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.