System performance views
General
System performance views describe how a system's performance can be viewed and the purpose of the views.
Every system performance characteristic belongs to one of two system performance views:
The performance views are complementary, i.e. metrics from both views are required to understand and improve a system's performance.
The External view of a system's performance
The External view of a system's performance is a system's performance characteristics as observed and measured from outside the tested system.
External system performance characteristics are also referred to as "User Experienced Performance".
Examples of external system performance characteristics are response time, response time variations, various capacity metrics, availability metrics, stability metrics, and many more.
External system performance figures show the aggregated performance efforts of a system.
External system performance characteristics show the tested system's behaviour as towards its users, but doesn't explain the tested system's delivery limits.
The Internal view of a system's performance
The Internal view of a system's performance is a system's performance characteristics as observed and measured from inside the tested system.
The internal system performance characteristics show the performance of the tested system's components.
Examples of internal system performance characteristics are are CPU load, memory usage, queue lengths, and many more.
Internal system performance characteristics are measurements of what limits the system's external performance. The measurements are made to find the sources of deviations from performance requirements, such as capacity bottlenecks.
Internal system performance characteristics explain possible causes of a system's service delivery limits, but not the system performance as experienced by users (the external performance characteristics).
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