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From: Tender Wang <tndrwang@gmail.com>
Date: Thu, 16 Apr 2026 09:45:05 +0800
Message-ID: 
 <CAHewXNmp1s7WOfF+QtSThO304b6XONJzHj_xkUE+xXqUuzkh1A@mail.gmail.com>
Subject: Re: pg_plan_advice
To: Robert Haas <robertmhaas@gmail.com>
Cc: Alexander Lakhin <exclusion@gmail.com>,
 Melanie Plageman <melanieplageman@gmail.com>,
	Nathan Bossart <nathandbossart@gmail.com>, Tom Lane <tgl@sss.pgh.pa.us>,
	Lukas Fittl <lukas@fittl.com>,
 PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>,
	"heikki.linnakangas" <heikki.linnakangas@iki.fi>
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 <https://www.postgresql.org/message-id/CAHewXNmp1s7WOfF%2BQtSThO304b6XONJzHj_xkUE%2BxXqUuzkh1A%40mail.gmail.com>
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Robert Haas <robertmhaas@gmail.com> =E4=BA=8E2026=E5=B9=B44=E6=9C=8816=E6=
=97=A5=E5=91=A8=E5=9B=9B 03:47=E5=86=99=E9=81=93=EF=BC=9A
>
> On Wed, Apr 15, 2026 at 6:30=E2=80=AFAM Tender Wang <tndrwang@gmail.com> =
wrote:
> > In the plan_showdown phase, in pgpa_qf_add_plan_rtis(), we can add 7,
> > 5, and 3 to qf->relids.
> > It seems difficult to add "6" to qf->relids when walking through the
> > plan tree.(Maybe have an easy way, I don't know too much
> > pg_plan_advice related code).
>
> Thanks for looking through this.  sj_unique_rtis is actually not set
> from the plan tree walk, but based on the calls to
> pgpa_join_path_setup that occur during planning, so it makes sense
> that the join RTI crept in there. I'm guessing that this is another
> place that needs a call to pgpa_filter_out_join_relids -- I've had a
> few of those bugs already.
I try a quick fix as follow:
diff --git a/contrib/pg_plan_advice/pgpa_planner.c
b/contrib/pg_plan_advice/pgpa_planner.c
index 72ef3230abc..971f301e950 100644
--- a/contrib/pg_plan_advice/pgpa_planner.c
+++ b/contrib/pg_plan_advice/pgpa_planner.c
@@ -541,6 +541,7 @@ pgpa_join_path_setup(PlannerInfo *root, RelOptInfo *joi=
nrel,
        {
                pgpa_planner_state *pps;
                RelOptInfo *uniquerel;
+               Bitmapset *relids;

                uniquerel =3D jointype =3D=3D JOIN_UNIQUE_OUTER ? outerrel =
: innerrel;
                pps =3D GetPlannerGlobalExtensionState(root->glob,
planner_extension_id);
@@ -562,8 +563,11 @@ pgpa_join_path_setup(PlannerInfo *root,
RelOptInfo *joinrel,
                        oldcontext =3D MemoryContextSwitchTo(pps->mcxt);
                        proot =3D pgpa_planner_get_proot(pps, root);
                        if (!list_member(proot->sj_unique_rels,
uniquerel->relids))
+                       {
+                               relids =3D
pgpa_filter_out_join_relids(uniquerel->relids, root->parse->rtable);
                                proot->sj_unique_rels =3D
lappend(proot->sj_unique_rels,
-
                         bms_copy(uniquerel->relids));
+
                         bms_copy(relids));
+                       }
                        MemoryContextSwitchTo(oldcontext);
                }
        }

postgres=3D# LOAD 'pg_plan_advice';
LOAD
postgres=3D# EXPLAIN (COSTS OFF, PLAN_ADVICE)SELECT 1 FROM t1 WHERE EXISTS
   (SELECT 1 FROM
     (SELECT 1 FROM
       (SELECT 1) LEFT JOIN t2 ON true),
     t2 WHERE a =3D b);
                    QUERY PLAN
---------------------------------------------------
 Hash Join
   Hash Cond: (t1.a =3D t2.b)
   ->  Seq Scan on t1
   ->  Hash
         ->  HashAggregate
               Group Key: t2.b
               ->  Nested Loop
                     ->  Nested Loop Left Join
                           ->  Result
                           ->  Seq Scan on t2 t2_1
                     ->  Materialize
                           ->  Seq Scan on t2
 Generated Plan Advice:
   JOIN_ORDER(t1 ("*RESULT*" t2#2 t2))
   NESTED_LOOP_PLAIN(t2#2)
   NESTED_LOOP_MATERIALIZE(t2)
   HASH_JOIN((t2 t2#2 "*RESULT*"))
   SEQ_SCAN(t1 t2#2 t2)
   SEMIJOIN_UNIQUE((t2 t2#2 "*RESULT*"))
   NO_GATHER(t1 t2 t2#2 "*RESULT*")
(20 rows)


--=20
Thanks,
Tender Wang