Characteristics Of VSAM Data Set Types |
I hope you have gone through my previous tutorial regarding VSAM terminology and concept. As you are already aware that there are 4 types of VSAM cluster/data sets i.e. KSDS, ESDS, LDS, RRDS.
In this tutorial, I have tried to compare the characteristics of the VSAM data set (i.e. ESDS, KSDS, RRDS, VRRDS).
This comparison of the VSAM data set organization would help you to understand the difference of each cluster.
The table provides a summary of the characteristics of VSAM data set types.
ESDS | KSDS | Fixed-length RRDS | Variable-length RRDS | Linear data sets |
Records are in the same order as they are entered | Records are in collating sequence by key field after load | Records are in relative record number order | Records are in relative record number order | No processing at a record level |
Records can be fixed or variable length | Records can be fixed or variable length | Records are fixed length | Records are variable length | No processing at a record level |
Direct access by RBA | Direct access by key or by RBA | Direct access by relative record number | Direct access by relative record number | Access with Data-In-Virtual (DIV) optionally |
Consist of a data component only | Consist of data and index components | Consist of a data component only | Consist of data and index components | Consist of a data component only |
Alternate index allowed | Alternate indexes allowed | No alternate index allowed | No alternate index allowed | No alternate index allowed |
A record’s RBA cannot change | A record’s RBA can change | A record’s relative record number cannot change | A record’s relative record number cannot change | No processing at a record level |
Space at the end of the data set is used for adding records | Free space is used for inserting and lengthening records | Empty slots in the data set are used for adding records | Free space is used for inserting and lengthening records | No processing at a record level |
A record cannot be deleted, but you can reuse its space for a record of the same length | Space that is given up by a deleted or shortened record becomes free space | A slot that is given up by a deleted record can be reused | Space that is given up by a deleted or shortened record becomes free space | No processing at a record level |
Spanned records allowed | Spanned records allowed | No spanned records | No spanned records | No spanned records |
Extended format allowed | Extended format or compression allowed | Extended format allowed | Extended format allowed | Extended format allowed |
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