Re: pg_plan_advice

On Thu, Mar 19, 2026 at 6:43 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> It would, but it's conceptually ugly and it might make it much harder
> to detangle the cause of a failure, so I don't care for it much.

It does carry that risk. *Typically* failures are going to be a
WARNING message complaining about something related to advice, so the
chance of confusion is perhaps not as high as it would be in some
other cases -- but the grison failure is a counterexample. I'm
somewhat inclined to discount that particular counterexample because
the bug is entirely unrelated to test_plan_advice or pg_plan_advice,
so I am not sure it really would have mattered if we hadn't known that
test_plan_advice was what precipitated it. But there might be other
cases where that isn't so.

> I don't have any great ideas here. Your point about the test having
> helped to find a lot of bugs is compelling, and so is the fact that
> it's seemingly exposing more issues we've not understood yet.
> Maybe we can eventually buy back the cycles by not running it by
> default, but clearly now is not the time for that.

OK, thanks. To be honest, my biggest fear here is not that the test
doesn't have enough value, but that it has a little too much value,
i.e. that we're going to find that future planner improvements require
pg_plan_advice adjustments more often than we're all comfortable with.
Hopefully that fear is unjustified, but we're not going to know for a
while.

--
Robert Haas
EDB: http://www.enterprisedb.com