Hints on performance (part 2)

For curiosity I often take a look into the the HTTP headers of websites I visit (I use the great Firefox plugin HTTP Live Headers for it). On some major websites I discovered that these don’t make use of HTTP pipelining, which is nowadays a major performance drawback, since today’s website include much more items (images, CSS, Javascripts) than a website of 1998.

Quoting http://www.w3.org/Protocols/HTTP/Performance/Pipeline.html:

For all our tests, a pipelined HTTP/1.1 implementation outperformed HTTP/1.0, even when the HTTP/1.0 implementation used multiple connections in parallel, under all network environments tested. The savings were at least a factor of two, and sometimes as much as a factor of ten, in terms of packets transmitted.

This point isn’t directly related to Day Communique, but can be aplied to all webpages. Take your browser and check if your site makes use of HTTP 1.1 pipelining. How?

Well, that’s pretty easy: Take your browser (I suggest Firefox and the above mentioned plugin Live HTTP Headers), open the plugin and then goto your website. Then check the answers if they contain the line “Connection: closed”; whenenver you see this line, it means that your browser must open a new TCP connection to fetch another file from the server. In the best case you should not find this header at all. If you find such a line, you should really sit down and try to get rid of it.

2 remarks to the dispatcher:

1. The apache webserver can deliver files from cache or from the dispatcher without breaking the HTTP pipelining. So here it doesn’t matter if a file is taken from the cache or fetched from CQ; if you configured your Apache correctly, you’ll never get a “Connection: closed”.
2. The dispatcher itself also fetches files using HTTP pipelining by default. You can force it not to do so, but I don’t recommend it. In a version before dispatcher 4.0 this behaviour was broken, but in the most recent versions it works perfectly. And of course: The servlet engine bundled with CQ 3.5.5 and newer supports HTTP pipelining out of the box.

For further reading I recommend Aaron Hopkins’ “Optimizing Page Load Times” and for general performance hints the Best Practices for Speeding Up Your Website by Yahoo.