A couple months ago we upgraded the RAM on our database servers from 48GB to 64GB. Immediately afterwards the new RAM was being used for page cache, which is what we want, but that seems to have dropped off over time, and there's currently actually like 12GB of totally unused RAM.
http://s76.photobucket.com/user/kgoesspb/media/db1-mem-historical.png.html Is that expected? Is there a setting we need to tune for that? We have 400GB of databases on this box, so I know it's not all fitting in that 49.89GB.
