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VSAM - What's a LDS (Linear Data Set) and what's it used for?

asked mar August 7, 2014 11:10 AM  

What's a LDS (Linear Data Set) and what's it used for?


1 Answers

answered By Mswami   0  

A Linear data set(LDS) is a VSAM data set with a control interval size of 4096 bytes to 32,768 bytes in increments of 4096 bytes. An LDS has no imbedded control information in its CI, that is, no record definition fields (RDFs) and no control interval definition fields (CIDFs). Therefore, all LDS bytes are data bytes. Logical records must be blocked and unblocked by the application program but logical records do not exist from the point of view of VSAM. 

IDCAMS is used to define a linear data set. An LDS has only a data component.

LDS files are special files used by DB2 and IMS database management systems to store special types of data. They are not generally used on their own for storing business data directly.

LDS is a VSAM dataset in name only. It has unstructured 4k (4096 bytes) fixed size CI¬ís which do not contain control fields and therefore from VSAM's standpoint they do not contain any logical records. There is no free space, and no access from Cobol. Can be accessed by DB2 and IMS fast path datasets. LDS is essentially a table of data maintained on disk. The 'table entries' must be created via a user program and can only be logically accessed via a user program. When passed, the entire LDS must be mapped into storage, and then data is accessed via base and displacement type processing.

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