Re: Re: [PATCH] Atomic pgrename on Windows

Hi, David!

On Tue, Mar 6, 2018 at 5:04 PM, David Steele <david(at)pgmasters(dot)net> wrote:

> On 1/20/18 10:13 AM, Magnus Hagander wrote:
> >
> > On Tue, Nov 28, 2017 at 2:47 AM, Michael Paquier
> > <michael(dot)paquier(at)gmail(dot)com <mailto:michael(dot)paquier(at)gmail(dot)com>> wrote:
> >
> > On Mon, Nov 27, 2017 at 3:28 PM, Alexander Korotkov
> > <a(dot)korotkov(at)postgrespro(dot)ru <mailto:a(dot)korotkov(at)postgrespro(dot)ru>>
> wrote:
> > > Attached patch atomic-pgrename-windows-1.patch fixes this
> problem. It
> > > appears to be possible to atomically replace file on Windows –
> ReplaceFile()
> > > does that. ReplaceFiles() requires target file to exist, this is
> why we
> > > still need to call MoveFileEx() when it doesn't exist.
> >
> > Do you think that it could be safer to unlink the target file first
> > with pgunlink()? This way you make sure that the target file is
> > removed and not locked. This change makes me worrying about the
> > introduction of more race conditions.
> >
> > Unlinking it first seems dangerous, as pointed out by Andres.
> >
> > What about first trying ReplaceFile() and then if it fails with "target
> > doesn't exist", then call MoveFileEx().
> >
> > Or the other way around -- try MoveFileEx() first since that seems to
> > work most of the time today (if it mostly broke we'd be in trouble
> > already), and if it fails with a sharing violation, try ReplaceFile()?
> > And perhaps end up doing it something similar to what we do with shared
> > memory which is just to loop over it and try each a couple of time,
> > before giving up and failing?
>
> This patch was mistakenly left as Needs Review during the last
> commitfest but it's pretty clear that a new patch is required.
>

OK! No objections against marking this patch RWF.

------
Alexander Korotkov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company