網站加速最佳實踐 – 避免重定向

參考： http://developer.yahoo.com/performance/rules.html#redirects

 

Redirects are accomplished using the 301 and 302 status codes. Here's an example of the HTTP headers in a 301 response:

      


HTTP/1.1 301 Moved Permanently

      


Location: http://example.com/newuri

      


Content-Type: text/html

The browser automatically takes the user to the URL specified in the Location field. All the information necessary for a redirect is in the headers. The body of the response is typically empty. Despite their names, neither a 301 nor a 302 response is cached in practice unless additional headers, such as Expires or Cache-Control , indicate it should be. The meta refresh tag and JavaScript are other ways to direct users to a different URL, but if you must do a redirect, the preferred technique is to use the standard 3xx HTTP status codes, primarily to ensure the back button works correctly.

 

The main thing to remember is that redirects slow down the user experience. Inserting a redirect between the user and the HTML document delays everything in the page since nothing in the page can be rendered and no components can start being downloaded until the HTML document has arrived.

 

 

如果少了網址最後的“/”會讓重定向更慢！

One of the most wasteful redirects happens frequently and web developers are generally not aware of it. It occurs when a trailing slash (/) is missing from a URL that should otherwise have one. For example, going to http://astrology.yahoo.com/astrology results in a 301 response containing a redirect to http://astrology.yahoo.com/astrology/ (notice the added trailing slash). This is fixed in Apache by using Alias or mod_rewrite , or the DirectorySlash directive if you're using Apache handlers.

 

 

從舊網站連結到新網站通常會使用重定向，這樣做雖然簡單，但是會降低使用者體驗（速度）。

 

Connecting an old web site to a new one is another common use for redirects. Others include connecting different parts of a website and directing the user based on certain conditions (type of browser, type of user account, etc.). Using a redirect to connect two web sites is simple and requires little additional coding. Although using redirects in these situations reduces the complexity for developers, it degrades the user experience. Alternatives for this use of redirects include using Alias and mod_rewrite if the two code paths are hosted on the same server. If a domain name change is the cause of using redirects, an alternative is to create a CNAME (a DNS record that creates an alias pointing from one domain name to another) in combination with Alias or mod_rewrite .

 

 

301 redirect: 301 代表永久性轉移 (Permanently Moved) ，

302 redirect: 302 代表暫時性轉移 (Temporarily Moved ) ，

參考： http://blog.joycode.com/ghj/archive/2007/09/21/108696.aspx