Define a Key-Sequenced Cluster Specifying Data and Index Parameters: Example 3

In this example, a key-sequenced cluster is defined. The DATA and INDEX parameters are specified and the cluster's data and index components are explicitly named. This example assumes that an alias name VWX is defined for the catalog RSTUCAT1. This naming convention causes VWX.MYDATA to be cataloged in RSTUCAT1. 
//DEFCLU1  JOB    ...
//STEP1    EXEC   PGM=IDCAMS
//SYSPRINT DD     SYSOUT=A
//SYSIN    DD     *
    DEFINE CLUSTER -
           (NAME(VWX.MYDATA) -
           VOLUMES(VSER02) -
           RECORDS(1000 500)) -
         DATA -
           (NAME(VWX.KSDATA) -
           KEYS(15 0) -
           RECORDSIZE(250 250) -
           FREESPACE(20 10) -
           BUFFERSPACE(25000)  ) -
         INDEX -
           (NAME(VWX.KSINDEX) -
         CATALOG (RSTUCAT1)
/*
The DEFINE CLUSTER command builds a cluster entry, a data entry, and an index entry to define the key-sequenced cluster VWX.MYDATA. The parameters for the cluster as a whole are:
  • NAME indicates that the cluster's name is VWX.MYDATA.
  • VOLUMES is used when the cluster is to reside on volume VSER02.
  • RECORDS specifies that the cluster's space allocation is 1000 data records. The cluster is extended in increments of 500 records. After the space is allocated, VSAM calculates the amount required for the index and subtracts it from the total.
In addition to the parameters specified for the cluster as a whole, DATA and INDEX parameters specify values and attributes that apply only to the cluster's data or index component. The parameters specified for the data component of VWX.MYDATA are:
  • NAME indicates that the data component's name is VWX.KSDATA.
  • KEYS shows that the length of the key field is 15 bytes and that the key field begins 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 for I/O buffers. A large area for I/O buffers can help to improve access time with certain types of processing. For example, with direct processing if the high-level index can be kept in virtual storage, access time is reduced. With sequential processing, if enough I/O buffers are available, VSAM can perform a read-ahead, thereby reducing system overhead and minimizing rotational delay.
  • FREESPACE specifies that 20% of each control interval and 10% of each control area are to be left free when records are loaded into the cluster. After the cluster'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:
  • NAME specifies that the index component's name is VWX.KSINDEX.
  • CATALOG specifies the catalog name.