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Specifying a larger value for MAXSOCKETS than MXT in the CICS SIT

Technote (FAQ)


Since the maximum task specification (MXT) limits the number of active user tasks you can have in a CICS Transaction Server for z/OS (CICS TS) region, why would you want to specify the maximum number of ip sockets (MAXSOCKETS) as a higher value than MXT? Should you specify a value for MAXSOCKETS more like TCLASS, that is as a 'subset' of MXT?


When you define a TCPIPSERVICE for HTTP, you should either specify SOCKETCLOSE(NO) or some length of time. That allows the HTTP sessions to be persistent which saves the overhead of setting up a new socket for the next request. This is particularly important if SSL is being used. But, you are afraid that the CWXN transactions will remain in the CICS region and cause the region to go MXT.


No, the system initialization table (SIT) parameter MAXSOCKETS should not be a subset of MXT. While CICS is waiting for the next request there is no transaction running apart from the CSOL listener associated with the socket. When the next request comes in the listener attaches a CWXN transaction to process it. Depending on the setting of SOCKETCLOSE there could be many more sockets open than the MXT.

Prior to CICS TS 3.1, the CWXN transaction would remain in the CICS region for the duration of the persistent session as document in section Changes to CICS-supplied transactions of the CICS TS 3.1 information center:

Before CICS Transaction Server for z/OS, Version 3 Release 1, if a Web client and CICS had a persistent connection, the CWXN transaction would remain in the system for the duration of the persistent connection. Now, the CWXN transaction terminates after each request from the Web client has been passed to the alias transaction (CWBA or another transaction), or after the static response has been delivered. The Sockets listener task monitors the socket and initiates a new instance of CWXN for each request on the persistent connection. This behavior, known as an asynchronous receive, avoids the possibility of a deadlock in a situation where the maximum task specification (MXT) has been reached. It also means that the maximum number of concurrent connections between CICS and Web clients is no longer limited by the MXT value, but can in theory be up to 64000. In terms of system activity, if you used persistent connections before CICS Transaction Server for z/OS, Version 3 Release 1, you should now see an increased transaction rate, but a decrease in the number of concurrent tasks.

Related information

How CICS support handles persistent sessions

Product Alias/Synonym

CICS/TS CICS TS CICS Transaction Server

Document information

More support for: CICS Transaction Server

Software version: 3.1, 3.2, 4.1, 4.2

Operating system(s): z/OS

Reference #: 1596250

Modified date: 28 May 2012