| From: | Andres Freund <andres(at)anarazel(dot)de> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Justin Pryzby <pryzby(at)telsasoft(dot)com>, Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com>, Erik Rijkers <er(at)xs4all(dot)nl>, Matthias van de Meent <boekewurm+postgres(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: TRAP: FailedAssertion("HaveRegisteredOrActiveSnapshot()", File: "toast_internals.c", Line: 670, PID: 19403) |
| Date: | 2022-04-15 01:30:10 |
| Message-ID: | 20220415013010.2fctkwpi5js6dfno@alap3.anarazel.de |
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| Lists: | pgsql-hackers |
Hi,
On 2022-04-14 15:05:50 -0400, Tom Lane wrote:
> Andres' complaint is that that snapshot might get invalidated when you
> weren't expecting it, but I'm not really convinced that we have all
> that many bugs of that ilk. Wouldn't CLOBBER_CACHE_ALWAYS testing
> find them?
Don't see why it would - we don't have any mechanism in place for
enforcing that we don't update / delete a tuple we've looked up with an
xmin that wasn't continually enforced. A typical pattern is to use a
catalog cache (registered an all) for a syscache lookup, but then not
have a registered / active snapshot until an eventual update / delete
(after the syscache scan ends). Which isn't safe, because without a
MyProc->xmin set, the tuple we're updating / deleting could be updated,
removed and replaced with another tuple.
Greetings,
Andres Freund
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