Software performance testing and load testing

oftware performance testing is a means of quality assurance (QA). It involves testing software applications to ensure they will perform well under their expected workload.

Features and Functionality supported by a software system is not the only concern. A software application’s performance like its response time, do matter. The goal of performance testing is not to find bugs but to eliminate performance bottlenecks

The focus of Performance testing is checking a software program’s

• Speed – Determines whether the application responds quickly
• Scalability – Determines maximum user load the software application can handle.
• Stability – Determines if the application is stable under varying loads

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 (or Service Level Agreements - SLAs).  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 the 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 conducted 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 SLAs. 

Difference between Performance Testing and Load Testing

Performance testing is the testing, which is performed, to ascertain how the components of a system are performing, given a particular situation. Resource usage, scalability and reliability of the product are also validated under this testing. This testing is the subset of performance engineering, which is focused on addressing performance issues in the design and architecture of software product.

Performance Testing Goal:
The primary goal of performance testing includes establishing the benchmark behaviour of the system. There are a number of industry-defined benchmarks, which should be met during performance testing.

Performance testing does not aim to find defects in the application, it address a little more critical task of testing the benchmark and standard set for the application. Accuracy and close monitoring of the performance and results of the test is the primary characteristic of performance testing.

Example:
For instance, you can test the application network performance on Connection Speed vs. Latency chart. Latency is the time difference between the data to reach from source to destination. Thus, a 70kb page would take not more than 15 seconds to load for a worst connection of 28.8kbps modem (latency=1000 milliseconds), while the page of same size would appear within 5 seconds, for the average connection of 256kbps DSL (latency=100 milliseconds). 1.5mbps T1 connection (latency=50 milliseconds) would have the performance benchmark set within 1 second to achieve this target.

For example, the time difference between the generation of request and acknowledgement of response should be in the range of x ms (milliseconds) and y ms, where x and y are standard digits. A successful performance testing should project most of the performance issues, which could be related to database, network, software, hardware etc…


Load testing is meant to test the system by constantly and steadily increasing the load on the system till the time it reaches the threshold limit. It is the simplest form of testing which employs the use of automation tools such as LoadRunner or any other good tools, which are available. Load testing is also famous by the names like volume testing and endurance testing.

The sole purpose of load testing is to assign the system the largest job it could possible handle to test the endurance and monitoring the results. An interesting fact is that sometimes the system is fed with empty task to determine the behaviour of system in zero-load situation.

Load Testing Goal:
The goals of load testing are to expose the defects in application related to buffer overflow, memory leaks and mismanagement of memory. Another target of load testing is to determine the upper limit of all the components of application like database, hardware and network etc… so that it could manage the anticipated load in future. The issues that would eventually come out as the result of load testing may include load balancing problems, bandwidth issues, capacity of the existing system etc…

Example:
For example, to check the email functionality of an application, it could be flooded with 1000 users at a time. Now, 1000 users can fire the email transactions (read, send, delete, forward, reply) in many different ways. If we take one transaction per user per hour, then it would be 1000 transactions per hour. By simulating 10 transactions/user, we could load test the email server by occupying it with 10000 transactions/hour.