On Wed, Apr 11, 2012 at 09:23:09PM +0100, Bob Proulx wrote: > Karl E. Jorgensen wrote: > > Bob Proulx wrote: > > > But at some point the daemon is going to need to write a file to disk. > > > That data will get cached at that time. Or are you saying that mysql > > > is using or should using O_DIRECT and avoid the cache explicitly? > > > > No - although that might help (marginally) too. The point is that > > caching of data in MySQL will be more efficient than caching in the > > kernel disk cache; less layers and whatnot. > > The point I was trying to make (and apparently failing miserably) is > that unless the mysql daemon is really trying hard to avoid it then as > soon as it writes a file it will end up in the filesystem buffer > cache.
ah. The miserable failing was at the receiving end - sorry :-) > In any case, from the original 'free' output it isn't possible to know > if the filesystem buffer cache is due to mysql or due to other > activity across the filesystem. Such as backup for example. It could > have come from any other activity. There could be files being copied > to or from the system. Could be anything. Agreed > Normally filesystem buffer cache is a good healthy indication. > Because if the operating system becomes starved for memory it will > free filesystem buffer cache in order to obtain it. If a system has > no files cached and lots of truly free ram it may indicate that some > process is frequently consuming a lot of memory, forcing all buffers > to be flushed, and then exiting causing that memory to be free memory. > Free memory as opposed to working-for-you memory in the buffer cache. > Normally I would say memory used for filesystem buffer cache is good > healthy use of the memory. And when I say normally here I am not > talking about a database daemon which will of course have special > needs. Definitely special needs. -- Karl E. Jorgensen IT Operations -- To UNSUBSCRIBE, email to debian-user-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org Archive: http://lists.debian.org/20120413144316.GG11957@hawking
