Load Testing

In performing a load test, it is important to construct the test process and levels so as to identify the load domain in which the system perform as intended (or as well as it is capable of) the level at which the system performance would start to become poor inthe users eyes, and the point and manner in which the system fails when presented with too much load.

A Load Testing System should support: Multiple useage scenarios Variable scenario mixtures across tests Ramping up to/down from target load Sustained load for long periods Per scenario state management Per scenario authentication detailed resource reporting Trending & comparison

Caching and Content Distribution Networks (CDN) must be considered carefully when planning and conducting and load tests. While caching is essential in high performance systems care must be taken when testing such systems to avoid a situation where the load test receives atypical caching behavior. Particular care should be taken when using 'WYSYWIG' tools that record user behavior as a means of generating data to be used in a load test. While this is a convenient way (for testing end user web sites) to capture the requests generated by an individual user - simply repeating such requests in volume to generate a 'load' results in all the 'simulated users' requesting the same small set of resources/services.

In an environment using caching such a load will result in an abnormally high cache hit rate and hence performance. Generating a complex item in response to a user request can take thousands to hundreds of thousande of times more server resources than providing the same item from a cache of recently constructed responses. In such a situation, even a relatively small percentage of requests for 'non cached' items can be the system's bottleneck. Combined with the natural tendency of operations staff (and management even more so) to hear 'good news' such tests can be grossly misleading.

E-insights can draw on extensive experience and deep systems understanding to ensure tests are thorough and exhaustive. A sample Load Test report can be seen here.