| From: | David Rowley <dgrowleyml(at)gmail(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Andres Freund <andres(at)anarazel(dot)de>, Scott Ribe <scott_ribe(at)elevated-dev(dot)com>, PostgreSQL General <pgsql-general(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: bad JIT decision |
| Date: | 2020-07-26 00:04:48 |
| Message-ID: | CAApHDvo+Wxzs8Pb_iPvT64j8vCFsnqQk8qwqvm2h-CLHSS1ahw@mail.gmail.com |
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| Lists: | pgsql-general |
On Sun, 26 Jul 2020 at 02:54, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
> David Rowley <dgrowleyml(at)gmail(dot)com> writes:
> > ... nested at the bottom level join, about 6 joins deep. The lack of
> > any row being found results in upper level joins not having to do
> > anything, and the majority of the plan is (never executed).
>
> On re-reading this, that last point struck me forcibly. If most of
> the plan never gets executed, could we avoid compiling it? That is,
> maybe JIT isn't JIT enough, and we should make compilation happen
> at first use of an expression not during executor startup.
That's interesting. But it would introduce an additional per
evaluation cost of checking if we're doing the first execution.
David
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