Re: MultiXact member wraparound protections are now enabled

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.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company