Performance Tests are tests that determine end to end timing (benchmarking) of various time critical business processes and transactions, while the system is under low load, but with a production sized database. This sets ‘best possible’ performance expectation under a given configuration of infrastructure. It also highlights very early in the testing process if changes need to be made before load testing should be undertaken. For example, a customer search may take 15 seconds in a full sized database if indexes had not been applied correctly, or if an SQL 'hint' was incorporated in a statement that had been optimized with a much smaller database. Such performance testing would highlight such a slow customer search transaction, which could be remediated prior to a full end to end load test.
It is 'best practice' to develop performance tests with an automated tool, such as WinRunner, so that response times from a user perspective can be measured in a repeatable manner with a high degree of precision. The same test scripts can later be re-used in a load test and the results can be compared back to the original performance tests.
Performance Tests Precede Load Tests
The best time to execute performance tests is at the earliest opportunity after the content of a detailed load test plan have been determined. Developing performance test scripts at such an early stage provides opportunity to identify and remediate serious performance problems and expectations before load testing commences.
For example, management expectations of response time for a new web system that replaces a block mode terminal application are often articulated as 'sub second'. However, a web system, in a single screen, may perform the business logic of several legacy transactions and may take 2 seconds. Rather than waiting until the end of a load test cycle to inform the stakeholders that the test failed to meet their formally stated expectations, a little education up front may be in order. Performance tests provide a means for this education.
Another key benefit of performance testing early in the load testing process is the opportunity to fix serious performance problems before even commencing load testing.
A common example is one or more missing indexes. When performance testing of a "customer search" screen yields response times of more than ten seconds, there may well be a missing index, or poorly constructed SQL statement. By raising such issues prior to commencing formal load testing, developers and DBAs can check that indexes have been set up properly.
Performance problems that relate to size of data transmissions also surface in performance tests when low bandwidth connections are used. For example, some data, such as images and "terms and conditions" text are not optimized for transmission over slow links.
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