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From: Ayush Tiwari <ayushtiwari.slg01@gmail.com>
Date: Mon, 27 Apr 2026 17:42:57 +0530
Message-ID: <CAJTYsWU6BxT5T_kqdAhnQncGGj0aCR-P1aKQdxexdd3aW_WdiA@mail.gmail.com>
Subject: Re: BUG #19468: Prevent SIGSEGV on FETCH after ALTER TYPE of cursor rowtype
To: haogangmao@gmail.com, pgsql-bugs@lists.postgresql.org
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Hi,

On Mon, 27 Apr 2026 at 17:03, PG Bug reporting form <noreply@postgresql.org>
wrote:

> The following bug has been logged on the website:
>
> Bug reference:      19468
> Logged by:          HaoGang Mao
> Email address:      haogangmao@gmail.com
> PostgreSQL version: 17.3
> Operating system:   OS: Linux (Docker)
> Description:
>
> Summary:
> PostgreSQL crashes with SIGSEGV when a cursor is open over a composite
> type and the type is modified via ALTER TYPE during the same transaction,
> followed by a second FETCH.
>
> Reproduction steps (minimal):
>   CREATE TYPE foo AS (a INT, b INT);
>   BEGIN;
>   DECLARE c CURSOR FOR
>     SELECT (i, power(2, 30))::foo
>     FROM generate_series(1,10) i;
>   FETCH c;
>   ALTER TYPE foo ALTER ATTRIBUTE b TYPE TEXT;
>   FETCH c;
>   COMMIT;
>
> Expected: Error message (type modified during active cursor)
> Actual:   Server process terminated with signal 11 (Segmentation fault)
>
> Confirmed environment:
>   PostgreSQL 18.3, built from source with --enable-cassert --enable-debug
>   Docker image: sqleek-pg18-debug:18.3
>   Reproduction / stack script: report/postgres/get_stack3.sh
>   Full stack output: report/postgres/crash_stack4.txt
>

Looks the same as [1].

Regards,
Ayush

[1] PostgreSQL: Re: BUG #19466: Server crash (SIGSEGV) when FETCH after
ALTER TYPE during open cursor
<https://www.postgresql.org/message-id/CAJTYsWUJRkCEopx07tSMX8MGcxzf0CJQh3di2XhetquzdiiVOQ%40mail.gmail.com>

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<div dir=3D"ltr"><div>Hi,</div><br><div class=3D"gmail_quote gmail_quote_co=
ntainer"><div dir=3D"ltr" class=3D"gmail_attr">On Mon, 27 Apr 2026 at 17:03=
, PG Bug reporting form &lt;<a href=3D"mailto:noreply@postgresql.org">norep=
ly@postgresql.org</a>&gt; wrote:<br></div><blockquote class=3D"gmail_quote"=
 style=3D"margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);p=
adding-left:1ex">The following bug has been logged on the website:<br>
<br>
Bug reference:=C2=A0 =C2=A0 =C2=A0 19468<br>
Logged by:=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 HaoGang Mao<br>
Email address:=C2=A0 =C2=A0 =C2=A0 <a href=3D"mailto:haogangmao@gmail.com" =
target=3D"_blank">haogangmao@gmail.com</a><br>
PostgreSQL version: 17.3<br>
Operating system:=C2=A0 =C2=A0OS: Linux (Docker)<br>
Description:=C2=A0 =C2=A0 =C2=A0 =C2=A0 <br>
<br>
Summary:<br>
PostgreSQL crashes with SIGSEGV when a cursor is open over a composite<br>
type and the type is modified via ALTER TYPE during the same transaction,<b=
r>
followed by a second FETCH.<br>
<br>
Reproduction steps (minimal):<br>
=C2=A0 CREATE TYPE foo AS (a INT, b INT);<br>
=C2=A0 BEGIN;<br>
=C2=A0 DECLARE c CURSOR FOR<br>
=C2=A0 =C2=A0 SELECT (i, power(2, 30))::foo<br>
=C2=A0 =C2=A0 FROM generate_series(1,10) i;<br>
=C2=A0 FETCH c;<br>
=C2=A0 ALTER TYPE foo ALTER ATTRIBUTE b TYPE TEXT;<br>
=C2=A0 FETCH c;<br>
=C2=A0 COMMIT;<br>
<br>
Expected: Error message (type modified during active cursor)<br>
Actual:=C2=A0 =C2=A0Server process terminated with signal 11 (Segmentation =
fault)<br>
<br>
Confirmed environment:<br>
=C2=A0 PostgreSQL 18.3, built from source with --enable-cassert --enable-de=
bug<br>
=C2=A0 Docker image: sqleek-pg18-debug:18.3<br>
=C2=A0 Reproduction / stack script: report/postgres/get_stack3.sh<br>
=C2=A0 Full stack output: report/postgres/crash_stack4.txt<br></blockquote>=
<div><br></div><div>Looks the same as [1].<br><br>Regards,<br>Ayush<br><br>=
[1]=C2=A0<a href=3D"https://www.postgresql.org/message-id/CAJTYsWUJRkCEopx0=
7tSMX8MGcxzf0CJQh3di2XhetquzdiiVOQ%40mail.gmail.com">PostgreSQL: Re: BUG #1=
9466: Server crash (SIGSEGV) when FETCH after ALTER TYPE during open cursor=
</a></div></div></div>

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