Re: multixacts woes

On 2015-05-08 14:32:14 -0400, Robert Haas wrote:
> On Fri, May 8, 2015 at 2:27 PM, Andres Freund <andres@anarazel.de> wrote:
> > On 2015-05-08 14:15:44 -0400, Robert Haas wrote:
> >> Apparently, we have been hanging our hat since the release of 9.3.0 on
> >> the theory that the average multixact won't ever have more than two
> >> members, and therefore the members SLRU won't overwrite itself and
> >> corrupt data.
> >
> > It's essentially a much older problem - it has essentially existed since
> > multixacts were introduced (8.1?). The consequences of it were much
> > lower before 9.3 though.
> 
> OK, I wasn't aware of that.  What exactly were the consequences before 9.3?

I think just problems when locking a row. That's obviously much less bad
than problems when reading a row.

> > FWIW, I intend to either work on this myself, or help whoever seriously
> > tackles this, in the next cycle.
> 
> That would be great.

With "this" I mean freeze avoidance. While I obviously, having proposed
it as well at some point, think that freeze maps are a possible
solution, I'm not yet sure that it's the best solution.

> I'll investigate what resources EnterpriseDB can commit to this.

Cool.

Greetings,

Andres Freund