Enterprise Library Test Guide - Willy .Net

Testing for Performance and Scalability 219
Important concepts to keep in mind when you measure performance are:
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Utilization
Idle time
Saturation
Utilization is (Resource Busy Time/Total Time of service) *100. Many performance
counters measure utilization. They have names that include percentages such as Processor:
% Processor Time.
Idle time is 100 percent – Utilization. The Enterprise Library tests use the Logical
Disk: % Idle Time counter to measure utilization.
Saturation means that a resource is used to 100 percent of its capacity, or close to it.
There are two sets of performance counters you can use to measure an application
block’s performance. The first set records the use of system resources. System resources
include memory, disk I/O, CPU usage, network I/O, and specific counters
associated with the CLR memory and with contention. Also, where applicable, there
are performance counters to measure SQL Server performance. For more information
about these counters, see Detecting Performance Issues.
The second set of performance counters measure end-to-end transaction times and
transactions per second. Here is a summary of the goals for these metrics:
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The Process(w3wp_.exe)\Private Bytes and the Process(w3wp.exe)\Virtual
Bytes performance counters should not increase during the stress and performance
tests.
The number of CLR garbage collection handles or process handles should not
increase during stress and performance tests.
There should be no CLR lock contention coupled with a low measurement for
CPU usage. The CPU usage should be at close to 100 percent for all test cases,
except where there is dependency on an external resource such as during a SQL
Server query.
The ratio of context switches to system threads should not be more than 20.
The thread count should not increase during the stress and performance tests.
The transaction execution times and the transactions per second should remain
stable during stress and performance tests.
There should be no deadlocks or w3p3.exe process restarts.
The system memory and memory pools should be stable.
The latency times for reads and writes to logical drives should not be more than
7 ms.
Only the Exception Handling Application Block should have CLR exceptions.
Contention should not cause poor CPU usage.