[jira] [Issue Comment Deleted] (CASSANDRA-15810) Default StringTableSize parameter causes GC slowdown

["Benedict Elliott Smith (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/CASSANDRA-15810?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Benedict Elliott Smith updated CASSANDRA-15810:
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    Comment: was deleted

(was: +1; I saw this recently and was unconvinced by the usage, but didn't try to explore removing it.  If this is the only source of interning, I'd be strongly in favour of removing.  If we _really_ need to "intern" here, we can use something like a {{WeakHashMap}}, and perhaps intern the specific {{ApplicationState}} we think will benefit, but I'm uncertain if it's needed at all.  Perhaps we should do some back-of-envelope calculations for how much heap will be used in a huge cluster without "interning" vs with.)

> 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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