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@xxxxxxxxxxxxx http://www.gregsmith.com Baltimore, MD ---------------------------(end of broadcast)--------------------------- TIP 7: You can help support the PostgreSQL project by donating at http://www.postgresql.org/about/donate
