By Ravinder Singroha

In this series of blog, we will understand what we mean by performance testing of a web service, and with each upcoming series, we will take the various commercial and open source tools available to assist us in this venture. Let us first begin with a very basic question:

What is Web Service?

Web services are an XML based technology that allow applications to communicate with each other, regardless of the environment, by exchanging messages in a standardized format ( XML ) via web interfaces ( SOAP and WSDL APIs ). In simpler terms a Web services is a web enabled API. To read and understand further about web services you can visit, Pallavi’s blog.
Lets us now understand what we mean by the Performance Testing

What is Performance Testing?

Performance testing is the process of determining the speed or effectiveness of a computer, network, software program or device. This process can involve quantitative tests done in a lab, such as measuring the response time or the number of MIPS (millions of instructions per second) at which a system functions. Qualitative attributes such as reliability, scalability and interoperability may also be evaluated. Performance testing can verify whether a system or software meets the specifications claimed by its manufacturer or vendor. The process can compare two or more devices or programs in terms of parameters such as speed, data transfer rate, bandwidth, throughput, efficiency or reliability. For further reading, visit Himanshu’s blog.

Why Web Service Needs Performance Testing?

The next question that comes to our mind is why our web services need performance testing. Here I am going to assume that you are either an experienced reader or you had taken my recommendations seriously and visited the blogs mentioned above.
As you can see in the diagram below that, there is common service provider, which is used by all service requestors. These requestors would want assurance that the web service meets acceptable performance criteria when under stress/load. The goal of performance or load testing of a Web service application is to find how the web service scales as the number of clients accessing it increases. Also, to gather the performance and stability information of the server such as throughput, CPU usage, the time taken to get a response from a web method, etc. when there are, say, 5, 50, 200, 500 concurrent users or more.
The service requestors require these statistics to ensure that the provider is meeting the SLA’s set. Whether they can expect a reliable user experience when a web service is used under load, which may be caused due to, increase in the number of users accessing it and under volume stress, which may be caused when large requests and responses are generated.
In addition, the service providers need to ensure that they have enough web server resources where the service is hosted to cater to the expected load and the web service is scalable enough to function rightly under stress.

Web Service Performance Criteria:

There are various performance criteria, which one should consider when testing a web service for performance.

Server Side:

Throughput: It is measured as number of request sent per second.

Latency (Transaction Time): It is the time taken between service request arriving and being serviced per second. We test the response time as we,
a. Increase the size of web service request, b. Increase the number of virtual users

Resource Utilization: We should be able to figure out the resource demand of the web service under various virtual user workloads/requests volume, so that an optimum resource can be provided for the expected load.

Client Side:

Latency: Time taken for service call to return the earliest response bytes, includes network latency.

Throughput: Average bytes flow per unit time including latency.

Conclusion:
Loosely coupled service environments provide unique benefit for the organizations that utilize them but they introduce new challenges. Both the service providers and consumers should be aware of the performance of the service so that they can ensure it meets the SLA’s specified. Many tools and profilers are available to detect and optimize the performance of a web service. In the next series of blogs, I would be taking a few tools and understand how to do performance testing of a web service using the various tools.

(to be continued…)

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