Re: datfrozenxid not dropping after vacuum

Hi Alvaro, thanks for the quick reply.

I'm scheduled to do my patching maintenance at the end of this month -
but at this point I don't think I'm going to make it.

Other than patching, is there a work around?  For example, in #2 above:
>The fix for 2) is simpler,
>    simply always remove both the shared and local init files.

I'm not familiar with the differences between 'shared' and 'local'
init files (I'd imagine I referenced a 'local' file in my original
post)?



Thanks!

Matt

On Wed, Sep 1, 2021 at 3:00 PM Alvaro Herrera <alvherre@alvh.no-ip.org> wrote:
>
> On 2021-Sep-01, Matthew Tice wrote:
>
> [ problem table is pg_database ]
>
> > My primary, read/write database is Postgresql 10.4 (CentOS 7) while my
> > standby databases have been patched to 10.17.
>
> Hmm, I think there was a bug in the early 10.x versions where advancing
> the xid age of shared tables would not work correctly for some reason ...
> Ah yes, this was fixed in 10.5, a mere three years ago:
>
> Author: Andres Freund <andres@anarazel.de>
> Branch: master Release: REL_11_BR [a54e1f158] 2018-06-12 11:13:21 -0700
> Branch: REL_10_STABLE Release: REL_10_5 [2ce64caaf] 2018-06-12 11:13:21 -0700
> Branch: REL9_6_STABLE Release: REL9_6_10 [6a46aba1c] 2018-06-12 11:13:21 -0700
> Branch: REL9_5_STABLE Release: REL9_5_14 [14b3ec6f3] 2018-06-12 11:13:21 -0700
> Branch: REL9_4_STABLE Release: REL9_4_19 [817f9f9a8] 2018-06-12 11:13:22 -0700
> Branch: REL9_3_STABLE Release: REL9_3_24 [9b9b622b2] 2018-06-12 11:13:22 -0700
>
>     Fix bugs in vacuum of shared rels, by keeping their relcache entries current.
>
>     When vacuum processes a relation it uses the corresponding relcache
>     entry's relfrozenxid / relminmxid as a cutoff for when to remove
>     tuples etc. Unfortunately for nailed relations (i.e. critical system
>     catalogs) bugs could frequently lead to the corresponding relcache
>     entry being stale.
>
>     This set of bugs could cause actual data corruption as vacuum would
>     potentially not remove the correct row versions, potentially reviving
>     them at a later point.  After 699bf7d05c some corruptions in this vein
>     were prevented, but the additional error checks could also trigger
>     spuriously. Examples of such errors are:
>       ERROR: found xmin ... from before relfrozenxid ...
>     and
>       ERROR: found multixact ... from before relminmxid ...
>     To be caused by this bug the errors have to occur on system catalog
>     tables.
>
>     The two bugs are:
>
>     1) Invalidations for nailed relations were ignored, based on the
>        theory that the relcache entry for such tables doesn't
>        change. Which is largely true, except for fields like relfrozenxid
>        etc.  This means that changes to relations vacuumed in other
>        sessions weren't picked up by already existing sessions.  Luckily
>        autovacuum doesn't have particularly longrunning sessions.
>
>     2) For shared *and* nailed relations, the shared relcache init file
>        was never invalidated while running.  That means that for such
>        tables (e.g. pg_authid, pg_database) it's not just already existing
>        sessions that are affected, but even new connections are as well.
>        That explains why the reports usually were about pg_authid et. al.
>
>     To fix 1), revalidate the rd_rel portion of a relcache entry when
>     invalid. This implies a bit of extra complexity to deal with
>     bootstrapping, but it's not too bad.  The fix for 2) is simpler,
>     simply always remove both the shared and local init files.
>
>     Author: Andres Freund
>     Reviewed-By: Alvaro Herrera
>     Discussion:
>         https://postgr.es/m/20180525203736.crkbg36muzxrjj5e@alap3.anarazel.de
>         https://postgr.es/m/CAMa1XUhKSJd98JW4o9StWPrfS=11bPgG+_GDMxe25TvUY4Sugg@mail.gmail.com
>         https://postgr.es/m/CAKMFJucqbuoDRfxPDX39WhA3vJyxweRg_zDVXzncr6+5wOguWA@mail.gmail.com
>         https://postgr.es/m/CAGewt-ujGpMLQ09gXcUFMZaZsGJC98VXHEFbF-tpPB0fB13K+A@mail.gmail.com
>     Backpatch: 9.3-
>
>
> --
> Álvaro Herrera           39°49'30"S 73°17'W
> "El número de instalaciones de UNIX se ha elevado a 10,
> y se espera que este número aumente" (UPM, 1972)