Re: MultiXact member wraparound protections are now enabled

On 28 July 2015 at 14:20, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:

> On Sat, Jul 25, 2015 at 4:11 AM, Simon Riggs <simon(at)2ndquadrant(dot)com>
> wrote:
> > On 22 July 2015 at 21:45, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> >> But it seemed to me that this could be rather confusing. I thought it
> >> would be better to be explicit about whether the protections are
> >> enabled in all cases. That way, (1) if you see the message saying
> >> they are enabled, they are enabled; (2) if you see the message saying
> >> they are disabled, they are disabled; and (3) if you see neither
> >> message, your version does not have those protections.
> >
> > (3) would imply that we can't ever remove the message, in case people
> think
> > they are unprotected.
> >
> > If we display (1) and then we find a further bug, where does that leave
> us?
> > Do we put a second "really, really fixed" message?
> >
> > AIUI this refers to a bug fix, its not like we've invented some
> anti-virus
> > mode to actively prevent or even scan for further error. I'm not sure
> why we
> > need a message to say a bug fix has been applied; that is what the
> release
> > notes are for.
> >
> > If something is disabled, we should say so, but otherwise silence means
> > safety and success.
>
> Well, I think that we can eventually downgrade or remove the message
> once (1) we've actually fixed all of the known multixact bugs and (2)
> a couple of years have gone by and most people are in the clear. But
> right now, we've still got significant bugs unfixed.
>
> https://wiki.postgresql.org/wiki/MultiXact_Bugs
>
> Therefore, in my opinion, anything that might make it harder to debug
> problems with the MultiXact system is premature at this point. The
> detective work that it took to figure out the chain of events that led
> to the problem fixed in 068cfadf9e2190bdd50a30d19efc7c9f0b825b5e was
> difficult; I wanted to make sure that future debugging would be
> easier, not harder. I still think that's the right decision, but I
> recognize that not everyone agrees.

I do now, thanks for explaining.

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