[Bug]: Go SDK uses PTransform UniqueName as key instead of the global PID for a transform.

[lostluck]

What happened?

While adding a timer integration test, it was determined that

https://github.com/apache/beam/blob/master/sdks/go/pkg/beam/core/runtime/exec/translate.go#L530

is incorrect and the Go SDK is inconsistently referring to transforms when talking to the runner. It should be using the global map key for the transform here instead of the user readable UniqueName. (also used for combines later in the file)

A spot check shows this prevents timers from firing correctly on the Flink runner, but it's also lead to oddities in how Prism displays metrics to it's web UI needing to be worked around by having two indexes.

While this should not break update compatibility, it would change some things in user visible ways, so it needs to be made with care to fix them where possible.

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The minimal fix is to simply update how Timers are looked up, as they're a relatively new feature, and would fix execution on Flink (and also, eventually Prism).

Issue Priority

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

Issue Components

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[lostluck]

Internal Google testing show at least against FlumeGo and Dataflow this is a no-op. It does the UniqueName lookups as a fallback, and then proceeds to use the normal global ID.

#29842 shows that it allows the included "bounded" timer test to pass on Spark and Flink, and that some additional tests could be run by the py portable runner.

Once #29829 has been merged in, I'll produce a clean version of #29842 to resolve this issue.