| From: | Bruce Momjian <bruce(at)momjian(dot)us> |
|---|---|
| To: | Andres Freund <andres(at)anarazel(dot)de> |
| Cc: | pgsql-hackers(at)lists(dot)postgresql(dot)org, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Caching query plan costs |
| Date: | 2018-09-03 22:01:29 |
| Message-ID: | 20180903220129.GG25700@momjian.us |
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| Thread: | |
| Lists: | pgsql-hackers |
On Mon, Sep 3, 2018 at 02:53:59PM -0700, Andres Freund wrote:
> On 2018-09-03 14:56:28 -0400, Bruce Momjian wrote:
> > On Mon, Sep 3, 2018 at 11:42:31AM -0700, Andres Freund wrote:
> > > > and JIT, so it doesn't have to be 100% accurate.
> > >
> > > JIT decision is done after main planning, so we know the cost.
> >
> > Well, as I remember, we are considering disabling JIT in PG 11 because
> > of the use of fixed costs to trigger it. Could executor information
> > help decide to use JIT?
>
> I don't think so. The issues with JIT planning are more that it's
> costing is simplistic (for good-ish reason, to avoid increasing the
> number of plans), and that there's no caching (lots of infrastructure
> work needed).
Uh, yeah, that was my question. If we knew the cost was high before we
plan, could we realistically increase the number of plans to avoid the
cost-trigger issue?
--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com
+ As you are, so once was I. As I am, so you will be. +
+ Ancient Roman grave inscription +
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