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https://issues.apache.org/jira/browse/BEAM-101?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17545942#comment-17545942
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Danny McCormick commented on BEAM-101:
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This isn't actually real, but this issue has been migrated to
https://github.com/apache/beam/issues/17853
> Data-driven triggers
> --------------------
>
> Key: BEAM-101
> URL: https://issues.apache.org/jira/browse/BEAM-101
> Project: Beam
> Issue Type: New Feature
> Components: beam-model
> Reporter: Robert Bradshaw
> Priority: P3
>
> For some applications, it's useful to declare a pane/window to be emitted (or
> finished) based on its contents. The simplest of these is the AfterCount
> trigger, but more sophisticated predicates could be constructed.
> The requirements for consistent trigger firing are essentially that the state
> of the trigger form a lattice and that the "should fire?" question is a
> monotonic predicate on the lattice. Basically it asks "are we high enough up
> the lattice?"
> Because the element types may change between the application of Windowing and
> the actuation of the trigger, one idea is to extract the relevant data from
> the element at Windowing and pass it along implicitly where it can be
> combined and inspected in a type safe way later (similar to how timestamps
> and windows are implicitly passed with elements).
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