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

and secondary GBP structures have the CF request batching capability. Since CF request
batching will only be used for reading castout pages from the primary GBP, there is no
additional CPU saving for castout with or without GBP Duplexing. However, if you do not
consider prefetch, then the additional CPU saving with CF request batching in a duplexed
GBP environment will be half of the CPU saving without GBP duplexing.
Table 8-4 shows extracts from RMF reports for the same batch workload.
Table 8-4 CF Request Batching - RMF extract (batch)
Once again, we can see z/OS 1.4 results in significantly fewer requests to the coupling facility
(6,715 compared to 14,627). We can also see the service times for both synchronous
requests and asynchronous requests to the coupling facility have increased slightly, as well as
notice the coupling facility utilization has decreased slightly.
The table also shows quite a jump in asynchronous requests when CF request batching was
used, over 12% of all requests, compared with only 2% when CF request batching was not
used. This trend is similar to what we noticed when we earlier reviewed the RMF extracts for
the OLTP workload. The increase can be attributed to the heuristic conversion by the CFCC
of synchronous requests to asynchronous requests due to more work being processed in
each batch request.
Table 8-5 compares the CPU used by the DBM1 address space for the OLTP workload
compared with the batch workload.
Table 8-5 CF Request Batching - DB2 CPU
This table shows CF request batching has potential for significant saving in CPU charged to
DBM1 address space, in both OLTP and batch workloads, but particularly batch.
The overall CPU times in this table include the transaction class 2 CPU times, the MSTR,
DBM1 and IRLM CPU times. So, we can see the overall impact of CF request batching was
324 DB2 UDB for z/OS Version 8 Performance Topics
z/OS 1.3 z/OS 1.4
Requests / sec 14,627 6,715
Sync Requests
Serv time
(usec)
Async Requests
Serv time
(usec)
% of all req 10.5 98.0 12.0 87.7
% of all req 209.8 2.0 241.4 12.3
CF Utilization (%) 15.7 14.4
DBM1 - (OLTP)
(msec / commit)
z/OS 1.3 z/OS 1.4 Delta
(1.4 / 1.3)
0.536 0.545 0.427 0.473 -17%
Overall CPU time 3.229 3.224 3.111 3.368 +0%
DBM1 - (Batch)
(msec / commit)
119.88 130.11 81.5 89.68 -32%
Overall CPU time 656.40 709.74 618.98 680.89 -5%