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From "Anton Kedin (JIRA)" <>
Subject [jira] [Commented] (BEAM-3345) [SQL] Reject Unsupported Joins
Date Wed, 10 Jan 2018 17:31:00 GMT


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:
>             Project: Beam
>          Issue Type: Task
>          Components: dsl-sql
>            Reporter: Anton Kedin
>            Assignee: Anton Kedin
> Related to .
> 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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