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From "Hiller, Dean" <Dean.Hil...@nrel.gov>
Subject Re: 1000's of column families
Date Thu, 27 Sep 2012 14:11:49 GMT
We have 1000's of different building devices and we stream data from these devices.  The format
and data from each one varies so one device has temperature at timeX with some other variables,
another device has CO2 percentage and other variables.  Every device is unique and streams
it's own data.  We dynamically discover devices and register them.  Basically, one CF or table
per thing really makes sense in this environment.  While we could try to find out which devices
"are" similar, this would really be a pain and some devices add some new variable into the
equation.  NOT only that but researchers can register new datasets and upload them as well
and each dataset they have they do NOT want to share with other researches necessarily so
we have security groups and each CF belongs to security groups.  We dynamically create CF's
on the fly as people register new datasets.

On top of that, when the data sets get too large, we probably want to partition a single CF
into time partitions.  We could create one CF and put all the data and have a partition per
device, but then a time partition will contain "multiple" devices of data meaning we need
to shrink our time partition size where if we have CF per device, the time partition can be
larger as it is only for that one device.

THEN, on top of that, we have a meta CF for these devices so some people want to query for
streams that match criteria AND which returns a CF name and they query that CF name so we
almost need a query with variables like select cfName from Meta where x = y and then select
* from cfName where xxxxx. Which we can do today.

Dean

From: Marcelo Elias Del Valle <mvallebr@gmail.com<mailto:mvallebr@gmail.com>>
Reply-To: "user@cassandra.apache.org<mailto:user@cassandra.apache.org>" <user@cassandra.apache.org<mailto:user@cassandra.apache.org>>
Date: Thursday, September 27, 2012 8:01 AM
To: "user@cassandra.apache.org<mailto:user@cassandra.apache.org>" <user@cassandra.apache.org<mailto:user@cassandra.apache.org>>
Subject: Re: 1000's of column families

Out of curiosity, is it really necessary to have that amount of CFs?
I am probably still used to relational databases, where you would use a new table just in
case you need to store different kinds of data. As Cassandra stores anything in each CF, it
might probably make sense to have a lot of CFs to store your data...
But why wouldn't you use a single CF with partitions in these case? Wouldn't it be the same
thing? I am asking because I might learn a new modeling technique with the answer.

[]s

2012/9/26 Hiller, Dean <Dean.Hiller@nrel.gov<mailto:Dean.Hiller@nrel.gov>>
We are streaming data with 1 stream per 1 CF and we have 1000's of CF.  When using the tools
they are all geared to analyzing ONE column family at a time :(.  If I remember correctly,
Cassandra supports as many CF's as you want, correct?  Even though I am going to have tons
of funs with limitations on the tools, correct?

(I may end up wrapping the node tool with my own aggregate calls if needed to sum up multiple
column families and such).

Thanks,
Dean



--
Marcelo Elias Del Valle
http://mvalle.com - @mvallebr

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