Optimizations to reduce website loading time

Question

What are some important optimizations that can be made to a website to reduce the loading time?

Answer 1

There are two sides you can care about, when optimizing :

• The server side : what matters is generating the ouput faster
• The client side : what matters is getting all that has to be displayed faster.

Note : we, as developpers, often think about optimizing the server-side first... Which in most cases only represents less than 10% percent of the loading-time of the page !

On the server side, you'll generally want to :

• profile, to determine what's long
• optimize your SQL queries, and reduce their number
• use caching

For more informations, you can take a look to the answer I gave some time ago to this question : Optimizing Kohana-based Websites for Speed and Scalability

On the client side, the biggest gains are generally achieved by :

• Reducing the number of HTTP requests -- the easiest way being to reduce the number of JS/CSS/images files, by combining several files into one
• Compressing CSS/JS/HTML, using for instance Apache's mod_deflate.

About that, there is a lot of great stuff on Yahoo's Exceptional Performance : they've released lots of good pratices and tools, such as yslow.

Answer 2

The first optimisation is: Decide if it is slow, and if not, don't bother.

This is trickier than it sounds, because it's not like testing a desktop app or game. A game is slow if when you play it on the target hardware, the frame rate is too low. This is very easy to measure.

A web site is trickier, because you, as the developer, are probably using a local test system with a very fast network. Even when you use your staging / system test servers, you're probably still on the local network. Even your production servers are in all likelihood, on the same continent.

The same is possibly not true for quite a lot of your users.

Therefore the options which exist are:

• Find out by asking your users, whether they find it to be slow
• Simulate a high latency environment and test it yourself (or your QA team)
• Guesswork

The latter is not recommended.

An option which the holier-than-thou Yahoo Web Sites performance book (which yes, is a book you can buy) doesn't mention a lot is HTTPS. Most web applications which handle important data run mostly or entirely over HTTPS, which changes the rules of the game rather a lot. Remember to do all testing with it enabled.

Answer 3

install firebug and pagespeed plugin follows all the pagespeed directives (until possible) and be happy http://code.google.com/intl/it/speed/page-speed/

anyway the most importante optimization in my experience is to reduce the number of HTTP requests to a minimum...

Answer 4

Load balancing would help to reduce the loading time immense.

Answer 5

i wrote some things about, see:

Google page speed test optimization

Answer 6

Here are a few "best practice" things:

• Caching CSS, JavaScript, images, etc.
• Minifying Javascript files.
• gzip content.
• Place links to JavaScript files, JavaScript code, and links to CSS files at the bottom of your page when possible.
• Load only what is necessary.
• For an existing website, before you do any of this determine where your bottlenecks are with tools like Firebug and as someone else mentioned YSlow (I highly recommend this tool).