Here’s all about access modes in VSAM file. Those are sequential, random and dynamic reads. When to use , in COBOL’ explained in this article.

VSAM File Access Modes

Sequential read

Only sequentially you can read. First you need to give START command to establish a key. Then READ NEXT to get next record and so on.

START file-name 
KEY IS EQUAL TO ALTERNATE-RECORD-KEY

Random read

You can go to any key either forward way or backward way.

Dynamic read

• You can read a record Sequentially and also you can read random record. When a direct READ is performed for a VSAM indexed file, based on an alternate index for which duplicates exist, only the first record in the data set (base cluster) with that alternate key value is retrieved.
• You need a series of READ NEXT statements to retrieve each of the data set records with the same alternate key.

File status codes

A file status code of 02 is returned if there are more records with the same alternate key value to be read; a code of 00 is returned when the last record with that key value has been read.

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