Re: RFC: Logging plan of the running query

On Fri, Feb 23, 2024 at 10:23 AM Robert Haas <robertmhaas@gmail.com> wrote:
>
> On Fri, Feb 23, 2024 at 7:50 PM Julien Rouhaud <rjuju123@gmail.com> wrote:
> > On Fri, Feb 23, 2024 at 10:22:32AM +0530, Robert Haas wrote:
> > > On Thu, Feb 22, 2024 at 6:25 AM James Coleman <jtc331@gmail.com> wrote:
> > > > This is potentially a bit of a wild idea, but I wonder if having some
> > > > kind of argument to CHECK_FOR_INTERRUPTS() signifying we're in
> > > > "normal" as opposed to "critical" (using that word differently than
> > > > the existing critical sections) would be worth it.
> > >
> > > It's worth considering, but the definition of "normal" vs. "critical"
> > > might be hard to pin down. Or, we might end up with a definition that
> > > is specific to this particular case and not generalizable to others.
> >
> > But it doesn't have to be all or nothing right?  I mean each call could say
> > what the situation is like in their context, like
> > CHECK_FOR_INTERRUPTS(GUARANTEE_NO_HEAVYWEIGHT_LOCK | GUARANTEE_WHATEVER), and
> > slowly tag calls as needed, similarly to how we add already CFI based on users
> > report.
>
> Absolutely. My gut feeling is that it's going to be simpler to pick a
> small number of places that are safe and sufficient for this
> particular feature and add an extra call there, similar to how we do
> vacuum_delay_point(). The reason I think that's likely to be better is
> that it will likely require changing only a relatively small number of
> places. If we instead start annotating CFIs, well, we've got hundreds
> of those. That's a lot more to change, and it also inconveniences
> third-party extension authors and people doing back-patching. I'm not
> here to say it can't work; I just think it's likely not the easiest
> path.

Yes, I suspect it's not the easiest path. I have a small hunch it
might end up paying more dividends in the future: there isn't just one
of these things that is regularly a thorny discussion for the same
reasons each time (basically "no way to trigger this safely from
another backend interrupting another one at an arbitrary point"), and
if we were able to generalize a solution we may have multiple wins (a
very obvious one in my mind is the inability of auto explain to run an
explain at the precise time it's most useful: when statement timeout
fires).

But it's also possible there are simply ways that get us more than
this scenario also, so I might be wrong; it's merely a hunch.

Regards,
James Coleman