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From Jonathan Ellis <>
Subject Re: Follow-up post on cassandra configuration with some experiments on GC tuning
Date Fri, 27 Aug 2010 22:49:03 GMT
I supsect something else is making the difference for ecapriolo.  The
documentation says,

The incremental mode is meant to lessen the impact of long concurrent
phases by periodically stopping the concurrent phase to yield back the
processor to the application. [Remember, "concurrent" means "not
blocking other threads" in this context.]  This mode (referred to here
as “i-cms”) divides the work done by concurrently by the collector
into small chunks of time which are scheduled between young generation
collections. This feature is useful when applications that need the
low pause times provided by the concurrent collector are run on
machines with small numbers of processors (e.g., 1 or 2)

There's also close to a dozen tuning options for i-cms.  It seems a
little fragile to me.

On Fri, Aug 27, 2010 at 4:53 PM, Benjamin Black <> wrote:
> ecapriolo's testing seemed to indicate it _did_ change the behavior.
> wonder what the difference is?
> On Fri, Aug 27, 2010 at 6:23 AM, Mikio Braun <> wrote:
>> Hash: SHA1
>> Dear all,
>> thanks for your comments, and I'm glad that you found my post helpful.
>> Concerning the incremental CMS, I've recently updated my post and added
>> the experiments repeated on one of our cluster nodes, and for some
>> reason incremental CMS doesn't look that different anymore. So I guess
>> it's ok to stick with the non-incremental CMS for now.
>> - -M
>> On 08/27/2010 09:12 AM, Peter Schuller wrote:
>>>> Whether or not this is likely to happen with Cassandra I don't know. I
>>>> don't know much about the incremental duty cycles are scheduled and it
>>>> may be the case that Cassandra is not even remotely close to having a
>>>> problem with incremental mode.
>>> I should further weaken my statement by pointing out that I never did
>>> any exhaustive tweaking to get around the problem (other than
>>> disabling incremental mode, since my primary goal has tended to be
>>> ensure low pause times and not so much even GC activity). It may be
>>> the case that even in stressful cases where it fails by default it is
>>> simply a matter of tweaking.
>>> So, I guess I should re-phrase: In terms of just turning on
>>> incremental mode without at least application specific tweaking (if
>>> not deployment specific testing), I would suggest caution.
>> - --
>> Dr. Mikio Braun                        email:
>> TU Berlin                              web:
>> Franklinstr. 28/29                     tel: +49 30 314 78627
>> 10587 Berlin, Germany
>> Version: GnuPG v1.4.9 (GNU/Linux)
>> Comment: Using GnuPG with Mozilla -
>> 604AoKVua1+5bYK2yF9CWwFQmLHDt0Fn
>> =CIal
>> -----END PGP SIGNATURE-----

Jonathan Ellis
Project Chair, Apache Cassandra
co-founder of Riptano, the source for professional Cassandra support

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