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

8.5 Miscellaneous items
In this section we describe some miscellaneous enhancements that impact DB2 data sharing.
8.5.1 Impact on coupling facility
You do not need to resize the group buffer pools, lock structure or SCA in the coupling facility
as a result of moving to DB2 V8, even though the virtual buffer pools have now moved above
the bar and have a longer memory address. This is true provided of course, you have not
made any significant changes when you migrate to DB2 V8.
However, you may wish to review your coupling facility structure sizes after you have migrated
to DB2 V8. For example, you may like to revise your virtual buffer pool sizes now that there
are no hiperpools or buffer pools in data spaces.
We do recommend you review your coupling facility structure sizes as you prepare to
implement CFLEVEL 12. This is required to take advantage of the CF Request Batch
performance enhancements, described earlier. When migrating CFLEVELs, coupling facility
structure sizes might need to be increased to support the new function. For example, when
you upgrade from CFLEVEL 9 to CFLEVEL 11 or from CFLEVEL 10 to CFLEVEL 12, the
required size of the structures might increase by up to 768 KB.
The following “Rule of Thumb” formulas may be used to estimate the required coupling facility
structure sizes, based on migrating from CFLEVEL 10 or 11 to CFLEVEL 12. The thumb rules
are only rough approximations.
CFLEVEL 12 structure size = CF level 10 (or 11) structure size PLUS the following based
on type of structure and entry:element ratio:
Lock structure:
Without record data: 0
With record data: 20% of level 10 or 11
List or cache structure:
No data (no elements): 0
Entry:element ratio = 1:1: 2MB + 10%
Entry:element ratio >= 100:1(scale % factor for ratios in between): 2MB + 50%
and should only be used if methods 2 and 3 are not applicable.
For example, given a DB2 group buffer pool structure of 100 Mb, and an entry:element ratio of
5:1 and you are at CFLEVEL 10, then CFLEVEL 12 will require an extra:
100 + 2 + 12% x 100 = 114 MB
If the higher CFLEVEL is accessible in your configuration and is defined in the CFRM policy,
and OW54685 is applied, then structure rebuilds from lower CFLEVELs to higher CFLEVELs
will resize the structure automatically based on its current structure object counts.
Alternatively, we suggest you use the CFSIZER to check your coupling facility structure sizes.
The CFSIZER can be found at:
http://www.ibm.com/servers/eserver/zseries/cfsizer/
8.5.2 Improved LPL recovery
Prior to DB2 V8, when you issue the -START DATABASE command to recover LPL pages, the
command must drain the entire table space or partition. The "drain" means that the command
must wait until all current users of the table space or partition reach their next commit point.
336 DB2 UDB for z/OS Version 8 Performance Topics