Defining the Catalog Data Space Cache (COFVLFxx)

Attributes Defined in SYS1.PARMLIB(COFVLFxx)
Catalogs eligible for the catalog data space cache Amount of storage used for the catalog data space cache

The COFVLFxx member of SYS1.PARMLIB determines which catalogs are eligible for the catalog data space (VLF) cache. Tape volume catalogs can be in the VLF cache. The cache is not actually started until you enter the START VLF operator command, which is explained in z/OS MVS System Commands . For an explanation of the catalog data space cache, and how to determine which catalogs should be eligible for data space caching, see Caching Catalogs.

Although the COFVLFxx member can also be used by other components, the discussion here focuses strictly on its use with catalogs. For more information on this SYS1.PARMLIB member, see z/OS MVS Initialization and Tuning Reference.

Besides specifying the catalogs eligible for the catalog data space cache, you can also specify the amount of storage that you will allow VLF to use to cache catalog records.

The syntax of the CLASS statement for defining the catalog data space cache is:

Statement	Keywords
CLASS	NAME(IGGCAS)
	EMAJ(catname)
	[EMAJ(catname)]
	[...]
	MAXVIRT({ 4096\|size})

where:

NAME(IGGCAS)

specifies the class name for the catalog data space cache.

EMAJ(catname)

specifies the name of a catalog eligible for catalog data space caching.

You can include any number of EMAJ parameters on the CLASS statement, but each EMAJ parameter must specify one, and only one, catalog.

Catalogs cached in the catalog data space cache cannot be simultaneously cached in the in-storage catalog. For a complete discussion of caching catalogs, see Caching Catalogs.

MAXVIRT({4096|size})

specifies the maximum virtual storage that VLF can use to cache catalog records. The decimal value is multiplied by 4096 (4K blocks). The minimum value for size is 256 decimal (256 equates to one megabyte). The maximum value for size is 524288 decimal. If you specify a decimal value that is not in the valid range, VLF defaults to 4096 decimal. To determine the optimum size for MAXVIRT, seeEvaluating Catalog Data Space Cache Performance. You can also refer to the z/OS MVS Initialization and Tuning Reference.

For example, the following CLASS statement identifies four catalogs as eligible for catalog data space caching:

CLASS   NAME(IGGCAS)
        EMAJ(USER.ICFCAT.PROJECT1)
        EMAJ(USER.ICFCAT.PROJECT2)
        EMAJ(USER.ICFCAT.PRODUCT1)
        EMAJ(USER.ICFCAT.PRODTEST)
        MAXVIRT(256)

You can monitor and evaluate the performance of the catalog data space cache with the information supplied by the MODIFY REPORT,CACHE operator command. See Monitoring the Catalog Address Space for more information.