

Splits current restriction based on fractionOfRemainder.

If splitting the current restriction is possible, the current restriction is split into a primary and residual restriction pair. This invocation updates the RestrictionTracker.currentRestriction() to be the primary restriction effectively having the current DoFn.ProcessElement execution responsible for performing the work that the primary restriction represents. The residual restriction will be executed in a separate DoFn.ProcessElement invocation (likely in a different process). The work performed by executing the primary and residual restrictions as separate DoFn.ProcessElement invocations MUST be equivalent to the work performed as if this split never occurred.

The fractionOfRemainder should be used in a best effort manner to choose a primary and residual restriction based upon the fraction of the remaining work that the current DoFn.ProcessElement invocation is responsible for. For example, if a DoFn.ProcessElement was reading a file with a restriction representing the offset range [100, 200) and has processed up to offset 130 with a fractionOfRemainder of 0.7, the primary and residual restrictions returned would be [100, 179), [179, 200) (note: currentOffset + fractionOfRemainder * remainingWork = 130 + 0.7 * 70 = 179).

fractionOfRemainder = 0 means a checkpoint is required.

The API is recommended to be implemented for a batch pipeline to improve parallel processing performance.

The API is required to be implemented for a streaming pipeline.

Specified by:

trySplit in class RestrictionTracker<OffsetRange,java.lang.Long>

Parameters:

fractionOfRemainder - A hint as to the fraction of work the primary restriction should represent based upon the current known remaining amount of work.

Returns:

a SplitResult if a split was possible, otherwise returns null. If the fractionOfRemainder == 0, a null result MUST imply that the restriction tracker is done and there is no more work left to do.

tryClaim

public boolean tryClaim(java.lang.Long i)

Description copied from class: RestrictionTracker

Attempts to claim the block of work in the current restriction identified by the given position. Each claimed position MUST be a valid split point.

If this succeeds, the DoFn MUST execute the entire block of work. If this fails:

• DoFn.ProcessElement MUST return DoFn.ProcessContinuation#stop without performing any additional work or emitting output (note that emitting output or performing work from DoFn.ProcessElement is also not allowed before the first call to this method).
• RestrictionTracker.checkDone() MUST succeed.

Specified by:

tryClaim in class RestrictionTracker<OffsetRange,java.lang.Long>

checkDone

public void checkDone()
               throws java.lang.IllegalStateException

Description copied from class: RestrictionTracker

Called by the runner after DoFn.ProcessElement returns.

Must throw an exception with an informative error message, if there is still any unclaimed work remaining in the restriction.

Specified by:

checkDone in class RestrictionTracker<OffsetRange,java.lang.Long>

Throws:

java.lang.IllegalStateException

toString

public java.lang.String toString()

Overrides:

toString in class java.lang.Object

getProgress

public RestrictionTracker.Progress getProgress()

Description copied from interface: RestrictionTracker.HasProgress

A representation for the amount of known completed and known remaining work.

It is up to each restriction tracker to convert between their natural representation of completed and remaining work and the double representation. For example:

• Block based file source (e.g. Avro): The number of bytes from the beginning of the restriction to the current block and the number of bytes from the current block to the end of the restriction.
• Pull based queue based source (e.g. Pubsub): The local/global size available in number of messages or number of message bytes that have processed and the number of messages or number of message bytes that are outstanding.
• Key range based source (e.g. BigQuery, Bigtable, ...): Scale the start key to be one and end key to be zero and interpolate the position of the next splittable key as a position. If information about the probability density function or cumulative distribution function is available, work completed and work remaining interpolation can be improved. Alternatively, if the number of encoded bytes for the keys and values is known for the key range, the number of completed and remaining bytes can be used.

The work completed and work remaining must be of the same scale whether that be number of messages or number of bytes and should never represent two distinct unit types.

Specified by:

getProgress in interface RestrictionTracker.HasProgress