Matthias J. Sax created KAFKA-12909:
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Summary: 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
Fix For: 3.0.0
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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