Load Testing Blog
Bandwidth, latency and geographical distance in load testing
Because we usually talk about latency in tiny numbers (e.g. 20 milleseconds of latency) it is easy to overlook just how big an effect latency can have on the effective bandwidth between geographically distant locations. While running some recent tests to measure the available bandwidth from our cloud engines, I accidentally ran a test between a load engine and a server that were more than 2600 miles apart. Knowing that our server and engine should have both delivered better results, it took me a few minutes to realize that one mistaken click (where to start the load engine) had … Continue reading »
Javascript/JSON Support in Load Tester 4.3
Over the last year, Web Performance engineers have been working to make Load Tester smarter and easier to configure. Load Tester 4.2 introduced the new Fields View, which allows test case developers to write out HTTP requests using a flexible and composable assortment of data sources.
Starting with Load Tester 4.3, Load Tester will automatically recognize JSON content in any HTTP request. As a consequence, each JSON element will become a configurable name-value pair field in the Fields View. We believe this will make it much easier to configure complex AJAX and RESTful style test cases.
Furthermore, whenever Load Tester’s Application … Continue reading »
How much bandwidth can we expect from cloud engines during a load test?
I got into a discussion in the Performance Testing group on LinkedIn which raised a question that we had answered internally, but had neglected to share with our customers – how much bandwidth do our cloud engines have available?
Before I proceed, I must make this disclaimer: our cloud engines run on Amazon’s EC2 infrastructure, so the rules that apply there also apply to our cloud engines. Amazon does not make any guarantees for bandwidth, so anytime your test results look suspicious, we recommend doing a quick bandwidth test. Note that there is a Bandwidth Test wizard in Load … Continue reading »
How HTTP Authentication works and why load testers should care
The most commonly used authentication method for websites is a login form on a web page. We’ve all seen them – enter your username and password into fields on the web page and press the Submit or Login button. From the standpoint of the underlying technology, this is no different than submitting any other form – only the names of the fields distinguish them as login or password fields and the security mechanism is implemented within the web application.
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Our experts … Continue reading »
What’s new in Load Tester 4.2
The 4.2 release focuses on platform compatibility and productivity increases from our services work in the past year with such clients as the US Census and the New York Marathon.
With a slew of new browsers and operating systems available, this release also includes support for 64-bit Windows and AIX operating systems, the latest versions of Internet Explorer, as well as the Chrome and Safari browsers.
On the productivity side there are some pretty big changes to allow testers to configure more complex testcases with less effort than ever before. Some of those changes are evident in the new Fields View and … Continue reading »
Load Testing Data Population: How Many Rows?
A common problem when setting up a load testing configuration in Load Tester is figuring out how many rows of data you need for a particular test. For example, you need to have a set of user names and passwords to be used during the test, but how many do you need to ensure that the test will complete?
To answer this question, you need to know three things: the duration of the test, the expected duration of the test case, and how many concurrent users the test will simulate. Fortunately, these things are usually easy to determine. The test duration … Continue reading »
How To Manually Modify HTTP Requests in Load Tester 4.2
In older versions, Load Tester provided a simple interface for modifying the URI portion of an HTTP request. For example, you could add a query parameter or a path segment by adding it directly to the request line in the Edit HTTP Request-line/URL dialog.
In Load Tester 4.2, this process has been made slightly more complex but vastly more powerful. We’ll start by manipulating the URI field directly. To do so, select the specific transaction you wish to edit, then select the Fields View, then choose “Customize” from the “Choose customization” drop-down menu in the upper right … Continue reading »
Load Testing Basics: How Many Concurrent Users is Enough?
How Many Users Can Your Website Handle?
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The most common question regarding a website’s performance is not how fast the website is or how it scales, but something more fundamental:
What should the performance goal be in terms of concurrent users?
Should it be one hundred concurrent users? A thousand? Ten thousand? Does it require one server or a hundred to handle the load?
There’s a good reason for how many times this question comes up: it’s tricky and … Continue reading »
Load Testing Back to Basics: Avoiding the KeepAliveTimeout Race Condition
You’ve recorded your test case, configured your datasets, and run your replays. You start up the load test and … you see numerous errors like this:
“The connection with the server was unexpectedly closed before starting the response.”
What’s going on? Well, one common reason for this error is a connection-related race condition between Load Tester and the web server due to the server’s configured persistent connection timeout.
Persistent connections are an HTTP mechanism for minimizing network connection overhead between the browser and the web server. If the client has the Connection request header set to Keep-Alive, and the server responds with the … Continue reading »
IE8, favicon.ico and silly server stunts
At first glance, load testing software seems like it should be pretty straightforward. And like most things, it turns out to be really complex — at least, if you want to do it well. Simulating a browser could be pretty easy – except for the need to do it very, very, very efficiently, so that the solution can scale to simulate hundreds or thousands of virtual users per computer.
What does this have to do with favicon.ico and IE8? Occasionally while helping a customer use Load Tester, we run into some behavior that is difficult to explain, and this was one … Continue reading »