Speeding Up Web Page Loading - Part I (1)
As more and more businesses go online, just having a web presence is no longer enough to succeed. It takes a reliable, high-performance Web site that loads quickly too. After all, nothing makes an Internet user leave a site quicker than having to wait ages for a web page to load.
A previous post briefly identified the factors that determine how fast (or slow) your web pages load, namely:
* Size (of your web page)
* Connectivity (quality of your host's network connections and bandwidth)
* Number (of sites sharing your server).
This article will now discuss ways that webmasters can ensure their sites' pages load quickly and efficiently, by focusing on the first factor.
File size - the total of the file sizes of all the parts of your web page (graphics, music file, html, etc.) should be small enough to download quickly. A reasonably fast loading page is sized at around 50 - 70Kb, with up to 120Kb for more graphics intensive pages. You can optimize your file size by:
1. Reducing page weight:
* Eliminate unnecessary whitespace (use tools like HTML Tidy to automatically strip leading whitespace and extra blank lines from valid HTML source) and comments
* Cut down on extras (buttons, graphics) and don't put a lot of graphics and big midi files on the same page
* Move webrings from your homepage to their own page
* Reduce the file size of some of your graphics (use GifBot, an on-line gif reducer at Net Mechanic)
* Redesign pages so it works over 2 different pages instead of just one
2. Reducing the number of inline scripts or /Moving them into external files - inline scripts slow down page loading since the parser must assume that an inline script can modify the page structure. You can:
* Reduce the use of document.write to output content
* Use modern W3C DOM methods to manipulate page content for modern browsers rather than older approaches based on document.write
* Use modern CSS and valid markup - CSS reduces the amount of markup as well as the need for images in terms of layout. It can also replace images which are actually only images of text. Valid markups stop browsers from having to perform "error correction" when parsing the HTML and allows free use of other tools which can pre-process your web pages.
* Minimize CSS/script files for performance while keeping unrelated CSS/scripts in separate files for maintenance
* Use External HTML Loading - involves using an IFrame for Internet Explorer and Netscape 6, and then shifting that content via innerHTML over to a
tag. Benefits: keeps initial load times down to a minimum and provides a way to easily manage your content. Downside: we have to load content along with all the interface elements, which can severely impair the user experience of the page. A tutorial on externally loading HTML can be found here.
3. Minimizing the number of files referenced in a web page to lower the number of HTTP connections required to download a page
4. Reducing domain lookups (since each separate domain costs time in a DNS lookup) - be careful to use only the minimum number of different domains in your pages as is possible
5. Chunking your content - the size of the full page is less important if the user can quickly start acting on some information. How?
* Replace table-based layout with divs
* Break tables into smaller ones that can be displayed without having to download the entire page's content
o Avoid nesting tables
o Keep tables short
o Avoid using tables to lay out elements on the page
o Exploit several coding techniques:
+ split the page layout into multiple independent tables to preserve the browsers' ability to render each of them step-by-step (use either vertically stacked or horizontally stacked tables)
+ use floating tables or regular HTML codes that flow around the floating objects
+ use the fixed table-layout CSS attribute
* Order page components optimally - successive transmission of the DHTML code enables the browser to render the page during loading
o download page content first (so users get the quickest apparent response for page loading) along with any CSS or script required for its display;
o disable any DHTML features that require the page to complete loading before being used initially and only enable it after the page loads;
o allow the DHTML scripts to be loaded after the page contents to improve the page load's overall appearance
6. Specifying image and table sizes - browsers are able to display web pages without having to reflow content if they can immediately determine the height and/or width of your images and tables
7. Using software and image compression technology
* Use mod_gzip, a compression module using the standard zlib compression library, to compress output - compressing the data being sent out from the Web server, and having the browser decompress this data on the fly reduces the amount of data sent and increases the page display speed; HTTP compression results in 150-160% performance gain (sizes of web pages can be reduced by as much as 90%, and images, up to 50%)
8. Caching previously received data/reused content - make sure that any content that can be cached is cached with appropriate expiration times since caching engines reduce page loading time and script execution by performing optimizations and various types of caching; cuts down latency by as much as 20-fold, by preventing dynamic pages from doing any repetitive work, and reducing the turnaround time for each request
9. Choosing your user agent requirements wisely - specify reasonable user agent requirements for projects; basic minimum requirements should be based upon modern browsers which support the relevant standards
The next post will focus on the other two factors, as well as other ways that
webmasters can speed up their web page loading.
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