[jira] [Commented] (CASSANDRA-16161) Validation Compactions causing Java GC pressure

["Michael Semb Wever (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-16161?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17224483#comment-17224483 ] 

Michael Semb Wever commented on CASSANDRA-16161:
------------------------------------------------

bq. This could almost be classified as a bug. In conf/cassandra.yaml it states for compaction_throughput_mb_per_sec: "Note that this account for all types of compaction, including validation compaction"

I am keen on making this a bug and throttling validation compactions under {{compaction_throughput_mb_per_sec}}, as the existing documentation says it already does. But have some questions, like some of the past discussion in CASSANDRA-3635. There are differences between clusters on how validation and normal compactions interact, with each using resources differently: validations use more cpu and only read IO compared to normal compactions.

If validation compactions are made to honour {{compaction_throughput_mb_per_sec}}, what impact might that have on existing clusters? (particularly those unsuspecting to such a change in a patch upgrade). If there are users that are dependent on validation compactions being unthrottled and completing faster than other compactions, how would they achieve that after this change?

> Validation Compactions causing Java GC pressure
> -----------------------------------------------
>
>                 Key: CASSANDRA-16161
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-16161
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Local/Compaction, Local/Config, Tool/nodetool
>            Reporter: Cameron Zemek
>            Assignee: Stefan Miklosovic
>            Priority: Normal
>             Fix For: 3.11.x, 3.11.8
>
>         Attachments: 16161.patch
>
>
> Validation Compactions are not rate limited which can cause Java GC pressure and result in spikes in latency.



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