code: static MapKeyLoader.Role assignRole(boolean isPartitionOwner, boolean isMapNamePartition,
                                          boolean isMapNamePartitionFirstReplica) {
          if (isMapNamePartition) {
              if (isPartitionOwner) {
                  // map-name partition owner is the SENDER
                  return MapKeyLoader.Role.SENDER;
              } else {
                  if (isMapNamePartitionFirstReplica) {
                      // first replica of the map-name partition is the SENDER_BACKUP
                      return MapKeyLoader.Role.SENDER_BACKUP;
                  } else {
                      // other replicas of the map-name partition do not have a role
                      return MapKeyLoader.Role.NONE;
                  }
              }
          } else {
              // ordinary partition owners are RECEIVERs, otherwise no role
              return isPartitionOwner ? MapKeyLoader.Role.RECEIVER : MapKeyLoader.Role.NONE;
          }
      }
docs: Returns the role for the map key loader based on the passed parameters.
  The partition owner of the map name partition is the sender.
  The first replica of the map name partition is the sender backup.
  Other partition owners are receivers and other partition replicas do
  not have a role.
  
  @param isPartitionOwner               if this is the partition owner
  @param isMapNamePartition             if this is the partition containing the map name
  @param isMapNamePartitionFirstReplica if this is the first replica for the partition
  containing the map name
  @return the map key loader role