Re: pg_upgrade failing for 200+ million Large Objects

On Fri, Jan 05, 2024 at 03:02:34PM -0500, Tom Lane wrote:
> On further reflection, there is a very good reason why it's done like
> that. Because pg_upgrade is doing schema-only dump and restore,
> there's next to no opportunity for parallelism within either pg_dump
> or pg_restore. There's no data-loading steps, and there's no
> index-building either, so the time-consuming stuff that could be
> parallelized just isn't happening in pg_upgrade's usage.
>
> Now it's true that my 0003 patch moves the needle a little bit:
> since it makes BLOB creation (as opposed to loading) parallelizable,
> there'd be some hope for parallel pg_restore doing something useful in
> a database with very many blobs. But it makes no sense to remove the
> existing cross-database parallelism in pursuit of that; you'd make
> many more people unhappy than happy.

I assume the concern is that we'd end up multiplying the effective number
of workers if we parallelized both in-database and cross-database? Would
it be sufficient to make those separately configurable with a note about
the multiplicative effects of setting both? I think it'd be unfortunate if
pg_upgrade completely missed out on this improvement.

--
Nathan Bossart
Amazon Web Services: https://aws.amazon.com