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https://issues.apache.org/jira/browse/BEAM-3345?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16320688#comment-16320688
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Anton Kedin commented on BEAM-3345:
-----------------------------------
Details are in [BEAM-3190]
In short, at the moment we can reason about join results only in couple of
known tigger configurations:
- DefaultTrigger with allowedLateness=0 in any accumulation mode;
- AfterWatermark.pastEndOfWindow() with allowedLateness=0 in any accumulation
mode;
These guarantee that joins are executed once per window over the whole window
contents.
I am updating the SQL join implementation to reject any inputs with other
configurations.
> [SQL] Reject Unsupported Joins
> ------------------------------
>
> Key: BEAM-3345
> URL: https://issues.apache.org/jira/browse/BEAM-3345
> Project: Beam
> Issue Type: Task
> Components: dsl-sql
> Reporter: Anton Kedin
> Assignee: Anton Kedin
>
> Related to https://issues.apache.org/jira/browse/BEAM-3190 .
> We don't know what meaningful join semantics is, in presence of multiple
> trigger firings. I.e. in accumulating mode it will result in multiple
> duplicated join results, and in discarding mode it will only join deltas,
> both of these scenarios seem to be super subtle and can lead to
> misunderstanding and misuse by the end users.
> Until we have a way to implement a correct join semantics (e.g. using
> retractions) we should reject unsupported window/trigger combinations.
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