From: Tom Lane <tgl@sss.pgh.pa.us>
To: Peter Geoghegan <pg@bowt.ie>
cc: David Rowley <dgrowleyml@gmail.com>, Robert Haas <robertmhaas@gmail.com>,
        Julien Rouhaud <rjuju123@gmail.com>,
        Magnus Hagander <magnus@hagander.net>,
        Andres Freund <andres@anarazel.de>,
        Justin Pryzby <pryzby@telsasoft.com>,
        PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: Add parameter jit_warn_above_fraction
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Comments: In-reply-to Peter Geoghegan <pg@bowt.ie>
	message dated "Tue, 29 Mar 2022 13:35:53 -0700"
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Date: Tue, 29 Mar 2022 18:04:32 -0400
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Peter Geoghegan <pg@bowt.ie> writes:
> On Tue, Mar 29, 2022 at 1:06 PM David Rowley <dgrowleyml@gmail.com> wrote:
>> That means that even if the total execution time of a plan was a true
>> reflection of the total estimated plan cost, then the fraction of time
>> spent (as is measured by jit_warn_above_fraction) doing JIT would
>> entirely depend on the number of expressions to compile.   Of course,
>> the planner's not that good, but does that not indicate that the JIT
>> costing should really account for the number of expressions and not
>> just the total plan cost?

> That's a good point.

I think David's questions are sufficiently cogent and difficult
that we should not add jit_warn_above_fraction at this time.
Maybe we'll eventually decide it's the best we can do; but I do
not think we have a problem there that's so pressing that we need
to rush out a partially-baked bandaid.  Especially not at the
tail end of the development cycle, with not much time to gain
experience with it before we ship.

			regards, tom lane