What is the purpose of load tests?

The purpose of any load test should be clearly understood and documented. A load test usually fits into one of the following categories:
- Quantification of risks :
Determine, through formal testing, the likelihood that system performance will meet the formal stated performance expectations of stakeholders, such as response time requirements under given levels of load. This is traditional quality assurance(QA) type test. The load testing does not mitigate risk directly, but through identification and quantification of risk, presents tuning opportunities and an impetus for remediation that will mitigate risk.

- Determination of minimum configuration : Determine, through formal testing, the minimum configuration that will allow the system to meet the formal stated performance expectations, so that extraneous hardware, software and the associated cost of ownership can be minimized. This is a Business Technology Optimization (BTO) type test.

Basis for determining the business functions/processes to be included in a test

- High Frequency Transactions : The most frequently used transactions have the potential to impact the performance of all of the other transactions if they are not efficient.
- Critical Transactions : The more important transactions that facilitate the core objectives of the system should be included, as failure under load of these transactions has the greatest impact.
- Read Transactions : At least one READ ONLY transaction should be included, so that performance of such transactions can be differentiated from other more complex transactions.
- Update Transactions : At least one update transaction should be included so that performance of such transactions can be differentiated from other transactions.

What are Load Tests - End to End performance tests

Load Tests are end to end performance tests under anticipated production load. The objective such tests are to determine the response times for various time critical transactions and business processes and ensure that they are within documented expectations. Load tests also measures the capability of an application to function correctly under load, by measuring transaction pass/fail/error rates. An important variation of the load test is the network sensitivity test which incorporates WAN segments into a load test as most applications are deployed beyond a single LAN.

Load tests are major tests, requiring substantial input from the business, so that anticipated activity can be accurately simulated in a test environment. If the project has a pilot in production then logs from the pilot can be used to generate 'usage profiles' that can be used as part of the testing process, and can even be used to drive large portions of load test.

Load testing must be executed on today's production size database, and optionally with a projected database. If some database tables will be much larger in some months time, then load testing should also be performed against a projected database. It is important that such tests are repeatable, and give the same results for identical runs. They may need to be executed several times in the first year of wide scale deployment, to ensure that new releases and changes in database size do not push response times beyond prescribed service level agreements.