Specifying access modes for VSAM files
You can access records in VSAM sequential files only sequentially. You can access records in VSAM indexed and relative files in three ways: sequentially, randomly, or dynamically.
About this task
For sequential access, code ACCESS IS SEQUENTIAL in
the FILE-CONTROL entry. Records in indexed files
are then accessed in the order of the key field selected (either primary
or alternate). Records in relative files are accessed in the order
of the relative record numbers.
For random access, code ACCESS
IS RANDOM in the FILE-CONTROL entry. Records
in indexed files are then accessed according to the value you place
in a key field. Records in relative files are accessed according to
the value you place in the relative key.
For dynamic access, code ACCESS IS DYNAMIC in the FILE-CONTROL
entry. Dynamic access is a mixed sequential-random access in the same program. Using dynamic access,
you can write one program to perform both sequential and random processing, accessing some records
in sequential order and others by their keys. To determine if you want to alter the
COBOL runtime ACCESS IS DYNAMIC logic path, see VSAM dynamic access optional logic path in the Performance Tuning Guide.