On Saturday 12 April 2008 05:57:49 Brian Butterworth wrote:
> If it were all doing using HTTP it would be easily cached, of course, as
> you can do this with a proxy server, either a configured-in one as used on
> corporate and educational networks, or as a transparent proxy.
Ignores the fact that most caches will not cache objects over a certain size.
(The maximum usually based on average object size, which is dominated by
small images and HTML). Also it depends on the purpose the cache is there
for - speed or bandwidth savings, and even then you still need a maximum, it's
just where you set it which will vary.
There are algorithms that will take into account object size and popularity
(combination of LFU & GDS approaches), but they're still mainly targetted at
object size distributions below the 90-95th percentile.
You can use whitelisting, but the maintainence overhead of such a whitelist
can become quite spectacular, and can depend on the purpose behind
caching in their network ((peceived) speed saving or bandwidth saving[1]).
Thus, whitelisting or changing the maximum object size can massively
impacts the effectiveness of the cache infrastructure as a whole.
[1] These two do not always correlate, since one is based on percentiles,
the other is absolute figures.
(I worked for the best part 5 years looking at this sort of stuff in great
detail in both theoretical and (a wide variety of) operational environments,
so I'm summarising :-)
Also, none of this is any use for streaming over RTMP. (and HTTP streaming
has major issues, not least the fact that you can't index sensibly by time
without impacting (or working around) patents)
NB. I'm all in favour of making websites cacheable where possible/reasonable
since it's a really, really, good idea, but it's just worth remembering we're
looking at outlying values regarding a non-HTTP protocol.
Michael.
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