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From Peter Schuller <>
Subject Re: Nodes frozen in GC
Date Tue, 08 Mar 2011 15:08:52 GMT
>                 $client->batch_mutate($mutations,
> cassandra_ConsistencyLevel::QUORUM);

Btw, what are the mutations? Are you doing something like inserting
both very small values and very large ones?

In any case: My main reason to butt back into this thread is that
under normal circumstances you shouldn't be seeing very frequent
long-term pauses due to GC. If your workload is not doing something
particularly unusual, even if you do end up triggering a GC fallback
to full stop-the-world GC, it should happen comparatively infrequently
and you should be seeing many CMS cycles in between each such long

That's why I asked about the frequency. If you're doing a long-term
stress test and seeing a 30 second pause once per week, that's a lot
more likely to be "normal" for your workload than if you're seeing it
happen once ever three minutes. The issue is that if you want to fix
your problem, one must first figure out what the problem *is*. Based
on past mailing list traffic, it seems most people's problems that are
seemingly "due to GC" end up being because of a too high live set size
or the CMS phase triggering too late. These are fixable issues if are
running into them.

If all you have is a single column family with a 64 mb flush threshold
and doing a bunch of insertions, and have a heap size of 5 (was it?)
gig, you should not be having these issues. But stating that helps no
one, which is why I'm asking for more information. (Widely
extrapolating and suggesting that all Cassandra nodes will always
freeze for 30 seconds every now and then is also helping no one, other
than not being true.)

/ Peter Schuller

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