Systems that work well during development, deployed on a small scale, can fail to meet performance goals when the deployment is scaled up to support real levels of use.
An apposite example of this comes from a major blue chip company that recently outsourced the development of an innovative high technology platform. Though development was behind schedule this was deemed acceptable. The system gradually passed through functional elements of the user acceptance testing and eventually it looked like a deployment date could be set. But then the supplier started load testing and scalability testing. There followed a prolonged and costly period of architectural changes and changes to the system requirements. The supplier battled heroically to provide an acceptable system, until finally the project was mothballed.
This is not an isolated case. IT folklore abounds with similar tales. From ambulance dispatch systems to web-sites for the electronic submission of tax returns, systems fail as they scale and experience peak demands. All of these projects appear not to have identified and ordered the major risks they faced. This is a fundamental stage of risk based testing, and applies equally to scalability testing or load testing as it does to functionality testing or business continuity testing. With no risk assessment they did not recognise that scaling was amongst the biggest risks, far more so that delivering all the functionality
Recent trends towards Service Oriented Architecture (SOA) attempt to address the issue of scalability but also introduce new issues. Incorporating externally provided services into your overall solution means that your ability to scale now depends upon these external system operate under load. Assuring this is a demanding task and sadly the load testing and stress testing here is often overlooked.
Better practice is to start the development of a large scale software system with its performance clearly in mind, particularly scalability testing, volume testing and load testing. To create this performance testing focus:
Mark is an experienced consultant working in performance testing, scalability testing and load testing. For further information visit: http://www.acutest.co.uk or http://www.acutest.co.uk/performance-testing.html
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Article Submitted On: October 08, 2005
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