The official answer, engraved in stone tablets, and carried down from the mountain: “Although having more than dozens or hundreds of tables defined is almost certainly a Bad Idea (just as it is a design smell in a relational database), it's relatively straightforward to allow disabling the SlabAllocator.” Emphasis on “almost certainly a Bad Idea.”
See: https://issues.apache.org/jira/browse/CASSANDRA-5935 “Allow disabling slab allocation” IOW, this is considered an anti-pattern, but... -- Jack Krupansky From: tommaso barbugli Sent: Wednesday, July 2, 2014 2:16 PM To: user@cassandra.apache.org Subject: Re: keyspace with hundreds of columnfamilies Hi, thank you for you replies on this; regarding the arena memory is this a fixed memory allocation or is some sort of in memory caching? I ask because I think that a substantial portion of the column families created will not be queried that frequently (and some will become inactive and stay like that really long time) Thank you, Tommaso 2014-07-02 18:35 GMT+02:00 Romain HARDOUIN <romain.hardo...@urssaf.fr>: Arena allocation is an improvement feature, not a limitation. It was introduced in Cassandra 1.0 in order to lower memory fragmentation (and therefore promotion failure). AFAIK It's not intended to be tweaked so it might not be a good idea to change it. Best, Romain tommaso barbugli <tbarbu...@gmail.com> a écrit sur 02/07/2014 17:40:18 : > De : tommaso barbugli <tbarbu...@gmail.com> > A : user@cassandra.apache.org, > Date : 02/07/2014 17:40 > Objet : Re: keyspace with hundreds of columnfamilies > > 1MB per column family sounds pretty bad to me; is this something I > can tweak/workaround somehow? > > Thanks > Tommaso > > 2014-07-02 17:21 GMT+02:00 Romain HARDOUIN <romain.hardo...@urssaf.fr>: > The trap is that each CF will consume 1 MB of memory due to arena allocation. > This might seem harmless but if you plan thousands of CF it means > thousands of mega bytes... > Up to 1,000 CF I think it could be doable, but not 10,000. > > Best, > > Romain > > > tommaso barbugli <tbarbu...@gmail.com> a écrit sur 02/07/2014 10:13:41 : > > > De : tommaso barbugli <tbarbu...@gmail.com> > > A : user@cassandra.apache.org, > > Date : 02/07/2014 10:14 > > Objet : keyspace with hundreds of columnfamilies > > > > Hi, > > Are there any known issues, shortcomings about organising data in > > hundreds of column families? > > At this present I am running with 300 column families but I expect > > that to get to a couple of thousands. > > Is this something discouraged / unsupported (I am using Cassandra 2.0). > > > > Thanks > > Tommaso
