On 18/10/2023 13:39, Richard Guo wrote:
On Fri, Oct 13, 2023 at 6:18 PM Andrei Lepikhov
<a.lepik...@postgrespro.ru <mailto:a.lepik...@postgrespro.ru>> wrote:
On 23/8/2023 12:37, Richard Guo wrote:
> To fix it we may need to modify RelOptInfos for Path, BitmapHeapPath,
> ForeignPath and CustomPath, and modify IndexOptInfos for
IndexPath. It
> seems that that is not easily done without postponing
reparameterization
> of paths until createplan.c.
>
> Attached is a patch which is v5 + fix for this new issue.
Having looked into the patch for a while, I couldn't answer to myself
for some stupid questions:
Thanks for reviewing this patch! I think these are great questions.
1. If we postpone parameterization until the plan creation, why do we
still copy the path node in the FLAT_COPY_PATH macros? Do we really
need it?
Good point. The NestPath's origin inner path should not be referenced
any more after the reparameterization, so it seems safe to adjust the
path itself, without the need of a flat-copy. I've done that in v8
patch.
2. I see big switches on path nodes. May it be time to create a
path_walker function? I recall some thread where such a suggestion was
declined, but I don't remember why.
I'm not sure. But this seems a separate topic, so maybe it's better to
discuss it separately?
Agree.
3. Clause changing is postponed. Why does it not influence the
calc_joinrel_size_estimate? We will use statistics on the parent table
here. Am I wrong?
Hmm, I think the reparameterization does not change the estimated
size/costs. Quoting the comment
Agree. I have looked at the code and figured it out - you're right. But
it seems strange: maybe I don't understand something. Why not estimate
selectivity for parameterized clauses based on leaf partition statistic,
not the parent one?
--
regards,
Andrey Lepikhov
Postgres Professional
