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Investigating the impact of Ajax on server load in a Web 2.0 application

Brian TooneSamford University

brtoone@samford.edu

What is Web 2.0?

Mind Map by Markus Angermeier

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Our focus

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Mind Map by Markus Angermeier

Web 2.0 example

FacebookPopular social networking web applicationWeb 2.0 application

Social software, encourages participation, sharing Convergence, 3rd party applications and most importantly for this talk … usability

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Usability enhancements

Reduce number of context switchesUser constantly sees context of page updatesNo browser busy icon or screen flickerMinimal change to the updated page

Reduce latency by reducing server loadRetrieve only what is necessary to update the pageReduces the amount of data fetched from serverReduces overall server load

Web Architecture 101

Web servers store web pages (static and dynamic)Web browsers use HTTP to request pages

Static page simply fetched from server hard driveScripts must execute to create dynamic pages (e.g., php, jsp)HTML document sent to the web browserImages, CSS, Javascript require additional HTTP requestsSame initial process for Ajax and non-Ajax pages

Ajax 101

Ajax – Asynchronous Javascript And XMLAjax affects what happens after the initial page loadAjax-enabled page has Javascript code to submit HTTP requests asynchronously without refreshing the current page

Ajax 101

Ajax 101 … without Ajax or Ajax-equivalent

Impossible to submit data without page refreshImpossible to update the display with new data from the server without page refreshImpact of a page refresh:

So far, so good, so what is the problem?

Facebook data requirements are relatively smallFacebook user interactions are relatively limitedConsider a mapping application…

Without Ajax With Ajax

The Ajax impact on server load

Without Ajax, user “encouraged” to use appropriate zoom tools to minimize thenumber of requestsWith Ajax, the opposite is true – the Rich Internet Application (RIA) “encourages” the user to zoom and pan Potential explosive increase in HTTP requestsWeb server must respond to each requestIncrease in bandwidth and processing load

Our focus and goal

Our focus is not to argue whether Ajax increases or decrease server load in general

That debate is meaningless because….The answer is entirely dependent upon…

Specific website implementation of Ajax functionality The overall usage of the site by the target audience

Our goal: a developer tool for quantifying the impact of Ajax performance on a web server hosting a specific Web 2.0 application

An Extreme Example

Each Ajax request consumes server resourcesCPU cyclesBandwidthDisk I/O

Extreme ExampleAn onmousemoveevent initiates an Ajax request to retrieve data from the server.Every time every user moves the mouse, a new request is issued!

onmousemove Example, cont’d

Our Ajax Performance Monitoring Toolkit

See the server impact of Ajax calls in real-timeNot meant to be a load tester, many already existHelp a web developer before the site is deployed

Measurement for the client (individual page)Measurement for the server (all accesses)

What do we measure? (currently)

Client measurementsTotal number of Ajax calls made from an individual pageTotal number of Ajax responses received from serverTotal number of “pending” page calls still awaiting responses

Server load measurementsTotal number of Ajax calls processedTotal number of Ajax calls currently being processedThroughput (calls/min)

Integrating toolkit into web appsCLIENT SIDE

Javascript “include” file<div> for outputGlobal variable declarationInit global variable in onload functionWrap Ajax request creation and cleanup

SERVER SIDEMake sure each Ajax service script is isolated (cannot be loaded independently from an Ajax request)Include the provided header and footer at the top and bottom of each Ajax service requestDo not die()

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Integrating toolkit - clientside

Integrating toolkit - serverside

Not as much to show!Necessary monitoring code embedded in the header and footer scripts

Conclusion

Measuring the impact of Ajax calls is trickyThe Ajax Performance Monitoring toolkit can give a web developer real-time display of Ajax calls and impact on server load

Future Work

Finer granularity of reported statistics (individual “named” Ajax calls)Better isolation of the specific Ajax impact on server load … count and report specific # of cpu cycles spent executing Ajax functionsLess dependence on web developer following conventions correctly (e.g., could have negative number of outstanding requests if developer calls cleanup multiple times per single request)

Thank you!

Questions?For more information

brtoone@samford.eduhttp://faculty.samford.edu/~brtoone

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• Min/Max/Avg CPU load for the entire time a user interacts with the page

• Min/Max/Avg CPU load for the most recent burst of activity (defined as delay > 5 seconds between user interaction)

• Real-time display of current server load– CPU load– Bandwidth

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