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TCP/IP connection limits

On any platform, there is a limit to the number of outstanding connection requests that can be queued at a single TCP/IP port. This is not the same as the maximum number of clients we can attach to a WebSphere MQ server. We can connect more clients to a server, up to the level determined by the server system resources. The backlog values for connection requests are shown in the following table:

Table 12. Maximum outstanding connection requests queued at a TCP/IP port

Server platform	Maximum connection requests
AIX	100
HP-UX	20
Linux	100
i5/OS	255
Solaris	100
Windows Server	100
Windows Workstation	100
z/OS	255

If the connection limit is reached, the client receives a return code of MQRC_Q_MGR_NOT_AVAILABLE from the MQCONN call, and an AMQ9202 error in the client error log (var/mqm/AMQERR0n on UNIX systems or amqerr0n.log in the errors subdirectory of the WebSphere MQ client installation on Windows). If the client retries the MQCONN request, it might be successful.

To increase the number of connection requests we can make, and avoid error messages being generated by this limitation, we can have a listener listening on more than one port, or have more than one queue manager.

 

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