Re: postgres_fdw join pushdown (was Re: Custom/Foreign-Join-APIs)

> > In such a
> > case, which userid should be stored in UserMapping structure?It might
> look
> > like setting GetUserId() as userid in UserMapping is wise, but not
> really.
> > All the foreign tables might have different effective userids, each
> > different from GetUserId() and what GetUserId() would return might have a
> > user mapping different from the effective userids. What userid should
> > UserMapping structure have in that case? I thought, that's why Hanada-san
> > used invalid userid there, so left as it is.
>
> Well, we kind of need to get it right, not just be guessing.
>
> It looks to me as though GetConnection() only uses the user ID as a
> cache lookup key. What it's trying to do is ensure that if user A and
> user B need different user mapping options, we don't use the same
> connection for both. So, actually, passing InvalidOid seems like it's
> not really a problem here. It's arguably more correct than what we've
> been doing up until now, since it means we cache the connection under
> user OID whose options we used, rather than the user OID that asked
> about the options.
>

That means that, right now, for two different local users which use public
user mapping we will be creating two different connections to the foreign
server with the same credentials. That doesn't look good. If we obtained
user mapping using user mapping oid (which will have invalid user id for
public user mapping) and used userid from that structure, we will get rid
of this problem.

>
> --
> Robert Haas
> EnterpriseDB: http://www.enterprisedb.com
> The Enterprise PostgreSQL Company
>

--
Best Wishes,
Ashutosh Bapat
EnterpriseDB Corporation
The Postgres Database Company