On Sun, May 1, 2011 at 9:48 PM, Jake Luciani <firstname.lastname@example.org>
If you have N column families you need N * memtable size of RAM to support this. If that's not an option you can merge them into one as you suggest but then you will have much larger SSTables, slower compactions, etc.
I don't necessarily agree with Tyler that the OS cache will be less effective... But I do agree that if the sizes of sstables are too large for you then more hardware is the solution...
If you merge CFs which are hardly accessed with one which are accessed frequently, when you read the SSTable you load data that is hardly accessed to the OS cache.