| From: | Richard Guo <guofenglinux(at)gmail(dot)com> |
|---|---|
| To: | Tomas Vondra <tomas(at)vondra(dot)me> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Robert Haas <robertmhaas(at)gmail(dot)com>, Peter Eisentraut <peter(at)eisentraut(dot)org>, David Rowley <dgrowleyml(at)gmail(dot)com>, Tender Wang <tndrwang(at)gmail(dot)com>, Pg Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: Reduce "Var IS [NOT] NULL" quals during constant folding |
| Date: | 2025-07-30 07:55:43 |
| Message-ID: | CAMbWs48QA+SU+8YFXNFg9nt45hvhi9ZHtDvwmz_oktt3Pa24tg@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Wed, Jul 30, 2025 at 3:17 PM Richard Guo <guofenglinux(at)gmail(dot)com> wrote:
> create table t (a int, b int, c int);
>
> explain (costs off)
> select * from t t1
> natural join t t2
> natural join t t3
> natural join t t4
> natural join t t5
> natural join t t6
> natural join t t7
> natural join t t8
> natural join t t9
> natural join t t10
> ;
FWIW, for this query, I've observed that table_open/table_close are
also called for each RTE_RELATION in build_physical_tlist(). Not sure
if we should also be concerned about those calls.
It's not clear to me how much performance impact an extra table_open
might have, especially when the lock is already held, and the relation
is likely present in the relcache.
Thanks
Richard
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