z/OS V1R6.0 DFSMS Access Method Services for Catalogs

DEFINE ALTERNATEINDEXBefore you can assign catalog names for SMS-managed data sets, you musthave access to the RACF STGADMIN.IGG.DIRCAT FACILITY class. See“Storage Management Subsystem (SMS) Considerations” on page 2 for moreinformation.catnameNames the catalog.Abbreviation: CATIf the catalog’s volume is physically mounted, it is dynamically allocated.Mount the volume as permanently resident or reserved.CONTROLINTERVALSIZE(size)Defines the size of the alternate index’s control intervals. This depends on themaximum size of data records, and on the amount of buffer space given.LSR/GSR buffering technique users can ensure buffer pool selection byexplicitly defining data and index control interval sizes.When you do not specify the control interval size, VSAM determines thecontrol interval size. If you have not specified BUFFERSPACE and the size ofyour records permits, VSAM selects the optimum size for the data controlinterval size and 512 bytes for the index control interval size.sizeThe size of the alternate index’s data and index components.Because an alternate index always has the spanned attribute, the controlinterval size can be less than the maximum record length. You can define asize from 512, to 8K in increments of 512 or from 8K to 32K in incrementsof 2K (where K is 1024 in decimal notation). If you use a size that is not amultiple of 512 or 2048, VSAM chooses the next higher multiple.The index control interval should be large enough to accommodate all ofthe compressed keys in a data control area. If the index control intervalsize is too small, unnecessary control area splits can occur. After the firstdefine (DEFINE), a catalog listing ( LISTC ) shows the number of controlintervals in a control area and the key length of the data set. To make ageneral estimate of the index control interval size needed, multiplyone-half of the key length (KEYLEN) by the number of data controlintervals per control area (DATA CI/CA):(KEYLEN/2 ) * DATA CI/CA ≤ INDEX CISIZEFor information about the relationship between control interval size andphysical block size, see z/OS DFSMS: Using Data Sets for the relationshipbetween control interval size and physical block size. This document alsoincludes restrictions that apply to control interval size and physical blocksize.Abbreviations: CISZ or CNVSZDATACLASS(class)The 1 to 8 character name of the data class for the data set. The DATACLASSparameter provides the allocation attributes for new data sets. Your storageadministrator defines the data class. However, you can override the parametersdefined for DATACLASS by explicitly defining other attributes. See “SpecifyingAttribute Selection Order” on page 14 for the order of precedence (filtering) thesystem uses to select which attribute to assign. The record organizationattribute of DATACLASS is not used for DEFINE ALTERNATEINDEX.132 z/OS V1R6.0 DFSMS Access Method Services for Catalogs