A DB2 performance enhancement shipped with z/OS that is often overlooked is the setting for USEZOSV1R9RULES.
It changes the memory allocation algorithm and is advertised as being helpful particularly for large DB2 shops.
If you go to the z/OS operator's console and issue D DIAG you'll probably get an answer that looks like this:
IGV007I 15.43.25 DIAG DISPLAY
VSM TRACK CSA(ON) SQA(ON)
VSM TRACE GET(OFF) FREE(OFF)
VSM ALLOWUSERKEYCSA(NO)
VSM BESTFITCSA(NO)
VSM USEZOSV1R9RULES(YES)
TRAPS NAME()
CBLOC
VIRTUAL24()
VIRTUAL31()
REUSASID(YES)
AUTOIPL SADMP(NONE) MVS(NONE)
Note the USEZOSV1R9RULES setting --- YES is the default.
I'm not going to go into an explanation - google and you'll find out all you need to know.
--- HOWEVER ---
There is risk with this setting. The reason the default is the old way of memory allocation is because some programs are not well-behaved.
For example, this APAR for Netview Distribution Manager:
PI20869 NetView Distribution Manager
FOR Z/OS 1.10 AND HIGHER, USEZOSV1R9RULES(YES) IN SYSTEM PARMLIB
DIAGXX MEMBER IS REQUIRED
ERROR DESCRIPTION:
The NvDM code needs to have storage allocated in the way
that the USEZOSV1R9RULES(YES) parameter does - this value is
the default value. USEZOSV1R9RULES(NO) must not be coded or
abends or other problems may occur.
To document this restriction, the following change will be
made to the Tivoli NetView Distribution Manager for MVS IBM
Installation and Customizationmanual ( Release 7 SH19-6794-06 )
in appendix A (Installation Requirements):
After the sentence which ends with "see the target
system requirements specification in the NetView DM for MVS Base
ProgramDirectory." add the following:
.
Note: For z/OS 1.10 and higher, the DIAGxx parameter
USEZOSV1R9RULES(YES) is required. This is the default value.
Coding USEZOSV1R9RULES(NO) will cause unpredictable results.
If you think this would be of benefit to you then thoroughly test before implementing in production.
CMOD has no problem with this...it's been tested with all supported releases on z/OS.
Ed
