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Date: Fri, 20 Jan 2012 19:37:40 -0800
From: Maxim Potekhin <potekhin@bnl.gov>
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To: user@cassandra.apache.org
Subject: Re: Cassandra to Oracle?
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What makes you think that RDBMS will give you acceptable performance?

I guess you will try to index it to death (because otherwise the "ad 
hoc" queries won't work well if at all), and at this point you may be 
hit with a performance penalty.

It may be a good idea to interview users and build denormalized views in 
Cassandra, maybe on a separate "look-up" cluster. A few percent of users 
will be unhappy, but you'll find it hard to do better. I'm talking from 
my experience with an industrial strength RDBMS which doesn't scale very 
well for what you call "ad-hoc" queries.

Regards,
Maxim


On 1/20/2012 9:28 AM, Brian O'Neill wrote:
>
> I can't remember if I asked this question before, but....
>
> We're using Cassandra as our transactional system, and building up 
> quite a library of map/reduce jobs that perform data quality analysis, 
> statistics, etc.
> (> 100 jobs now)
>
> But... we are still struggling to provide an "ad-hoc" query mechanism 
> for our users.
>
> To fill that gap, I believe we still need to materialize our data in 
> an RDBMS.
>
> Anyone have any ideas?  Better ways to support ad-hoc queries?
>
> Effectively, our users want to be able to select count(distinct Y) 
> from X group by Z.
> Where Y and Z are arbitrary columns of rows in X.
>
> We believe we can create column families with different key structures 
> (using Y an Z as row keys), but some column names we don't know / 
> can't predict ahead of time.
>
> Are people doing bulk exports?
> Anyone trying to keep an RDBMS in synch in real-time?
>
> -brian
>
> -- 
> Brian ONeill
> Lead Architect, Health Market Science (http://healthmarketscience.com)
> mobile:215.588.6024
> blog: http://weblogs.java.net/blog/boneill42/
> blog: http://brianoneill.blogspot.com/
>