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

For each coupling facility structure associated with a coupling facility log stream or streams, use the AVGBUFSIZE parameter to specify the average log block size that system logger applications will write to log streams associated with the structure. System logger uses AVGBUFSIZE to calculate the initial entry-to-element ratio for a coupling facility structure for a log stream.

System logger only uses the AVGBUFSIZE specified initially to set the entry-to-element ratio for the structure. After that, system logger will automatically manage the entry-to-element ratio for a structure dynamically, based on actual structure usage.

To find the current entry-to-element ratio system logger is using for a structure associated with a log stream, use the REPORT or LIST parameters in the IXCMIAPU utility. See Administrative data utility for information.

See z/OS MVS System Management Facilities (SMF) for details about SMF record type 88.

For a logrec log stream, IBM® suggests an AVGBUFSIZE of 4068.

For an OPERLOG log stream, IBM suggests an AVGBUFSIZE of 508.

If you select a value for AVGBUFSIZE that is different from the actual average block size, structure space will be wasted. If you run out of structure entries for a structure, a structure full condition will result, even if you have many unused elements in the structure. This disruptive condition will cause frequent offload processing for the structure.

IBM suggests that you do not try to manage the entry-to-element ratio for system logger coupling facility structures using the IXLALTER service. System logger will manage the ratio for optimal structure usage; using IXLALTER will just conflict with system logger's entry-to-element ratio.

For more the directory-to-entry ratio see the connection services topic in z/OS MVS Programming: Sysplex Services Guide.