> Previously, mark-and-sweep would run around 5.5GB, and would cut heap
> usage to 4GB. Now, it still runs at 5.5GB, but it shrinks all the way
> down to 2GB used. This behavior was consistent in every machine I
> increased read-concurrent on.

So each full CMS cycles brings it down to 4 on a maximum heap size of
5.5GB? Or are you using VM options such that Xms != Xmx?

If 5.5 is the maximum heap size and you're at 4 gig after the
completion of a mark-and-sweep, I'd say it would be a good idea to
pre-emptively up the heap size a bit (or decreases memtables/key/row
caches).


-- 
/ Peter Schuller