Bruce Momjian wrote:

write 0.000360
write & fsync 0.001391
write, close & fsync 0.001308
open o_fsync, write 0.000924

That's 1 milliseconds vs. 1.3 milliseconds. Neither value is realistic - I guess the hw cache on and the os doesn't issue cache flush commands. Realistic values are probably 5 ms vs 5.3 ms - 6%, not 30%. How large is the syscall latency with BSD/OS 4.3?

One advantage of a seperate write and fsync call is better performance for the writes that are triggered within AdvanceXLInsertBuffer: I'm not sure how often that's necessary, but it's a write while holding both the WALWriteLock and WALInsertLock. If every write contains an implicit sync, that call would be much more expensive than necessary.


---------------------------(end of broadcast)--------------------------- TIP 7: don't forget to increase your free space map settings

Reply via email to