What are different characteristics of load testing?

Load testing can be defined as the process of putting demands on a software system or application or a device and measuring the response of the software system or application or that device.

- Usually load testing is carried out to determine the behavior of the software system, application or device under both kinds of conditions namely the normal load condition and anticipated peak load condition.

- Load testing helps to determine the maximum degree of the operating capacity of the software system or application along with any bottlenecks and to check which element or error and bug is causing degradation of the software system or the application.

- Sometimes the load levied on the software system or application is increased beyond the normal usage limits, in order to test the response and behavior of the software system at unusually high and peak loads. This kind of testing is known as stress testing.

- The load is usually kept so high that the expected result is nothing more than loads of errors and bugs.

- In load testing there is no clear boundary is known to exist when an operation ceases to be a load test and gets converted to a stress test.

Till date it is not very much clear that what are the specific goals of load testing?

The term load testing is often used synonymously with reliability testing, software performance testing and volume testing.

- Load testing is classified under the category of non-functional testing. The term load testing carries a wide number of meanings in the field of software testing.
- Load testing can be said to refer to the practice of determining the expected usage of a software system, program or application by simulating multiple user situation in which many users are accessing the program at the same time.

- Load testing holds more relevance for multi- user software systems or applications which are often built using a client or a server model i.e., using the web servers.
- This does not implies that only the software systems built using client or server model can only undergo the load testing. Also the other types of software systems or applications which are not built using server or client model are also eligible for load testing.

- The most accurate and efficient and effective load testing simulates the actual usage environment, as compared to testing the software system or application using theoretical modeling or the analytical modeling.
- Load testing allows us to measure the QOS performance quotient of any website based on the actual behavior of the customers.
- Most of the tools and frame works that are used to carry out load testing follow the procedure of the classical load testing paradigm.

Overview of Reporting on response time at various levels of load, Fail-over Tests, Fail-back Testing

REPORTING ON RESPONSE TIME AT VARIOUS LEVELS OF LOAD
Expected output from a load test often includes a series of response time measures at various levels of load. It is important when determining the response time at any particular level of load, that the system has run in a stable manner for a significant amount of time before taking measurements.
For example, a ramp-up to 500 users may take ten minutes, but another ten minutes may be required to let the system activity stabilize. Taking measurements over the next ten minutes would then give a meaningful result. The next measurement can be taken after ramping up to the next level and waiting a further ten minutes for stabilization and ten minutes for the measurement period and so on for each level of load requiring detailed response time measures.

FAIL-OVER TESTS
Failover tests verify of redundancy mechanisms while the system is under load. This is in contrast to load tests which are conducted under anticipated load with no component failure during the course of a test. For example, in a web environment, failover testing determines what will happen if multiple web servers are being used under peak anticipated load, and one of them dies.
Failover testing allows technicians to address problems in advance, in the comfort of a testing situation, rather than in the heat of a production outrage. It also provides a baseline of failover capability so that a sick server can be shutdown with confidence, in the knowledge that the remaining infrastructure will cope with the surge of failover load.

FAIL-BACK TESTING
After verifying that a system can sustain a component outage, it is also important to verify that when the component is back up, that it is available to take load again, and that it can sustain the influx of activity when it comes back online.

How to set up a Load Test using LoadRunner?

The important thing to understand in executing such a load test is that the load is generated at a protocol level, by the load generators, that are running scripts that are developed with the VUGen tool. Transaction times derived from the VUGen scripts do not include processing time on the client PC, such as rendering (drawing parts of the screen) or execution of client side scripts such as JavaScript.The WinRunner PC(s) is utilized to measure end user experience response times. Most load tests would not employ a WinRunner PC to measure actual response times from the client perspective but is highly recommended where complex and variable processing is performed on the desktop after data has been delivered to the client.

The LoadRunner controller is capable of displaying real-time graphs of response times as well as other measures such as CPU utilization on each of the components behind the firewall. Internal measures from products such as Oracle, Websphere are also available for monitoring during test execution.
After completion of a test, the analysis engine can generate a number of graphs and correlations to help locate any performance bottlenecks.

In simplified load test, the controller communicates directly to a load generator that can communicate directly to the load balancer. No WinRunner PC is utilized to measure actual user experience. The collection of statistics from various components is simplified as there is no firewall between the controller and the web components being measured.

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.

Load test Process and why to use JMeter ?

Why to use JMeter

Easy to install and use Free!
- Java — most platforms.
- GUI vs. command line.
- Just download and run.
Feature-rich Post forms
- Record from browser.
- Load test data from files.
- Add logic, variables & functions.
- Run one test from multiple machines.
- Test many protocols, not just HTTP.

Load Test Process

- System Analysis : Enable customers to convert their goals and requirements into a successful test script. You can create your own test Script consistently and carefully UI design allows you to create your own test easily.
- Creating Virtual User Scripts: Tester must emulate the real user by driving the real application as a client. JMeter support this by adding thread group element. This would tell the number of users you want to simulate, how often the users send requests, how many requests they send, what request (FTP Request, HTTP Request, and JDBC request) and validate that your application is returning the results you expect.
- Defining User Behavior : JMeter allows you to simulate human actions more closely by controlling how long JMeter engine delays between each sample so you can define the way that the script runs.
- Creating a Load Test Scenario : JMeter offers support for this step by assigning scripts to individual virtual user, tester can define any number of virtual users needed to run the tests, allowing the user to simulate concurrent connections to server application, enabling user to create multiple threads ( virtual user) executing different test plan and increasing the number of virtual users in a controlled fashion.
- Running Load Test Scenario : With JMeter you can run your tests in a very easy way.
- Analyzing Results : JMeter offers support for this step by:
. displaying the data visually (Graph Results).
. save data in file.
. allows user to see one multiple views of the data.
. displays the response from the server.
. shows the URL of each sample taken.
. listeners will show different sets of data.
. it can send email based on test results.