On Mon, 2006-03-20 at 15:17, Ron wrote: > At 03:44 PM 3/21/2006, Simon Riggs wrote: > >On Mon, 2006-03-20 at 15:59 +0100, Mikael Carneholm wrote: > > > > > This gives that 10Gb takes ~380s => ~27Mb/s (with fsync=off), > > compared to the raw dd result (~75.5Mb/s). > > > > > > I assume this difference is due to: > > > - simultaneous WAL write activity (assumed: for each byte written > > to the table, at least one byte is also written to WAL, in effect: > > 10Gb data inserted in the table equals 20Gb written to disk) > > > - lousy test method (it is done using a function => the > > transaction size is 10Gb, and 10Gb will *not* fit in wal_buffers :) ) > > > - poor config > > > > > checkpoint_segments = 3 > > > >With those settings, you'll be checkpointing every 48 Mb, which will be > >every about once per second. Since the checkpoint will take a reasonable > >amount of time, even with fsync off, you'll be spending most of your > >time checkpointing. bgwriter will just be slowing you down too because > >you'll always have more clean buffers than you can use, since you have > >132MB of shared_buffers, yet flushing all of them every checkpoint. > IIRC, Josh Berkus did some benches that suggests in pg 8.x a value of > 64 - 256 is best for checkpoint_segments as long as you have the RAM available. > > I'd suggest trying values of 64, 128, and 256 and setting > checkpoint_segments to the best of those. I've also found that modest increases in commit_siblings and commit_delay help a lot on certain types of imports.
