Re: preserving db/ts/relfilenode OIDs across pg_upgrade (was Re: storing an explicit nonce)

On Mon, Jan 17, 2022 at 9:57 AM Shruthi Gowda <gowdashru(at)gmail(dot)com> wrote:
> I have rebased and generated the patches on top of PostgreSQL commit
> ID cf925936ecc031355cd56fbd392ec3180517a110.
> Kindly apply v8-0001-pg_upgrade-Preserve-relfilenodes-and-tablespace-O.patch
> first and then v8-0002-Preserve-database-OIDs-in-pg_upgrade.patch.

OK, so looking over 0002, I noticed a few things:

1. datlastsysoid isn't being used for anything any more. That's not a
defect in your patch, but I've separately proposed to remove it.

2. I realized that the whole idea here depends on not having initdb
create more than one database without a fixed OID. The patch solves
that by nailing down the OID of template0, which is a sufficient
solution. However, I think nailing down the (initial) OID of postgres
as well would be a good idea, just in case somebody in the future
decides to add another system-created database.

3. The changes to gram.y don't do anything. Sure, you've added a new
"OID" token, but nothing generates that token, so it has no effect.
The reason the syntax works is that createdb_opt_name accepts "IDENT",
which means any string that's not in the keyword list (see kwlist.h).
But that's there already, so you don't need to do anything in this
file.

4. I felt that the documentation and comments could be somewhat improved.

Here's an updated version in which I've reverted the changes to gram.y
and tried to improve the comments and documentation. Could you have a
look at implementing (2) above?

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