Re: found xmin from before relfrozenxid on pg_catalog.pg_authid

Hi,
We were working on this issue and thinking if we could actually make pg_class(rd_rel) part of recache entry upgradable.
To achieve this we can allocate Form_pg_class structures (for shared relations… a small number) on shared memory.
We do not need global pg_internal_init file as new backend during boot up will be set to point at already stored Form_pg_class structure.

Thanks,
Nishant

On 5/27/18, 1:01 PM, "Andres Freund" <andres(at)anarazel(dot)de> wrote:

Hi,

On 2018-05-27 13:22:21 -0400, Tom Lane wrote:
> But I don't think there's any need for special magic here: we just
> have to accept the fact that there's a need to flush that cache
> sometimes. In normal use it shouldn't happen often enough to be a
> performance problem.

Yea, it's not that problematic. We already remove the local init
file. I started out trying to write a version of invalidation that also
WAL logs shared inval, but that turns out to be hard to do without
breaking compatibilty. So I think we should just always unlink the
shared one - that seems to work well.


> FWIW, I'm not on board with "memcpy the whole row". I think the right
> thing is more like what we do in RelationReloadIndexInfo, ie copy over
> the specific fields that we expect to be mutable.

But that's what RelationReloadIndexInfo() etc do?
relp = (Form_pg_class) GETSTRUCT(pg_class_tuple);
memcpy(relation->rd_rel, relp, CLASS_TUPLE_SIZE);
I don't think we need to modify anything outside of rd_rel at this
point?

I've a patch that seems to work, that mostly needs some comment
polishing.

Greetings,

Andres Freund