scott.marlowe wrote: > On Thu, 9 Oct 2003, Bruce Momjian wrote: > > > scott.marlowe wrote: > > > I was testing to get some idea of how to speed up the speed of pgbench > > > with IDE drives and the write caching turned off in Linux (i.e. hdparm -W0 > > > /dev/hdx). > > > > > > The only parameter that seems to make a noticeable difference was setting > > > wal_sync_method = open_sync. With it set to either fsync, or fdatasync, > > > the speed with pgbench -c 5 -t 1000 ran from 11 to 17 tps. With open_sync > > > it jumped to the range of 45 to 52 tps. with write cache on I was getting > > > 280 to 320 tps. so, not instead of being 20 to 30 times slower, I'm only > > > about 5 times slower, much better. > > > > > > Now I'm off to start a "pgbench -c 10 -t 10000" and pull the power cord > > > and see if the data gets corrupted with write caching turned on, i.e. do > > > my hard drives have the ability to write at least some of their cache > > > during spin down. > > > > Is this a reason we should switch to open_sync as a default, if it is > > availble, rather than fsync? I think we are doing a single write before > > fsync a lot more often than we are doing multiple writes before fsync. > > Sounds reasonable to me. Are there many / any scenarios where a plain > fsync would be faster than open_sync?
Yes. If you were doing multiple WAL writes before transaction fsync, you would be fsyncing every write, rather than doing two writes and fsync'ing them both. I wonder if larger transactions would find open_sync slower? -- Bruce Momjian | http://candle.pha.pa.us [EMAIL PROTECTED] | (610) 359-1001 + If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania 19073 ---------------------------(end of broadcast)--------------------------- TIP 3: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
