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https://issues.apache.org/jira/browse/KAFKA-12909?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17525714#comment-17525714
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Patrik Kleindl commented on KAFKA-12909:
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Your example actually seems wrong to me, if a >right<-hand-side input is
received at 95 then I would not expect an eager result on a >left<-join at all.
If I switch the side the yes, I would expect 3 results.
Thanks for the link, I hope I get the idea now, it just feels strange to delay
the "incomplete" join until the end of the window but it is understandable if
there can be only one result for either the left side alone or the join.
> Allow users to opt-into spurious left/outer stream-stream join improvement
> --------------------------------------------------------------------------
>
> Key: KAFKA-12909
> URL: https://issues.apache.org/jira/browse/KAFKA-12909
> Project: Kafka
> Issue Type: Improvement
> Components: streams
> Reporter: Matthias J. Sax
> Assignee: Matthias J. Sax
> Priority: Blocker
> Fix For: 3.1.0
>
>
> https://issues.apache.org/jira/browse/KAFKA-10847 improves left/outer
> stream-stream join, by not emitting left/outer results eagerly, but only
> after the grace period passed.
> While this change is desired, there is an issue with regard to upgrades: if
> users don't specify a grace period, we fall back to a 24h default. Thus,
> left/outer join results would only be emitted 24h after the join window end.
> This change in behavior could break existing applications when upgrading to
> 3.0.0 release. – And even if users do set a grace period explicitly, it's
> still unclear if the new delayed output behavior would work for them.
> Thus, we propose to disable the fix of KAFAK-10847 by default, and let user
> opt-into the fix explicitly instead.
> To allow users to enable the fix, we want to piggy-back on KIP-633
> (https://issues.apache.org/jira/browse/KAFKA-8613) that deprecated the
> existing `JoinWindows.of()` and `JoinWindows#grace()` methods in favor of
> `JoinWindows.ofSizeAndGrace()` – if users don't update their code, we would
> keep the fix disabled, and thus, if users upgrade their app nothing changes.
> Only if users switch to the new `ofSizeAndGrace()` API, we enable the fix and
> thus give users the opportunity to opt-in expliclity and pick an appropriate
> grace period for their application.
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