Statements and parameters for COFVLFxx

CLASS

Each group of objects that VLF processes must have a CLASS statement defining it. The CLASS statement indicates that the following parameters define that particular group of objects to VLF.

ALERTAGE(alert_age)

ALERTAGE specifies the age, in seconds, for objects in the specified class. The IBM® Health Checker for z/OS® check IBMVLF, VLF_MAXVIRT uses the ALERTAGE to determine whether objects are being trimmed too rapidly to meet the installation's usage goals for VLF. You can specify an ALERTAGE in the range from 0 (which indicates that the check will find no exceptions for this class) to 99999999.

The default value is ALERTAGE(60).

The higher the ALERTAGE value you specify, the more likely it is that the VLF_MAXVIRT check will issue an exception message. See the check description for VLF_MAXVIRT in IBM Health Checker for z/OS User's Guide for more information.

EDSN(dsn) [VOL(vol)]

For a PDS class, EDSN(dsn) identifies a partitioned data set name whose members are eligible to be the source for VLF objects in the class. The dsn can be 1 to 44 alphanumeric characters, including @, #, $, and periods (.).

You do not need to specify the volume if the cataloged data set is the desired one. If the data set is not cataloged, or if you have multiple data sets with the same name on different volumes, you must specify VOL(vol). Without the volume serial number, an uncataloged data set is not included in the eligible data set name list. The system issues an informational message to the operator identifying any data sets where the system cannot find the catalog entry to extract the volume.

The vol can be any combination of alphanumeric characters, including @, #, and $, or a dash (-).

Multiple occurrences of the same data set name with different volumes is acceptable. However, if duplicate entries of the same data set name and the same volume occur, the system issues an informational message and ignores the redundant information.

Do not use the EDSN parameter and the EMAJ parameter on the same CLASS statement.

EMAJ(majname)

EMAJ identifies an eligible major name (majname) for a non-PDS class, a class that does not have major names and minor names that are related to partitioned data sets and their members. The majname can be 1 to 64 alphanumeric characters except comma (,), blank, or right parenthesis ( ) ); for example EMAJ(LLA).

Do not use the EMAJ parameter and the EDSN parameter on the same CLASS statement.

MAXVIRT(nnnnnn)

MAXVIRT(nnnnnn) is an optional parameter that allows you to specify, in 4 K blocks, the maximum amount of virtual storage that VLF can use to store objects for the class.

The value for n must be a decimal number from 256 through 524288. You can specify up to six digits, including leading zeros. The maximum value is the maximum data space size. If the system cannot obtain the amount of storage that is specified on MAXVIRT, it obtains as much as possible.

VLF trims least frequently used objects when the amount of storage that is used for a class approaches 90 percent of its MAXVIRT value. For example, if the MAXVIRT value of a class is 1024, VLF begins trimming when the objects of the class exceed 921 4-K blocks of storage. By way of trimming, VLF keeps the most frequently used objects in storage. Small amounts of trimming should be considered normal. A continuous large amount of trimming might indicate that VLF effectiveness is constrained. In this case, it might be advisable to address the trimming. To lessen the chance of trimming, specify a large enough value for MAXVIRT. Specifying a MAXVIRT value that is too large can, in some cases, cause high CPU utilization in VLF. The IGGCAS class for CATALOG is one class where caution should be paid to avoid over specifying MAXVIRT.

Note: Subtype 3 of SMF record type 41 can be used to examine any trimming that might be occurring.

If the value for n is not in the valid range, the system uses 16 megabytes (4096 4 K blocks.)

Default: MAXVIRT(4096)

NAME(classname)

NAME(classname) specifies the name of the VLF class. The classname can be one to seven alphanumeric characters including @, #, and $. IBM-supplied VLF class names begin with the letters A through I, for example, NAME(CSVLLA). See the COFVLFxx member of SYS1.SAMPLIB for the IBM-supplied VLF class names. Installation-supplied class names must begin with the letters J-Z or @, #, or $.

NAME(classname) is required on the CLASS statement.