Re: making EXPLAIN extensible

Hi! I agree with your idea to expand the explain.

On 28.02.2025 22:26, Robert Haas wrote:
> 0002 provides hooks that you can use to make your new EXPLAIN options
> actually do something. In particular, this adds a new hook that is
> called once per PlanState node, and a new nook that is called once per
> PlannedStmt. Each is called at an appropriate point for you to tack on
> more output after what EXPLAIN would already produce.
>
> 0003 adds a new contrib module called pg_overexplain, which adds
> EXPLAIN (DEBUG) and EXPLAIN (RANGE_TABLE). I actually think this is
> quite useful for planner hacking, and maybe a few more options would
> be, too. Right now, if you want to see stuff that EXPLAIN doesn't
> clearly show, you have to use SET debug_print_plan = true, and that
> output is so verbose that finding the parts you actually want to see
> is quite difficult. Assuming it gives you the details you need,
> EXPLAIN (RANGE_TABLE) looks way, way better to me, and if we end up
> committing these patches I anticipate using this semi-regularly.
>
>
> There are plenty of debatable things in this patch set, and I mention
> some of them in the commit messages. The hook design in 0002 is a bit
> simplistic and could be made more complex; there's lots of stuff that
> could be added to or removed from 0003, much of which comes down to
> what somebody hacking on the planner would actually want to see. I'm
> happy to bikeshed all of that stuff; this is all quite preliminary and
> I'm not committed to the details. The only thing that would disappoint
> me is if somebody said "this whole idea of making EXPLAIN extensible
> is stupid and pointless and we shouldn't ever do it." I will argue
> against that vociferously. I think even what I have here is enough to
> disprove that hypothesis, but I have a bunch of ideas about how to do
> more. Some of those require additional infrastructure and are best
> proposed with that other infrastructure; some can be done with just
> this, but I ran out of time to code up examples so here is what I have
> got so far.
>
> Hope you like it, sorry if you don't.

while writing the AQO extension [0] we were just adding a hook (we
called it ExplainOnePlan_hook) similar to this one to add a description
for the node used in the plan, in particular its identifier and the
cardinality that is used during query planning. We also added a guc that
allows user to disable this debug information, since it can only be
useful when analyzing a problematic query, but not all the time.
Therefore, I think this work is necessary and needed to provide the
necessary output of additional information about the plan, which may be
necessary for extensions like this.

[0] https://github.com/postgrespro/aqo

--
Regards,
Alena Rybakina
Postgres Professional