Configuring VSAM RLS for impact analysis (Optional, for VSAM RLS only)

About this task

To setup VSAM RLS , two levels of changes are needed: System-level change and VSAM-level change.

Procedure

  1. System-level change
    1. Define Sharing Control Data Set (SHCDS)
    2. Define CF cache structures
    3. Define CF lock structures
    4. SMS definitions
    5. Modifying the PARMLIB IGDSMSxx Member
    Note: The above system configuration changes may require a system administrator, as users may not have access privileges to implement. For more information, refer to Chapter 5.1 of VSAM Demystified (http://www.redbooks.ibm.com/redbooks/SG246105/wwhelp/wwhimpl/java/html/wwhelp.htm).
  2. VSAM-level change
    1. Change LOG parameter. VSAM RLS requires adding LOG parameter to IDCAMS, so the IA administrator needs to alter/define data set as:
      • LOG(UNDO/ALL) : Indicates file is recoverable
      • LOG(NONE) : Indicates file is non-recoverable
    2. Change storage class parameter. VSAM RLS requires RLS data sets must be assigned to a storage class with a cache set defined and must be SMS managed.

Example

The following is an example of how to define a VSAM RLS data set:
DEFINE CLUSTER (NAME(SIBIN.CCZVSAM.BASE) - 
	   INDEXED -                                  
	   CYLINDERS(8 100) -                         
	   LOG(NONE) -                                
	   STORCLAS(NORMALG) -                        
	   DATACLAS(NOCACHE) -                        
	   KEYS(58 0) -                               
	   CISZ(18324) -                              
	   SHR(2 3) -                                 
	   RECORDSIZE(112 112))

What to do next

Some tips on VSAM RLS performance tuning:
  • The minimum cache size is 30M, because XCF needs some room for structures control.
  • RLS_Max_Pool_Size should be 20 percent larger than cache size, because the LRU becomes active after the pool is 80 percent full and starts aging buffers out.
  • False contention is related with lock structure size only. If false contention is high, lock structure size should be increased.
  • For single system, set up a DATACLASS for VSAM RLS and set RLSCFCACHE(NONE) parameter for this data class. This will improve performance.
  • Too large AIX record size will downgrade the VSAM RLS performance.