Re: Incomplete freezing when truncating a relation during vacuum

On 2013-12-01 18:02:27 -0500, Tom Lane wrote:
> Andres Freund <andres@2ndquadrant.com> writes:
> > On 2013-12-01 17:15:31 -0500, Tom Lane wrote:
> >> Is there really a significant risk of clog access errors due to this bug?
> >> IIUC, the risk is that tuples in pages that vacuum skips due to being
> >> all-visible might not be frozen when intended.
> 
> > Unfortunately it's not actually too hard to hit due to following part of the
> > code in vacuumlazy.c:
> 
> >     /*
> >      * If we're not scanning the whole relation to guard against XID
> >      * wraparound, it's OK to skip vacuuming a page.  The next vacuum
> >      * will clean it up.
> >      */
> 
> Ah.  So it's only been *seriously* broken since commit bbb6e559c, ie 9.2.

Well, even before that crash recovery/replication didn't necessarily
preserve the hint bits. Even more so if somebody dared to set
full_page_writes=off.

I personally think full_page_writes=off should conflict with wal_level
!= minimal, btw, but I don't see much chance of gaining acceptance for
that.

Greetings,

Andres Freund

-- Andres Freund                       http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training &
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