We are upgrading to new release of CICS.
What can be causing this?
This is due to the CPLT task waiting for an open TCBs to become available. The USS option takes up one open TCB so if there are insufficient open TCBs defined the CPLT task will hang. You can confirm this by looking at a CICS SVC dump and checking if the CPLT task waiting on resource DISPATCH OPENPOOL.
Follow this procedure to analyse the dump with IPCS:
VERBEXIT DFHPD670 'JOB=CURRENT,KE=3,DS=1,TR=3'
You need to use the correct DFHPDxxx for the release of CICS you are using. CICS TS 4.2 is CICS 6.7 so you need DFHPD670. DFHPD650 is for CICS TS 3.2.
You also need the CTS420.SDFHLINK in the STEPLIB.
Look for 'KE_TASK Summary' in the report and search for the CPLT task:
You can see above CPLT is task 0020 with an address of 166E0630.
Now find 'DS: TASKS SUMMARY' and look in the KE_TASK column for address 166E0630:
==DS: TASKS SUMMARY
DS_TOKEN KE_TASK T S F P TT RESOURCE RESOURCE_NAME W TIME OF TIMEOUT
This shows the task is waiting on resource DISPATCH OPENPOOL
Increase the value for the MAXOPENTCBS parameter in the CICS DFHSIT.
Alternatively you can specify MAXOPENTCBS in the JCL in the PARM paramerter of the EXEC statement or in the SYSIN data set of the CICS startup.