Re: backup tools ought to ensure created backups are durable

On 2016-03-28 11:35:57 +0200, Magnus Hagander wrote:
> On Mon, Mar 28, 2016 at 3:11 AM, Michael Paquier <michael.paquier@gmail.com>
> wrote:
> 
> > On Mon, Mar 28, 2016 at 8:30 AM, Andres Freund <andres@anarazel.de> wrote:
> > > As pointed out in
> > >
> > http://www.postgresql.org/message-id/20160327232509.v5wgac5vskusedin@awork2.anarazel.de
> > > our backup tools (i.e. pg_basebackup, pg_dump[all]), currently don't
> > > make any efforts to ensure their output is durable.
> > >
> > > I think for backup tools of possibly critical data, that's pretty much
> > > unaceptable.
> >
> > Definitely agreed, once a backup/dump has been taken and those
> > utilities exit, we had better ensure that they are durably on disk.
> > For pg_basebackup and pg_dump, as everything except pg_dump/plain
> > require a target directory for the location of the output result, we
> > really can make things better.
> >
> >
> Definitely agreed on fixing it. But I don't think your summary is right.
> 
> pg_basebackup in tar mode can be sent to stdout, does not require a
> directory. And the same for pg_dump in any mode except for directory. So we
> can't just drive it off the mode, some more detailed checks are required.

if (!isastty(stdout)) ought to do the trick, afaics? And maybe add a
warning somewhere in the docs about the tools not fsyncing if you pipe
their output data somewhere?

Andres