Tom Lane wrote: > "Marc G. Fournier" <[EMAIL PROTECTED]> writes: > > One question, more directed to Tom here ... since they are seperate right > > now, if WAL is fsync, and "regular writing" is no-fsync, doesn't that > > potentially open us up to some *serious* problems? WAL sees the > > transaction as complete, but the write for the rest of the system hasn't > > happened yet? > > No, that's pretty much the whole point of WAL: once you've fsynced the > transaction's log entries to WAL, it's committed. You don't have to > fsync the data-file writes, or even write the changes out at all. > (In most cases the pages stay in shared buffer cache, dirty, until the > background writer gets to them.) If you crash then the data-file > changes will get redone by replaying the WAL entries. > > You do have to fsync data-file writes when trying to complete a > checkpoint, but that's outside the critical path for normal > transactions. > > One of the reasons I dislike Bruce's proposal is that I don't think it > pays any attention to this basic duality between normal operations > (fsync WAL) and checkpoints (fsync data). We just finished finding a > long-standing bug in this area, so I'm pretty hesitant to whack it > around on the basis of unproven ideas about performance improvements.
I have to show some performance numbers to make it worthwhile. -- 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
