"40-60% of Yahoo!'s users have an empty cache experience and ~20% of
all page views are done with an empty cache. To my knowledge, there's
no other research that shows this kind of information. And I don't
know about you, but these results came to us as a big surprise. It
says that even if your assets are optimized for maximum caching,
there are a significant number of users that will always have an
empty cache. This goes back to the earlier point that reducing the
number of HTTP requests has the biggest impact on reducing response
time. The percentage of users with an empty cache for different web
pages may vary, especially for pages with a high number of active
(daily) users. However, we found in our study that regardless of
usage patterns, the percentage of page views with an empty cache is
always ~20%."
I found this really informative and a little surprising (especially
since I think most people who use Yahoo use it on a fairly frequent
basis.)
On a related note:
I did some testing with Yslow a few months back and I noticed that it does
not always correctly report what is cached and what is not. It's been the
primary reason why I've avoided trusting it blindly when optimizing pages.
This happened when we introduced full image caching on one of our
heavy-traffic sites. I was struggling for quite a while when it seemed that
no matter what we did, not all stuff got cached, according to Yslow. Turning
Yslow off and using a web proxy (Charles) to check for traffic we noticed
that actually the images were cached as they should, although Yslow reported
otherwise.
I could investigate this a bit more and provide a demo page when I find the
time for that.
Of course the numbers above where propably generated from server logs so
they should be correct - and equally alarming.
Just a heads up.
--
Suni
