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VSAM vs. DB2

What's the difference between VSAM and DB2? And why is there a need for converting VSAM to DB2?
VSAM is a file access method. The acronym stands for Virtual Storage Access Method. VSAM offers faster access than flat files because it uses an inverted index (B+tree). The index is used to access the data faster than simply reading every record until the right one is found. For more details comparing DB2 to VSAM, consult an article I wrote on the subject.

As to why one would need to convert from VSAM to DB2, if your application is running fine today and you do not...

have any additional data access or manipulation requirements for the VSAM data, then there is no need to convert the VSAM data to DB2. The predominant reason that people convert to DB2 is to ease data access.

It is much easier to write ad hoc SQL against DB2 tables than it is to code programs that access VSAM files. The time saved by not having to code the VSAM programs can cost justify a conversion of the data to DB2 if your reporting or manipulation needs are varied and frequent. But do not do a simple conversion. By this I mean that the data needs to be analyzed in detail and a logical data model needs to be created. VSAM files quite often are not normalized and do not lend themselves to a "quick and dirty" conversion to DB2 (or any other "relational" DBMS).

This was last published in December 2004

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