Any Web system that is subjected to testing will exhibit performance bottlenecks. But what is a bottleneck? Below is a list of terms used to describe some of the causes and effects of those bottlenecks, as well as solutions to those problems.

Bottleneck – A term used to describe a limiting resource in the system under test. Bottlenecks are typically identified as the cause of slow or unacceptable performance. They directly affect both the performance and scalability of the system under test. Also, at any SINGLE point in time, only one bottleneck is causing the system to slow for a specific transaction.
Performance – In system testing, this generally refers to the ability of a system to meet the requirements defined prior to testing. Systems are usually said to exhibit good or poor performance, depending on what criteria are used to measure that performance. Performance can be expressed in terms of concurrent users, transactions per day, average response time, or any other measure of speed.
Scalability – The ability of a system to perform as the number of concurrent users or requests increases. A system that can handle the specified user count or request rate as load is added has good scalability.
Symptom or Problem – The symptom or problem is how a bottleneck will show itself in the system under test. Symptoms are seldom the actual cause of the bottleneck. Symptoms are used together with other data to find the causes of the bottlenecks. Examples may include slow page performance, errors, or crashed servers.
Bottleneck Cause or Indicator – The single point in the system under test that is causing the system to exhibit slow performance.
Solution – The fix used to repair the bottleneck cause.
Measurement Point – The specific metric used to determine when and where a bottleneck exists. Examples are CPU utilization, free memory, response time, and error rates.