September 2007
Intermediate to advanced
170 pages
4h 24m
English
Content preview from High Performance Web Sites
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Parallel Downloads
The biggest impact on response time is the number of components in the page. Each component generates an HTTP request when the cache is empty, and sometimes even when the cache is primed. Knowing that the browser performs HTTP requests in parallel, you may ask why the number of HTTP requests affects response time. Can't the browser download them all at once?
The explanation goes back to the HTTP/1.1 specification, which suggests that browsers download two components in parallel per hostname (http://www.w3.org/protocols/rfc2616/rfc2616-sec8.html#sec8.1.4). Many web pages download all their components from a single hostname. Viewing these HTTP requests reveals a stair-step pattern, as shown in Figure 8-1.
Figure 8-1. Downloading two components in parallel
If a web page evenly distributed its components across two hostnames, the overall response time would be about twice as fast. The HTTP requests would behave in the pattern shown in Figure 8-2, with four components downloaded in parallel (two per hostname). To give a visual cue as to how much faster this page loads, the horizontal width of the box is the same as in Figure 8-1.
Figure 8-2. Downloading four components in parallel
Limiting parallel downloads to two per hostname is a guideline. By default, both Internet Explorer ...
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.