Package org.apache.beam.sdk.transforms

Annotation Interface DoFn.TruncateRestriction

Enclosing class:
DoFn<InputT extends @Nullable Object,OutputT extends @Nullable Object>
@Documented @Retention(RUNTIME) @Target(METHOD) public static @interface DoFn.TruncateRestriction
Annotation for the method that truncates the restriction of a splittable DoFn into a bounded one. This method is invoked when a pipeline is being drained.

This method is used to perform truncation of the restriction while it is not actively being processed.

Signature: @Nullable TruncateResult<RestrictionT> truncateRestriction(<arguments>);

This method must satisfy the following constraints:

  • If one of its arguments is tagged with the DoFn.Element annotation, then it will be passed the current element being processed; the argument must be of type InputT. Note that automatic conversion of Rows and DoFn.FieldAccess parameters are currently unsupported.
  • If one of its arguments is tagged with the DoFn.Restriction annotation, then it will be passed the current restriction being processed; the argument must be of type RestrictionT.
  • If one of its arguments is tagged with the DoFn.Timestamp annotation, then it will be passed the timestamp of the current element being processed; the argument must be of type Instant.
  • If one of its arguments is a RestrictionTracker, then it will be passed a tracker that is initialized for the current DoFn.Restriction. The argument must be of the exact type RestrictionTracker<RestrictionT, PositionT>.
  • If one of its arguments is a subtype of BoundedWindow, then it will be passed the window of the current element. When applied by ParDo the subtype of BoundedWindow must match the type of windows on the input PCollection. If the window is not accessed a runner may perform additional optimizations.
  • If one of its arguments is of type PaneInfo, then it will be passed information about the current triggering pane.
  • If one of the parameters is of type PipelineOptions, then it will be passed the options for the current pipeline.

Returns a truncated restriction representing a bounded amount of work that must be processed before the pipeline can be drained or null if no work is necessary.

The default behavior when a pipeline is being drained is that RestrictionTracker.IsBounded.BOUNDED restrictions process entirely while RestrictionTracker.IsBounded.UNBOUNDED restrictions process till a checkpoint is possible. Splittable DoFns should only provide this method if they want to change this default behavior.