Count effective classes without walking a large source bucket for a small
edit set. A caller-supplied source domain is counted through the canonical
iterator instead (for example IFCX, whose STEP type index is empty).
Source classes with no surviving records retain a zero row.
Count effective classes without walking a large source bucket for a small edit set. A caller-supplied source domain is counted through the canonical iterator instead (for example IFCX, whose STEP type index is empty). Source classes with no surviving records retain a zero row.