Load Testing

Preparing for a Load Test

The first step in designing a Web site load test is to measure as accurately as possible the current load levels.
Measuring Current Load Levels
The best way to capture the nature of Web site load is to identify and track, [e.g. using a log analyzer] a set of key user session variables that are applicable and relevant to your Web site traffic.
Some of the variables that could be tracked include:
the length of the session (measured in pages)
the duration of the session (measured in minutes and seconds)
the type of pages that were visited during the session (e.g., home page, product information page, credit card information page etc.)
the typical/most popular ‘flow’ or path through the website
the % of ‘browse’ vs. ‘purchase’ sessions
the % type of users (new user vs. returning registered user)


Measure how many people visit the site per week/month or day. Then break down these current traffic patterns into one-hour time slices, and identify the peak-hours (i.e. if you get lots of traffic during lunch time etc.), and the numbers of users during those peak hours. This information can then be used to estimate the number of concurrent users on your site.

Estimating Target Load Levels

Once you have identified the current load levels, the next step is to understand as accurately and as objectively as possible the nature of the load that must be generated during the testing.

Using the current usage figures, estimate how many people will visit the site per week/month or day. Then divide that number to attain realistic peak-hour scenarios.

It is important to understand the volume patterns, and to determine what load levels your web site might be subjected to (and must therefore be tested for).

There are four key variables that must be understood in order to estimate target load levels:
how the overall amount of traffic to your Web site is expected to grow
the peak load level which might occur within the overall traffic
how quickly the number of users might ramp up to that peak load level
how long that peak load level is expected to last

Once you have an estimate of overall traffic growth, you’ll need to estimate the peak level you might expect within that overall volume.

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