The real challenging point is many VSAM programmers who are working on mainframe projects not aware about these facts.
What are these facts…
The advantages or merits of VSAM access method. It is also called virtual storage access method.
The superior merits (advantages)…
- The retrieval of records is faster because of efficiency organised index. The index is small because of a key compression algorithm used to store and retrieve its records
- Imbedded free space makes insertion of records easy, and datasets therefore requires less re-organization.
- The deletion of records in VSAM unlike that in ISAM means that they are physically deleted, thus allowing the reclaiming of free space within the dataset
- VSAM datasets are device independent
- VSAM catalogs are portable between operating systems
- Records can be accessed randomly by key or by address and also can be accessed by sequentially
The demerits (Disadvantages)
- To take advantage of the partial self-re-organization capabilities of VSAM datasets, free space must deliberately be left. For datasets that are used for read only purposes, no free space is required.
- Except for read-only datasets, the integrity of VSAM datasets in cross system and cross region sharing must be controlled by the user. Data integrity must be a prime consideration in the initial design of applications that will be shared across systems
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