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

On Wed, Mar 05, 2025 at 09:35:27AM -0600, Nathan Bossart wrote:
> 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.

Here's another attempt at the patch based on the latest discussion.

--
nathan