BUG #19469: Prevent SIGSEGV on FETCH after ALTER TYPE of cursor rowtype
The following bug has been logged on the website:
Bug reference: 19469
Logged by: HaoGang Mao
Email address: haogangmao@gmail.com
PostgreSQL version: 17.3
Operating system: OS: Linux (Docker)
Description:
An open cursor can continue returning tuples built with the old physical
layout of a named composite type. If that type is changed in the same
transaction (for example ALTER TYPE ... ALTER ATTRIBUTE ... TYPE), a later
FETCH may format the tuple using updated descriptor and output metadata.
Minimal Reproduction SQL:
```sql
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;
```
On 27/04/26 07:53, PG Bug reporting form wrote:
The following bug has been logged on the website:
Bug reference: 19469
Logged by: HaoGang Mao
Email address: haogangmao@gmail.com
PostgreSQL version: 17.3
Operating system: OS: Linux (Docker)
Description:An open cursor can continue returning tuples built with the old physical
layout of a named composite type. If that type is changed in the same
transaction (for example ALTER TYPE ... ALTER ATTRIBUTE ... TYPE), a later
FETCH may format the tuple using updated descriptor and output metadata.Minimal Reproduction SQL:
```sql
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;
```
It looks the same as as [1]/messages/by-id/19466-dc32827173299fd4@postgresql.org and [2]/messages/by-id/19382-4c2060ffee72759b@postgresql.org
[1]: /messages/by-id/19466-dc32827173299fd4@postgresql.org
/messages/by-id/19466-dc32827173299fd4@postgresql.org
[2]: /messages/by-id/19382-4c2060ffee72759b@postgresql.org
/messages/by-id/19382-4c2060ffee72759b@postgresql.org
--
Matheus Alcantara
EDB: https://www.enterprisedb.com