[jira] [Commented] (KAFKA-9062) Handle stalled writes to RocksDB

["Bradley Peterson (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/KAFKA-9062?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17149437#comment-17149437 ] 

Bradley Peterson commented on KAFKA-9062:
-----------------------------------------

I have just a question -- would these stalls block heartbeats or just polling? We have hit this issue in the past and raised out max.poll.interval.ms very high (12 hours) to work around it. But, sometimes after a state restoration we still instances kicked out of the group by the group coordinator. Our session.timeout.ms is 30 minutes, so that suggests to me that something is blocking heartbeats for over 30 minutes.

> 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: Sophie Blee-Goldman
>            Priority: Major
>
> 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



--
This message was sent by Atlassian Jira
(v8.3.4#803005)