Re: ICU locale validation / canonicalization

On Thu, Mar 30, 2023 at 08:59:41AM +0200, Peter Eisentraut wrote:
> On 30.03.23 04:33, Jeff Davis wrote:
> >Attached is a new version of the final patch, which performs
> >canonicalization. I'm not 100% sure that it's wanted, but it still
> >seems like a good idea to get the locales into a standard format in the
> >catalogs, and if a lot more people start using ICU in v16 (because it's
> >the default), then it would be a good time to do it. But perhaps there
> >are risks?
>
> I say, let's do it.

The following is not cause for postgresql.git changes at this time, but I'm
sharing it in case it saves someone else the study effort. Commit ea1db8a
("Canonicalize ICU locale names to language tags.") slowed buildfarm member
hoverfly, but that disappears if I drop debug_parallel_query from its config.
Typical end-to-end duration rose from 2h5m to 2h55m. Most-affected were
installcheck runs, which rose from 11m to 19m. (The "check" stage uses
NO_LOCALE=1, so it changed less.) From profiles, my theory is that each of
the many parallel workers burns notable CPU and I/O opening its ICU collator
for the first time. debug_parallel_query, by design, pursues parallelism
independent of cost, so this is working as intended. If it ever matters in
non-debug configurations, we might raise the default parallel_setup_cost or
pre-load ICU collators in the postmaster.