Re: pg_get_expr locking

Peter Eisentraut <peter@eisentraut.org> writes:
> On 07.02.24 16:26, Tom Lane wrote:
>> Why would a test be applying pg_get_expr to a table it doesn't
>> control?

> I think the situation is that one test (domain) runs pg_get_expr as part 
> of an information_schema view, while at the same time another test 
> (alter_table) drops a table that the pg_get_expr is just processing.

The test case that's failing is, IIUC,

+SELECT * FROM information_schema.domain_constraints
+  WHERE domain_name IN ('con', 'dom', 'pos_int', 'things')
+  ORDER BY constraint_name;

I see no use of pg_get_expr() in the domain_constraints view:

CREATE VIEW domain_constraints AS
    SELECT CAST(current_database() AS sql_identifier) AS constraint_catalog,
           CAST(rs.nspname AS sql_identifier) AS constraint_schema,
           CAST(con.conname AS sql_identifier) AS constraint_name,
           CAST(current_database() AS sql_identifier) AS domain_catalog,
           CAST(n.nspname AS sql_identifier) AS domain_schema,
           CAST(t.typname AS sql_identifier) AS domain_name,
           CAST(CASE WHEN condeferrable THEN 'YES' ELSE 'NO' END
             AS yes_or_no) AS is_deferrable,
           CAST(CASE WHEN condeferred THEN 'YES' ELSE 'NO' END
             AS yes_or_no) AS initially_deferred
    FROM pg_namespace rs, pg_namespace n, pg_constraint con, pg_type t
    WHERE rs.oid = con.connamespace
          AND n.oid = t.typnamespace
          AND t.oid = con.contypid
          AND (pg_has_role(t.typowner, 'USAGE')
               OR has_type_privilege(t.oid, 'USAGE'));

I'm a little suspicious that the failure is actually coming from
somewhere down inside has_type_privilege(), but I traced through
that quickly and don't see how it could reach such an error.
In any case I thought we'd hardened all those functions in 403ac226d.
So I'm still pretty mystified.  Have you had any luck in making
the failure reproducible?

            regards, tom lane