On Thu, Apr 14, 2022 at 3:05 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> If you don't register it, then you need to also make sure that it's
> destroyed whenever that older snapshot is. Which I think would require
> either a lot of useless/inefficient CatalogSnapshot destructions, or
> infrastructure that's more or less isomorphic to the RegisteredSnapshot
> heap.
Well, if that's true, then I agree that it's a good argument against
that approach. But I guess I'm confused as to why we'd end up in that
situation. Suppose we do these two things:
1. Decree that SnapshotResetXmin calls InvalidateCatalogSnapshot. It's
the other way around right now, but that's only because we're
registering the catalog snapshot.
2. Bomb out in GetCatalogSnapshot if you don't have an active or
registered snapshot already.
Is there some reason we'd need any more infrastructure than that?
> Well, we DO have a snapshot, and it is 100% perfectly safe to use, if it's
> registered. 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?
Hmm, that's a good question. I don't know.
--
Robert Haas
EDB: http://www.enterprisedb.com