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

3.11.1 Performance
3.11.2 Conclusion
can provide a large elapsed time improvement in all cases where the DSNREXX module
is not already loaded in LLA/VLF to reduce the module fetch time.
Figure 3-43 shows the measurements of a REXX application fetching 100k rows from a table
in V7 and V8. There are very significant reductions in elapsed time and some reduction in
CPU time.
Figure 3-43 REXX support improvement
The measurements show that the elapsed time of programs in REXX language can be
significantly reduced (if the DSNREXX module was not already preloaded by other means.)
The improvement is larger with larger number of SQL statements.
CPU time is also reduced.
3.11.3 Recommendations
REXX support improvement
REXX application which issues 100k
fetches against a TPCD table.
Class 1 elapsed time 29X better than V7
Class 1 CPU time 30% better
You do not need to do anything to have the performance benefits if you are using REXX
programs that issue a large number of calls.
3.12 Dynamic scrollable cursors
V7CL1 V8 CL1
Before DB2 V7, you could only scroll cursors in a forward position. So when a cursor was
opened, the cursor would be positioned before the first row of the result set. When a fetch was
executed, the cursor would move forward one row.
DB2 V7 introduced static scrollable cursors as cursors which can be scrolled backwards or
forwards, and to an absolute position or to a relative position. They use a DECLARED
TEMPORARY TABLE (DTT) introduced first in DB2 V6. When the cursor is opened, DB2
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Chapter 3. SQL performance 91