Jeff <threshar@xxxxxxxxxxxxx> wrote: > If you have a halfway OK raid controller, CFQ is useless. You can fire > up something such as pgbench or pgiosim, fire up an iostat and then > watch your iops jump high when you flip to noop or deadline and > plummet on cfq. An interesting data point, but not, by itself, conclusive. One of the nice things about a good scheduler is that it allows multiple writes to the OS to be combined into a single write to the controller cache. I think that having a large OS cache and the deadline elevator allowed us to use what some considered extremely aggressive background writer settings without *any* discernible increase in OS output to the disk. The significant measure is throughput from the application point of view; if you see that drop as cfq causes the disk I/O to drop, *then* you've proven your point. Of course, I'm betting that's what you do see.... -Kevin -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
