func (snap *ZoneSnapshot) GetRecordsForSerial(zone string, serial int) []*endpoint.Endpoint {
	lastSerial, ok := snap.serials[zone]
	if !ok {
		// no mapping
		return nil
	}

	if lastSerial != serial {
		// outdated mapping
		return nil
	}

	endpoints, ok := snap.endpoints[zone]
	if !ok {
		// probably a bug
		return nil
	}

	return endpoints
}
func (snap *ZoneSnapshot) GetRecordsForSerial(zone string, serial int) []*endpoint.Endpoint {
	lastSerial, ok := snap.serials[zone]
	if !ok {
		// no mapping
		return nil
	}

	if lastSerial != serial {
		// outdated mapping
		return nil
	}

	endpoints, ok := snap.endpoints[zone]
	if !ok {
		// probably a bug
		return nil
	}

	return endpoints
}
// GetRecordsForSerial retrieves from memory the last known recordset for the (zone, serial) tuple