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Posts Tagged ‘Load Testing’

Compression,Decompression,Mobile Performance and LoadRunner

February 4, 2013 by kiranbadi1991 | 2 Comments | Filed in Decompression, Development, LoadRunner, Performance Center, Performance Engineering, Scripting, SilkPerformer

Recently I inherited some of the  LR scripts from one of my colleagues,it was all about building the json calls for stressing the backend spring security framework which was first layer of entry into the mobile infrastructure.Those scripts were simple scripts  built using the custom request with json string as a body part.One of the things that really surprised me as part of this effort was that web custom request in itself was taking close to 100ms to 300ms to do decompression of the server response during load testing.

Okay first let me give you some background,servers were configured to send the response compressed in gzip format with content encoding header as gzip.The functionality under scope had SLA of 1 sec max and quite a few functionality in scope also had SLA that was less than 500ms.Quite a challenging SLA’s I would say.But again these functionality were supposed to be accessed over the mobile device,so probably less the response time better it is for users.

Most of the response coming from the server for all functionality was served as chunked bytes,so what it means is that server sends initially some bytes as response in compressed gzip format,LR decompresses  those bytes in 5 to 10ms and then again server sends next range of bytes as chunked gzip response and then again LR will spend close to 5 to 10ms to decompress those bytes and like wise the process continues till we have final set of bytes.All these process happens in the single connection and connection never closes with the server.In case if you do have some server response validation in place, then expect that it will add another 10ms to do that validation.

Now I have measured all these times in the single iteration of vugen,these times increase exponentially when we are running the Load Test in controller or PC and this overhead of decoding the gzip content becomes a quite an issue when response time SLA are in ms.

Here is how it looks when you see the behavior in LR Vugen with decompression on in the script.You can see that it takes 5ms to decode the 154 bytes of response.Now imagine the normal webpage will have size of 2mb of data gzipped,so you can see the impact of this decoding  when size of page increase specially when response is coming as chunked bytes with no fixed content length from the server.

pic1

 

I think HP LR team might also be aware of this behavior and probably that the reason as why they might have come up with function to disable this.Use Web set option with decode content flag turned off if you are running the scripts which do not require validation and has response time SLA’s in ms.The drawback of disabling this feature is that all your correlation and other checks for server response will fail since server response will show up as binary content like below.

pic3

 

I would suggest you to disable this feature if you can and do the response validation by using the other techniques like verifying server logs etc.By disabling this you will gain close to 15 to 20% reduction in response time reported by LR.

Is this expected behavior of LoadRunner ?, I think they have to do this,unless they decode the response, none of the other function like web reg save param or web reg find will work and these functions are core functions of LoadRunner.Probably the right way is that LR should not add these decompression timing in their transaction markers.These timing really pollute the results specially for web applications or probably they can increase the speed of this decompression library what they are using in LoadRunner.

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Performance Testing Web based Ajax Applications–Then Read this

June 23, 2012 by kiranbadi1991 | 2 Comments | Filed in Browser, Development, LoadRunner, Others, Performance Center, Performance Engineering, Performance Test Tools, Scripting, SilkPerformer, Testing

From past couple of days,lot of people have asked me about Ajax,Ajax protocol and how to Load Test Ajaxified Applications. So I though let me write a short code and try explain my thoughts about this. Ajax is often used in the web site to do quick and short interaction with servers for implementing some of the if then condition to implement some requirement.Ajax helps a lot in bringing some interactivity or I can say it creates VOW experience.Of course I am not the hard core front end engineer ,but yes having written couple  of lines of CSS/HTML/Javascript, I can visualize and make a sense as how to write the front end code which brings some interactivity to the site.

For the sake of this post, I have used Jquery library which has rich methods for making Ajax calls.It also has excellent methods of interacting with CSS and HTML markup elements.With Jquery we can easily write the call back function and write the response data to the DOM on the fly based on some conditions.Few drawbacks Which I noticed using  Jquery library is that it makes you lazy (If you really want to become good front end engineer, then having good gasp of Raw javascript is must) and just for implementing one or 2 functionality , I have to import 10 k lines of code.But again with Jquery benefits outweighs the risks.

Implementation of Ajax with Jquery looks something like below

$(document).ready(function(){
    $(“form”).submit(function(event){  
         event.preventDefault();
        var ae = $(“#idtxt1”).val();
        var ap= $(“#idtxt2”).val();
           alert(ae);
           alert(ap);
        var request = $.ajax({  
            url: “TestAjax.do”,
            type: “POST”,
            data: {
               email:ae,password:ap
            },
            cache: false,
            ifModifiedBoolean:false,
            beforeSend:function(){
              $(“#idspan”).val(“”);  
            },
            success:function (data){
//                $(“#idspan”).append(data);
                if(data == “Success”){ //redirect…
                      window.location = “/mysite/mypage.php”;
                } else { //report failure…
                       $(“#idspan”).append(data);
                }

            },
            error: function(data) {
               $(“span”).append(“data”);
                 
            }
        })            
    });
});

 

The granular level of details of Jquery Ajax function can be found here. So you might be thinking as why I have written this piece of code when it’s already available. This post is not about Jquery or how to use Jquery, this post is about understanding Ajax and how they are implemented and based on that coming up with proper solution for load testing Ajax based web applications.

If you look at the above code closely,you can observe that it does post request on the form submit event.As soon as user clicks on the submit button it does the call to the backend program.This is how browsers operate.Browsers bring interactivity to the site using event driven methods.This understanding is the key to know as how Ajax calls are made, every Ajax call is associated with some user driven event on the HTML Element. Events could be on Click, on Submit, on Hover,onMousein,onMouseOut,Focus in,Focus out,onKeyPressup and onKeyPressdown.These are some of the events which are associated with the HTML Elements and Javascript is used bring some interactivity to the site on occurrence of the these events.So every Ajax call has some event associated with it.Please note that there are many many events associated with each HTML element and complete reference of those can be found ECMA Javascript Guide or Web Standards document.

So continuing further, the above code makes the Ajax post call to TestAjax. do function which resides on the backend server.In above Ajax function call I am collecting value of 2 text fields name #idtxt1 and #idtxt 2 and passing those values as post body request to my backend J2ee program.Most of the Ajax calls irrespective of the library used do these things in the similar way(almost 99.99% of time),they capture the user inputs with Javascript methods and then post the data to the backend program which resides on some application servers.The program which resides on the backend servers communicates to the Ajax call whether the request has passed or succeeded.If the request succeeds , for example in above code if my backend program sends me the data as “success”, I redirect the request to mypage.php and if requests fails, I write some error text to the HTML  page within Span Element.

The browsers developers tools also helps in understanding the way Ajax often works,

      image

If you capture the network trace with Browser’s developer’s tool, the trace would look something like above, in the trace you are clearly see that Initiator of the call was  XMLHttpRequest. This is nothing but the core method which implements Ajax calls in the browsers.Since the above request was of type GET, values were appended to the url of the request and send to the backend program.In addition to this these tools bar also give lot of other information like http status code, which event initiated the request etc.However I will not suggest you to measure the response time of Ajax calls with these tools as I believe they somewhat give incomplete picture of response time.

The response data received from the server can also be viewed via browser developer’s tool and in my case it was looking some thing like below,

image

This response data(“Username not available”) is later appended to the page elements which is viewed the end users.

So coming back to original purpose of this post, I keep hearing from various Performance Engineers that existing Web Http protocol is insufficient in testing Ajax based web applications, now having implemented real time Ajax with fat datasets, I believe there isn’t much challenge to load test Ajax based applications.We just need to keep some key things in mind while working with Ajax based applications,

  • Understand the functionality of your application from technical prospective.
  • Ask developers explicitly, which functionality in the application is using Ajax call, is the Ajax call synchronous or Asynchronous.With Synchronous Calls,one cannot proceed unless he receive the data from the server for his Ajax call and with Asynchronous calls, one can work on the other parts of the page(Technically with Async Calls, browser need not wait for server response to build DOM Tree and with Sync calls, it has to wait for server response).
  • If you believe some events for your applications are not getting recorded via regular HTTP protocol, then probably you are not triggering the Ajax call at all.Remember to trigger Ajax call, you need to Trigger an event on the html element and it could be that you need to tab out of the element or bring focus in that element etc etc.Ask your developer as how to trigger a Ajax call for the business process under scope.
  • If you believe that you are not able to record Ajax call, then probably your Ajax request is cached.Ajax calls are heavily cached by browsers since they contain all JS/CSS files in them.Clear browser cache/cookies etc etc and Try again.Use Developer tools bars to debug such cases,ensure that you get 200 status for all your resources.
  • Ajax calls irrespective of libraries or technology uses regular GET/POST types which is nothing but http calls.Http calls should and must be recorded if tool claims to support HTTP Protocol.
  • If you see some unique values getting generated at the client side and these values are not seen in the server response, don’t get scared or nervous, they might be Unix style timestamp or Microsoft tick timestamp(However If you get Tick, you have solid reason to worry and it could be your pure good luck if your application is not using complete power of Tick.If it heavily uses Tick, then probably you need to go temple and prey God.You will surely require his blessing.Most of the current set of tools don’t go beyond Unix style timestamps and Tick is much more powerful timestamp format than Unix style timestamp).These values are generated by JS library in order to force browser not to cache the key JS files.However lot depends on the headers as well.
  • Thick client web based applications often uses chained JS calls to build different parts of the page, All you need to do in these cases is to ensure that you follow the right steps, trigger the events which chains many events during recording and then do your regular steps.
  • Remember for Load Testing Ajax based application still the goal would be capture the network traffic which goes out of the application to the server and stress the server for those calls.If your Ajax calls are slow, then it gives an impression that front end is taking more time,most often it is never true.Spinning wheel which keeps spinning for minute or seconds indicates server bottleneck and not client side bottlenecks.
  • Remember client side performance measurement metrics/techniques are different than Server side performance measurement/techniques.They require different skillsets and tools.Just having lot of Ajax calls do not necessarily mean that you have client side performance issues.However it does mean that you do lot of DOM Work and always browser needs to keep working or guessing so as to where and how much some space for response data.So repainting and refills of DOM happens quite often.

So finally you must be wondering if Ajax can be done with regular http protocol, then why are companies like HP coming up with new Ajax based protocol etc for Load Testing.

Answer is simple, they want to save some time for scripting and time is money in corporate world.

How much time it saves ?

Again I cannot say as I have never used these protocols myself.But I have some doubt whether they can successfully emulate the calls for all events.There are lot many ways to trigger Ajax calls.If you use Ajax protocol without understanding the fundamentals of Ajax, then I would say probably its incorrect way of doing the Job.There exists a high risk that your text checks will always succeed not matter what as most tools do not have JS Engine or HTML Parser in them, so they have limited ability to read or write to the HTML document.With Ajax most of the time error validation is done without browser refresh based on some conditions.So you have extra cautious here.

If you still believe we cannot test Ajax based application with regular http protocol, then I would like to hear from you about such cases and would appreciate your feedback with some sample test use case.

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Sessions, Client Side Javascript and Correlation

June 8, 2012 by kiranbadi1991 | Comments Off on Sessions, Client Side Javascript and Correlation | Filed in Browser, Development, Environment, LoadRunner, Performance Engineering, Performance Test Tools, SilkPerformer

Recently I one of my good friend asked me a question ” How do I correlate the session id information which is created via javascript with LoadRunner”

Well this was an interesting question and of course he was not the first one to ask about this, there are lot many people who had asked this question in various online forums like LinkedIn etc.So I thought let me write some of my thoughts on this,

Http protocol as known today technically is the stateless protocol.It means that it cannot distinguish between the first time visitor or a regular visitors.It just forgets the client as soon as request is serviced and this behavior of the HTTP creates the need for maintaining the session information.This is reason as why session generation and maintenance is handled by the programming languages.

Session management with http is normally done by using below techniques

URL Rewriting

With this method of session handling, session ids are often appended to the query string of the url and the query string looks something like below,

http://www.mydomain.com/mysite/someproduct.aspx%7someurl?name1=value1&name2=value2&name3=value3…etc

Depending on the way we design the application, session information can pass as query string parameters namely in key/value or name/value format and this applies even to session ids.Also at times this method is often used whenever client do not accept cookies for some reason.In fact some servers like web logic etc automatically switches the session handling to this method once they detect that client is not accepting cookies from the server.

URL Rewriting often  leads to ugly urls  so at times these url’s are hidden from the client and replaced by good and short looking url’s.This trick is done by server side modules which can rewrite the urls on the fly(Apache mod rewrite is one such example).The best way to identify if your application uses this method of session handling is to block all cookies via browser and test it.Also there exists some restriction on the length of the url with regard to some browsers like IE.IE cannot take length of the url beyond 2k bytes.

http://support.microsoft.com/kb/208427

Also using this method at times could lead to security hole as referrer tag are leaked if one navigates in the via same browser window.

Hidden fields

In this method of session handling, extra form fields are sent to the client and these extra form fields always hidden from the client.The hidden fields look something like,

<input type=’hidden’ name=’id’ value=’a’/>

Hidden fields are also used to maintain the page information across the pages and is one of the frequently used method  to maintain session information.The good thing of this method is that url’s remains short and large data can be passed over the server for processing.In addition to session information, hidden fields can also be used to persists the client entered data across the pages.

Cookies

I feel this is simplest way to maintain the session information and definitely better than url rewriting and hidden fields.Most application as soon as they receive first request, server drop the cookies on the client computer and later on for every subsequent request , they check for its existence in client requests with regard to  further communication.So if we as performance engineer comment out these cookies, then obviously we are asking application to do more work and is definitely a wrong load model as well.Cookies are never commented out in real world scenario and should not be commented out during load testing as well.

HttpSession Objects

These are objects which are created on the server side to store session information.These session objects are never passed on the client.However there might be cases where unique identifier namely jsessionid is appended to the url and send across to the client,in case client do not accept cookies.In this method session is stored in the memory and if the session object is too large, then it gets serialized to the file system or to some disk.Personally I have seen good performance with this method of session handling whenever the user base is small.How ever storing session in the httpsession objects could lead to heavy resources consumption given that sessions cannot moved outside the servers.In other words, application using this method of session handling cannot effectively use  server farms or web gardens as sessions are inproc. Also using this method leads to inefficient usage of load balancers.

Now having discussed some basics on sessions,so where does client side javascript fit in all these ?

Storing or accessing the session via javascript is all big security hole. I don’t recollect even a single instance where javascript was used to maintain sessions for any of my projects.So I doubt if any one uses Javascript to create session or store session information.

So with javascript can we create or access the sessions or session ids ?

I would say yes.Javascript provides rich set of methods to access url’s/cookies/hidden fields and with Ajax , we can definitely create and maintain the session information with javascript.However interesting point here is that what if client turns off javascript in their browsers ? 

Knowing  these risks, do you still believe that people are going to use Javascript to store session information ?

If yes, then probably I need to write another post on how to get around these type of cases given that no load generating tool existing in the market today can execute or capture javascript events correctly as done by the browsers in real sense.

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