Using the RLS_MAX_POOL_SIZE parameter to limit local buffer pool size

You can use the RLS_MAX_POOL_SIZE parameter of the IGDSMSxx parmlib member to limit the maximum size of the local buffer pools. The value you specify can be either larger or smaller than the default maximum pool size of 100 MB, but it must be supported with the available real and expanded storage. Although VSAM RLS can in some cases ascertain how much buffer space is supported before paging begins to occur, specifying an RLS_MAX_POOL_SIZE value ensures that the local buffer pool does not grow beyond the value you specify.

If RLS_Max_Pool_Size is greater than 1500M, SMS will pass a value of 9999. The value will then be reset to 1728M. A default upper limit is set and this internal upper limit can be changed.

Tip: In some instances, the local buffer pool might temporarily grow larger than the RLS_MAX_POOL_SIZE value. Setting a RLS_MAX_POOL_SIZE value that is too low might result in unnecessarily degrading the local hit rate.

Recommendation: Initially, set the RLS_MAX_POOL_SIZE value to 50% more than the sum of the local buffers on a single system. The following table illustrates this, assuming that each CICS® FOR is on a separate system:

File Owning Region	LSR pool size	Hiperspace™ pool size	Sum Total	RLS_MAX_POOL_SIZE
FOR_1	20 MB	30 MB	50 MB	75 MB
FOR_2	40 MB	no pool	40 MB	60 MB
FOR_3	30 MB	50 MB	80 MB	120 MB

If you have multiple applications using RLS, the RLS_MAX_POOL_SIZE value needs to take into account the requirements for all of the applications.

You can use the information from the SMF type 42 record with subtype 19 to evaluate the local buffer hit rates for each of the individual systems. Use this information together with the local system paging rates to help you make additional tuning adjustments to the RLS_MAX_POOL_SIZE parameter.