What is Load Testing?
Load testing is a kind of Performance Testing which determines a system's performance under real-life load conditions. This testing helps determine how the application behaves when multiple users access it simultaneously.
This testing usually identifies -
• The maximum operating capacity of an application
• Determine whether the current infrastructure is sufficient to run the application
• Sustainability of application with respect to peak user load
• Number of concurrent users that an application can support, and scalability to allow more users to access it.
It is a type of non-functional testing. In Software Engineering, Load testing is commonly used for the Client/Server, Web-based applications - both Intranet and Internet.
Need of Load Testing:
Some extremely popular sites have suffered serious downtimes when they get massive traffic volumes. E-commerce websites invest heavily in advertising campaigns, but not in Load Testing to ensure optimal system performance, when that marketing brings in traffic.
Consider the following examples
• Popular toy store Toysrus.com, could not handle the increased traffic generated by their advertising campaign resulting in loss of both marketing dollars, and potential toy sales.
• An Airline website was not able to handle 10000+ users during a festival offer.
• Encyclopedia Britannica declared free access to their online database as a promotional offer. They were not able to keep up with the onslaught of traffic for weeks.
Many sites suffer delayed load times when they encounter heavy traffic. Few Facts -
• Most users click away after 8 seconds' delay in loading a page
• $ 4.4 Billion Lost annually due to poor performance
Why Load Testing?
• Load testing gives confidence in the system & its reliability and performance.
• Load Testing helps identify the bottlenecks in the system under heavy user stress scenarios before they happen in a production environment.
• Load testing gives excellent protection against poor performance and accommodates complementary strategies for performance management and monitoring of a production environment.
Goals of Load Testing:
Loading testing identifies the following problems before moving the application to market or Production:
• Response time for each transaction
• Performance of System components under various loads
• Performance of Database components under different loads
• Network delay between the client and the server
• Software design issues
• Server configuration issues like a Web server, application server, database server etc.
• Hardware limitation issues like CPU maximization, memory limitations, network bottleneck, etc.
Prerequisites of load testing:
The chief metric for load testing is response time. Before you begin load testing, you must determine -
• Whether the response time is already measured and compared - Quantitative
• Whether the response time is applicable to the business process - Relevant
• Whether the response time is justifiable - Realistic
• Whether the response time is achievable - Achievable
• Whether the response time is measurable using a tool or stopwatch - Measurable
Strategies of load Testing:
There are many numbers of ways to perform load testing. Following are a few load testing strategies-
• Manual Load Testing: This is one of the strategies to execute load testing, but it does not produce repeatable results, cannot provide measurable levels of stress on an application and is an impossible process to coordinate.
• In house developed load testing tools: An organization, which realizes the importance of load testing, may build their own tools to execute load tests.
• Open source load testing tools: There are several load testing tools available as open source that are free of charge. They may not be as sophisticated as their paid counterparts, but if you are on a budget, they are the best choice.
• Enterprise-class load testing tools: They usually come with capture/playback facility. They support a large number of protocols. They can simulate an exceptionally large number of users.
How to do Load Testing
The load testing process can be briefly described as below -
1.Create a dedicated Test Environment for load testing
2.Determine the following
3.Load Test Scenarios
4.Determine load testing transactions for an application
o Prepare Data for each transaction
o Number of Users accessing the system need to be predicted
o Determine connection speeds. Some users may be connected via leased lines while others may use dial-up
o Determine different browsers and operating systems used by the users
o A configuration of all the servers like web, application and DB Servers
5.Test Scenario execution and monitoring. Collecting various metrics
6.Analyze the results. Make recommendations
7.Fine-tune the System
Guidelines for load testing
1.Load testing should be planned once the application becomes functionally stable.
2.A large number of unique data should be ready in the data pool
3.Number of users should be decided for each scenario or scripts
4.Avoid creation of detailed logs to conserve the disk IO space
5.Try to avoid downloading of images in the site
6.The consistency of response time over the elapsed period should be logged & the same should be compared with various test runs
Advantages and disadvantages of Load testing:
Following are the advantages of Load testing:
• Performance bottlenecks identification before production
• Improves the scalability of the system
• Minimize risk related to system downtime
• Reduced costs of failure
• Increase customer satisfaction
Disadvantages of Load testing:
• Need programming knowledge to use load testing tools.
• Tools can be expensive as pricing depends on the number of virtual users supported.