We are thinking a lot about multi-tenancy, but features to support multiple tenants on a cluster are only beginning to make their way into Cassandra. See http://wiki.apache.org/cassandra/MultiTenant
for a short listing of features that are being considered (including a mention of memory considerations).
If you have more thoughts on the matter, please feel free to add them to that page.
From: "Aaron Morton" <email@example.com>
Sent: Sunday, August 22, 2010 9:51pm
To: "Cassandra User" <firstname.lastname@example.org>
Subject: Multiple Keyspaces and memtables
Am playing with the dynamic schema features of 0.7 and thinking about the impact of more keyspaces. Memtable settings are per CF, and so per Keyspace - so adding more keyspaces increases the amount of memory needed for memtables on the node.
There are also some new features in the config for multi tenant installs. Which seems to support using more keyspaces.
So my (rambling) question is: Are there any other features to support managing memory in a cluster with many keyspaces? Am I right in thinking that for every keyspace every node needs to support at least ((num CF) * memtable_throughoput_in_mb) * 2 ?
Is anyone out there running more than a couple of keyspaces in a single cluster?