Package org.apache.beam.sdk.transforms.splittabledofn

Class OffsetRangeTracker

    • Field Detail

      • lastClaimedOffset

        protected @Nullable java.lang.Long lastClaimedOffset

      • lastAttemptedOffset

        protected @Nullable java.lang.Long lastAttemptedOffset

    • Constructor Detail

      • OffsetRangeTracker

        public OffsetRangeTracker​(OffsetRange range)

    • Method Detail

      • 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 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.

        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)
        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
        Checks whether the restriction has been fully processed.

        Called by the SDK harness after DoFn.ProcessElement returns.

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

        This method is required to be implemented in order to prevent data loss during SDK processing.

        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