Re: pg15b2: large objects lost on upgrade

From: "Jonathan S(dot) Katz" <jkatz(at)postgresql(dot)org>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, 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, Shruthi Gowda <gowdashru(at)gmail(dot)com>
Subject: Re: pg15b2: large objects lost on upgrade
Date: 2022-08-03 14:53:06
Message-ID: E642BD53-E3A3-4C10-89A6-66F04084D2E9@postgresql.org
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> On Aug 3, 2022, at 10:14 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>>> On Tue, Aug 2, 2022 at 3:51 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>>> I also think that ">=" is a sufficient requirement.
>
>> 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%.
>
> If you have a different solution that you can implement by, say,
> tomorrow, then go for it. But I want to see some fix in there
> within about 24 hours, because 15beta3 wraps on Monday and we
> will need at least a few days to see if the buildfarm is actually
> stable with whatever solution is applied.

Yeah, I would argue that the current proposal
guards against the false positives as they currently stand.

I do think Robert raises a fair point, but I wonder
if another test would catch that? I don’t want to
say “this would never happen” because, well,
it could happen. But AIUI this would probably
manifest itself in other places too?

> A possible compromise is to allow new values that are between
> old value and old-value-plus-a-few-dozen.

Well, that’s kind of deterministic :-) I’m OK
with that tweak, where “OK” means not thrilled,
but I don’t see a better way to get more granular
details (at least through my phone searches).

I can probably have a tweak for this in a couple
of hours if and when I’m on plane wifi.

Jonathan

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