A load test in practice may be carried out several times during the project life-cycle, but the end product might not always be a good one. Unfortunately, it is quite possible that load tests are done in mere quantities such as, page visiting to assess the performance. However, using the best load testing tools is a much more structured and reliable way of accomplishing that. This lack of quality can result in a low quality of results, these are the issues which this article will address and briefly go over the main principles which should be followed in order to properly execute a load test for a well designed application. A serious load test should mimic actual load on the system under test and should provide figures that reflect the behavior of SUT while under load conditions .
1:What is the purpose?
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Load testing is not primarily about overloading the system, though it may seem so; the main idea of a load test is in the examination and watchful monitoring of the SUT. The point of obtaining and comparing these measurements is so the information captured has to be accurate, so it’s crucial to do everything possible to ensure the collected information is meaningful and reliable:
- In order to use measurement values in a way to reflect what we want to test, a proper injection set should be used and it should be applied properly.
- The reported metrics should be actionable, that is, they should offer such information as throughput, the number of users served concurrently by SUT, and average response time per users all in relation to the concurrent users.
- As much as it is with other types of load test, it is crucial to appreciate the fact that the main goal of a load test is not to detect hot spots within an application despite the injection methods used. It is important to use quality load performance testing tools when trying to come up with the best results. Equipment for hotspot detection may cause overhead which may skew the results that are then obtained. Even though incorporated into the load testing theory, hotspot detection requires performing some actions more, for instance, using probes, detailed procedures for logging, a profiler, traffic monitoring and much more such as I/O, CPU, RAM, frame collisions etc.
2:Load testing – which one to choose?
When it comes to load testing, the key issue is what aspect you are going to measure. There are five types:
- Load holding test
- Overload test
- Robustness test
- Stress Testing
- Spike Testing
Load holding test
This kind of test is meant for checking the capability of the SUT, which is assumed to be a black box. To this end, representative scenarios are introduced simultaneously, which is called the load created by virtual users. Since load resistance tests aim at determining the maximum amounts of continuous load the system is capable of handling, it makes sense that as many test runs are needed as there are virtual users in a host application.
The impact of SUT reaching maximum occupancy is that the performance of the application will begin to decline, response time consequently, throughput rate will decrease. At this stage it might be possible to observe an inflection point on collected metrics like response time, number of requests per second and kinds of response. As these tests are used to derive valuable metrics measures, especially for APIs, it is vital to perform load testing with matrices of high-quality load testing APIs. These tests should normally be done using runs of several minutes or even tens of minutes.
Overload test
This kind of test is intended to assess the behavior of the SUT once it is subjected to a load in excess of its capacity and as assessed by the load resistance test. While it is understood that the SUT’s performance will degrade under a critical load, it is crucial to observe how the system behaves afterward: does it come back to a stable state or do you have to restart a system? The intention is not to obtain characterization values during the overload but to study the SUT behavior after the test.
Robustness test
This is a type of test meant to prove the behavior of the SUT following continuous operation most especially when it is dealing with a resource-constrained environment. In simple terms, a well-devised system should ideally be up and running most of the time, at least for a few months at a stretch rather than hours. Nevertheless, there are often conflicts such as memory contention after long periods of operation, due to resonance phenomena initiated by specific events. For assessment of this, a specific robustness test should be done at maximum allowable load for sometime, preferably several hours according to the load resistance test done earlier.
Stress Testing:
Stress testing is one form of performance evaluation that seeks to establish the conditions of use of a system where heavy loads are utilized. It aids in defining the process failure points and critical constraints because it works beyond the normal process stress levels. This increases reliability, stability and allows organizations to provide service during a sudden surge in customer demand.
Spike Testing:
Spike testing tests functions of a system based on heavy usages or spikings in a short time. The first test assists in establishing the behavior of the system in the occurrence of fluctuations in traffic with or without the stability of the system. By running performance tests during these surges of user load, the developers are able to monitor the application for strength during serious load demand.
3:What to measure and how?
I have listed a number of load tests earlier, so now it’s time to learn more about the metrics and their gathering. It has been said before that the goal of the load testing campaign is to accumulate values contributing to the assessment of the SUT. For instance, the optimal maximum continuous allowable throughput is best defined by using response time or load chart.
4:Extracting useful metrics
All points on the plot should correspond to a load test made for a certain number of virtual users. Load testing campaign strategy implies sequential running of a number of scenarios. All reliable load injection tools then sum the response time by the particular query and the total amount. Still, the purpose is typically to learn how the SUT behaves with several virtual users simultaneously. To this end, it is suggested calculating the median of the results obtained for a certain number of virtual users, offering one point capable of defining the inflection point.Extracting useful metrics
The median is used more often than the mean simply because it provides a better figure in case of the presence of outliers. But it is normal to have different results when two tests with the same scenario and same number of virtual users are conducted. Thus, the results are applied to make calculations regarding the exact inflection point of the curve preferable to make many trials, and eliminate runs that are extreme or unusual, then make the median.
Once that has been done, meaningful measurements for each load can be calculated (having conducted several tests, removing outliers and taking the median), followed by the calculation of the aggregation, which gets the desired inflection point. To do this, there must be determination of the loads at which the SUT displays linearity.
This is possible through using linear regression between the execution time and the load. In this case the membrane resistance is calculated with respect to the selected data hence the requirement to select data that optimizes this regression.
Conclusion
Therefore, one way to structure a development process to create solid, high performance systems is through the adoption of good structured load testing. Other companies such as PFLB, which deals in performance and load testing solutions and services, help organizations get the best out of such tests. PFLB is designed to assist teams in verifying more system functions, detecting bottlenecks, and providing users with non-interfered positive experiences. Hiring the services of experts in load testing ensures that systems meet the real world requirements that may be required to satisfy the needs of the users.
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