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: 2020-07-14T01:26:38Z
Lists: pgsql-hackers 
Robert Haas <robertmhaas@gmail.com> writes:
> On Mon, Jul 13, 2020 at 8:58 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> 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.

> I understand that it's not too great when we give people access to
> sharp tools and they hurt themselves with said tools. But this is open
> source. That's how it goes.

I think you're attacking a straw man.  I'm well aware of how open source
works, thanks.  What I'm saying is that contrib is mostly seen to be
reasonably harmless stuff.  Sure, you can overwrite data you didn't want
to with adminpack's pg_file_write.  But that's the price of having such a
capability at all, and in general it's not hard for users to understand
both the uses and risks of that function.  That statement does not apply
to the functions being proposed here.  It doesn't seem like they could
possibly be safe to use without very specific expert advice --- and even
then, we're talking rather small values of "safe".  So I wish we had some
other way to distribute them than via contrib.

			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.