CICS warm-up and cool-down, facilitated by z/OS Workload Manager health service

With z/OS® Workload Manager (z/OS WLM) health service, you can enable CICS® to have a warm-up process after the end of system initialization to control flow of work into the region until the region is fully ready to receive work. You can also enable CICS to have a cool-down process before system shutdown to limit flow of work into the region.

Benefits

Using the z/OS WLM health service to control flow of work into the CICS region after the completion of system initialization and before CICS shutdown has the following benefits:

A system warm-up process can mitigate problems that might be caused by work flowing into a CICS region just after the completion of system initialization.: Even though message DFHSI1517 signals the end of system initialization, CICS might still not be fully ready to receive or process work. This is because in some cases initialization continues after this message. For example, some bundle-defined resources are being installed asynchronously; so resources such as JVMSERVERs required for some applications have not completed initialization, even though the TCP/IP listener is open and accepting work. This condition might cause transactions to abend. For web services, a pipeline scan might not have completed, so web service requests will fail before the scan completes.
A system warm-up process can be used to control work flowing into CICS when the region is not yet running at optimum performance.
You have flexibility in the control of the warm-up or cool-down process.: The time a CICS region needs to warm up before it is fully healthy depends on the types of applications being processed and the set of resources they employ. You can control the warm-up or cool-down process based on the need of each CICS region.

How to activate and set up the z/OS WLM health service

The z/OS WLM health service is enabled by default. If the service is disabled, to activate this service for a CICS region, you must set the WLMHEALTH system initialization parameter. In WLMHEALTH, you must specify an interval value and a health adjustment value.

When the region is operating, you can change the interval value and health adjustment value by using the SET WLMHEALTH SPI command, CEMT SET WLMHEALTH, the CICSPlex® SM web user interface, or CICS Explorer®.

What happens during CICS warm-up or cool-down

When the z/OS WLM health service is active in a CICS region, CICS informs the z/OS Workload Manager of the health state of the region through the z/OS WLM health value. The health value is an integer in the range 1 - 100. A value of 100 means that the region is fully capable to process work without any health problems whereas 0 means that it cannot process any work.

CICS warm-up process: During early CICS initialization, the region's health value is set to zero. When the DFHSI1517 message is returned, the CICS warm-up process starts. At each interval, CICS calls the z/OS Workload Manager Health (IWM4HLTH) API to increment the region's health value from zero, by a specified adjustment value, until the health value reaches 100.
If the interval value on the WLMHEALTH parameter is set to zero, the health value of the region remains at zero. To initiate a warm-up process for this region, you must change the interval to a non-zero value and set WLMHEALTH open by issuing a SET WLMHEALTH command.
CICS cool-down process: You can initiate a cool-down process by using the SET WLMHEALTH CLOSE command. At each interval, CICS calls the z/OS Workload Manager Health (IWM4HLTH) API to decrement the region's health value from 100, by the specified adjustment value, until the health value is zero.

How use of z/OS WLM health service affects CICS and CICSPlex SM components

The health state of a CICS region affects how favorable the region is a target for connections. CICS and CICSPlex SM components react to the region's health state.

TCP/IP: When TCP/IP is configured to use the WLM health, the health value provided by CICS will feed into the WLM server recommendations to Sysplex Distributor and the TCP/IP port sharing service, affecting when new connections are established with a CICS region in a cluster. For more information, see z/OS Communications Server: IP Configuration Reference and z/OS Communications Server: IP Configuration Guide.
MQMONITOR: Changes in the region's health state might affect when MQMONITORs with attribute AUTOSTART(YES) are started or stopped. When the health value is less than 100, all started MQMONITORs are subject to a throttle limiting the messages that a single MQMONITOR can process. For details, see Effect of z/OS Workload Manager Health service on MQMONITORs.
CICSPlex SM: CICSPlex SM workload distribution use the z/OS WLM health value of the region in the routing algorithm. When CICSPlex SM Workload Manager decides where to route work, a region with a health value of zero is not eligible to receive work, and Workload Manager routes work only to a region with a non-zero health value. The greater the health value, the more favorable the region will be in the routing decision. For details, see Effect of the z/OS WLM health service on CICSPlex SM workload routing.