APPC/IMS flood control migration considerations

In IMS 14, the new APPC/IMS flood control function is active by default and the IMS system will take action if the default flood thresholds are reached unless you change the default thresholds or disable the function.

The default thresholds were 5,000 and 1,000,000 in IMS 14. In IMS 15.1 and later versions, the default thresholds are changed to 5,000 and 10,000. If the number of active APPC conversations exceeds the default threshold of 5,000, subsequent APPC requests are queued in 64-bit storage until IMS can accept them for processing. If the number of APPC requests that are queued in 64-bit storage exceeds 10,000, IMS stops all APPC input from z/OS®. When the number of conversations gets close to the flood thresholds, IMS issues warning messages.

You can modify or disable APPC/IMS flood control by specifying the APPCMAXC= parameter in the DFSDCxxx PROCLIB member. To disable the function, specify APPCMAXC=0.

The /DISPLAY ACT command output is modified to include a MAXC= output field that shows the maximum number of APPC conversations that can be active before APPC requests are queued in 64-bit storage.