Setting the Catalog Control Interval and Area Size

You can specify the control interval sizes, or the catalog can be allowed to select the CISIZE. The BCS is a catalog key-sequenced data set; therefore, the standard control interval and control area calculations are used.

To set a specific control interval size (CISIZE), use one of the following guidelines:

From 512 bytes to 8KB, CISIZE must be specified in multiples of 512 bytes
From 8 kilobytes to 32 kilobytes, CISIZE must be specified in multiples of 2 kilobytes.

Selecting a 4096 or the 8192 byte control interval size provides an acceptable compromise between minimizing data transfer time and reduces the occurrence of a record that spans a control interval. The resulting values for the catalog should be the same as for a key-sequenced data set with spanned records.

Additional considerations include:

For data records less than 1 kilobyte, specify a smaller control interval size (less than 32 768) for the data component. Most of the processing is random and little benefit is gained from larger control interval sizes.
Large or multivolume data records (catalog records larger than the CISIZE) require a second read to obtain the record and this has a direct impact on performance. Specifying a larger control interval size can provide improved performance for catalog-key sequenced data sets with many volumes (or alternate data indices), or Generation Data Groups containing large, multivolume data sets.

For more information on CISIZE considerations, see z/OS DFSMS Using Data Sets z/OS DFSMS Using Data Sets

The control area size for the data component is the smaller of the primary allocation quantity, secondary allocation quantity, or one cylinder.

The control area size is never smaller than a track or greater than one cylinder. It should be large enough to contain a maximum-length record; the default maximum record length for the BCS (a spanned record data set) is 32 400 bytes.

To optimize catalog performance, choose a control area of one cylinder. This can be accomplished if you allocate space in cylinders, or if you specify a number of kilobytes, megabytes, records, or tracks that are one cylinder or larger.

Restriction: If you add entries to a catalog in ascending sequence, it may result in control interval splits. For more information, see z/OS DFSMS Using Data Sets.