Re: pg_upgrade and toasted pg_largeobject

On Mon, May 2, 2016 at 12:30 PM, Alvaro Herrera
<alvherre(at)2ndquadrant(dot)com> wrote:
> A customer of ours was unable to pg_upgrade a database, with this error:
>
> old and new databases "postgres" have a mismatched number of relations
> Failure, exiting
>
> After some research, it turned out that pg_largeobject had acquired a
> toast table. After some more research, we determined that it was
> because right after initdb of the old database (months or years prior)
> they moved pg_largeobject to another, slower tablespace, because for
> their case it is very bulky and not used as much as the other data.
> (This requires restarting postmaster with the -O parameter).
>
> While I understand that manual system catalog modifications are frowned
> upon, it seems to me that we should handle this better. The failure is
> very confusing and hard to diagnose, and hard to fix also.

I think that if you use -O, and it breaks something, you get to keep
both pieces. pg_largeobject is a big problem, and we should replace
it with something better. And maybe in the meantime we should support
moving it to a different tablespace. But if it's not officially
supported and you do it anyway, I don't think it's pg_upgrade's job to
cope.

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