> "Magnus Hagander" <[EMAIL PROTECTED]> writes: > > Is there actually a reason why we don't use O_DIRECT on Unix? > > Portability, or rather the complete lack of it. Stuff that isn't in the > Single Unix Spec is a hard sell.
Well, how about this (ok, maybe I'm way out in left field): Change fsync option from on/off to on/off/O_SYNC. On win32 we treat O_SYNC as opened with FILE_FLAG_WRITE_THROUGH. When we are in O_SYNC mode, all files, WAL or otherwise, are assumed to be synced when written and are therefore not synced during pg_fsync(). WAL syncing may of course be overridden using alternate sync methods in postgresql.conf. I suspect that this will drastically alter windows performance, especially on raid systems. What is TBD is the safety aspect. What I like about this that now are not dealing with a win32-only hack, any unix system now has another performance setting top play with. We also don't touch the O_DIRECT flag (on win32: FILE_FLAG_WRITE_THROUGH | FILE_FLAG_NO_BUFFERING) leaving that can of worms for another day. Under normal situations, we would expect O_SYNCing everything all the time to slow stuff down, especially during checkpoints, but it might actually help on a caching raid controller. On win32, it will help because the performance of fsync() sucks so horribly, even or raid. Merlin ---------------------------(end of broadcast)--------------------------- TIP 2: you can get off all lists at once with the unregister command (send "unregister YourEmailAddressHere" to [EMAIL PROTECTED])