Re: [HACKERS] fsync method checking

[Manfred Spraul]

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.

--
   Manfred
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