For the consoles XCF groups, SYSMCS and SYSMCS2, the length of messages vary. The maximum length of a message is 4K.

The dump analysis elimination (SYSDAE) group issues one message per dump request, whether or not the dump is suppressed. Each message is approximately 400 bytes long.

• RING mode

  For the global resource serialization XCF group, SYSGRS, the most important message to consider is the RSA-message, which holds information about requests for global resources. The RSA-message can contain up to 32K bytes of data. The RSA-message will be sent frequently and will have high performance requirements. (For example, the performance of data base programs and the speed with which access to data sets is granted will depend on the speed with which the RSA-message is processed.) If an alternate serialization method is used, then the performance requirements for global resource serialization signaling are not as critical.

• STAR mode

  Global resource serialization uses the SYSGRS group for QSCAN (GQSCAN and ISGQUERY), global ENQ contention notification, and Enhanced Contention Analysis (ECA) processing. Signals for these functions might be different in size. The maximum size a signal can be is 61K bytes. If more than 61K bytes of data is required to complete the request, the message is split into more than one part.

Global resource serialization also creates the SYSGRS2 XCF group in RING and STAR modes but does not use the SYSGRS2 XCF group in XCF communications. Global resource serialization is used in all sysplex configurations even if a different serialization product is used. Global requests that are managed by GRS must be processed immediately.

The JES3 group uses XCF messages to transport JES3 staging areas between the JES3 XCF group members in the sysplex. Most staging areas are less than 1K in length; however, the JES3 XCF group combines multiple staging areas and transports them in a single message that can be up to 64K bytes long.

The WLM group, SYSWLM, sends a message approximately once every ten seconds. The length of the message depends on the number of service classes defined in the WLM policy definition. It is advantageous, but not critical, for the message to be received at once.

Estimate the size needed as follows: 320 bytes * the number of service class periods (in all service classes) that have a response time or velocity goal.

The message is sent by MVS images running in GOAL mode to other MVS images running in GOAL mode. If you have not yet migrated two systems to GOAL mode, no messages will be sent.

The XCF group, SYSXCF, issues several different kinds of messages:

Signals requesting data from some other system in the sysplex

These signals are typically less than 956 bytes.

Signals responding to such requests

The length of these responding messages depends on the amount of data to be returned. As used by XCF, the response provides information about the members that reside on the system that is asked to gather the data. If the queried group on such system has only one member, the response is typically less than 956 bytes. For groups that have many members, tens of thousands of bytes of data is possible.

Signals issued by a system that voluntarily sends member data to other systems in the sysplex

Such signals are typically less than 956 bytes

Signals issued on behalf of an XCF Client/Server service exploiter

The sizes of these signals are based on the amount of data the exploiter wishes to send.

With current usage, the first three types of signals usually occur infrequently since they are sent in response to the DISPLAY,XCF,GROUP,grpname,memname command. They are also broadcast to the sysplex when an XCF group member is considered stalled. If the stall persists, the signals might reoccur periodically, typically on the order of minutes. If future applications elect to exploit the IXCMG GATHERFROM=OTHER service to collect data from other systems, the frequency, size, and performance requirements can change in response to their usage.

The frequency and size of the Client/Server related signals depend on the usage of the service exploiters.