Horton

Re: doc: expand note about pg_upgrade's --jobs option

Nathan Bossart <nathandbossart@gmail.com>

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From: Nathan Bossart <nathandbossart@gmail.com>
To: Magnus Hagander <magnus@hagander.net>
Cc: Daniel Gustafsson <daniel@yesql.se>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Date: 2025-03-05T15:35:27Z
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  1. doc: Adjust note about pg_upgrade's --jobs option.

  2. Introduce framework for parallelizing various pg_upgrade tasks.

On Wed, Mar 05, 2025 at 01:52:40PM +0100, Magnus Hagander wrote:
> Another option that I think would also work is to just cut down the details
> to just "The <option>--jobs</option> option allows multiple CPU cores to be
> used".

That's fine with me.  It's probably not particularly actionable
information, anyway.  If anything, IMHO we should make it clear to users
that the parallelization is per-database (except for file transfer, which
is per-tablespace).  If you've just got one big database in the default
tablespace, --jobs won't help.

> I think this is also slightly confusing, but maybe that's a
> non-native-english thing: "a good place to start is the maximum of the
> number of  CPU cores and tablespaces.". Am I supposed to set it to
> max(cpucores, ntablespaces) or to max(cpucores+ntablespaces)?

I've always read it to mean the former.  But I'm not sure that's great
advice.  If you have 8 cores and 100 tablespaces, does it make sense to use
--jobs=100?  Ordinarily, I'd suggest the number of cores as the starting
point.

-- 
nathan