Re: Should vacuum process config file reload more often

On Mon, Apr 3, 2023 at 3:08 PM Andres Freund <andres(at)anarazel(dot)de> wrote:
> On 2023-04-03 14:43:14 -0400, Tom Lane wrote:
> > Melanie Plageman <melanieplageman(at)gmail(dot)com> writes:
> > > v13 attached with requested updates.
> >
> > I'm afraid I'd not been paying any attention to this discussion,
> > but better late than never. I'm okay with letting autovacuum
> > processes reload config files more often than now. However,
> > I object to allowing ProcessConfigFile to be called from within
> > commands in a normal user backend. The existing semantics are
> > that user backends respond to SIGHUP only at the start of processing
> > a user command, and I'm uncomfortable with suddenly deciding that
> > that can work differently if the command happens to be VACUUM.
> > It seems unprincipled and perhaps actively unsafe.
>
> I think it should be ok in commands like VACUUM that already internally start
> their own transactions, and thus require to be run outside of a transaction
> and at the toplevel. I share your concerns about allowing config reload in
> arbitrary places. While we might want to go there, it would require a lot more
> analysis.

As an alternative for your consideration, attached v14 set implements
the config file reload for autovacuum only (in 0003) and then enables it
for VACUUM and ANALYZE not in a nested transaction command (in 0004).

Previously I had the commits in the reverse order for ease of review (to
separate changes to worker limit balancing logic from config reload
code).

- Melanie