[#32003][prism] Support empty transform input sets, such as for flattens.#32029
[#32003][prism] Support empty transform input sets, such as for flattens.#32029damondouglas merged 1 commit intoapache:masterfrom
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| // In very rare cases, we can have a stage without any inputs, such as a flatten. | ||
| // In that case, there's nothing that will start the watermark refresh cycle, | ||
| // so we must do it here. | ||
| if len(inputIDs) == 0 { |
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Non-PR blocking comment to validate my understanding. Do I understand correctly?
In the PTransform with no PCollection case, there are no inputIDs because the result of internal.transformPreparer.PrepareTransform returns an internal.prepareResult where prepResult.SubbedComps.GetPcollections() is empty.
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Effectively yes, but basically it's due to flatten being special: all Other Stages must have a single parallel input pCollection. Flattens may have any number, which apparently includes 0.
In this case, by construction, the flatten has no inputs to begin with.
Impulses and TestStream are also special: Impulses are required to kick off SDK side processing. TestStream is just weird.
… flattens. (apache#32029) Co-authored-by: lostluck <13907733+lostluck@users.noreply.github.com>
In very rare cases a transform, such as a flatten can be in a pipeline without any real inputs.
Without inputs, nothing kicked off watermark processing, which then blocked use of the empty flatten output as a side input, which blocked that transform from executing.
This manifested as the upstream stage (the flatten), never getting watermark refreshed, and therefore the downstream stage never being able to execute, since the side input data from the upstream stage was never ready.
The solution in this PR is when a stage is added without inputs, it must be part of the initial watermark refresh set. Further taken to keep this part of the "impulse" set when a TestStream is involved in the Pipeline, since that manipulates initial refreshes.
Additionally adds a line to the stuck pipeline dump to clarify the inputs and output consumers of each stage, to make the progression structure clearer.
Fixes #32003.
In particular allows the Java Validates Runner tests in "org.apache.beam.sdk.transforms.FlattenTest" testEmptyFlattenAsSideInput, testFlattenPCollectionsEmptyThenParDo, and testFlattenPCollectionsEmpty now pass.
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