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https://issues.apache.org/jira/browse/KAFKA-9062?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Bruno Cadonna resolved KAFKA-9062.
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Resolution: Won't Fix
> Handle stalled writes to RocksDB
> --------------------------------
>
> Key: KAFKA-9062
> URL: https://issues.apache.org/jira/browse/KAFKA-9062
> Project: Kafka
> Issue Type: Bug
> Components: streams
> Reporter: A. Sophie Blee-Goldman
> Priority: Major
> Labels: new-streams-runtime-should-fix
>
> RocksDB may stall writes at times when background compactions or flushes are
> having trouble keeping up. This means we can effectively end up blocking
> indefinitely during a StateStore#put call within Streams, and may get kicked
> from the group if the throttling does not ease up within the max poll
> interval.
> Example: when restoring large amounts of state from scratch, we use the
> strategy recommended by RocksDB of turning off automatic compactions and
> dumping everything into L0. We do batch somewhat, but do not sort these small
> batches before loading into the db, so we end up with a large number of
> unsorted L0 files.
> When restoration is complete and we toggle the db back to normal (not bulk
> loading) settings, a background compaction is triggered to merge all these
> into the next level. This background compaction can take a long time to merge
> unsorted keys, especially when the amount of data is quite large.
> Any new writes while the number of L0 files exceeds the max will be stalled
> until the compaction can finish, and processing after restoring from scratch
> can block beyond the polling interval
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