|Constructor and Description
|Modifier and Type
|Method and Description
Splits current restriction based on
checkDone, currentRestriction, toString, tryClaim
public @Nullable SplitResult<OffsetRange> trySplit(double 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
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.
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
0.7, the primary and residual restrictions returned would be
[100, 179), [179, 200)
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 recommended to be implemented for batch pipeline given that it is very important for pipeline scaling and end to end pipeline execution.
The API is required to be implemented for a streaming pipeline.
trySplit in class
fractionOfRemainder - A hint as to the fraction of work the primary restriction should
represent based upon the current known remaining amount of work.
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.