Josh Berkus wrote:
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.
Wasn't that before 8.3, where the whole checkpoint spreading logic showed up? That's really a whole different write pattern now than it was then. 8.2 checkpoint writes were one big batch write amenable to optimizing for throughput. The new ones are not; the I/O is intermixed with reads most of the time.
Man, we'd need a lot of testing to settle this. I guess that's why Linux gives us the choice of 4 ...
A recent on of these I worked on started with 4096 possible I/O configurations we pruned down the most likely good candidates from. I'm almost ready to schedule a week on Mark's HP performance test system in the lab now, to try and nail this down in a fully public environment for once.
-- Greg Smith 2ndQuadrant Baltimore, MD PostgreSQL Training, Services and Support greg@xxxxxxxxxxxxxxx www.2ndQuadrant.com -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
