Date: Thu, 14 Apr 2022 11:03:32 -0700
From: Andres Freund <andres@anarazel.de>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Robert Haas <robertmhaas@gmail.com>,
	Justin Pryzby <pryzby@telsasoft.com>,
	Kyotaro Horiguchi <horikyota.ntt@gmail.com>,
	Erik Rijkers <er@xs4all.nl>,
	Matthias van de Meent <boekewurm+postgres@gmail.com>,
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: TRAP: FailedAssertion("HaveRegisteredOrActiveSnapshot()", File:
 "toast_internals.c", Line: 670, PID: 19403)
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Hi,

On 2022-04-14 13:36:51 -0400, Tom Lane wrote:
> What if the reason we need a snapshot is to detoast some toasted item
> we read from a catalog with the CatalogSnapshot?  There might not be
> any other valid snapshot, so I don't think I buy your argument here.

We definitely do have places doing that, but is it ever actually safe?
Part of the catalog access might cause cache invalidations to be
processed, which can invalidate the snapshot (including resetting
MyProc->xmin). Afaics we always would have push or register the
snapshot, either will copy the snapshot, I think?

Greetings,

Andres Freund