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

DEFINE CLUSTERvvvvKEYS shows that the length of the key field is 15 bytes and that the key fieldbegins in the first byte (byte 0) of each data record.RECORDSIZE specifies fixed-length records of 250 bytes.BUFFERSPACE verifies that a minimum of 25 000 bytes must be provided forI/O buffers. A large area for I/O buffers can help to improve access time withcertain types of processing. For example, with direct processing if the high-levelindex can be kept in virtual storage, access time is reduced. With sequentialprocessing, if enough I/O buffers are available, VSAM can perform aread-ahead, thereby reducing system overhead and minimizing rotational delay.FREESPACE specifies that 20% of each control interval and 10% of each controlarea are to be left free when records are loaded into the cluster. After thecluster’s records are loaded, the free space can be used to contain new records.The parameters specified for the index component of VWX.MYDATA are:vvNAME specifies that the index component’s name is VWX.KSINDEX.CATALOG specifies the catalog name.Define a Key-Sequenced Cluster and an Entry-SequencedCluster: Example 4In this example, two VSAM clusters are defined. The first DEFINE commanddefines a key-sequenced VSAM cluster, VWX.EXAMPLE.KSDS1. The secondDEFINE command defines an entry-sequenced VSAM cluster,KLM.EXAMPLE.ESDS1. In both examples, it is assumed that alias names, VWXand KLM, have been defined for user catalogs RSTUCAT1 and RSTUCAT2,respectively.//DEFCLU2 JOB ...//STEP1 EXEC PGM=IDCAMS//SYSPRINT DD SYSOUT=A//SYSIN DD *DEFINE CLUSTER -(NAME(VWX.EXAMPLE.KSDS1) -MODEL(VWX.MYDATA) -VOLUMES(VSER02) -NOIMBED )DEFINE CLUSTER -(NAME(KLM.EXAMPLE.ESDS1) -RECORDS(100 500) -RECORDSIZE(250 250) -VOLUMES(VSER03) -NONINDEXED )/*The first DEFINE command builds a cluster entry, a data entry, and an index entryto define the key-sequenced cluster VWX.EXAMPLE.KSDS1. Its parameters are:vvvNAME specifies the name of the key-sequenced cluster, VWX.EXAMPLE.KSDS1.The cluster is defined in the user catalog for which VWX has been established asan alias.MODEL identifies VWX.MYDATA as the cluster to use as a model forVWX.EXAMPLE.KSDS1. The attributes and specifications of VWX.MYDATA thatare not otherwise specified with the DEFINE command parameters are used todefine the attributes and specifications of VWX.EXAMPLE.KSDS1.VWX.MYDATA is located in the user catalog for which VWX has beenestablished as an alias.VOLUMES specifies that the cluster is to reside on volume VSER02.Chapter 14. DEFINE CLUSTER 169