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https://issues.apache.org/jira/browse/KAFKA-10005?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Guozhang Wang resolved KAFKA-10005.
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Fix Version/s: 2.6.0
Assignee: Guozhang Wang
Resolution: Fixed
> Decouple RestoreListener from RestoreCallback and not enable bulk loading for
> RocksDB
> -------------------------------------------------------------------------------------
>
> Key: KAFKA-10005
> URL: https://issues.apache.org/jira/browse/KAFKA-10005
> Project: Kafka
> Issue Type: Improvement
> Components: streams
> Reporter: Guozhang Wang
> Assignee: Guozhang Wang
> Priority: Major
> Fix For: 2.6.0
>
>
> In Kafka Streams we have two restoration callbacks:
> * RestoreCallback (BatchingRestoreCallback): specified per-store via
> registration to specify the logic of applying a batch of records read from
> the changelog to the store. Used for both updating standby tasks and
> restoring active tasks.
> * RestoreListener: specified per-instance via `setRestoreListener`, to
> specify the logic for `onRestoreStart / onRestoreEnd / onBatchRestored`.
> As we can see these two callbacks are for quite different purposes, however
> today we allow user's to register a per-store RestoreCallback which is also
> implementing the RestoreListener. Such weird mixing is actually motivated by
> Streams internal usage to enable / disable bulk loading inside RocksDB. For
> user's however this is less meaningful to specify a callback to be a listener
> since the `onRestoreStart / End` has the storeName passed in, so that users
> can just define different listening logic if needed for different stores.
> On the other hand, this mixing of two callbacks enforces Streams to check
> internally if the passed in per-store callback is also implementing listener,
> and if yes trigger their calls, which increases the complexity. Besides,
> toggle rocksDB for bulk loading requires us to open / close / reopen /
> reclose 4 times during the restoration which could also be costly.
> Given that we have KIP-441 in place, I think we should consider different
> ways other than toggle bulk loading during restoration for Streams (e.g.
> using different threads for restoration).
> The proposal for this ticket is to completely decouple the listener from
> callback -- i.e. we would not presume users passing in a callback function
> that implements both RestoreCallback and RestoreListener, and also for
> RocksDB we replace the bulk loading mechanism with other ways of
> optimization: https://rockset.com/blog/optimizing-bulk-load-in-rocksdb/
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