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

esolve any contention. This extra activity to the lock structure also increases the coupling
facility CPU utilization.
However these tests show that the increase in synchronous requests to the lock structure and
the resulting increase in coupling facility CPU utilization do not appear to be excessive for our
workload. Nothing comes for free!
Now we have a look at the impact on the CPU consumed by DB2. Table 8-10 shows extracts
from DB2 PE statistics reports for the same test.
Table 8-10 Protocol Level 2 - DB2 PE Statistics Report extract
IRLM
(msec / commit)
Total DB2 CPU time
(msec / commit)
For our IRWW workload, we see a dramatic reduction in IRLM SRB time. This is because
there is less XES contention to resolve. Remember that XES must defer to the IRLMs to
resolve any XES contention and this activity drives IRLM CPU.
Our workload also achieved a significant increase in transaction throughput. This is a result of
the workload suffering fewer class 3 suspensions, waiting for XES contention to be resolved.
In the past, a number of customers have opted to BIND their high use plans and packages
using RELEASE(DEALLOCATE) rather than RELEASE(COMMIT).
RELEASE(DEALLOCATE) has a number of performance advantages. DB2 does not have to
release and re-acquire table space level locks after a commit. Some customers have also
used RELEASE(DEALLOCATE) to reduce the amount of XES contention in their data sharing
environments. However there is a cost in availability. It may be more difficult to execute DDL
as the DB2 objects are allocated longer to the plans and packages.
So, let us have a look at the impact the new locking protocol has on the BIND RELEASE
parameter. Table 8-11 compares the impact on performance of RELEASE(COMMIT)
compared to RELEASE(DEALLOCATE) in both DB2 V7 and DB2 V8.
Table 8-11 Protocol Level 2 - RELEASE(DEALLOCATE) vs. RELEASE(COMMIT)
We can see that for DB2 V7, RELEASE(DEALLOCATE) has on average an 18% reduction in
CPU time per transaction, compared to RELEASE(COMMIT). There is less reduction, 7%, in
DB2 V8 when the new locking protocol is use. RELEASE(DEALLOCATE) still uses less CPU
time, but the delta is much smaller with V8 and protocol 2.
The table also shows an 18% improvement in transaction throughput by using
RELEASE(DEALLOCATE) in DB2 V7. This gain is reduced to only a 5% improvement in
transaction throughput when the new locking protocol is used.
330 DB2 UDB for z/OS Version 8 Performance Topics
DB2 V7 DB2 V8 Delta
(V8 / V7)
0.330 0.317 0.012 0.015 -96%
3.447 3.708 3.109 3.357 -10%
Group ITR 823.56 897.00 +9%
DB2 V7 DB2 V8
Transaction CPU time -18% -7%
Global ITR +18% +5%