[jira] Commented: (CASSANDRA-1968) Increase JVM young generation size

["Peter Schuller (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-1968?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12980364#action_12980364 ] 

Peter Schuller commented on CASSANDRA-1968:
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Hmmm. The young gen will also directly affect the pause times for most collection pauses, as I'm sure you're aware. Depending on total heap size and depending on CPU count, 1/4 heap going to young gen might be huge and cause significant pause times.

It's certainly expected that larger young gens, up to a point, increase performance by avoiding promotion to old-gen, but should the out-of-the-box settings be so aggressive given the potential effects on latency?

How about something like min(max_sensible_default, 1/4 heap size) or perhaps min(max_sensible_per_modern_cpu_core*num_cores, 1/4 heap size)?



> Increase JVM young generation size
> ----------------------------------
>
>                 Key: CASSANDRA-1968
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-1968
>             Project: Cassandra
>          Issue Type: Improvement
>    Affects Versions: 0.7.0
>            Reporter: Brandon Williams
>            Assignee: Brandon Williams
>             Fix For: 0.7.1
>
>         Attachments: 1968.txt
>
>
> Increasing the young generation size has a profound effect on performance and cpu utilization.  We should set it explicitly.

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