Re: Re: BUG #12990: Missing pg_multixact/members files (appears to have wrapped, then truncated)

On Tue, Apr 28, 2015 at 6:23 PM, Alvaro Herrera
<alvherre@2ndquadrant.com> wrote:
> Thomas Munro wrote:
>
>> One thing I noticed about your patch is that it effectively halves the
>> amount of multixact members you can have on disk.  Sure, I'd rather
>> hit an error at 2^31 members than a corrupt database at 2^32 members,
>> but I wondered if we should try to allow the full range to be used.
>
> Ah, yeah, we do want the full range; that's already built in the code
> elsewhere.
>
> In this version, I used your WouldWrap function, but there was a bug in
> your formulation of the call site: after the WARNING has been issued
> once, it is never issued again for that wraparound cycle, because the
> second time around the nextOffset has already crossed the boundary and
> your routine returns false.  IMO this is wrong and the warning should be
> issued every time.  To fix that problem I removed the offsetWarnLimit
> altogether, and instead do WouldWrap() of the value against
> offsetStopLimit minus the 20 segments.  That way, the warning is issued
> continuously until the offsetStopLimit is reached (once there,
> obviously, only the error is thrown, not the warning, which is correct.)

+1

Tomorrow I will send a separate patch for the autovacuum changes that
I sent earlier.  Let's discuss and hopefully eventually commit that
separately.

--
Thomas Munro
http://www.enterprisedb.com