Re: Migrating to 8.3 - checkpoints and background writer

On Mon, 5 Nov 2007, Steinar H. Gunderson wrote:

> I'm a bit puzzled by this part, though: "All tests are on linux with the
> anticipatory I/O scheduler. The default I/O scheduler for Linux is CFQ
> (Completely Fair Queue), which does not work well for PostgreSQL in my
> tests."

The syncronized scan articles were from Jeff Davis and I can't answer for
him. I will say I don't actually agree with that part of the document
myself and almost put a disclaimer to that effect in my message; here it
is now that you bring it up. I suspect the strong preference for avoiding
CFQ in his tests comes from the limitations of how simple (S)ATA drives
are handled in Linux, and that tests with a more robust disk subsystem may
very well give different results. Certainly the adaptive scheduler
appears stronger compared to CFQ as disk seek times go up, and that's the
area where regular hard drives are weakest relative to what's normally in
a server-class system.

--
* Greg Smith gsmith(at)gregsmith(dot)com http://www.gregsmith.com Baltimore, MD