| From: | Andrei Lepikhov <a(dot)lepikhov(at)postgrespro(dot)ru> |
|---|---|
| To: | Alexander Korotkov <aekorotkov(at)gmail(dot)com>, Alexander Lakhin <exclusion(at)gmail(dot)com>, Richard Guo <guofenglinux(at)gmail(dot)com> |
| Cc: | "Gregory Stark (as CFM)" <stark(dot)cfm(at)gmail(dot)com>, Michał Kłeczek <michal(at)kleczek(dot)org>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: Removing unneeded self joins |
| Date: | 2024-05-02 09:44:54 |
| Message-ID: | 8100af4a-d0aa-450d-a09f-541f26b04ac2@postgrespro.ru |
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| Lists: | pgsql-hackers |
On 5/1/24 18:59, Alexander Korotkov wrote:
> I think we probably could forbid SJE for the tables with TABLESAMPLE
> altogether. Please, check the attached patch.
Your patch looks good to me. I added some comments and test case into
the join.sql.
One question for me is: Do we anticipate other lateral self-references
except the TABLESAMPLE case? Looking into the extract_lateral_references
implementation, I see the only RTE_SUBQUERY case to be afraid of. But we
pull up subqueries before extracting lateral references. So, if we have
a reference to a subquery, it means we will not flatten this subquery
and don't execute SJE. Do we need more code, as you have written in the
first patch?
--
regards,
Andrei Lepikhov
Postgres Professional
| Attachment | Content-Type | Size |
|---|---|---|
| 0001-Forbid-self-join-elimination-on-table-sampling-scans.patch | text/x-patch | 3.7 KB |
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