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From "Jonathan Ellis (JIRA)" <>
Subject [jira] Created: (CASSANDRA-1469) adaptive default heap size
Date Sat, 04 Sep 2010 15:30:33 GMT
adaptive default heap size

                 Key: CASSANDRA-1469
             Project: Cassandra
          Issue Type: New Feature
          Components: Packaging
            Reporter: Jonathan Ellis
             Fix For: 0.7 beta 2

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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