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From: Justin Pryzby <pryzby@telsasoft.com>
To: Peter Eisentraut <peter.eisentraut@enterprisedb.com>
Cc: David Rowley <dgrowleyml@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-hackers@postgresql.org, Andres Freund <andres@anarazel.de>
Subject: Re: jit and explain nontext
Date: Sat, 21 Nov 2020 10:26:00 -0600
Message-ID: <20201121162600.GN24784@telsasoft.com> (raw)
In-Reply-To: <e5f51922-a6af-4ada-62fa-a18ca6d0b469@enterprisedb.com>
References: <20201014193859.GS9241@telsasoft.com>
	<CAApHDvpPt=iN=f5gHQSCA073mp5KO46gsEZFgTWc4xbzKshb9g@mail.gmail.com>
	<3643530.1602724513@sss.pgh.pa.us>
	<CAApHDvqK2HAm-BWxgo7=7GG5xERuECwgny+Sxh3iLfXmhR_yBQ@mail.gmail.com>
	<20201015014326.GU9241@telsasoft.com>
	<CAApHDvozf41o7bUyLL42LWwAjqjRuDToeWy-S5jwR4BieM7SYA@mail.gmail.com>
	<20201017192134.GD9241@telsasoft.com>
	<a56f853c-e671-c4b1-7e0e-a1f0a18621e4@enterprisedb.com>
	<20201120161622.GI24784@telsasoft.com>
	<e5f51922-a6af-4ada-62fa-a18ca6d0b469@enterprisedb.com>

On Sat, Nov 21, 2020 at 08:39:11AM +0100, Peter Eisentraut wrote:
> On 2020-11-20 17:16, Justin Pryzby wrote:
> > It matters if it was planned with jit but executed without jit.
> > 
> > postgres=# DEALLOCATE p; SET jit=on; SET jit_above_cost=0; prepare p as select from generate_series(1,9); explain(format yaml) execute p; SET jit=off; explain(format yaml) execute p;
> > 
> > Patched shows this for both explains:
> >     JIT:                              +
> >       Functions: 3                    +
> > 
> > Unpatched shows only in the first case.
> 
> In this context, I don't see the point of this change.  If you set jit=off
> explicitly, then there is no need to clutter the EXPLAIN output with a bunch
> of zeroes about JIT.

I think the idea is that someone should be able to parse the YAML/XML/other
output by writing something like a['JIT']['Functions'] rather than something
like a.get('JIT',{}).get('Functions',0)

The standard seems to be that parameters that can change during execution
should change the *values* in the non-text output, but the *keys* should not
disappear just because (for example) parallel workers weren't available, or
someone (else) turned off jit.  We had discussion about this earlier in the
year:
https://www.postgresql.org/message-id/20200728033622.GC20393@telsasoft.com

(Since it's machine-readable output, Key: 0 is Consistency and Completeness,
not Clutter.)

-- 
Justin





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