[
https://issues.apache.org/jira/browse/KAFKA-14624?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17676934#comment-17676934
]
Matthias J. Sax commented on KAFKA-14624:
-----------------------------------------
Thanks for reporting this issue – will need to think about the details more
(and look into you project that reproduces it) – my first reaction was, "why is
the cache not empty"? Registering the call-back on the cache might introduce a
lot of overhead during restore, and thus, I have doubts if it's a good fix.
{quote}If a partition moves from instance 1 to 2 and then back to instance 1
{quote}
If the task/partition moves from 1 to 2, the task on one should be closed and
the cache should be gone? Or are you saying the task on instance 1 becomes a
standby?
> 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
> 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!
--
This message was sent by Atlassian Jira
(v8.20.10#820010)
