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https://issues.apache.org/jira/browse/KAFKA-12960?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17367795#comment-17367795
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A. Sophie Blee-Goldman commented on KAFKA-12960:
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+1 on pushing this responsibility to the state stores. Imo this was always
intended to be a contract of the state store interface itself and was just not
strictly enforced, ie it's more like a bug to fix than a matter of "pushing"
the responsibility onto them
> WindowStore and SessionStore do not enforce strict retention time
> -----------------------------------------------------------------
>
> Key: KAFKA-12960
> URL: https://issues.apache.org/jira/browse/KAFKA-12960
> Project: Kafka
> Issue Type: Improvement
> Components: streams
> Reporter: Matthias J. Sax
> Priority: Major
>
> WindowedStore and SessionStore do not implement a strict retention time in
> general. We should consider to make retention time strict: even if we still
> have some record in the store (due to the segmented implementation), we might
> want to filter expired records on-read. This might benefit PAPI users.
> Atm, InMemoryWindow store does already enforce a strict retention time.
> As an alternative, we could also inject such a filter in the wrapping
> `MeteredStore` – this might lift the burden from users who implement a custom
> state store.
> As an alternative, we could change all DSL operators to verify if data from a
> state store is already expired or not. It might be better to push this
> responsibility into the stores though.
> It's especially an issue for stream-stream joins, because the operator relies
> on the retention time to implement it's grace period.
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