Horton

Re: recovering from "found xmin ... from before relfrozenxid ..."

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Amit Kapila <amit.kapila16@gmail.com>, Robert Haas <robertmhaas@gmail.com>, Ashutosh Sharma <ashu.coek88@gmail.com>, Mark Dilger <mark.dilger@enterprisedb.com>, Masahiko Sawada <masahiko.sawada@2ndquadrant.com>, "Andrey M. Borodin" <x4mmm@yandex-team.ru>, MBeena Emerson <mbeena.emerson@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Peter Eisentraut <peter.eisentraut@2ndquadrant.com>, Stephen Frost <sfrost@snowman.net>
Date: 2020-09-21T21:20:03Z
Lists: pgsql-hackers 
On 2020-09-21 17:03:53 -0400, Tom Lane wrote:
> Andres Freund <andres@anarazel.de> writes:
> > On 2020-09-21 16:40:40 -0400, Tom Lane wrote:
> >> Andres Freund <andres@anarazel.de> writes:
> >>> I think that's an argument for what I suggested elsewhere, which is that
> >>> we should move the logic for a different horizon for temp tables out of
> >>> vacuum_set_xid_limits, and into procarray.
> 
> >> But procarray does not seem like a great place for
> >> table-persistence-dependent decisions either?
> 
> > That ship has sailed a long long time ago though. GetOldestXmin() has
> > looked at the passed in relation for a quite a while, and even before
> > that we had logic about 'allDbs' etc.  It doesn't easily seem possible
> > to avoid that, given how intimately that's coupled with how snapshots
> > are built and used, database & vacuumFlags checks etc.
> 
> OK.  Given that you've got strong feelings about this, do you want to
> propose a patch?  I'm happy to fix it, since it's at least in part my
> bug, but I probably won't do it exactly like you would.

I can give it a try. I can see several paths of varying invasiveness,
not sure yet what the best approach is. Let me think about if for a bit.

Greetings,

Andres Freund

Commits

  1. Fix wrong data table horizon computation during backend startup.

  2. Centralize horizon determination for temp tables, fixing bug due to skew.

  3. pg_surgery: Try to stabilize regression tests.

  4. New contrib module, pg_surgery, with heap surgery functions.

  5. Set cutoff xmin more aggressively when vacuuming a temporary table.

  6. snapshot scalability: Don't compute global horizons while building snapshots.

  7. Introduce vacuum errcontext to display additional information.