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https://issues.apache.org/jira/browse/KAFKA-7591?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17016372#comment-17016372
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Sophie Blee-Goldman commented on KAFKA-7591:
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That's fair, I suppose if it _was_ the window size that changed then all bets
are off anyway, while users who just changed the retention period will be able
to benefit. We should just change it and log that we did, maybe in the meantime
including a warning about what is/isn't a compatible change.
Tangentially, we should compile a list of compatible changes that can be made
dynamically vs incompatible changes that require a reset, and document that
somewhere. This seems like a common question/source of confusion
> Changelog retention period doesn't synchronise with window-store size
> ---------------------------------------------------------------------
>
> Key: KAFKA-7591
> URL: https://issues.apache.org/jira/browse/KAFKA-7591
> Project: Kafka
> Issue Type: Improvement
> Components: streams
> Reporter: Jon Bates
> Priority: Major
>
> When a new windowed state store is created, the associated changelog topic's
> `retention.ms` value is set to `window-size +
> CHANGELOG_ADDITIONAL_RETENTION_MS`
> h3. Expected Behaviour
> If the window-size is updated, the changelog topic's `retention.ms` config
> should be updated to reflect the new size
> h3. Actual Behaviour
> The changelog-topic's `retention.ms` setting is not amended, resulting in
> possible loss of data upon application restart
>
> n.b. Although it is easy to update changelog topic config, I logged this as
> `major` due to the potential for data-loss for any user of Kafka-Streams who
> may not be intimately aware of the relationship between a windowed store and
> the changelog config
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