MIME-Version: 1.0
References: <19484-a3cb82c8cde3c8fa@postgresql.org>
 <CAJTYsWXY9C3B-7NZw72OKen2L2rZt=c-t6=kjTJzgj=ZaNPe8g@mail.gmail.com>
 <DIPI7GSQFV1C.20OALZACS6KLI@gmail.com>
 <CA+FpmFc10Dtnr9dr=xqK2cNYQ4-1VuOyvOT7-eqXPmiQJoyPew@mail.gmail.com>
 <DJ4M4TOUHLM0.B38DAVN79FPH@gmail.com>
 <CAJTYsWWUfgCZau2fvrZVruXmC+dyOx45L=TyaGzXdywsywDyHQ@mail.gmail.com>
 <DJ5BM93JVJ7C.MQC43GITCBOY@gmail.com>
 <CA+HiwqHVMY1a5E+6Ei369+RqQ8qKSSgon_C=3yBk-TPJDwZ2nQ@mail.gmail.com>
 <CA+HiwqHjUO0uXFZ2dECJiNime6B1FDL5+mJ=XN+1XgzkY=m9DA@mail.gmail.com>
 <CAPmGK16GNiwcnAxM3XU=ZTOP_8oiv7_FOUwo5hZp8b+qfv2L7g@mail.gmail.com>
 <CA+HiwqEVwEPSE4yMvuwVT5bb+ziMHLfqd_HuiQPAFAixNHbhrQ@mail.gmail.com>
 <CA+HiwqHO0Bbi6cyk4F+UGvZEV3NEo7o0YT3-Js7K7hvasoWBVw@mail.gmail.com>
 <CAPmGK16fALJqbyR1Oir7-TsN8k_yAR-JcOg5nWOUmDmivTmDtA@mail.gmail.com>
 <CAPmGK14Qh_Wb4GNPNkZ1o9=vTcMKShzPNSWa=wNf9vJpg8qT+Q@mail.gmail.com>
 <CA+HiwqHRDsYDqJ-7f5P_QpJo=U1BYzMnfDnNOr6Vx3Rw36O0iQ@mail.gmail.com>
 <CAPmGK15nR_pePb9QAMViq+AGuWeJSqPnLTJVLsr96aU2TFmcmw@mail.gmail.com>
 <CA+HiwqFT0VDOCAdN1bcVZTOF0oBbR4kzLF-OwEcgPOf01me-Kw@mail.gmail.com>
In-Reply-To: 
 <CA+HiwqFT0VDOCAdN1bcVZTOF0oBbR4kzLF-OwEcgPOf01me-Kw@mail.gmail.com>
From: Etsuro Fujita <etsuro.fujita@gmail.com>
Date: Tue, 23 Jun 2026 17:27:39 +0900
Message-ID: 
 <CAPmGK15nx4a_QkTcbD2BwsDuDPtbS25Pzmq_sc-xM4EitoHaxw@mail.gmail.com>
Subject: Re: BUG #19484: Segmentation fault triggered by FDW
To: Amit Langote <amitlangote09@gmail.com>
Cc: Matheus Alcantara <matheusssilv97@gmail.com>,
 Ayush Tiwari <ayushtiwari.slg01@gmail.com>,
	Rafia Sabih <rafia.pghackers@gmail.com>, 798604270@qq.com,
	pgsql-bugs@lists.postgresql.org, Amit Langote <amitlan@postgresql.org>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Archived-At: 
 <https://www.postgresql.org/message-id/CAPmGK15nx4a_QkTcbD2BwsDuDPtbS25Pzmq_sc-xM4EitoHaxw%40mail.gmail.com>
Precedence: bulk

Amit-san,

On Mon, Jun 22, 2026 at 5:28=E2=80=AFPM Amit Langote <amitlangote09@gmail.c=
om> wrote:
> On Fri, Jun 19, 2026 at 8:59=E2=80=AFPM Etsuro Fujita <etsuro.fujita@gmai=
l.com> wrote:

> > +-- Runtime pruning of result relations must keep ModifyTable's per-rel=
ation
> > +-- FDW arrays (fdwPrivLists, fdwDirectModifyPlans) aligned with the ke=
pt
> > +-- resultRelations.  Otherwise BeginForeignModify() reads the wrong
> > +-- fdw_private and segfaults.
> >
> > This comment isn't 100% correct, because this issue happens with
> > DirectModify as well.  I think we could expand the comment to mention
> > that as well, but the comment is already too much/detailed IMO; I
> > don't think we add such a comment for a test case, so how about
> > simplifying the comment like this: "Test that direct modify and
> > foreign modify work with runtime pruning of result relations (bug
> > #19484)"
>
> I agree that the details shouldn't leak into test code and have been
> trying to follow that principle.  Also, bug numbers shouldn't be
> mentioned because one can always use `git blame` to find them.
> However, since different committers have different styles, I'm fine
> with it; kept in the attached updated patch.

Thanks!

> > @@ -1446,6 +1446,12 @@ typedef struct ModifyTableState
> >     int         mt_nrels;       /* number of entries in resultRelInfo[]=
 */
> >     ResultRelInfo *resultRelInfo;   /* info about target relation(s) */
> >
> > +   /*
> > +    * Re-indexed fdw private data lists, aligned with resultRelInfo[] =
after
> > +    * pruning
> > +    */
> > +   List       *mt_fdwPrivLists;
> >
> > For v18, I think we should put this at the end of the ModifyTableState
> > struct, to avoid ABI breakage.
>
> Good point on ABI. Rather than placing it differently per branch, how
> about putting mt_fdwPrivLists at the end of the struct alongside
> mt_updateColnosLists/mt_mergeActionLists/mt_mergeJoinConditions, which
> are the same kind of unpruned-filtered lists? That keeps it ABI-safe
> and lets master and 18 share an identical change. I'd fold it into
> their existing comment too.

That's a good idea!  So +1

> Updated patch attached.

LGTM.

Best regards,
Etsuro Fujita