232 IBM Enterprise Workload Manager
Figure 9-4 Resources usage on i5/OS domain manager
9.2.9 i5/OS test methodology
? The java heap in i5/OS is structured very differently than those on other platforms. The
initial heap size is also the Garbage Collector (GC) allocation threshold. That number
indicates how much the heap should be allowed to grow between GC cycles. After a GC
cycle the heap shrinks to the size necessary to contain the objects that still have valid
references. After several cycles, this value can be much larger or smaller than the initial
heap. Setting the maximum heap is impractical on i5/OS because it causes the Garbage
Collector to run in a synchronous manner which is very degrading to performance.
? The initial heap setting has a very large impact on CPU and memory usage. Users will
need to specify this value to achieve acceptable performance.The initial heap setting
determines the balance of CPU versus memory usage. The initial heap is set by putting
"os400.gc.heap.size.init=SOMEVALUE" in the /home/qwlm/SystemDefault.properties file
where SOMEVALUE is the initial heap size in kilobytes. This must be done before calling
STRWLM. If the os400.gc.heap.size.init option is omitted or set too low, the domain
manager's CPU usage will rise drastically. This is because the Garbage Collector is
working hard to keep the memory usage down. If it is set too high, then the memory
footprint will grow.
OS: i5/OS
Processor: 4-way partition of an iSeries Model 825 6-way (6600 CPW), 5.7GB RAM
Policy: Complex
3060
2772
2657
2373
0
1
2
3
4
5
Thousands
Total java heap usage (MB)
( Domain Manager + WAS processes )
45.4
16.2
31.8
14.6
26.4
39.6
63.6
0
20
40
60
80
100
Peak CPU
Avg CPU
System CPU %
# Servers
63 252126 504
# Servers
63 252126 504
955
519
292
197
0
200
400
600
800
1000
1200
Database Disk (MB)
# Servers
63 252126 504
Note: See 'i5/OS Test Methodology' & 'General Sizing recommendations on i5/OS'.
These Java heap statistics do NOT represent recommended java heap settings.
Chapter 9. Initial performance considerations 233
? The i5/OS charts in this book represent processor and memory utilization with the initial
heap size set to 1200MB. In practice, domain managers managing fewer than 300 servers
would most likely run with the initial heap size at 256MB or less, greatly reducing the
memory footprint of the domain manager.
? Performance metrics were captured during “Steady State” and with “Control Center
activity” windows:
– Steady State: The base domain manager processes that gather and aggregate the
managed servers statistics. The Control Center was started but there was no end user
activity (no reporting, no policy changes, and so forth). This measurement is a
ten-minute average.
– Control Center activity: A user requests a transaction class listing.
? We utilized default system settings. No specific I/O or system performance tuning was
conducted.
Detailed results are shown in Table 9-7.
Table 9-7 Metrics observations for Complex Policy
Where:
? Servers is the number of the managed server in the EWLM management domain.
? Average system CP utilization Steady State is the average total processor utilization for
the server. During steady state, the domain manager process consumes more than 98%
of the total processor utilization.
? System CP Utilization spikes w/Control Center activity is the highest average system
processor utilization monitored (over a 10 second interval) upon requesting reporting data
or conducting a policy switch or combination of both. The domain manager and
WebSphere Application Server Control Center processes make up more than 98% of the
total System processor utilization.
? DM java heap size w/Control Center activity represents the maximum expanded
domain manager java heap. The java heap constitutes the majority of the domain
manager process memory requirements.
? CC java heap size w/Control Center activity represents the maximum expanded
Control Center WebSphere Application Server java heap. The java heap constitutes the
majority of the Control Center WebSphere Application Server process memory
requirements.
Servers
Avg system CP util
Steady State
System CP util spikes
with Control Center
activity
DM java heap size with
Control Center activity
(MB)
Control Center
WebSphere
Application Server
java heap size with
Control Center activity
(MB)
Total java heap usage
(MB)
EWLM DB size (MB)
Elaps time: 60min
interval report (sec)
63 2.2 28 190 196 438 194 2.0
126 5.1 39 340 280 672 290 2-3
252 12.3 53 533 340 974 520 4-10
504 23.9 81 1240 403 1790 995 10-30
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