code: func maxIndexForService(tx *memdb.Txn, serviceName string, serviceExists, checks bool) uint64 {
  	idx, _ := maxIndexAndWatchChForService(tx, serviceName, serviceExists, checks)
  	return idx
  }
docs: // maxIndexForService return the maximum Raft Index for a service
  // If the index is not set for the service, it will return the missing
  // service index.
  // The service_last_extinction is set to the last raft index when a service
  // was unregistered (or 0 if no services were ever unregistered). This
  // allows blocking queries to
  //   * return when the last instance of a service is removed
  //   * block until an instance for this service is available, or another
  //     service is unregistered.