From: | Andres Freund <andres(at)2ndquadrant(dot)com> |
---|---|
To: | Noah Misch <noah(at)leadboat(dot)com> |
Cc: | Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: Incomplete freezing when truncating a relation during vacuum |
Date: | 2013-12-01 12:55:45 |
Message-ID: | 20131201125544.GB14419@alap2.anarazel.de |
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Lists: | pgsql-hackers |
On 2013-12-01 13:33:42 +0100, Andres Freund wrote:
> On 2013-11-27 14:53:27 -0500, Noah Misch wrote:
> > How would you characterize the chances of this happening with default
> > *vacuum_freeze_*_age settings? Offhand, it seems you would need to encounter
> > this bug during each of ~10 generations of autovacuum_freeze_max_age before
> > the old rows actually become invisible.
>
> On second thought, it's quite possible to see problems before that
> leading to more problems. A single occurance of such a illegitimate
> increase in relfrozenxid can be enough to cause problems of a slightly
> different nature.
> As relfrozenxid has been updated we might now, or after vacuuming some
> other tables, become elegible to truncate the clog. In that case we'll
> get ERRORs about "could not access status of transaction" if the tuple
> hasn't been fully hinted when scanning it later.
And indeed, a quick search shows up some threads that might suffer from
it:
BD7EE863F673A14EBF99D95562AEE15E44B1DA71(at)digi-pdc(dot)digitilitiprod(dot)int
CAAzPmNxfDrV72wDmBEv5tcQOByE_wvGSeqRkQj0FizXmCYyaPQ(at)mail(dot)gmail(dot)com
CAK9oVJwvAZLmdMrHMPg1+s37z16j+BZ8FbarZSpmrHsXxH-4GQ(at)mail(dot)gmail(dot)com
Greetings,
Andres Freund
--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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