PDSE Address Space Tuning

Several initialization parameters in SYS1.PARMLIB member IGDSMSxx can be used to tune the capacity and performance of PDSE processing. One set of parameters allows you to retain directory and member data in memory cache after the close of a PDSE data set. Specifying these parameters can improve performance for programs that repeatedly open, read, and close the same members of a PDSE. Another set of parameters let you specify an amount of 64-bit virtual storage to be used to cache PDSE directory buffers in the PDSE address spaces. Specifying 64-bit virtual storage can help you increase the number of concurrently open PDSE members and avoid possible directory space constraints. The parameters are as follows:

PDSE_BUFFER_BEYOND_CLOSE: For the SMSPDSE address space, specifies that directory and member data be retained in memory cache beyond the last close of each PDSE data set.
PDSE1_BUFFER_BEYOND_CLOSE: For the SMSPDSE1 address space, specifies that directory and member data be retained in memory cache beyond the last close of each PDSE data set.
PDSE_DIRECTORY_STORAGE(nnn|2G): Specifies the number of megabytes (nnnM) or gigabytes (nnnG) of 64-bit virtual storage will be used to cache PDSE directory buffers in the SMSPDSE address space. By default, two gigabytes of 64-bit virtual storage will be used.
PDSE1_DIRECTORY_STORAGE(nnn|2G): Specifies the number of megabytes (nnnM) or gigabytes (nnnG) of 64-bit virtual storage will be used to cache PDSE directory buffers in the SMSPDSE1 address space. By default, two gigabytes of 64-bit virtual storage will be used.

Several initialization parameters in SYS1.PARMLIB member IGDSMSxx can be used specify the size of the hiperspace in megabytes that is used for PDSE member caching for SMSPDSE1 and SMSPDSE.

PDSE1_HSP_SIZE: For the SMSPDSE1 address space, specifies the size of the hiperspace in megabytes that is used for PDSE member caching. You can use the PDSE1_HSP_SIZE parameter to request up to 2047 megabytes for the PDSE1 hiperspace. Or, you can indicate that the hiperspace is not to be created by setting PDSE1_HSP_SIZE to 0. If the hiperspace is not created, the system will not cache PDSE members.
PDSE_HSP_SIZE: For the SMSPDSE address space, specifies the size of the hiperspace in megabytes that is used for PDSE member caching. You can use the PDSE_HSP_SIZE parameter to request up to 2047 megabytes for the PDSE1 hiperspace. Or, you can indicate that the hiperspace is not to be created by setting PDSE_HSP_SIZE to 0. If the hiperspace is not created, the system will not cache PDSE members.

For more information about these initialization parameters, see z/OS MVS Initialization and Tuning Reference.

You can display PDSE caching statistics dynamically, using the DISPLAY SMS,PDSE or DISPLAY SMS,PDSE1 commands with the HSPSTATS and the VSTOR parameters. The HSPSTATS parameter displays information related to the use of member caching in a hiperspace, including the size of the hiperspace, the current LRUTIME value, the current LRUCYCLE value, data sets eligible for caching, and data sets which are in cache. VSTOR displays the current PDSE 64-bit buffer virtual storage utilization. These DISPLAY commands generate a scrollable list on the operator's console showing the current caching statistics. For details, see z/OS MVS System Commands.

Activate the PDSE member-level caching before any caching statistics can be displayed. To activate the PDSE member-level caching, specify the PDSE_HSP_SIZE or PDSE1_HSP_SIZE parameters in the IGDSMSxx member of SYS1.PARMLIB.