| From: | Richard Guo <guofenglinux(at)gmail(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Jian Guo <gjian(at)vmware(dot)com>, Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)com>, Hans Buschmann <buschmann(at)nidsa(dot)net>, "pgsql-hackers(at)lists(dot)postgresql(dot)org" <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Zhenghua Lyu <zlyu(at)vmware(dot)com> |
| Subject: | Re: Wrong rows estimations with joins of CTEs slows queries by more than factor 500 |
| Date: | 2023-11-20 02:42:31 |
| Message-ID: | CAMbWs49gAHeEOn0rpdUUYXryaa60KZ8JKwk1aSERttY9caCYkA@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Fri, Nov 17, 2023 at 11:38 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> That line of argument also leads to the conclusion that it'd be
> okay to expose info about the ordering of the CTE result to the
> upper planner. This patch doesn't do that, and I'm not sufficiently
> excited about the issue to go write some code. But if someone else
> does, I think we shouldn't exclude doing it on the grounds of wanting
> to preserve an optimization fence. The fence is sort of one-way
> in this line of thinking: information can propagate up to the outer
> planner level, but not down into the CTE plan.
In the light of this conclusion, I had a go at propagating the pathkeys
from CTEs up to the outer planner and came up with the attached.
Comments/thoughts?
Thanks
Richard
| Attachment | Content-Type | Size |
|---|---|---|
| v1-0001-Propagate-pathkeys-from-CTEs-up-to-the-outer-query.patch | application/octet-stream | 5.7 KB |
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