From: Tom Lane <tgl@sss.pgh.pa.us>
To: "Dirschel, Steve" <steve.dirschel@thomsonreuters.com>
cc: "pgsql-performance@lists.postgresql.org"
 <pgsql-performance@lists.postgresql.org>
Subject: Re: Problem getting query to use index inside a function
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Comments: In-reply-to "Dirschel, Steve" <steve.dirschel@thomsonreuters.com>
	message dated "Wed, 05 Nov 2025 16:02:27 +0000"
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Date: Wed, 05 Nov 2025 11:18:39 -0500
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"Dirschel, Steve" <steve.dirschel@thomsonreuters.com> writes:
> Here is the function I'm having difficulties with:

> CREATE OR REPLACE FUNCTION public.steve1(param_requestid text[], param_p=
roductid integer DEFAULT 1)
> RETURNS TABLE(objectid text, n text, v text, vt integer)
> LANGUAGE sql
> AS $function$
> SELECT       objectid::text
>              , i->>'n'::text
>              , i->>'v'::text
>              , (i->>'vt') :: INT as vt
> FROM   request r
>              , jsonb_array_elements(data -> 'i') i
> WHERE objectid =3D ANY($1)
>              AND productid=3D$2

> $function$
> ;

> Query:

> shared=3D> explain (analyze, buffers)
> shared-> SELECT objectid::text, n::text, v::text, vt::int FROM steve1(AR=
RAY['5ab8e0ca-abb5-48c9-a95e-2bb2a375d903','adcbe251-6723-48a8-8385-55133f=
ab704a'], 1);
>                                                    QUERY PLAN
> ------------------------------------------------------------------------=
----------------------------------------
> Function Scan on steve1  (cost=3D0.25..10.25 rows=3D1000 width=3D100) (a=
ctual time=3D42.694..42.942 rows=3D3368 loops=3D1)

I think you would have better luck if the planner were "inlining"
this function, which we can see it's not since you get a Function Scan
on steve1 rather than the contained query.

I think the only thing stopping that from happening is that the
function is (by default) VOLATILE.  Try marking it STABLE so that
it can share the calling query's snapshot.

(v18 should handle such cases better than previous versions, BTW.
But you'd still be better off marking the function STABLE.)

			regards, tom lane