The ClickHouse service type in ClickHouse's own terms: databases, their tables and the tables' columns, and the server as a whole, with access types that map to ClickHouse's privileges, and row filters that become ClickHouse row policies. Lookups read the system tables through ClickHouse's own Java client over HTTP, from one server or the next when one cannot be reached, signing in with a password or a TLS client certificate. Packaged as a plugin directory ...