High performance web site - reading notes (4)

11. Avoid Redirects
Redirects hurt performance
Response status code is 3xx for redirects (300-307, and 304 is for conditional Get)
Redirects delays html doc, CSS impacts rendering, JS impacts rendering and parallel download
Missing Trailing Slash
    Apache alias/mod_rewrite/DirectorySlash
    autoindexing
Connecting Web Sites
Tracking internal traffic - referer logging
Tracking outbound traffic - beacon (http request contains tracking info in the URL)
Prettier URL - Avoid redirect using Alias, mod_rewrite, DirectorySlash and directly linking

12. Remove duplicate scripts
Unnecessary HTTP requests
Wasted JS execution
Implement a script management module in templating system
Script has a getVersion() function



13. Configure (Avoid) ETags
Entity tags - a mechanism that web servers and browsers use to validate cached components
ETag is a string, must be quoted, introduced in Http 1.1
If-Non-Match takes precedence over If-Modified-Since
ETag is typically constructed using attributes that make them unique to a specific server hosting a Web site
Apache ETag uses inode-size-timestampe, and FileETag directive removes inode
IIS ETag uses Filetimestamp:ChangeNumber (# of configuration changes to IIS)

14. Make ajax cacheable
Web2.0, DHTML, Ajax
Yahoo Mail caches ajax result
Use packet sniffer to monitor active/passive Ajax requests