[jira] [Commented] (CASSANDRA-15810) Default StringTableSize parameter causes GC slowdown

["Robert Stupp (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-15810?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17176835#comment-17176835 ] 

Robert Stupp commented on CASSANDRA-15810:
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ISTM that it's better to remove the only usage of {{String.intern()}} in {{org.apache.cassandra.gms.VersionedValue#VersionedValue(java.lang.String)}} and the {{-XX:StringTableSize}} JVM argument entirely. [~benedict] WDYT?

There's [evidence|https://shipilev.net/jvm/anatomy-quarks/10-string-intern/] that String-interning can cause GC and performance issues.


> Default StringTableSize parameter causes GC slowdown
> ----------------------------------------------------
>
>                 Key: CASSANDRA-15810
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-15810
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Local/Config
>            Reporter: Tom van der Woerdt
>            Priority: Normal
>              Labels: gc, performance
>
> While looking at tail latency on a Cassandra cluster, it came up that the default StringTableSize in Cassandra is set to a million:
> {code:java}
> # Larger interned string table, for gossip's benefit (CASSANDRA-6410)
> -XX:StringTableSize=1000003{code}
> This was done for CASSANDRA-6410 by [~jbellis] in '13, to optimize heap usage on a test case, running with 500 nodes and num_tokens=512.
> Until Java 13, this string table is implemented as native code, and has to be traversed entirely during the GC initial marking phase, which is a STW event.
> Some testing on my end shows that the pause time of a GC cycle can be reduced by approximately 10 milliseconds if we lower the string table size back to the Java 8 default of 60013 entries.
> Thus, I would recommend this patch (3.11 branch, similar patch for 4.0):
> {code:java}
> diff --git a/conf/jvm.options b/conf/jvm.options
> index 01bb1685b3..c184d18c5d 100644
> --- a/conf/jvm.options
> +++ b/conf/jvm.options
> @@ -107,9 +107,6 @@
>  # Per-thread stack size.
>  -Xss256k
> -# Larger interned string table, for gossip's benefit (CASSANDRA-6410)
> --XX:StringTableSize=1000003
> -
>  # Make sure all memory is faulted and zeroed on startup.
>  # This helps prevent soft faults in containers and makes
>  # transparent hugepage allocation more effective.
>  {code}
> It does need some testing on more extreme clusters than I have access to, but I ran some Cassandra nodes with {{-XX:+PrintStringTableStatistics}} which suggested that the Java default will suffice here.



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