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From aaron morton <>
Subject Re: Multiple keyspace question
Date Sun, 08 Jul 2012 18:31:01 GMT
I would do a test to see the latency difference under load between having 1 KS with 5 CF's
and 50 KS with 5 CF's. 

Your test will need to read and write to all the CF's. Having many CF's may result in more
frequent memtables flushes. 

(Personally it's not an approach I would take.)

Aaron Morton
Freelance Developer

On 7/07/2012, at 8:15 AM, Shahryar Sedghi wrote:

> Aaron
> I am going to have many (over 50 eventually) keyspaces with limited number of CFs (5-6)
do you think this one can cause a problem too.
> Thanks
> On Fri, Jul 6, 2012 at 2:28 PM, aaron morton <> wrote:
> Also, all CF's in the same KS share one commit log. So all writes for the row row key,
across all CF's, are committed at the same time. 
> Some other settings, such as caches in 1.1, are machine wide. 
> If you have a small KS for something like app config, I'd say go with whatever feels
right. If you are talking about two full "application" KS's I would think about their prospective
workloads and growth patterns. Will you always want to manage the two together ?
> Cheers
> -----------------
> Aaron Morton
> Freelance Developer
> @aaronmorton
> On 6/07/2012, at 9:47 PM, Robin Verlangen wrote:
>> Hi Ben,
>> The amount of keyspaces is not the problem: the amount of column families is. Each
column family adds a certain amount of memory usage to the system. You can cope with this
by adding memory or using generic column families that store different types of data.
>> With kind regards,
>> Robin Verlangen
>> Software engineer
>> W
>> E
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>> 2012/7/6 Ben Kaehne <>
>> Good evening,
>> I have read multiple keyspaces are bad before in a few discussions, but to what extent?
>> We have some reasonably powerful machines and looking to host an additional (currently
we have 1) 2 keyspaces within our cassandra cluster (of 3 nodes, using RF3).
>> At what point does adding extra keyspaces start becoming an issue? Is there anything
special we should be considering or watching out for as we implement this?
>> I could not imagine that all cassandra users out there are running one massive keyspace,
and at the same time can not imaging that all cassandra users have multiple clusters just
to host different keyspaces.
>> Regards.
>> -- 
>> -Ben
> -- 
> "Life is what happens while you are making other plans." ~ John Lennon

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