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Use the TCP listener backlog option

 

In TCP, connections are treated incomplete unless three-way handshake takes place between the server and the client. These connections are called outstanding connection requests. A maximum value is set for these outstanding connection requests. This can be considered a backlog of requests waiting on the TCP port for the listener to accept the request. The default listener backlog values are shown in Table 1.

Default outstanding connection requests
Platform Default listener backlog value
AIX V4.2 or later 100
AIX V4.1 10
HP-UX 20
Solaris 100
Linux 100
All others 5

If the backlog reaches the values shown in Table 1, the TCP/IP connection is rejected and the channel will not be 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 should retry the connection at a later time.

However, to avoid this error, we can add an entry in the qm.ini file: 

TCP:
ListenerBacklog = n
This overrides the default maximum number of outstanding requests (see Table 1) for the TCP/IP listener.

Some operating systems support a larger value than the default. If necessary, this can be used to avoid reaching the connection limit.

To run the listener with the backlog option switched on either:

For information about the RUNMQLSR command, see the WebSphere MQ System Administration Guide book. For information about the DEFINE LISTENER command, see the Websphere MQ Script (MQSC) Command Reference.

 

Parent topic:

Receiving on TCP


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