Schema of the value map returned by FetcherBase.fetchGroupBys: the derived schema when the
groupBy declares derivations, otherwise the base value schema.
Schema of the value map returned by FetcherBase.fetchGroupBys: the derived schema when the
groupBy declares derivations, otherwise the base value schema. Cached because resolving
derived fields can involve Catalyst, which is far too expensive to redo per request.
(Since version ) see corresponding Javadoc for more information.