Guozhang Wang created KAFKA-10005:
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Summary: 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
Reporter: Guozhang Wang
Assignee: Guozhang Wang
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.
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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