Re: System username in pg_stat_activity

Hi,

On Fri, Jan 12, 2024 at 05:16:53PM +0100, Magnus Hagander wrote:
> On Thu, Jan 11, 2024 at 5:55 PM Bertrand Drouvot
> <bertranddrouvot(dot)pg(at)gmail(dot)com> wrote:
> >
> > I'm wondering if it would make sense to populate it for parallel workers too.
> > I think it's doable thanks to d951052, but I'm not sure it's worth it (one could
> > join based on the leader_pid though). OTOH that would be consistent with
> > how the SYSTEM_USER behaves with parallel workers (it's populated).
>
> I guess one could conceptually argue that "authentication happens int
> he leader". But we do populate it with the other user records, and
> it'd be weird if this one was excluded.
>
> The tricky thing is that pgstat_bestart() is called long before we
> deserialize the data. But from what I can tell it should be safe to
> change it per the attached? That should be AFAICT an extremely short
> window of time longer before we report it, not enough to matter.

Thanks! Yeah, that seems reasonable to me. Also, I think we should remove the
"MyProcPort" test here then (looking at v3):

+ if (MyProcPort && MyClientConnectionInfo.authn_id)
+ strlcpy(lbeentry.st_auth_identity, MyClientConnectionInfo.authn_id, NAMEDATALEN);
+ else
+ MemSet(&lbeentry.st_auth_identity, 0, sizeof(lbeentry.st_auth_identity));

to get the st_auth_identity propagated to the parallel workers.

> >
> > Same remark regarding the parallel workers case +:
> >
> > - Would it be better to use the `name` datatype for auth_identity?
>
> I've been going back and forth. And I think my conclusion is that it's
> not a postgres identifier, so it shouldn't be. See the earlier
> discussion, and for example that that's what we do for cert names when
> SSL is used.

Yeah, Okay let's keep text then.

>
> > - what about "Contains the same value as the identity part in <xref linkend="system-user" />"?

Not sure, but looks like you missed this comment?

> >
> > + /*
> > + * Trust doesn't set_authn_id(), but we still need to store the
> > + * auth_method
> > + */
> > + MyClientConnectionInfo.auth_method = uaTrust;
> >
> > +1, I think it is useful here to provide "trust" and not a NULL value in the
> > context of this patch.
>
> Yeah, that's probably "independently correct", but actually useful here.

+1

> > +# Users with md5 auth should show both auth method and name in pg_stat_activity
> >
> > what about "show both auth method and identity"?
>
> Good spot, yeah, I changed it over to identity everywhere else so it
> should be here as well.

Did you forget to share the new revision (aka v4)? I can only see the
"reorder_parallel_worker_bestart.patch" attached.

Regards,

--
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com