- The Cover
Whats the bird on the cover?
The animal on the cover of Web Caching is a rock thrush.
Rock thrushes belong to the order Passeriformes, the largest
order of birds, containing 5,700 species, or over half of
all living birds. Passerines, as birds of this order are
called, are perching birds with four toes on each foot,
three that point forward and one larger one that points
backward. Rock thrushes belong to either the genus Monticola
or the genus Petrocossyphus, such as Monticola solitarius,
the blue rock thrush, and Petrocossyphus imerinus, the
littoral rock thrush.
- Formula on p. 161
I am afraid that the formula listed in the book is
not correct. It should be (1-(1-1/M)^(k*n)) ^K.
The formulas are essentially equivalent for interesting (large) values
of M. I used Bloom's formula, which, as the footnote notes, requires
K distinct bits to be turned on for each of the N items.
- Uncachable objects percentage
In appendix A.7, the result for uncacheable object is 24%,
which has a large gap of the result of Wolman et.al SOSP'99 paper. They
observed that 40-50 percent is dynamic.
First of all our two data sets are different. That could cause some differences.
But more importantly, their paper looks at requests, and does
not remove the effects of popularity. So, a really popular, uncachable
object increases the uncachable percentage in their analysis.
My analysis is on responses and filters out duplicates.
I also consider only ``200 Ok'' responses.
I'm saying that 25% of objects living on origin servers
are uncachable -- in my data!
- Squid private objects
In page 153, you mentioned that an object is either public or
private in Squid. I am very interested in this this. do you have some
document to describe this in more detail? or can you tell me more about
this? How can the same user benefits from the private objects in cache
Squid's private objects are only temporary. They either become public
(when headers are parsed) or get removed. Here are some documents that
talk about private and public objects: