Re: pg15b2: large objects lost on upgrade

On Sat, Jul 2, 2022 at 11:49 AM Justin Pryzby <pryzby(at)telsasoft(dot)com> wrote:
> I suppose it's like Bruce said, here.
>
> https://www.postgresql.org/message-id/20210601140949.GC22012%40momjian.us

Well, I feel dumb. I remember reading that email back when Bruce sent
it, but it seems that it slipped out of my head between then and when
I committed. I think your patch is fine, except that I think maybe we
should adjust this dump comment:

-- For binary upgrade, set pg_largeobject relfrozenxid, relminmxid and
relfilenode

Perhaps:

-- For binary upgrade, preserve values for pg_largeobject and its index

Listing the exact properties preserved seems less important to me than
mentioning that the second UPDATE statement is for its index --
because if you look at the SQL that's generated, you can see what's
being preserved, but you don't automatically know why there are two
UPDATE statements or what the rows with those OIDs are.

I had a moment of panic this morning where I thought maybe the whole
patch needed to be reverted. I was worried that we might need to
preserve the OID of every system table and index. Otherwise, what
happens if the OID counter in the old cluster wraps around and some
user-created object gets an OID that the system tables are using in
the new cluster? However, I think this can't happen, because when the
OID counter wraps around, it wraps around to 16384, and the
relfilenode values for newly created system tables and indexes are all
less than 16384. So I believe we only need to fix pg_largeobject and
its index, and I think your patch does that.

Anyone else see it differently?

--
Robert Haas
EDB: http://www.enterprisedb.com