Reducing HTTP Requests
A visitor using the Google Chrome browser can only open six TCP connections to your server at once, so the browser has to queue（队列） the remaining 13 requests.
However, if you consolidate all of the template images into a single sprite image, you can reduce the number of requests from 19 to just four.
The CDN Factor
File Compression
Cache Optimization
HTTP cache headers play an important role in the way browsers parse a website, for they determine which content items are cached and for how long.
Caching is storing your static files, which tend to be your largest ones, outside of your server—either on visitors’ local drives or a nearby CDN PoP. This can vastly improve the website’s load speed.
The downside is that manual cache header management can be a tedious and inefficient task. Moreover, caching mechanisms often run into issues when handling dynamically generated content created on-the-fly as a page begins to load (e.g., AJAX objects and even dynamically generated HTML files).
