org.apache.beam.sdk.transforms.splittabledofn

Class OffsetRangeTracker

java.lang.Object

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

org.apache.beam.sdk.transforms.splittabledofn.OffsetRangeTracker

All Implemented Interfaces:

Sizes.HasSize

@Experimental(value=SPLITTABLE_DO_FN)
public class OffsetRangeTracker
extends RestrictionTracker<OffsetRange,java.lang.Long>
implements Sizes.HasSize

A RestrictionTracker for claiming offsets in an OffsetRange in a monotonically increasing fashion.

Constructor Summary

Constructors

Constructor and Description
OffsetRangeTracker(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.
double	getSize() A representation for the amount of known work represented as a size.
java.lang.String	toString()
boolean	tryClaim(java.lang.Long i) Attempts to claim the given offset.
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

OffsetRangeTracker

public OffsetRangeTracker(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.

tryClaim

public boolean tryClaim(java.lang.Long i)

Attempts to claim the given offset.

Must be larger than the last successfully claimed offset.

Specified by:

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

Returns:

true if the offset was successfully claimed, false if it is outside the current OffsetRange of this tracker (in that case this operation is a no-op).

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

getSize

public double getSize()

Description copied from interface: Sizes.HasSize

A representation for the amount of known work represented as a size. Size double representations should preferably represent a linear space.

It is up to each restriction tracker to convert between their natural representation of outstanding work and this representation. For example:

• Block based file source (e.g. Avro): From the end of the current block, the remaining number of bytes 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 not been processed.
• Key range based source (e.g. Shuffle, Bigtable, ...): Scale the start key to be one and end key to be zero and interpolate the position of the next splittable key as the size. If information about the probability density function or cumulative distribution function is available, size 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 remaining bytes can be used.

Specified by:

getSize in interface Sizes.HasSize