[Bug]: PeriodicSequence reports large amount of remaining work / size when used with infinite stop time

[scwhittle]

What happened?

PeriodicSequence uses a restriction tracker that reports Progress as the portion of the range it has completed compared to the remaining outputs for the range.

Since the dofn it does not implement GetSize this ends up reporting a steady state of backlog even if the source is idle waiting for real-time to pass. It seems that it should report the size of the backlog (ie the scheduled events that have not yet fired but are behind now) instead.

This can cause runners to autoscale inappropriately for pipelines involving PeriodicSequence/PeriodicImpulse.

Issue Priority

Priority: 2 (default / most bugs should be filed as P2)

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