Entries from September 2008 ↓

Even fast connections suffer from multiple HTTP request overhead because of network latency and HTTP request processing overhead.
MSIE7 opens no more than 2 connections per domain, Firefox3 - 4-6 connections, Google Chrome - 6 connections.
Let’s suppose that time to first byte is 70ms (typical response time of http://google.com via 1.5 Mbps ADSL connection from Dulles)
If a page view involves loading of 20 images from the same domain, then total overhead in MSIE7 is 20/2*70ms = 700ms. The more images site contains, the more time visitor will have to wait.
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Caching speeds up repeated page views and saves a lot of traffic by preventing downloading of unchanged content every page view.
We can use Cache-Control: max-age=… to inform browser that the component won’t be changed for defined period. This way we avoid unneeded further requests if browser already has the component in its cache and therefore primed-cache page views will be performed faster.
Modern browsers able to cache static files even without any cache control headers using some heuristic methods but they will do it more efficient if we define caching headers implicitly.
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Compressing content on server before sending it over HTTP is a good practice since it saves a lot of traffic and makes transfers faster.
For example, Prototype.js is 123KB size and after Gzip compression it becomes only 28KB.
GZIP Compression also affects HTML so even primed cache requests that downloads mostly only HTML will be faster.
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