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From Martin Meyer <>
Subject How expensive are additional keyspaces?
Date Tue, 11 Mar 2014 14:17:00 GMT
Hey all -

My company is working on introducing a configuration service system to
provide cofig data to several of our applications, to be backed by
Cassandra. We're already using Cassandra for other services, and at
the moment our pending design just puts all the new tables (9 of them,
I believe) in one of our pre-existing keyspaces.

I've got a few questions about keyspaces that I'm hoping for input on.
Some Google hunting didn't turn up obvious answers, at least not for
recent versions of Cassandra.

1) What trade offs are being made by using a new keyspace versus
re-purposing an existing one (that is in active use by another
application)? Organization is the obvious answer, I'm looking for any
technical reasons.

2) Is there any per-keyspace overhead incurred by the cluster?

3) Does it impact on-disk layout at all for tables to be in a
different keyspace from others? Is any sort of file fragmentation
potentially introduced just by doing this in a new keyspace as opposed
to an exiting one?

4) Does it add any metadata overhead to the system keyspace?

5) Why might we *not* want to make a separate keyspace for this?

6) Does anyone have experience with creating additional keyspaces to
the point that Cassandra can no longer handle it? Note that we're
*not* planning to do this, I'm just curious.


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