Using the TCP listener backlog option

When receiving on TCP/IP, a maximum number of outstanding connection requests is set. These outstanding requests can be considered a backlog of requests waiting on the TCP/IP port for the listener to accept the request.

The default listener backlog value on z/OS® is 255. If the backlog reaches this values, the TCP/IP connection is rejected and the channel is not able to start.

For MCA channels, this results in the channel going into a RETRY state and retrying the connection at a later time.

For client connections, the client receives an MQRC_Q_MGR_NOT_AVAILABLE reason code from MQCONN and can retry the connection at a later time.