Enterprise COBOL for z/OS, Version 4.2, Programming Guide

By using the VSAM JCL parameter RLS, you can specify record-level sharing with VSAM.
Specifying RLS is the only way to request the RLS mode when running COBOL programs.

Use RLS=CR when consistent read protocols are required, and RLS=NRI when no read integrity protocols are required.
You cannot specify RLS if you allocate your VSAM data set with an environment variable

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