Re: Use pg_pwritev_with_retry() instead of write() in dir_open_for_write() to avoid partial writes?

On Tue, Sep 27, 2022 at 10:27 AM Nathan Bossart
<nathandbossart@gmail.com> wrote:
> On Mon, Sep 26, 2022 at 08:33:53PM +0530, Bharath Rupireddy wrote:
> > Irrespective of what Windows does with file pointers in WriteFile(),
> > should we add lseek(SEEK_SET) in our own pwrite()'s implementation,
> > something like [5]? This is rather hackish without fully knowing what
> > Windows does internally in WriteFile(), but this does fix inherent
> > issues that our pwrite() callers (there are quite a number of places
> > that use pwrite() and presumes file pointer doesn't change on Windows)
> > may have on Windows. See the regression tests passing [6] with the fix
> > [5].
>
> I think so.  I don't see why we would rather have each caller ensure
> pwrite() behaves as documented.

I don't think so, that's an extra kernel call.  I think I'll just have
to revert part of my recent change that removed the pg_ prefix from
those function names in our code, and restore the comment that warns
you about the portability hazard (I thought it went away with HP-UX
10, where we were literally calling lseek() before every write()).
The majority of users of these functions don't intermix them with
calls to read()/write(), so they don't care about the file position,
so I think it's just something we'll have to continue to be mindful of
in the places that do.

Unless, that is, I can find a way to stop it from doing that...  I've
added this to my Windows to-do list.  I am going to have a round of
Windows hacking quite soon.