This chapter describes how z/OS V2R2 now allows up to 2,000,000 data sets to be open at a time by address spaces while reducing the allocation time for data sets.

Application and data growth often translates into a larger and increased number of DB2 tables to handle the amount of data that is created. In z/OS V2R1, up to 200,000 linear data sets can be kept open at a time by DB2. Some large environments might require an increase in this limit to continue processing increasing workloads.

To increase this limit, z/OS V2R2 now allows up to 2,000,000 data sets to be open at a time by address spaces while reducing the allocation time for data sets.

Several changes were implemented to allocation routines to increase the maximum number of open data sets and enhance allocation times.

Now, all bits in SWA Virtual Addresses (SVAs) are used and redefined to be interpreted as an index and not as an offset. This change directly indexes to the appropriate SWA block address look-up table, which reduces elapsed time to open data sets.

In addition, SWA management infrastructure and the allocation’s SYSDSN management blocks were moved to storage above the bar, which releases space below the bar for application usage.

SYSZTIOT was also updated to shorten exclusive hold time, which improves parallelism.

These changes are automatic and transparent to users. IEFQMREQ and SWAREQ services use the new infrastructure and any program can see improved allocation times, if the following conditions are met:

Functions that are provided in older releases can also be used to improve allocation performance, including S99DASUP and MEMDSENQMGMT.

In a mixed z/OS V2R1 / z/OS V2R2 sysplex environment, customers must ensure that OA45946 and OA46874 are installed on their z/OS V2R1 systems if they intend to use the JES2 INTERPRET=JES function.