Note:  Functions that are provided in older releases can also be used to improve allocation  performance, including S99DASUP and MEMDSENQMGMT. Several measurements were conducted to observe the storage, CPU, and open/close data  set performance effect with Db2 V12 by using z/OS 2.2 on a z13 processor with eight CPs.  The measurements also had MEMDSENQMGT enabled, GRS STAR was used, and  enhanced catalog sharing was enabled. With 20 concurrent SQL jobs that were running to open 200,000 data sets, it took 465  seconds to open all the data sets. The measured total CPU time to open 200,000 data sets  with z/OS 2.2 on z13 processor was 384 seconds. Storage usage peaked at 942.12 MB of  31-bit storage and 1151 MB of 64-bit storage for a total of 2093.12 MB of real storage used. A DSMAX DSNZPARM value of 200,000 is the maximum value allowed in Db2 11 and 12. Using the same workload, DSMAX was changed to 100,000 (by using the  -SET SYSPARM command) to force the closing of 100,000 data sets. It took 6 minutes to close and reopen  those data sets. In update-intensive applications, the wait time for Db2 log write I/O (typically at commit time)  often makes up a significant portion of the transaction latency, especially when disk  synchronous mirroring is enabled. zHyperWrite is designed to speed up the latency of log writes in a synchronous peer-to-peer  remote copy (PPRC) environment. With zHyperWrite enabled, Db2 triggers a log write I/O to  the secondary disk subsystem in parallel to the log write I/O to the primary disk subsystem.  By overlapping the two I/Os (which are run serially without zHyperWrite enabled), a  significant reduction in Db2 log write I/O time is possible. zHyperWrite technology was introduced in the IBM DS8870 7.4 firmware release and  requires corresponding software usage os PTFs for z/OS V2.1 (APARs OA45662, OA45125  and OA44973) and z/OS 2.2 base code. Db2 use of this feature was developed in Db2 12 and  retrofitted back to Db2 10 and Db2 11 and is available through Db2 APAR PI25747. A new  Db2 system parameter REMOTE_COPY_SW_ACCEL is introduced to enable or disable the  zHyperWrite feature.  Although improved active log write performance can result in improved response time for Db2  operations, increased SRB time in the Db2 MSTR address space might be observed because  the extra (Media Manager) I/O requests are handled under MSTR SRB process when  zHyperWrite is enabled. The benefit of zHyperWrite reduces as the distance of replication increases. A number of performance measurements were conducted to evaluate zHyperWrite by using a  workload with concurrent batch inserts triggered by two members of a Db2 data sharing  group. In this environment, PPRC is configured without any distance between the storage  boxes.  122  IBM Db2 12 for z/OS Performance Topics Performance measurements with zHyperWrite  3.8 zHyperWrite  3.7.3 Performance evaluation