[tor-bugs] #13209 [Analysis]: Write a hidden service hsdir health measurer

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#13209: Write a hidden service hsdir health measurer
------------------------------+------------------------------
 Reporter:  arma              |          Owner:
     Type:  defect            |         Status:  new
 Priority:  normal            |      Milestone:  Tor: 0.2.???
Component:  Analysis          |        Version:
 Keywords:  SponsorR, tor-hs  |  Actual Points:
Parent ID:                    |         Points:
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 A given hidden service maps to six hsdirs (hidden service directories) at
 any given time, in terms of where it will publish its hsdesc (hidden
 service descriptor).

 But due to churn in relays, and different perspectives on the network
 (since clients and the hidden service likely don't have the very latest
 consensus), there's a chance that the client will choose an hsdir that
 doesn't have the hsdesc.

 It would be neat to look at the last few consensuses, and compute the
 union of all the hsdirs that might be in use, and then see which ones
 actually have the hsdesc.

 That answer will give us a handle on whether things are going as we
 expect, and also give us a sense of whether the number "six" is overkill
 or underkill or what.

 An alternate, perhaps parallel, approach would be to look at the
 historical metrics data involving relay churn (easy to see in the
 consensus) and relay restarts (where uptime resets) and calculate what the
 answer *ought* to be. And if our prediction is much different from the
 reality, why?

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/13209>
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