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

8.2.1 Performance
We ran a number of benchmarks to try to understand the impact of the new locking protocol.
Each test was performed using an IRWW benchmark executing against a two member data
sharing group.
The tests were performed with DB2 V7 defaults and DB2 V8 defaults. V7 uses LOCKPART
NO as the default, while V8 behaves as if the table spaces are defined with LOCKPART YES.
So, for some workloads DB2 V8 would need to propagate more locks to the coupling facility
than the same workload running in DB2 V7. This is true if the workload running does not
require all of the partitions to be GBP dependent. For these tests, all partitions were GBP
dependent. So, the impact of LOCKPART(NO) in V7 compared with V8 should be minimal.
We first review the impact on lock suspensions. Table 8-6 shows extracts from the Data
Sharing Locking section of DB2 PE statistics reports. The two columns under DB2 V7 and V8
represent each DB2 member.
Table 8-6 Protocol Level 2 - Statistics Report extract
Suspends per commit DB2 V7 DB2 V8
IRLM Global Contention 0.01 0.01 0.01 0.01
XES Contention 0.54 0.52 0.00 0.00
False Contention 0.13 0.11 0.00 0.00
You can see from Table 8-6 that the benchmark produced significantly less XES contention as
well as less false contention. This is because IX-L locks are now mapped to S XES locks
which are compatible locks. The lock requests do not need to be suspended while XES
communicates with the IRLMs to determine the IX-L locks are in fact compatible and can be
granted. False contention is reduced because fewer lock table entries are occupied by X-XES
locks. This is explained in more detail later in this section.
Table 8-7 shows extracts from DB2 PE accounting reports for the same test.
Table 8-7 Protocol Level 2 - Accounting Report extract
Class 3 suspend time
(msec / commit)
Lock / Latch
(DB2 + IRLM)
This table reveals that, on average, each transaction enjoyed significantly fewer suspensions
for lock and global contention. This is due to less XES contention, as a result of the new
locking protocol.
Now, we have a look at the impact on the coupling facility and XCF links. Table 8-8 shows
extracts from RMF XCF reports.
Table 8-8 Protocol Level 2 - RMF XCF Report extract
328 DB2 UDB for z/OS Version 8 Performance Topics
DB2 V7 DB2 V8
6.219 5.708 0.080 0.109
Global Contention 8.442 7.878 0.180 0.197
Req In
(req / sec)
DB2 V7 DB2 V8
2,300 2,200 17 18