[ https://issues.apache.org/jira/browse/BEAM-653 ]
Danny McCormick deleted comment on BEAM-653:
--------------------------------------
was (Author: JIRAUSER282469):
This issue has been migrated to https://github.com/apache/beam/issues/17947
> Refine specification for WindowFn.isCompatible()
> -------------------------------------------------
>
> Key: BEAM-653
> URL: https://issues.apache.org/jira/browse/BEAM-653
> Project: Beam
> Issue Type: New Feature
> Components: beam-model
> Reporter: Kenneth Knowles
> Priority: P3
>
> {{WindowFn#isCompatible}} doesn't really have a spec. In practice, it is used
> primarily when flattening together multiple PCollections. All of the
> WindowFns must be compatible, and then just a single WindowFn is selected
> arbitrarily for the output PCollection.
> In consequence, downstream of the Flatten, the merging behavior will be taken
> from this WindowFn.
> Currently, there are some mismatches:
> - Sessions with different gap durations _are_ compatible today, but probably
> shouldn't be since merging makes little sense. (The use of tiny proto-windows
> is an implementation detail anyhow)
> - SlidingWindows and FixedWindows _could_ reasonably be compatible if they
> had the same duration, though it might be odd.
> Either way, we should just nail down what we actually mean so we can arrive
> at a verdict in these cases.
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