Tom Lane wrote: > Greg Stark <[EMAIL PROTECTED]> writes: > > Tom Lane <[EMAIL PROTECTED]> writes: > >> Unfortunately, I cannot believe these numbers --- the near equality of > >> fsync off and fsync on means there is something very wrong with the > >> measurements. What I suspect is that your ATA drives are doing write > >> caching and thus the "fsyncs" are not really waiting for I/O at all. > > > I wonder whether it would make sense to have an automatic test for this > > problem. I suspect there are lots of installations out there whose admins > > don't realize that their hardware is doing this to them. > > Not sure about "automatic", but a simple little test program to measure > the speed of rewriting/fsyncing a small test file would surely be a nice > thing to have. > > The reason I question "automatic" is that you really want to test each > drive being used, if the system has more than one; but Postgres has no > idea what the actual hardware layout is, and so no good way to know what > needs to be tested.
Some folks have battery-backed cached controllers so they would appear as not handling fsync when in fact they do. -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (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
