Re: BUG #18545: \dt breaks transaction, calling error when executed in SET SESSION AUTHORIZATION

This commit seems to trigger elog(), not reproducible in the
parent commit.

6e086fa2e77 Allow parallel workers to cope with a newly-created session user ID.

postgres=# SET min_parallel_table_scan_size=0; CLUSTER pg_attribute USING pg_attribute_relid_attnum_index;
ERROR: pg_attribute catalog is missing 26 attribute(s) for relation OID 70321
postgres=# \errverbose
ERROR: XX000: pg_attribute catalog is missing 26 attribute(s) for relation OID 70321
LOCATION: RelationBuildTupleDesc, relcache.c:658

This is not completely deterministic:

postgres=# CLUSTER pg_attribute USING pg_attribute_relid_attnum_index;
CLUSTER
postgres=# CLUSTER pg_attribute USING pg_attribute_relid_attnum_index;
CLUSTER
postgres=# CLUSTER pg_attribute USING pg_attribute_relid_attnum_index;
CLUSTER
postgres=# CLUSTER pg_attribute USING pg_attribute_relid_attnum_index;
CLUSTER
postgres=# CLUSTER pg_attribute USING pg_attribute_relid_attnum_index;
ERROR: pg_attribute catalog is missing 26 attribute(s) for relation OID 70391

But I think this will be reproducible in any database with a nontrivial
number of attributes.