Why you need RLS?
RLS allows concurrent access in a sysplex to your VSAM data sets at record level, while also
maintaining data integrity.
How RLS works in CICS?
VSAM RLS is a method of accessing your existing VSAM data sets. It allows any number of users within your Parallel Sysplex to share your existing VSAM data sets. It can provide full data integrity (read and write). The serialization is at record level. However, to implement recoverable VSAM data sets the users must have their own backout log, as CICS has.
What happens when you give RLS?
In RLS mode, all VSAM buffers are moved from the CICS or batch jobs address spaces to
one of these locations:
- A 31-bit buffer pool in the SMSVSAM Data Space
- A 64-bit buffer pool in the SMSVSAM Address Space
These buffers are shared between all the address spaces in the same z/OS image.
Also, in RLS mode most of the VSAM control blocks are in the SMSVSAM Data Space,
except for the ACB, RPL, and EXLST.
How RLS works in VSAM?
The RLS data sharing environment is designed to support sharing of VSAM data sets among multiple cloned AORs. With VSAM RLS, you do not need FORs. Each z/OS system contains an SMSVSAM address space that manages locks within a coupling facility. Coupling facility configurations can be highly available. As you no longer have file owning regions, the single point of failure is eliminated. You can also scale by adding z/OS systems to the parallel sysplex, with each new system running an SMSVSAM address space.
What is alternative way we can share a dataset in CICS?
Without VSAM RLS, CICS uses a process that is called function shipping to share data sets
between CICS address spaces (regions). Function shipping is implemented by using a single
CICS region that is called an FOR to own a data set.
All access to the data set is through the corresponding FOR, which is a focal point for VSAM access. The role of the FOR is to provide file access. The CICS transactions run elsewhere in application-owning regions (AORs). These regions run programs which, when they want to access a shared VSAM data set, ship the access request off to the FOR for that data set. They then await the reply from the FOR.