Allows modification of the structure of system tables as well as certain other risky actions on system tables. This is otherwise not allowed even for superusers. Ill-advised use of this setting can cause irretrievable data loss or seriously corrupt the database system. Only superusers and users with the appropriate
SET privilege can change this setting.
Only available in single-user mode; this setting is for initdb and may be used in the future for upgrade-in-place.