| From: | Richard Guo <guofenglinux(at)gmail(dot)com> |
|---|---|
| To: | Alexander Korotkov <aekorotkov(at)gmail(dot)com> |
| Cc: | Ranier Vilela <ranier(dot)vf(at)gmail(dot)com>, Alena Rybakina <a(dot)rybakina(at)postgrespro(dot)ru>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Andrei Lepikhov <lepihov(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Alexander Lakhin <exclusion(at)gmail(dot)com>, "Gregory Stark (as CFM)" <stark(dot)cfm(at)gmail(dot)com>, Michał Kłeczek <michal(at)kleczek(dot)org>, Dean Rasheed <dean(dot)a(dot)rasheed(at)gmail(dot)com> |
| Subject: | Re: Removing unneeded self joins |
| Date: | 2025-04-04 02:53:54 |
| Message-ID: | CAMbWs48cO0UUkMT6SbCVyXSx+GvNcjvkEJwt1iDNhT1D2kRPyA@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Fri, Apr 4, 2025 at 1:02 AM Alexander Korotkov <aekorotkov(at)gmail(dot)com> wrote:
> I've got an off-list bug report from Alexander Lakhin involving a
> placeholder variable. Alena and Andrei proposed a fix. It is fairly
> simple: we just shouldn't remove PHVs during self-join elimination, as
> they might still be referenced from other parts of a query. The patch
> is attached. I'm going to fix this if no objections.
Hmm, I'm not sure about the fix. It seems to me that it simply
prevents removing any PHVs in the self-join removal case. My concern
is that this might result in PHVs that could actually be removed not
being removed in many cases.
Besides, there's the specific comment above this code explaining the
logic behind the removal of PHVs. Shouldn't that comment be updated
to reflect the changes?
Thanks
Richard
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