Re: compute_query_id and pg_stat_statements

Greetings,

* Alvaro Herrera (alvherre@alvh.no-ip.org) wrote:
> On 2021-Apr-26, Tom Lane wrote:
> 
> > Stephen Frost <sfrost@snowman.net> writes:
> > > * Magnus Hagander (magnus@hagander.net) wrote:
> > >> Thatäs why I suggested the three value one. Default to a mode where
> > >> it's automatic, which is what the majority is going to want, but have
> > >> a way to explicitly turn it on.
> > 
> > > This is certainly fine with me too, though it seems a bit surprising to
> > > me that we couldn't just figure out what the user actually wants based
> > > on what's installed/running for any given combination.
> > 
> > I'd be on board with having pg_stat_statement's pg_init function do
> > something to adjust the setting, if we can figure out how to do that
> > in a way that's not confusing in itself.  I'm not sure though that
> > the GUC engine offers a good way.
> 
> I think it's straightforward, if we decouple the tri-valued enum used
> for guc.c purposes from a separate boolean that actually enables the
> feature.  GUC sets the boolean to "off" initially when it sees the enum
> as "auto", and then pg_stat_statement's _PG_init modifies it during its
> own startup as needed.
> 
> So the user can turn the GUC off, and then pg_stat_statement does
> nothing and there is no performance drawback; or leave it "auto" and
> it'll only compute query_id if pg_stat_statement is loaded; or leave it
> on if they want the query_id for other purposes.

Yeah, this is more-or-less the same as what I was just proposing in an
email that crossed this one.  Using a separate boolean would certainly
be fine.

Thanks,

Stephen