I wanted a work-around for the PostgreSQL limitation (Hide unrelated schema/tables structure for a user).
I decided to go with the Row-Level-Security(RLS). The RLS seems working as expected for the user tables but did work for the internal tables such as pg_catalog.pg_namespace.
The screenshot shows the original data in the pg_catalog.pg_namespace table without RLS enbled.
--logged-in as a SUPERUSER(postgres)
SET allow_system_table_mods=on;
ALTER TABLE pg_catalog.pgnamespace ENABLE ROW LEVEL SECURITY;
ALTER TABLE pg_catalog.pg_namespace FORCE ROW LEVEL SECURITY;
REVOKE ALL ON TABLE pg_catalog.pg_namespace FROM public, utkarsh;
GRANT ALL ON TABLE pg_catalog.pg_namespace TO utkarsh;
CREATE POLICY ensure_right_table ON pg_catalog.pg_namespace
FOR ALL
USING ((pg_catalog.pg_namespace.nspacl::text = '{postgres=UC/postgres,utkarsh=UC/postgres}'));
--nspacl is not an unique column.
SET ROLE utkarsh;
SELECT * FROM pg_catalog.pg_namespace;
--I can still see all the rows
