On Thu, Mar 06, 2025 at 01:47:34PM -0500, Tom Lane wrote:
> 1. pg_upgrade has made a policy judgement to apply parallelism across
> databases not within a database, ie it will launch concurrent dump/
> restore tasks in different DBs but not authorize any one of them to
> eat multiple CPUs. That needs to be re-thought probably, as I think
> that decision dates to before we had useful parallelism in pg_dump and
> pg_restore. I wonder if we could just rip out pg_upgrade's support
> for DB-level parallelism, which is not terribly pretty anyway, and
> simply pass the -j switch straight to pg_dump and pg_restore.
That would certainly help for clusters with one big database with many LOs
or something, but I worry it would hurt the many database case quite a bit.
Maybe we could add a --jobs-per-db option that indicates how to parallelize
dump/restore. If you set --jobs=8 --jobs-per-db=8, the databases would be
dumped serially, but pg_dump would get -j8. If you set --jobs=8 and
--jobs-per-db=2, we'd process 4 databases at a time, each with -j2.
--
nathan
