Horton

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

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Andres Freund <andres@anarazel.de>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2020-07-14T00:58:43Z
Lists: pgsql-hackers 
Robert Haas <robertmhaas@gmail.com> writes:
> Oh, I hadn't realized that limitation. That would be good to fix. It
> would be even better, I think, if we could have VACUUM proceed with
> the rest of vacuuming the table, emitting warnings about each
> instance, instead of blowing up when it hits the first bad tuple, but
> I think you may have told me sometime that doing so would be, uh, less
> than straightforward. We probably should refuse to update
> relfrozenxid/relminmxid when this is happening, but I *think* it would
> be better to still proceed with dead tuple cleanup as far as we can,
> or at least have an option to enable that behavior. I'm not positive
> about that, but not being able to complete VACUUM at all is a FAR more
> urgent problem than not being able to freeze, even though in the long
> run the latter is more severe.

+1 for proceeding in this direction, rather than handing users tools
that they *will* hurt themselves with.

The more that I think about it, the more I think that the proposed
functions are tools for wizards only, and so I'm getting hesitant
about having them in contrib at all.  We lack a better place to
put them, but that doesn't mean they should be there.

			regards, tom lane

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.