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From Jonathan Ellis <jbel...@gmail.com>
Subject Re: ParNew (promotion failed)
Date Sun, 27 Mar 2011 14:48:19 GMT
On Sat, Mar 26, 2011 at 5:21 PM, Peter Schuller
<peter.schuller@infidyne.com> wrote:
>> So to resolve this i must tune young generation (HEAP_NEWSIZE) -Xmn, and
>> tune in_memory_compaction_limit_in_mb config parameter?
>
> More likely adjust the initial occupancy trigger and/or the heap size.
> Probably just the latter. This is assuming you're on 0.7 with mostly
> default JVM options. See cassandra-env.sh.
>
> In fact, you may even be helped by *decreasing* the young generation
> size if you're running a version which has a cassandra-env which
> specifies -Xmn. I'm not entirely sure because I don't know off hand
> exactly based on what the occupancy trigger is happening, but the
> young gen is large and the workload is such that young-gen gc:s
> promote a high percentage of it's data, I suspect that can lead to CMS
> triggering too late.  (So this paragraph is speculation.)

But he's talking about "promotion failed" which is about heap
fragmentation, not "concurrent mode failure" which would indicate CMS
too late.  So increasing young generation size + tenuring threshold is
probably the way to go (especially in a read-heavy workload;
increasing tenuring will just mean copying data in memtables around
between survivor spaces for a write-heavy load).

-- 
Jonathan Ellis
Project Chair, Apache Cassandra
co-founder of DataStax, the source for professional Cassandra support
http://www.datastax.com

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