I guess I'm still feeling fuzzy on this because my actual use-case isn't so black-and-white. I don't have any CFs that are accessed purely, or even mostly, in once-through batch mode. What I have is CFs with more and less data, and CFs that are accessed more and less frequently.

On Mon, May 2, 2011 at 7:52 PM, Tyler Hobbs <tyler@datastax.com> wrote:
On Mon, May 2, 2011 at 5:05 AM, David Boxenhorn <david@taotown.com> wrote:
Wouldn't it be the case that the once-used rows in your batch process would quickly be traded out of the cache, and replaced by frequently-used rows?

Yes, and you'll pay a cache miss penalty for each of the replacements.
This would be the case even if your batch process goes on for a long time, since caching is done on a row-by-row basis. In effect, it would mean that part of your cache is taken up by the batch process, much as if you dedicated a permanent cache to the batch - except that it isn't permanent, so it's better!

Right, but we didn't want to cache any of the batch CF in the first place, because caching that CF is worth very little.  With separate CFs, we could explicitly give it no cache.  Now we have no control over how much of the cache it evicts.