Top reason why ESDS in VSAM allows duplicate records

An entry-sequenced data set (ESDS) acts like sequential file organization but has the advantages of being under control of VSAM, some use of direct processing, and password facilities.

The ESDS data set is in the sequence in which it is created, and you normally (but not necessarily) process from the start to the end of the data set.

Sequential processing of an ESDS by RBA is known as addressed access, which is the method you use to create the data set. You may also process ESDS records directly by RBA. Since ESDS is not concerned with keys, the data set may legally contain duplicate records.

Assume an ESDS containing records with keys 001, 003, 004, and 006. The data set would appear as follows:

| 001 | 003 | 004 | 006 |

You may want to use ESDS for tables that are to load into programs, for small files that are always in ascending sequence, and for files extracted from a KSDS that are to be sorted.

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Author: Srini

Experienced software developer. Skills in Development, Coding, Testing and Debugging. Good Data analytic skills (Data Warehousing and BI). Also skills in Mainframe.