Re: compute_query_id and pg_stat_statements

On Tue, May 11, 2021 at 10:51 AM Julien Rouhaud <rjuju123(at)gmail(dot)com> wrote:
>
> On Tue, May 11, 2021 at 05:41:53PM +0900, Fujii Masao wrote:
> >
> > On 2021/05/11 16:35, Julien Rouhaud wrote:
> > > Anyway, PFA a patch that implement a [off | on | auto] compute_query_id, and
> > > provides a new queryIdWanted() function to let third party plugins inform us
> > > that they want a query id if possible.
> >
> > Thanks!
> >
> >
> > > As it was noted somewhere in that thread, that's a hack on top on the GUC
> > > machinery, so compute_query_id will display "on" rather than "auto" (or "auto
> > > and enabled" or whatever) since GUC isn't designed to handle that behavior.
> >
> > Can't we work around this issue by making queryIdWanted() set another flag like query_id_wanted instead of overwriting compute_query_id? If we do this, query id computation is necessary when "compute_query_id == COMPUTE_QUERY_ID_ON || (compute_query_id == COMPUTE_QUERY_ID_AUTO && query_id_wanted)".
>
> That's exactly what Magnus mentioned :) It's not possible because variable
> aren't inherited on Windows or EXEC_BACKEND. I didn't check but I'm
> assuming that it could work if the other flag was an internal GUC that couldn't
> be set by users, but then we would have some kind of internal flag that would
> have to be documented as "how to check if compute_query_id" is actually enabled
> or not, which doesn't seem like a good idea.

That doesn't fundamentally make it impossible, you just have to add it
to the list of variables being copied over, wouldn't you? See
save_backend_variables()

--
Magnus Hagander
Me: https://www.hagander.net/
Work: https://www.redpill-linpro.com/