Caching Tutorial

https://www.mnot.net/cache_docs/

Kinds of Web Caches

• browser caches
• proxy caches
• gateway caches

how to control caches

• html meta tags -> easy to use , but aren’t very effective . only honored by a few browser caches , not proxy caches
• http headers -> give you a lot of control over how both browser caches and proxies handle your representations . 

HTTP/1.1 200 OK

Date: Fri, 30 Oct 1998 13:19:41 GMT
Server: Apache/1.3.3 (Unix)
Cache-Control: max-age=3600, must-revalidate
Expires: Fri, 30 Oct 1998 14:19:41 GMT
Last-Modified: Mon, 29 Jun 1998 02:28:12 GMT
ETag: "3e86-410-3596fbbc"
Content-Length: 1040
Content-Type: text/html

Controlling Freshness with the Expires HTTP Header

• Expires -> it has some limitations , because there’s a date involved , clocks must be synchronized
• easy to forget that you’ve set some content to expire at a particular time

Cache-Control HTTP Headers

Useful Cache-Control response headers include:

• max-age = [seconds]
• s-maxage = [seconds]

Tips for Building a Cache-Aware Site

• Use URLS consistently
• Use common library of images and other elements
• Make caches store images and pages that don’t change often by using Cache-Control:max-age header with a large value
• Make caches recognize regularly 
• If a resource changes , change its name
• don’t change files unnecessarily
• Use cookies only where necessary
• Minimize use of SSL

Writing Cache-Aware Scripts

• only write file that have changed
• set an age-related header for as far in the future as practical  -> max-age
• parsing the HTTP headers : If-Modified-Since ,  304 Not Modified
• don’t use POST unless it’s appropriate .
• don’t embed user-specific information in the URL unless the content is unique to that user
• Don’t count on all request from a user coming from the same host
• Generate Content-Length response headers