When a user program issues the first command to the cluster database, the user is assigned to an active nucleus in the cluster. All commands from that user are routed to the assigned nucleus until the user issues a close (CL) command. At this point, the user is free to be assigned to another nucleus with the next open (OP) command.

Adabas Parallel Services keeps track of the number of users assigned to each nucleus and assigns new users to nuclei evenly to balance the load.