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Subject: Re: Fix a server crash problem from pg_get_database_ddl
From: Chao Li <li.evan.chao@gmail.com>
In-Reply-To: 
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Date: Thu, 16 Apr 2026 09:35:39 +0800
Cc: Jack Bonatakis <jack@bonatak.is>,
 pgsql-hackers@lists.postgresql.org
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To: Japin Li <japinli@hotmail.com>
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> On Apr 16, 2026, at 09:23, Japin Li <japinli@hotmail.com> wrote:
>=20
> On Wed, 15 Apr 2026 at 20:44, "Jack Bonatakis" <jack@bonatak.is> =
wrote:
>> I have reproduced this error against the current master:
>>=20
>> ```
>> CREATE TABLESPACE ts1 LOCATION '/workspace/tablespaces/pg_bug_ts1';
>> CREATE DATABASE db1 TABLESPACE ts1;
>> DELETE FROM pg_tablespace WHERE spcname =3D 'ts1';
>> SELECT * FROM pg_get_database_ddl('db1'::regdatabase);
>>=20
>> server closed the connection unexpectedly
>> This probably means the server terminated abnormally
>> before or while processing the request.
>> The connection to the server was lost. Attempting reset: Failed.
>> ```
>> Backend logs show:
>>=20
>> ```
>> [1] LOG:  client backend (PID 15420) was terminated by signal 11: =
Segmentation fault
>> [1] DETAIL:  Failed process was running: SELECT * FROM =
pg_get_database_ddl('db1'::regdatabase);
>> [1] LOG:  terminating any other active server processes
>> ```
>> After applying the patch:
>>=20
>> ```
>> SELECT * FROM pg_get_database_ddl('db1'::regdatabase);
>> ERROR:  tablespace with OID 16393 does not exist
>> HINT:  To recover, try ALTER DATABASE ... SET TABLESPACE ... to a =
valid tablespace.
>> ```
>> and backend logs show:
>>=20
>> ```
>> [56] ERROR:  tablespace with OID 16393 does not exist
>> [56] HINT:  To recover, try ALTER DATABASE ... SET TABLESPACE ... to =
a valid tablespace.
>> [56] STATEMENT:  SELECT * FROM =
pg_get_database_ddl('db1'::regdatabase);
>> ```
>> All tests pass.
>>=20
>> The only note I'd have on the code change is that there is no =
accompanying test. It seems like a TAP test would be
>> reasonable, but I am quite new and will defer to whether you think =
that's the right call or even necessary.=20
>>=20
>> Jack
>=20
> This seems similar to [1]. Could you please confirm?
>=20
> [1] =
https://www.postgresql.org/message-id/CAJTYsWXcd324VELk%3D9KdsfTsua9So3Yex=
qv7N3B23h9zAUD40g%40mail.gmail.com.
>=20
> --=20
> Regards,
> Japin Li
> ChengDu WenWu Information Technology Co., Ltd.
>=20
>=20

Thanks for printing out that. Yes, they are similar.

I agree with what Tom said in [2]:
```
This is not a bug. This is a superuser intentionally breaking
the system by corrupting the catalogs. There are any number
of ways to cause trouble with ill-advised manual updates to a
catalog table. Try, eg, "DELETE FROM pg_proc" (... but not in
a database you care about).
```

So, let me take back this patch.

[2] =
https://www.postgresql.org/message-id/1538113.1768921841@sss.pgh.pa.us

Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/