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https://issues.apache.org/jira/browse/KAFKA-14624?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Lucas Brutschy resolved KAFKA-14624.
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Resolution: Fixed
> State restoration is broken with standby tasks and cache-enabled stores in
> processor API
> ----------------------------------------------------------------------------------------
>
> Key: KAFKA-14624
> URL: https://issues.apache.org/jira/browse/KAFKA-14624
> Project: Kafka
> Issue Type: Bug
> Components: streams
> Affects Versions: 3.3.1
> Reporter: Balaji Rao
> Assignee: Lucas Brutschy
> Priority: Major
>
> I found that cache-enabled state stores in PAPI with standby tasks sometimes
> returns stale data when a partition moves from one app instance to another
> and back. [Here's|https://github.com/balajirrao/kafka-streams-multi-runner] a
> small project that I used to reproduce the issue.
> I dug around a bit and it seems like it's a bug in standby task state
> restoration when caching is enabled. If a partition moves from instance 1 to
> 2 and then back to instance 1, since the `CachingKeyValueStore` doesn't
> register a restore callback, it can return potentially stale data for
> non-dirty keys.
> I could fix the issue by modifying the `CachingKeyValueStore` to register a
> restore callback in which the cache restored keys are added to the cache. Is
> this fix in the right direction?
> {code:java}
> // register the store
> context.register(
> root,
> (RecordBatchingStateRestoreCallback) records -> {
> for (final ConsumerRecord<byte[], byte[]> record :
> records) {
> put(Bytes.wrap(record.key()), record.value());
> }
> }
> );
> {code}
>
> I would like to contribute a fix, if I can get some help!
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