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From Edward Capriolo <edlinuxg...@gmail.com>
Subject Re: For multi-tenant, is it good to have a key space for each tenant?
Date Fri, 07 Oct 2011 14:57:43 GMT
On Fri, Oct 7, 2011 at 10:47 AM, David McNelis
<dmcnelis@agentisenergy.com>wrote:

> So at the end of the day its going to be limited by available memory then?
>  Going by this line:
>
> Do note that a minimum of 1MB per memtable is used by the per-memtable
> arena allocator <https://issues.apache.org/jira/browse/CASSANDRA-2252> also
> introduced in 1.0, which is worth keeping in mind if you are looking at
> going from thousands to tens of thousands of ColumnFamilies.
>
>   Then you'd be looking at a requirement of 1gig  memory for each  1024
> column families had on your cluster, regardless of number of keyspaces those
> lived in.  So in order to have 10s of thousands of CFs, one would need 10s
> of gigs of ram on each node just to handle that overhead...at least as  of
>  v1.
>
> On Fri, Oct 7, 2011 at 9:40 AM, Jonathan Ellis <jbellis@gmail.com> wrote:
>
>> On Fri, Oct 7, 2011 at 9:36 AM, David McNelis
>> <dmcnelis@agentisenergy.com> wrote:
>> > In some documentation I've read it says that
>> > keyspace's take up the majority of the resources
>>
>> This has never been the case.
>>
>> > in a couple of older
>> > threads they talked about getting the number of column families down.
>>
>> This was good advice pre-0.8.
>>
>> I covered the state of 0.8 and 1.0 here:
>>
>> http://www.datastax.com/dev/blog/whats-new-in-cassandra-1-0-improved-memory-and-disk-space-management
>>
>> --
>> Jonathan Ellis
>> Project Chair, Apache Cassandra
>> co-founder of DataStax, the source for professional Cassandra support
>> http://www.datastax.com
>>
>
>
>
> --
> *David McNelis*
> Lead Software Engineer
> Agentis Energy
> www.agentisenergy.com
> o: 630.359.6395
> c: 219.384.5143
>
> *A Smart Grid technology company focused on helping consumers of energy
> control an often under-managed resource.*
>
>
>
You do not want to do multiple keyspaces because a Cassandra client needs to
do an RPC call to change keyspace. There will be no effective way to keep a
connect pool warm for each keyspace. Imagine you if 1000 keyspaces and 1000
servers. That is a lot of connections.

This shortcoming of having to make an RPC to change keyspace was my
motivation for suggesting:

https://issues.apache.org/jira/browse/CASSANDRA-3130

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