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https://issues.apache.org/jira/browse/KAFKA-7591?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17015408#comment-17015408
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Sophie Blee-Goldman commented on KAFKA-7591:
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Shouldn't you need to reset the app if the window size changes? On the other
hand, it might be a good idea to at least verify the topic configs (for all
internal topics), and log a warning or even throw an exception if they don't
match.
On a related note, users may want to increase the retention period to allow
querying the state for longer – in that case it does seem reasonable for
Streams to alter the changelog's retention. But it wouldn't be able to
distinguish a change in retention from a change in window size, thus I think
it's still better to just detect the discrepancy and alert the user so they can
consider the best course of action (reset app or alter topic config)
> 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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