Setting IGDSMSxx PARMLIB values for VSAM RLS data buffering

Use the following keywords in SYS1.PARMLIB member IGDSMSxx to specify the amount and placement of data buffer space for use by VSAM RLS:

RlsAboveTheBarMaxPoolSize(sysname1,value1;sysname2,value2;...) or (ALL,value): Specifies the total size of the buffer pool, in megabytes, to reside above the 2-megabyte bar on each named system or all systems. The system programmer can specify different values for individual systems in the sysplex, or one value that applies to all the systems in the sysplex. Valid values are 0 (the default), or values between 500 megabytes and 2000000 megabytes (2 terabytes).
RlsFixedPoolSize(sysname1,value1;sysname2,value2;...) or (ALL,value): Specifies the total real storage, in megabytes (above or below the 2-gigabyte bar) to be permanently fixed or "pinned" for the use of VSAM RLS data buffers. The default is 0. The system programmer can specify different values for individual systems in the sysplex, or one value that applies to all the systems in the sysplex. If the specified amount is 80% or more of the available real storage, the amount is capped at 80% and a write-to-operator (WTO) message is issued to warn of the limit being reached.
To help determine the amount of real storage to use for VSAM RLS buffering, you can check SMF record Type 42, subtype 19, for the hit ratio for VSAM RLS buffers. A large number of misses indicates a need for more real storage to be pinned for the use of VSAM RLS.

Note: If you have relatively small auxiliary storage size, permanently page-fixing buffers by the RlsFixedPoolSize keyword may require installing additional auxiliary storage. That is because the equivalent number of pages will likely be stolen to auxiliary storage to compensate for the decrease in real storage available for paging due to the permanent page fix.

These values can be changed later by using the SET SMS=xx command with these keywords specified in the IGDSMSxx member, or by using the SETSMS command with the specific keywords to be changed.

As usual, the changed parameters in IGDSMSxx cannot take effect until SET SMS=xx has been issued.

Other than modifying the IGDSMSxx PARMLIB member, the RlsAboveTheBarMaxPoolSize and RlsFixedPoolSize values can also be changed with the SETSMS command.

Note: The changes with SETSMS and SET SMS=xx do not take effect immediately. If the data set has been opened on a system, the SETSMS and SET SMS changes to RlsAboveTheBarMaxPoolSize and RlsFixedPoolSize do not take effect on that system until the SMSVSAM address space is recycled. If the data set has not been opened on that system, the SETSMS and SET SMS changes to the two keywords will take effect when the data set is opened the first time on the system, without the need to recycle SMSVSAM.

For more information about specifying IGDSMSxx parameters, see z/OS MVS Initialization and Tuning Reference. For more information about checking SMF records, seez/OS MVS System Management Facilities (SMF).See z/OS MVS System Commandsfor detailed information on the SET SMS and SETSMS commands.