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Performance Optimization for Cascading Style Sheets

web performance optimization of CSSAs we've documented previously on this blog, a majority of perceived Web page load time resides on the front end - i.e., in how a page is rendered to a user. A poorly designed Cascading Style Sheet (CSS) file can have a negative impact on the time it takes a page to display to the user. What's worse, a poor CSS design might load quickly, but inhibit subsequent performance due to expensive redraw behavior. The following article examines a few key issues in CSS performance, and more importantly, how to decide whether it's worth the effort in the first place.

 

Assessing the Web Performance Impact of CSS

A key principle of performance improvement is that any changes should be driven by data. Before tweaking your site's performance, you need data to tell you which functions or features are causing the biggest delays.

For CSS, the one factor that causes the most performance lags are selectors. Selectors are the statements that specify to which elements a given set of CSS styles will apply. Selectors can be simple, addressing an element by its type:


DIV {
font-weight: bold;
}

Or they can be complex, using a combination of tag name, ID, class and child references to style a specific subset of elements:


#menus ul ul li.current-menu-parent > a{
background:#222;color:#fff;text-shadow:0 0 0 #222;
}

CSS2 and CSS2 also support a sizable number of advanced selectors, including universal selectors, attribute selectors, and pseudo-classes.

Longer selectors generally run more slowly. To profile the running times of selectors, developers can use one of the many CSS profilers available on the Web which will run all of the selectors on a page and calculate their individual running times.

For a simple profiler, you can use Andy Edinborough's CSS Stress Test Bookmarklet, which profiles the running time of all CSS selectors included in a page. Many Web browsers are now shipping with style profilers built in. Opera included a Style Profiler with its Dragonfly release last year. Google Chrome has made CSS selector profiling available in its Page Speed browser extension.

Web Performance Optimization, Part 10: The Evolution of Client Side Caching

web performance optimization client side cachingWhile we've touched upon client side caching in our series on Web performance, we haven't discussed how client caching has grown more rich and useful over the years. In the initial days of the Web and the HTTP/1.0 protocol, caching was mostly limited to a handful of headers, including Expires, If-Modified-Since, and Pragma: no-cache. Since then, client caching has evolved to embrace greater granularity. Some new technologies even permit the deployment of offline-aware, browser-based applications.


Browser Request Caching

The most common and oldest type of client-side caching on the client is browser request caching. Built into the HTTP protocol standard, browser request caching allows the server to control how often the browser requests new copies of files from the server. We discussed the major aspects of browser request caching in part 1 of our series. Over time, Webmasters have taken to using different headers to improve caching on their site, including:

Pragma: no-cache. This old directive is used mostly by HTTP/1.0 servers, and instructs a client that a specific response's contents should never be cached. It is used for highly dynamic content that is apt to change from request to request.

Expires. Supported since HTTP/1.0, this header specifies an explicit expiration date for cached content. It can be superseded by the value of the Cache-Control header. For example, if Cache-Control: no-cache is sent in a response, this will take precedence over any value of the Expires header.

If-Modified-Since: Since the HTTP/1.0 protocol, clients have been able to use this header to request that the server only send data if the resource has been changed since the specified date. If there have been no changed, the server returns an HTTP 304 Not Modified response.

Web Performance Optimization, Part 9: Optimizing HTML

web performance optimization HTMLIn our past installments on Web performance optimization, we've seen how caching, server configuration, and the use of Content Delivery Networks (CDNs) can increase a Web site's responsiveness and improve Web performance metrics. Most of the techniques we've reviewed have focused on configuring the Web server or optimizing server applications. Unfortunately, a Web page that downloads quickly but is slow to parse or execute on the client will appear just as slow to a user as if the Web server were on its last megabyte of memory. In this article, we'll discuss some ways that Web page content can be streamlined for an optimal client-side experience.

 

Streamline JavaScript Includes

web page optimization fewer requestsJavaScript abounds on the Web. From jQuery to Dojo, the Web is full of JavaScript libraries that can easily be dropped into a Web application. And any site whose developers are actively adding features is going to accrue its own storehouse of .js files. Unless a site's JavaScript is carefully managed, its Web pages could end up making a dozen or more separate requests for scripts. As we've already discussed in our article on
web performance optimization non-caching strategies
, the more requests your site makes, the slower it will load.

Tip of the hat to TechAttitude.com for the graphic showing how Web page sizes and number of objects have grown tremendously over the past 16 years. In the interesting article they state, "...the average size of a web page has increased by more than five times since 2003" and "the use of mulitmedia is increasing by 100% each year".

Follow these guidelines to manage and reduce the burden of JavaScript on your Web pages.

Web Performance Optimization Part 7: WordPress Tuning

web performance optimization for WordPressIn recent years, the good folks at WordPress have made it easier to use their free software not just as a blog, but as the hub of a rich content management system (CMS), complete with static content and custom data types. Given that, it's no surprise that Webmasters and businesses around the world are increasingly basing entire sites around the platform. (And did we mention the "free" thing?)

While WordPress runs decently out of the box, site operators who employ a few tweaks and follow a few rules of thumb will achieve much better performance in the long run. In this article, we look at the best practices that will keep your WordPress site humming efficiently.
 

Limit the Number of Plugins

WordPress plugins are great. With a few clicks, ordinary users can add complex functionality to WordPress that otherwise might have taken hundreds or thousands of hours of programming.

But plugins also present a performance danger. Each plugin in the WordPress plugins directory must be loaded every time a new request is made. Even if the plugin is disabled, it will still load. This performance "gotcha" particularly affects sites on shared virtual hosting systems (e.g., Dreamhost, HostGator). Performance degradation can be dramatic on shared hosts; in some situations, user requests may never finish completing.

The number of plugins that will cause a site to slow down will vary based on a variety of factors. The author has been told by representatives of HostGator that they encourage customers to limit the number of installed plugins on their virtual hosting service to seven. Webmasters should select the WordPress plugins they employ carefully, and use a load testing service to measure the performance impact of any new plugins that they add to their system.

Web Performance Tuning = 10% Profit Increase

Your website is a little slow - so what? Well, it is probably costing you money. I have been researching published facts about web performance because we are always trying to understand our industry better. This post should help you realize that improving your web application performance can directly impact your bottom line by 10% or more. Don't believe me? Read on...

Load Balancing in ASP.NET

For large companies, load balancing is an important feature to use to increase performance. Large companies with the available resources will use web farms. Web farms give your applications the ability to use multiple servers for resources more commonly known as pooling resources. Load balancing helps distribute user requests through a dispatch application that redirects to the different web farm servers.

balancing load

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