A lot of oppinions has been expressed with regard to if the favicon should be default on or off since it might spam webservers with requests to a non-existing file.
It would be really interesting to get some hard numbers on this. Just looking at the current logs will not really say anything since very few people browse with a mozilla with this pref turned on. So we need to come up with some way to approximate the number of 404s per (for example) month in the event of a browser with, say, 30% marketshare using the current configuration. Since the absence of a /favicon.ico is cached the number of 404-ing requests will be much lower then the numbers of pagehits. Brendan says that the absense is cached "persistently and with never-expire", does that mean that mozilla won't request /favicon.ico again unless the user manually clears the cache? In that case the number of 404s will be approximatly equal to the number of "new users" every month * 30%. If it's not possible to extract the number of new users from the logs i think that the number of new IP-addresses * 1.5 is a good enough estimation. There are probably more then 1.5 user per IP on average, but all users probably don't visit the site. If someone have a better number then 1.5, please speak up, my guess is very uneducated. However it seems a bit wrong to me that a resource is cached "forever". What if a site want to start supporting /favicon.ico? Will only new users see the new icon? IMHO a resource should be reloaded at least sometime so that if the resource appears/changes we will eventually catch it. So say that we reload every 2 weeks. That means every user will reload /favicon.ico once every 14th day, which means that the number of 404s will be "number of destict users during 14-days" * 30% * 30/14. So, we've got: Hits = newUsersPerMonth * 0.3 if we cache indefenetly Hits = distinctUsersPerXDays * 0.3 * 30/X if we refetch every X days Where IP-addresses * 1.5 could approximate number of users. IMHO the right thing would be to use the second formula with X ~= 14. So it would be great if someone with access to the logs to a rather heavily used site could run these formulas and compare that to the number of "normal" 404s. / Jonas Sicking
