On Mon, Nov 17, 2003 at 12:46:34AM -0500, Bruce Momjian wrote:
> Tom Lane wrote:
> > > Do we know that having the background writer fsync a file that was
> > > written by a backend cause all the data to fsync?  I think I could write
> > > a program to test this by timing each of these tests:
> > 
> > That might prove something about the particular platform you tested it
> > on; but it would not speak to the real problem, which is what we can
> > assume is true on every platform...
> 
> The attached program does test if fsync can be used on a file descriptor
> after the file is closed and then reopened.  I see:
>       
>       write                  0.000613
>       write & fsync          0.001727
>       write, close & fsync   0.001633

> Does anyone have a platform where the last duration is significantly
> different from the middle timing?

write                  0.002807
write & fsync          0.015248
write, close & fsync   0.004696

This is a Linux 2.6.0-test5 on an old IDE disk.

The results change alot.  An other result shows:
write                  0.002737
write & fsync          0.006658
write, close & fsync   0.008431

The first time is stable, the other 2 aren't.

Averagly write & fsync would be about twice as big/slow as write,
close & fsync.


PS: Please specify some modes when creating files.

Kurt


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