If you think your website is fast enough, think again.

Slow web pages lose customers

experts at websiteoptimization.com have to say about the topic:

Google found that moving from a 10-result page loading in 0.4 seconds to a 30-result page loading in 0.9 seconds decreased traffic and ad revenues by 20% (Linden 2006). When the home page of Google Maps was reduced from 100KB to 70-80KB, traffic went up 10% in the first week, and an additional 25% in the following three weeks (Farber 2006).

Tests at Amazon revealed similar results: every 100 ms increase in load time of Amazon.com decreased sales by 1%. (Kohavi and Longbotham 2007).

(source)

I think a slow site is 1 second or more, for the basic page.

But once all the graphics, style sheets, google/facebook code loads, some pages can be as slow as 5-10 seconds.

There are a tonne of tricks to reduce the number of http requests, and size of pages and graphics. My favourite tool is apache mod pagespeed .

You need a fast database obviously, and all your caching turned on.

I think under 0.5 seconds for your home page is only reasonable. Even at this speed, a sudden spike in traffic will still crash your server.

The traditional approach is to scale up your web and database server, and separate out into different server. Then scale out the web servers with load balancing, and multiple databases, and it gets messy. If your traffic triples for Christmas, you have to triple all your servers, but what if it goes up 10 times, you are screwed.

Really fast pages get down to 0.01 seconds or less, these sorts of speeds have serious caching, and can handle all most any spikes. So its smarter to work your caching harder, and get your pages faster, and you have to scale out way way less. This strategy doesnt work with everything, but it can help dramatically in some situations.