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

On Tue, Jan 18, 2022 at 2:34 AM Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>
> 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.

okay

> 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.

I agree with your thought. In my latest patch, postgres db gets
created with a fixed OID.
I have chosen an arbitrary number 16000 as postgres OID from the
unpinned object OID range1200 - 16383.

> 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.

okay

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

The documentation and comment updates are more accurate with the
required details. Thanks.

> 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?

Attached is the patch that implements comment (2).

Shruthi KC
EnterpriseDB: http://www.enterprisedb.com