Sunday, 21 April 2019

A Summary Of The Characteristics Of VSAM Data Set Types | Comparing VSAM Data Set Organizations.


VSAM comparison
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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