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Network Latency in Performance Tests

In performance testing, the response time of web pages at the client end (browser-side) is an important measure.  It indicates how end users perceive the performance of the system at large. Even if an application is able to serve requests faster, the client-side response could be impacted because of network delays. In a complex, resource intensive web page - this impact is amplified as the client may have to do multiple round trips to the server to fetch web resources for loading the complete page. Thus, in troubleshooting any performance problems, it is important to isolate and understand whether the problem is with the system or the network.

The average response time of an URL at client-side as measured by most load testing software comprise of two elements - the time taken by the system to service the URL request (which is a characteristic of the system), and the time spent by the URL request/response traveling in the network (which is a characteristic of the network).

A web server's http access log, configured to include the 'Processing-Time' (or 'time-taken') field would indicate the time taken by the server to process a given URL request. Correlating this with the average response time data given by most load test software, you could easily arrive at impact of network latency for individual URLs.

To illustrate this, here's a sample web server log generated by JBoss server. The last field, in this case, denotes the 'processing time' of a request in milliseconds. Using a web log analysis tool, the average time taken to service individual URLs could be measured.

##IPADDRESS##159 - - [29/Jun/2010:03:23:51 +0000] "GET /MyApp/pages/SignUp.jsf HTTP/1.1" 200 661
##IPADDRESS##159 - - [29/Jun/2010:03:23:51 +0000] "GET /MyApp/pages/SignUp.jsf HTTP/1.1" 200 880
##IPADDRESS##159 - - [29/Jun/2010:03:25:31 +0000] "POST /MyApp/pages/Search.jsf HTTP/1.1" 200  14088
##IPADDRESS##159 - - [29/Jun/2010:03:25:31 +0000] "POST /MyApp/pages/Search.jsf HTTP/1.1" 200  12140
##IPADDRESS##159 - - [29/Jun/2010:03:26:28 +0000] "POST /MyApp/pages/Select.jsf HTTP/1.1" 200  2155
##IPADDRESS##159 - - [29/Jun/2010:03:26:28 +0000] "POST /MyApp/pages/Select.jsf HTTP/1.1" 200  2174
##IPADDRESS##159 - - [29/Jun/2010:03:26:32 +0000] "POST /MyApp/pages/Detail.jsf HTTP/1.1" 200  2355
##IPADDRESS##159 - - [29/Jun/2010:03:26:32 +0000] "POST /MyApp/pages/Detail.jsf HTTP/1.1" 200  2552
##IPADDRESS##159 - - [29/Jun/2010:03:36:55 +0000] "GET /MyApp/pages/Confirm.jsf HTTP/1.1" 302  269
##IPADDRESS##159 - - [29/Jun/2010:03:36:55 +0000] "GET /MyApp/pages/Confirm.jsf HTTP/1.1" 302  241

Now, for the same application, below is the data on average response time obtained through a load test tool.



Avg RT

/ MyApp /pages/SignUp.jsf


/ MyApp /pages/Search.jsf


/ MyApp /pages/Select.jsf


/ MyApp /pages/Detail.jsf


/ MyApp /pages/Confirm.jsf


The difference in response time observed by load test tool (client-side response time) and the web server http access log (server-side response time) would give an indication of the impact of network latency. Such information adds a lot of value into a test report and enables a performance analyst to narrow-down problems faster.


Thank you Vikas for putting up this note. Once this article is read, every developer will definitely take a note of network delays in his/her application testing.

Thank you for posting this article, I got good to go ahead with.

very good share Vikas. Thank you for explaining this in simpler way.

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