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From graham sanderson <gra...@vast.com>
Subject Re: 10000+ CF support from Cassandra
Date Wed, 27 May 2015 03:40:20 GMT
Are the CFs different, or all the same schema? Are you contractually obligated to actually
separate data into separate CFs? It seems like you’d have a lot simpler time if you could
use the part of the partition key to separate data.

Note also, I don’t know what disks you are using, but disk cache can be pretty helpful,
and you haven’t allowed for any in your machine sizing. Of course that depends on your stored
data volume also.

Also hard to answer your questions without an idea of read/write load system wide, and indeed
distribution across tenants.

> On May 26, 2015, at 10:32 PM, Arun Chaitanya <chaitan64arun@gmail.com> wrote:
> 
> Good Day Everyone,
> 
> I am very happy with the (almost) linear scalability offered by C*. We had a lot of problems
with RDBMS.
> 
> But, I heard that C* has a limit on number of column families that can be created in
a single cluster.
> The reason being each CF stores 1-2 MB on the JVM heap.
> 
> In our use case, we have about 10000+ CF and we want to support multi-tenancy.
> (i.e 10000 * no of tenants)
> 
> We are new to C* and being from RDBMS background, I would like to understand how to tackle
this scenario from your advice.
> 
> Our plan is to use Off-Heap memtable approach.
> http://www.datastax.com/dev/blog/off-heap-memtables-in-Cassandra-2-1 <http://www.datastax.com/dev/blog/off-heap-memtables-in-Cassandra-2-1>
> 
> Each node in the cluster has following configuration
> 16 GB machine (8GB Cassandra JVM + 2GB System + 6GB Off-Heap)
> IMO, this should be able to support 1000 CF with no(very less) impact on performance
and startup time.
> 
> We tackle multi-tenancy using different keyspaces.(Solution I found on the web)
> 
> Using this approach we can have 10 clusters doing the job. (We actually are worried about
the cost)
> 
> Can you please help us evaluate this strategy? I want to hear communities opinion on
this.
> 
> My major concerns being, 
> 
> 1. Is Off-Heap strategy safe and my assumption of 16 GB supporting 1000 CF right?
> 
> 2. Can we use multiple keyspaces to solve multi-tenancy? IMO, the number of column families
increase even when we use multiple keyspace.
> 
> 3. I understand the complexity using multi-cluster for single application. The code base
will get tightly coupled with infrastructure. Is this the right approach?
> 
> Any suggestion is appreciated.
> 
> Thanks,
> Arun


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