CircuitBuildTimeout Management and the Pareto Distribution

Mike Perry mikeperry at
Sat Jul 24 17:43:58 UTC 2010

Thus spake Cav (cav at

> I was wondering if the new CircuitBuildTimeout management code in the 
> release renders the pareto distribution code redundant in a sense ?
> It seems there is now, in that new code, a distorting effect on the 
> normal distribution of circuits that are built ?

I'm not 100% sure what you mean here. We are still using the pareto
distribution. In fact, we're using it more correctly than before, in
that instead of generating "synthetic" values for circuits that time
out, we allow circuits to continue to build until the 95th percentile
on the pareto curve (but do not use them). Circuits that take an
amount of time to build that is beyond the 95th percentile on the
curve get counted as "censored" values for a "right-censored" Pareto

This is documented in greater detail in path-spec.txt section 2.4.

The end result is that we expect to allow the fastest 80% of circuits
to be used for tor traffic. In practice we actually get pretty darn
close to this for my experimental setup and on the real network.

Mike Perry
Mad Computer Scientist evil labs
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