Re: [PATCHES] SRA Win32 sync() code

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

This shows that fsync works even after the file is closed and reopened.
I could test by writing using a subprocess, but I don't see how that
would be different, and it would mess up my timings.

Anyway, if we find all our platforms can pass this test, we might be
able to allow backends to do their own writes and just record the file
name somewhere for the checkpointer to fsync. It also shows write/fsync
was 3x slower than simple write.

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

I am keeping this discussion on patches because of the C program
attachment.

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