Hiperspace buffering

Multiple VSAM local shared resource pools enhance the benefits provided by Hiperspace buffering.

Hiperspace buffering allows you to extend the buffering of 4K and multiples of 4K buffers to include buffers allocated in expanded storage in addition to the buffers allocated in virtual storage. Using multiple local shared resource pools and Hiperspace buffering allows data sets with certain reference patterns (for example, a primary index data set) to be isolated to a subpool backed by Hiperspace, which reduces the VSAM read I/O activity needed for database processing.

Hiperspace buffering is activated at IMS initialization. In batch systems, you place the necessary control statements in the DFSVSAMP data set. In online systems, you place the control statements in the IMS.PROCLIB data set with the member name DFSVSMnn. Hiperspace buffering is specified for VSAM buffers through one or two optional parameters applied to the VSRBF subpool definition statement.

The total space that you can allocate to a Hiperspace buffer pool is limited to 2 GB. If the number of buffers multiplied by the buffer size exceeds 2 GB, IMS sets the pool size at 2 GB and issues a warning message.