| From: | Richard Guo <guofenglinux(at)gmail(dot)com> |
|---|---|
| To: | Ashutosh Bapat <ashutosh(dot)bapat(dot)oss(at)gmail(dot)com> |
| Cc: | Jakub Wartak <jakub(dot)wartak(at)enterprisedb(dot)com>, Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)com>, Zhihong Yu <zyu(at)yugabyte(dot)com>, arne(dot)roland(at)malkut(dot)net, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Julien Rouhaud <rjuju123(at)gmail(dot)com>, Etsuro Fujita <etsuro(dot)fujita(at)gmail(dot)com> |
| Subject: | Re: apply_scanjoin_target_to_paths and partitionwise join |
| Date: | 2024-07-24 04:12:13 |
| Message-ID: | CAMbWs48U9EqUtaDeC0dAbQgFTd_L0Zazfv5L2Y1__O=PE+TwsQ@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Wed, May 22, 2024 at 3:57 PM Ashutosh Bapat
<ashutosh(dot)bapat(dot)oss(at)gmail(dot)com> wrote:
> I will create patches for the back-branches once the patch for master is in a committable state.
AFAIU, this patch prevents apply_scanjoin_target_to_paths() from
discarding old paths of partitioned joinrels. Therefore, we can
retain non-partitionwise join paths if the cheapest path happens to be
among them.
One concern from me is that if the cheapest path of a joinrel is a
partitionwise join path, following this approach could lead to
undesirable cross-platform plan variations, as detailed in the
original comment.
Is there a specific query that demonstrates benefits from this change?
I'm curious about scenarios where a partitionwise join runs slower
than a non-partitionwise join.
Thanks
Richard
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