A common question is what the difference is between Load testing tools and page speed tools. They both measure response time and they both are important when it comes to assess the performance of your web site. So what it the difference and which one do I need?
For most webmasters, the answer is probably that you need both. But before we talk about why, let's try a car analogy.
Your own limousine business
Let's say that you are the CEO of a limousine business. Every single day, you get a call from a client that wants to be picked up at the airport and taken to the city hotel. You send out one of your cars to pick the client up at the airport. The car navigates through traffic and safely leaves the client at the hotel he wanted to go to. Pretty easy.
Now, every now and then, your drivers report that the client wants to get to the hotel quicker and if your business can't handle that, the client will switch to another limousine business. Since you don't want to lose your customer, you take the feedback very seriously and start looking into what you can do about it. If you have any intention to do your work seriously, you're probably going to start with measuring how long it actually takes to get the client from the airport to the hotel. A sensible thing to measure would be to look at the time elapsed from the client's phone call until he is left of at his hotel. You also look into how long time it takes after the call until the car is heading to the airport, how long time it takes to locate the client at the airport and how long time it takes to drive from the airport to the hotel.
After some careful analysis, you end up with a very good understanding of what takes time and you probably have a good idea about some of the things you can do to speed it up. Perhaps you decide to always have a car ready at the airport. You might want to change your stretch limousine car to a Ferrari or even to a motorcycle (an existing service in Paris among other cities) to make the actual trip a bit faster. There's a lot of different things you can do to make your service quicker. At some point, you are happy with the performance improvements and when you are, you have optimized your ability to take one client from one destination to another as fast as possible.
What does a limousine have to do with web pages?
Back to the subject of this article. A lot of web masters have received the same type of feedback as you did as CEO of the limousine service. But instead of complaining about how quick the clients gets to the hotel, they complain that your web page feels slow. And in reality, most of your clients won't even complain, they'll simply direct their browser to a different web site and never look back.
So, as a web master, you want to do the equivalent of measuring how fast your service is. To do this, you want to get hold of a page speed measurement tool, and there are plenty to select from. The two most well known tools are Google PageSpeed Tools and Yahoo! YSlow, they don't stop at measuring the actual page load times, they also give you a lot of insight into what is considered good enough and what you can do to improve the page load speed.
As you begin to implement various fixes to improve your page load time, you most likely go back to your tool of choice and redo your measurements in an iterative process. At some point, you are happy with the performance improvements and when you are, you have optimized your ability to serve one page to one client as fast as possible.
A more complicated limousine service
In reality, the limousine service has a lot of different clients. Not all of them is a single person that want to go from the airport to the hotel. Some clients is a single person that want to go from the train station to the hotel and another type of client is a party of 10 people that want to go from the hotel to the airport. And sometimes things gets really complicated, you get 100 clients calling pretty much at the same time wanting to go in all kinds of directions. For most business owners, having a lot of clients calling would be a nice problem, but it's even more important to be able to keep the service level high, otherwise you just get a lot of disappointed clients, fast.
So, some of the optimizations you made to serve one client really quick will still be valid. Having cars waiting at the airport probably still makes sense, but should you really have a Ferrari or a motorcycle waiting there? Perhaps the stretch limousine that takes 10 passengers was a pretty good thing after all, or a mix? Clearly, this is a much more complicated thing to measure and optimize and to be honest, if I was the CEO of the limousine service, I would have to think hard to even know where to begin.
Load testing tools
The purpose of load testing tools is to help you simulate how your web site performs when you have a lot of clients at the same time. You will find out that some of the optimizations you made to make a single page load really quick makes perfect sense also when you have a lot of concurrent clients. But other optimizations actually makes things worse. An example would be database optimizations, the very indexes that makes the web page super fast as long as the page only require good read performance may hurt you a lot when some client requests are writing to the same tables at the same time. Another example may be memory consumption. When one single web page is being requested, a script that uses a lot of memory can go unnoticed or even speed things up, but in a high load scenario, high memory consumption would almost certainly hurt performance when the web server starts to run out of memory.
So if I was a web master, I do have a pretty good idea where to begin when optimizing a web site for many concurrent users. I would start with a load testing tool.
Load testing tools vs page speed tools
Back to the original question. What is the difference between load testing tools and page speed tools and which one should I use? Again, the answer is that you probably should use both.
Fast loading web pages is crucial so you should absolutely use one of the page speed tools available. Web users turn their back to slow pages faster than you can type Google PageSpeed Tools in your search bar. And the bonus is that a lot of the things you do to optimize single page load times are going to help performance also in high load scenarios.
Fast loading web pages that keep working when you have a lot of visitors is perhaps even more crucial. At least if your web business relies on being able to serve users. If you want to know how your web page performs when you have 10, 100 or even 10000 users at the same time, you need to test this with a load testing tool such as loadimpact.com/
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