Define the coupling facility structures attributes in the CFRM function couple data set

This step applies to coupling facility log streams only. DASD-only log streams can omit this step.

Do the following:
  • Determine the attributes needed to define coupling facility structures used by system logger applications.

    See Planning a coupling facility policy to plan updates to the CFRM policy for system logger applications. When planning preference and exclusion list specifications, keep in mind that system logger requires a minimum CFLEVEL. See Understand the requirements for system logger for specific requirements.

    The ALLOWAUTOALT(NO|YES) parameter on a structure definition in the CFRM policy may affect structures used by system logger. Since logger connects to a coupling facility list structure using ALLOWALTER(YES), if you specify ALLOWAUTOALT(YES) on the list structure definition in the CFRM policy, Cross System Extended Services (XES) may automatically alter the size and ratio attributes of the structure as needed. If your coupling facility is size constrained and you must free up some space, you should probably consider other structures for automatic altering first. If you must allow automatic altering of the logger list structure, IBM® suggests that you also specify a minimum size for the logger list structure with the MINSIZE parameter, to ensure that logger always has enough space to do its work.

    The effects associated with the automatic altering of a list structure in use by logger can vary depending on the number of log streams connected to the structure. Consider the following cases:
    • Case 1: A single log stream is connected to the list structure.

      Depending on how your applications use the log stream, you can find that there are long periods when the log stream is relatively empty, followed by peaks of system activity when the log stream quickly approaches its high threshold. If you have specified ALLOWAUTOALT(YES), XES may decide to alter your structure size to a smaller size during a low usage period. When a period of peak usage occurs, write requests to this now smaller structure area for this log stream could result in a structure full condition, meaning there is no more space available in the structure for this log stream. You can avoid this by specifying a sufficient MINSIZE for the list structure.

    • Case 2: Multiple log streams are connected to the list structure.

      In this case, since there is more than one log stream mapped and connected to the list structure, the overall use of the structure space may not be indicative of how any one log stream is performing. For example, assume one log stream in the structure is using most, but not all, of its share of the list structure space, and a second log stream in the same structure is using very little of its share of the list structure space. If automatic monitoring and altering processing is allowed it could reduce this structure's size because the overall use of the list structure space is relatively low. This size reduction could cause the log stream that was using a large portion of its available space to now exceed its available space. Subsequent write requests to this log stream would result in a structure full condition, meaning there is no more space available in the structure for this log stream.

    The “structure full monitoring” function become available in OS/390® V2R9. See Monitoring structure utilization.

    To allow installations to control the monitor level, a new parameter was added to the CFRM policy, FULLTHRESHOLD. Use this parameter to set the utilization value to which XCF is to monitor the structure, with the default value being 80%. Setting FULLTHRESHOLD(0) disables the monitor for that structure. For system logger structures, it is advisable to set FULLTHRESHOLD to some value higher than the HIGHOFFLOAD log stream parameter. XCF, when monitoring the number of ENTRIES and ELEMENTS, will issue a warning message (IXC585E) when the value reaches the FULLTHRESHOLD value. System logger will not perform offload processing until the ELEMENTS value is at the HIGHOFFLOAD value. Note that the HIGHOFFLOAD parameter is on a per log stream basis, while the FULLTHRESHOLD parameter is on a structure basis. For this reason, try to group log streams together that have similar HIGHOFFLOAD values.

  • Add information to the CFRM function couple data set about the desired attributes of the coupling facility list structures for system logger applications. To use the IXCMIAPU utility to update the CFRM policy for logger information, see CFRM parameters for administrative data utility.

    Note that each coupling facility structure that you define in the LOGR policy must match those defined in the CFRM policy. See CFRM parameters for administrative data utility for using IXCMIAPU to update the CFRM policy.

  • Ensure adequate dump space is specified in a CF definition in the CFRM policy that could contain list structures that will be used by the system logger.

    See Determining the amount of coupling facility dump space for setting the DUMPSPACE parameter.

  • Activate the CFRM function couple data set using the SETXCF command.

    See z/OS MVS System Commands for the SETXCF command.