Re: Removing more vacuumlazy.c special cases, relfrozenxid optimizations

Hi,

On 2022-03-30 21:59:15 -0700, Andres Freund wrote:
> On 2022-03-30 21:29:16 -0700, Peter Geoghegan wrote:
> > On Wed, Mar 30, 2022 at 9:20 PM Andres Freund <andres(at)anarazel(dot)de> wrote:
> > > Perhaps we should just fetch the horizons from the "local" catalog for shared
> > > rels?
> >
> > Not sure what you mean.
>
> Basically, instead of relying on the relcache, which for shared relation is
> vulnerable to seeing "too new" horizons due to the shared relcache init file,
> explicitly load relfrozenxid / relminmxid from the the catalog / syscache.
>
> I.e. fetch the relevant pg_class row in heap_vacuum_rel() (using
> SearchSysCache[Copy1](RELID)). And use that to set vacrel->relfrozenxid
> etc. Whereas right now we only fetch the pg_class row in
> vac_update_relstats(), but use the relcache before.

Perhaps we should explicitly mask out parts of relcache entries in the shared
init file that we know to be unreliable. I.e. set relfrozenxid, relminmxid to
Invalid* or such.

I even wonder if we should just generally move those out of the fields we have
in the relcache, not just for shared rels loaded from the init
fork. Presumably by just moving them into the CATALOG_VARLEN ifdef.

The only place that appears to access rd_rel->relfrozenxid outside of DDL is
heap_abort_speculative().

Greetings,

Andres Freund