Re: BUG #19097: System catalog modifications are allowed by alter

On Wed, Oct 29, 2025 at 4:32 PM PG Bug reporting form
<noreply(at)postgresql(dot)org> wrote:
>
> The following bug has been logged on the website:
>
> Bug reference: 19097
> Logged by: RekGRpth
> Email address: rekgrpth(at)gmail(dot)com
> PostgreSQL version: 18.0
> Operating system: docker alpine
> Description:
>
> ```sql
> create table pg_catalog.t (i int);
> ERROR: permission denied to create "pg_catalog.t"
> DETAIL: System catalog modifications are currently disallowed.
>
> create table t (i int);
> CREATE TABLE
>
> alter table t set schema pg_catalog;
> ALTER TABLE
>
> \dS+ t
> Table "pg_catalog.t"
> Column | Type | Collation | Nullable | Default | Storage | Compression |
> Stats target | Description
> --------+---------+-----------+----------+---------+---------+-------------+--------------+-------------
> i | integer | | | | plain | |
> |
> Replica Identity: NOTHING
> Access method: heap
>
> drop table pg_catalog.t;
> DROP TABLE

Seems like this is intentionally kept like this, here is what comments
in heap_create says. Not sure what's the exact reason for not
allowing it to be created directly and it allowed to move it to
pg_catalog.

/*
* Don't allow creating relations in pg_catalog directly, even though it
* is allowed to move user defined relations there. Semantics with search
* paths including pg_catalog are too confusing for now.
*
* But allow creating indexes on relations in pg_catalog even if
* allow_system_table_mods = off, upper layers already guarantee it's on a
* user defined relation, not a system one.
*/
if (!allow_system_table_mods &&
((IsCatalogNamespace(relnamespace) && relkind != RELKIND_INDEX) ||
IsToastNamespace(relnamespace)) &&
IsNormalProcessingMode())
ereport(ERROR,
(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
errmsg("permission denied to create \"%s.%s\"",
get_namespace_name(relnamespace), relname),
errdetail("System catalog modifications are currently disallowed.")));

--
Regards,
Dilip Kumar
Google