DB2 UDB for z/OS Version 8 Performance Topics - IBM Redbooks

– LOCAL DYNAMIC STMT CACHE CTL BLKS = 0.99 MB
– THREAD COPIES OF CACHED SQL STMTS = 22.77 MB
DB2 V7 does not further break down the storage used for THREAD COPIES OF CACHED
SQL STMTS. So, the values are recorded as N/A.
► RDS OP POOL = 1.15 MB. For DB2 V7 there is a single RDS OP pool for all threads
which is used for sort, prepares and other similar functions.
► BUFFER & DATA MANAGER TRACE = 16.95 MB
Stack Storage and Fixed Pools
The TOTAL FIXED STORAGE is typically used for DB2 code and does not tend to vary a
great deal, while the TOTAL GETMAINED STACK STORAGE is typically used for program
stack usage, for example, save areas. It does vary as your workload varies.
DBM1 and MVS Storage below 2 GB
Figure 4-7 presents an overview of the MVS storage map. You may like to refer to this
illustration as we continue to explain more items in the DBM1 Storage Statistics extract in
Example 4-1.
Figure 4-7 MVS storage overview
MVS Storage Overview
MVS 64-bit (16 Exabyte) Virtual Address Space
64-Bit private storage
Extended Region
Nucleus, ECSA, ESQA, etc.
Nucleus, CSA, SQA, etc.
‘Below the line’
64 Bit End of Virtual
31 Bit ‘Bar’
31 bit High Private
31 bit low private
24 Bit ‘line’
24 bit high private
24 bit low private
The 31-bit EXTENDED LOW PRIVATE is the amount of used storage just above the 16 MB
line. It is generally used by unauthorized programs. DB2 code is loaded here, as well as data
set control blocks. This storage grows from the bottom up in the extended region. The 31-bit
EXTENDED HIGH PRIVATE is the amount of storage above the 16 MB line generally used by
authorized programs. This storage grows top down in the extended region. All GETMAINed
DB2 storage is obtained in this way. MVS has a rule that high private cannot grow into low
private. The REGION parameter in the JCL controls how high the low private storage can
grow (0 MB indicate indefinitely). For example, the REGION parameter can be used to save a
few MB of extended private storage by forcing some low private growth into 24-bit low private.
Extended low private is often controlled with the system-wide MVS IEFUSI exit which can
treat differently different address spaces.
Chapter 4. DB2 subsystem performance 161