Re: Multixid hindsight design

On 5 June 2015 at 11:02, Andres Freund <andres(at)anarazel(dot)de> wrote:

> On 2015-06-05 10:45:09 +0100, Simon Riggs wrote:
> > On 1 June 2015 at 20:53, Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com>
> wrote:
> >
> > > On Tue, May 12, 2015 at 9:20 AM, Heikki Linnakangas <hlinnaka(at)iki(dot)fi>
> > > wrote:
> > > > The beauty of this would be that the TED entries can be zapped at
> > > restart,
> > > > just like pg_subtrans, and pg_multixact before 9.3. It doesn't need
> to be
> > > > WAL-logged, and we are free to change its on-disk layout even in a
> minor
> > > > release.
> > >
> > > What about prepared transactions? They can lock rows FOR SHARE that
> > > survive server restarts.
> > >
> >
> > Interesting comment. I'm not aware that we do.
> >
> > If we do support row locking that survives server restart, how did it
> work
> > before 9.3?
>
> Multixacts were persistent before 9.3 as well. A good number of the bugs
> existed then as well, but their effect was much more limited. The
> difference is that now multixacts don't just have to survive till the
> last locker isn't running anymore (which was determined by a horizon),
> but that they have to live till they're vacuumed away, since xmax might
> be stored in the multixact.
>

Phew! Had me worried for a minute.

--
Simon Riggs http://www.2ndQuadrant.com/
<http://www.2ndquadrant.com/>
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