We had some serious trouble with dynamically adding CFs, although last time we tried we were using version 0.7, so maybe
that's not an issue any more.
Our problems were two:
- You are (were?) not supposed to add CFs concurrently. Since we had more servers talking to the same Cassandra cluster,
we had to use distributed locks (Hazelcast) to avoid concurrency.
- You must be very careful to add new CFs to different Cassandra nodes. If you do that fast enough, and the clocks of
the two servers are skewed, you will severely compromise your schema (Cassandra will not understand in which order the
updates must be applied).
As I said, this applied to version 0.7, maybe current versions solved these
problems.
Flavio
Il 2012/09/27 16:11 PM, Hiller, Dean ha scritto:
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 <mvall...@gmail.com<mailto:mvall...@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.hil...@nrel.gov<mailto:dean.hil...@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
