Accessing VSAM Data Sets

Using Record-Level Sharing with VSAM

SAS provides support for the record-level sharing (RLS) access feature for VSAM data sets. For the RLS access feature to work, you must define your VSAM clusters as eligible for RLS access.

RLS eligible data sets must be SMS data sets that were defined with a LOG specification. The details of RLS definition, restrictions, and use are contained in the IBM Data Facility Storage Management Subsystem (DFSMS) documentation.

SAS determines whether a VSAM data set is RLS eligible when it opens the data set. If the data set is RLS eligible, SAS automatically opens it in RLS mode. You can override this action by specifying the NRLS option in the INFILE statement that you use to define the data set to be opened. The VSAMRLS system option can be used to specify RLS processing for all VSAM data sets that are accessed during a SAS session. (See VSAMRLS System Option.) Opening the data set in non-RLS mode might generate the following results:

If you are opening the data set for output, then the OPEN operation will fail if another application has the data set open. Alternatively, an attempt to subsequently open the data set by another application will fail while the data set is open in non-RLS output mode by SAS.
If you are opening the data set for input, the OPEN operation will succeed, even though the data set is open by another application, as long as you specify SHAREOPTIONS(2) when you define the VSAM cluster.

The operation of RLS is essentially transparent to users. However, make sure you specify DISP=SHR in the statement that defines the VSAM file you are opening.

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