When should I use open_conn_lmt?

  Open_conn_lmt limits the total number of connections a Robot may open.
  This includes connection in all states (e.g. idle) and to all servers.
  It may be used to simulate browser or other agent behavior.

  Note when the open connections limit is reached, new transactions will
  be queued waiting for open connection level to go down. If your request
  rate is too high (or open_conn_lmt too low), this will lead to unlimited
  growth of the waiting queue and out of memory sooner or later.
  Wait_xact_lmt parameter may be used to limit waiting queue size.