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From "Brandon Williams (JIRA)" <>
Subject [jira] Commented: (CASSANDRA-1469) adaptive default heap size
Date Mon, 13 Sep 2010 19:29:32 GMT


Brandon Williams commented on CASSANDRA-1469:

I agree it would be cleaner, but embedding logic in felt wrong, since it's
all just config, and  the logic can't be moved to bin/cassandra, because it is the parent
that sources cassandra-env.

> adaptive default heap size
> --------------------------
>                 Key: CASSANDRA-1469
>                 URL:
>             Project: Cassandra
>          Issue Type: New Feature
>          Components: Packaging
>            Reporter: Jonathan Ellis
>            Assignee: Brandon Williams
>             Fix For: 0.7.0
>         Attachments: 0001_adaptively_determine_heap_size.txt
> Cassandra comes out of the box with very conservative defaults, especially in -Xmx and
memtable sizes, which leads to complaints of poor performance or even OOM conditions under
heavy load.  But changing these to be aggressive can cause the same problem: most servers
enable swap out of the box, so asking for a 4GB or 8GB heap could allocate happily but also
cause problems when it starts paging.
> Proposed solution is to update the start script to set Xmx to half of system ram ("free
-m | awk '/Mem:/ {print $2}'").  Memtable defaults will have to be handled by Java, but we
can do that based on heap size (Runtime.maxMemory).
> An alternative suggestion was to provide "small", "medium", "large" configurations, but
this plays poorly with rpm and deb packages.  I think the adaptive approach is more promising.

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