Re: BUG #19384: Server crash at textout

Hey,

I replaced the `tupDesc_identifier` with a 64-bit signature from its
structure. Stored Datums can detect stale definitions.

On Tue, Jan 20, 2026 at 8:33 PM Pierre Forstmann <pierre(dot)forstmann(at)gmail(dot)com>
wrote:

> I can also reproduce with 18.1.
>
> But if type foo is used in a table, type foo cannot be modified:
> DROP TYPE IF EXISTS foo CASCADE;
> psql:bug4.sql:1: NOTICE: drop cascades to column c of table bar
> DROP TYPE
> DROP TABLE if EXISTS bar CASCADE;
> DROP TABLE
> CREATE TYPE foo AS (a INT, b INT);
> CREATE TYPE
> CREATE TABLE bar(c foo);
> CREATE TABLE
> BEGIN;
> BEGIN
> INSERT into bar SELECT (i, power(2, 30))::foo FROM generate_series(1,10) i;
> INSERT 0 10
> ALTER TYPE foo ALTER ATTRIBUTE b TYPE TEXT;
> psql:bug4.sql:8: ERROR: cannot alter type "foo" because column "bar.c"
> uses it
>
> Should PG allow to modify a type if this type is used to cast a SELECT
> list column in the same transaction ?
>
>
> Le 20/01/2026 à 12:15, Rahila Syed a écrit :
>
> Hi,
>
> On Tue, Jan 20, 2026 at 2:29 PM PG Bug reporting form <
> noreply(at)postgresql(dot)org> wrote:
>
>> The following bug has been logged on the website:
>>
>> Bug reference: 19384
>> Logged by: Yuxiao Guo
>> Email address: dllggyx(at)outlook(dot)com
>> PostgreSQL version: 17.7
>> Operating system: Ubuntu 20.04 x86-64, docker image postgres:17.7
>> Description:
>>
>> Hi, I found a crash in PostgreSQL. Here are the details:
>>
>> PoC:
>> DROP TYPE IF EXISTS foo CASCADE;
>> 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;
>>
>>
>> Stacktrace:
>> #0 0x7ae1c818a00b (gsignal+0xcb)
>> #1 0x7ae1c8169859 (abort+0x12b)
>> #2 0x542fa7 (_ZN11__sanitizer5AbortEv+0x47)
>> #3 0x5414d1 (_ZN11__sanitizer3DieEv+0xc1)
>> #4 0x528a14 (_ZN6__asan19ScopedInErrorReportD2Ev+0x1c4)
>> #5 0x52a5da (_ZN6__asan18ReportGenericErrorEmmmmbmjb+0x5ba)
>> #6 0x523ef6 (__asan_memcpy+0x1d6)
>> #7 0x17772d5 (textout+0x1b5)
>> #8 0x1835834 (OutputFunctionCall+0x174)
>> #9 0x167a568 (record_out+0x828)
>> #10 0x1835834 (OutputFunctionCall+0x174)
>> #11 0x595848 (printtup+0x958)
>> #12 0x1336280 (RunFromStore+0x1d0)
>> #13 0x1333ec0 (PortalRunSelect+0x150)
>> #14 0x133321d (PortalRun+0x51d)
>> #15 0x132f1de (exec_simple_query+0x146e)
>> #16 0x1328627 (PostgresMain+0x2c57)
>> #17 0x13192e4 (BackendMain+0xe4)
>> #18 0x10a26c3 (postmaster_child_launch+0x193)
>> #19 0x10adb91 (ServerLoop+0x4821)
>> #20 0x10a76ec (PostmasterMain+0x241c)
>> #21 0xd5c2b8 (main+0x458)
>> #22 0x7ae1c816b083 (__libc_start_main+0xf3)
>> #23 0x4a9c6e (_start+0x2e)
>>
>>
>>
> This problem is reproducible, also the issue seems to be linked to cursors
> since the type cast with only SELECT statements runs fine.
>
> CREATE TYPE foo AS (a INT, b INT);
> ALTER TYPE foo ALTER ATTRIBUTE b TYPE TEXT;
>
> postgres=# SELECT (i, power(2, 30))::foo FROM
> generate_series(1,10) i;
> row
> -----------------
> (1,1073741824)
> (2,1073741824)
> (3,1073741824)
> (4,1073741824)
> (5,1073741824)
> (6,1073741824)
> (7,1073741824)
> (8,1073741824)
> (9,1073741824)
> (10,1073741824)
> (10 rows)
>
> Also, it happens only if ALTER TYPE to TEXT is run after DECLARING the
> cursor.
>
> Another observation is that when I lower the exponent to 10, the crash no
> longer occurs,
> but the output is different.
>
> CREATE TYPE foo AS (a INT, b INT);
> BEGIN;
> DECLARE c CURSOR FOR SELECT (i, power(2, 10))::foo FROM
> generate_series(1,10) i;
> DECLARE CURSOR
> FETCH c;
> row
> ----------
> (1,1024)
> (1 row)
>
> ALTER TYPE foo ALTER ATTRIBUTE b TYPE TEXT;
> FETCH c;
> row
> ----------
> (2,\x10)
> (1 row)
>
> Thank you,
> Rahila Syed
>
>