Re: Loaded footgun open_datasync on Windows

On Wed, Jun 27, 2018 at 12:09:24PM +0200, Laurenz Albe wrote:
> Michael Paquier wrote:
> > > I have added it to the July commitfest.
> >
> > Have you looked at the possibility of removing the log file constraints
> > in pg_upgrade with the change you are doing here so as things would be
> > more consistent with non-Windows platforms, simplifying some code on the
> > way?
>
> Can you explain what the "log file constraints" are?
> If it is in any way related, and I can handle it, sure.

See this comment in pg_upgrade.h:

/*
* WIN32 files do not accept writes from multiple processes
*
* On Win32, we can't send both pg_upgrade output and command output to the
* same file because we get the error: "The process cannot access the file
* because it is being used by another process." so send the pg_ctl
* command-line output to a new file, rather than into the server log file.
* Ideally we could use UTILITY_LOG_FILE for this, but some Windows platforms
* keep the pg_ctl output file open by the running postmaster, even after
* pg_ctl exits.
*
* We could use the Windows pgwin32_open() flags to allow shared file
* writes but is unclear how all other tools would use those flags, so
* we just avoid it and log a little differently on Windows; we adjust
* the error message appropriately.
*/

If you grep src/bin/pg_upgrade for WIN32, roughly a third of the hits are
workarounds for this problem. I agree with Michael that removing those
workarounds would be a good test of frontend pgwin32_open() and worth
including in the initial commit.