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https://issues.apache.org/jira/browse/KAFKA-12960?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17434056#comment-17434056
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A. Sophie Blee-Goldman commented on KAFKA-12960:
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[~mjsax] sounds like the cache itself layer doesn't enforce strict retention
time, I know the InMemoryWindowStore itself does (because I wrote it) but if we
blindly grab records from the cache instead of the underlying store and don't
check retention time in the caching layer, then...
> 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
> Assignee: Sagar Rao
> 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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