> That's basically what I've been trying to make clear all along: people > should keep an open mind, watch what happens, and not make any > assumptions. There's no clear cut preference for one scheduler or the > other in all situations. I've seen CFQ do much better, you and Albe > report situations where the opposite is true. I was just happy to see > another report of someone running into the same sort of issue I've been > seeing, because I didn't have very much data to offer about why the > standard advice of "always use deadline for a database app" might not > apply to everyone. Damn, you would have to make things complicated, eh? FWIW, back when deadline was first introduced Mark Wong did some tests and found Deadline to be the fastest of 4 on DBT2 ... but only by about 5%. If the read vs. checkpoint analysis is correct, what was happening is the penalty for checkpoints on deadline was almost wiping out the advantage for reads, but not quite. Those tests were also done on attached storage. So, what this suggests is: reads: deadline > CFQ writes: CFQ > deadline attached storage: deadline > CFQ Man, we'd need a lot of testing to settle this. I guess that's why Linux gives us the choice of 4 ... --Josh Berkus -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
