Steve Crawford <scrawford@pinpointresearch.com> writes:
> postgres@[local]=> CLUSTER pg_class USING pg_class_oid_index ;
> ERROR: "pg_class" is a system catalog
I think the DB is probably protecting you from yourself here ;-).
If memory serves there are some system indexes whose relfilenode
numbers can't change, and pg_class_oid_index is one of them. If
the CLUSTER had gone through you'd have hosed that database
irretrievably.
The protection check that is firing here is not so fine-grained as to
know the difference between pg_class and catalogs that this might be
safe for; but it does point up the moral that you need to know exactly
what you're doing if you are going to do DDL stuff on the system
catalogs.
regards, tom lane