Fifth International World Wide Web Conference
Existing Mechanisms
Naive (Netscape Navigator)
check always
- user waits for conditional GET to reach the home site
- popular sites are swamped -> useless in a hierarchy
never check
- in a large cache, pages are never naturally refreshed
- users have to RELOAD -> site swamping -> useless in a hierarchy
expiration-based coherence (W3C httpd, Netscape Proxy)
- commonly used on today's Web
- cache assigns an expiration date to a page upon its retrieval
- before expiration, pages treated as valid
- after expiration, pages checked via conditional get
- expiration derived from: Expires header, default expiration, LM-factor
(Last-Modified)
Web Cache Coherence
(A.Dingle,T.Partl)