| From: | Peter Geoghegan <pg(at)bowt(dot)ie> |
|---|---|
| To: | Andres Freund <andres(at)anarazel(dot)de> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, "Jonathan S(dot) Katz" <jkatz(at)postgresql(dot)org>, Noah Misch <noah(at)leadboat(dot)com>, Andrew Dunstan <andrew(at)dunslane(dot)net>, Bruce Momjian <bruce(at)momjian(dot)us>, Michael Paquier <michael(at)paquier(dot)xyz>, Justin Pryzby <pryzby(at)telsasoft(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>, Shruthi Gowda <gowdashru(at)gmail(dot)com> |
| Subject: | Re: pg15b2: large objects lost on upgrade |
| Date: | 2022-08-03 20:29:25 |
| Message-ID: | CAH2-WznRPrqYNY+BdLWNe3bkgS8gqiCEQiUuD3fkmfeB9zY6gQ@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Wed, Aug 3, 2022 at 1:20 PM Andres Freund <andres(at)anarazel(dot)de> wrote:
> > I don't really like this approach. Imagine that the code got broken in
> > such a way that relfrozenxid and relminmxid were set to a value chosen
> > at random - say, the contents of 4 bytes of unallocated memory that
> > contained random garbage. Well, right now, the chances that this would
> > cause a test failure are nearly 100%. With this change, they'd be
> > nearly 0%.
>
> Can't that pretty easily be addressed by subsequently querying txid_current(),
> and checking that the value isn't newer than that?
It couldn't hurt to do that as well, in passing (at the same time as
testing that newrelfrozenxid >= oldrelfrozenxid directly). But
deliberately running VACUUM afterwards seems like a good idea. We
really ought to expect VACUUM to catch cases where
relfrozenxid/relminmxid is faulty, at least in cases where it can be
proven wrong by noticing some kind of inconsistency.
--
Peter Geoghegan
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