[tor-bugs] #2649 [Tor Directory Authority]: Make the interval to become a hsdir a little longer

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#2649: Make the interval to become a hsdir a little longer
-------------------------------------+--------------------------------------
 Reporter:  Sebastian                |          Owner:  rransom           
     Type:  defect                   |         Status:  needs_review      
 Priority:  major                    |      Milestone:  Tor: 0.2.2.x-final
Component:  Tor Directory Authority  |        Version:                    
 Keywords:                           |         Parent:                    
   Points:                           |   Actualpoints:                    
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Comment(by rransom):

 See [attachment:hsdir-set-instability-graph.pdf hsdir-set-instability-
 graph.pdf] for a graph of (size of set symmetric difference between HSDir
 sets in consensus N and consensus N+i)/(size of HSDir set in consensus N),
 for i = 1..4.  (I'm counting relays entering the HSDir set as well as
 relays leaving the set because both events make an HSDir relay unavailable
 to hidden services and clients.)

 The ratio shown in the graph is an estimate of the probability that an HS
 will be unable to deliver a single copy of its descriptor to a client due
 to the HS, its client, and the HSDir relay responsible for that copy
 having different consensuses; my understanding is that clients (both HS
 clients and HS servers) routinely have consensuses out of date by two or
 three hours, and sometimes four hours.  We can probably assume that the
 disruptions are uniformly distributed around the HSDir ring, in which case
 the probability that an HS will be entirely unavailable to a client for a
 given hour due to HSDir-set instability is roughly one-sixth the three-
 hour probability shown in the graph for that hour.

 The scripts used to generate this graph are currently in
 [https://gitweb.torproject.org/rransom/metrics-
 tasks.git/shortlog/refs/heads/task-2649 task-2649] (
 `git://git.torproject.org/rransom/metrics-tasks.git task-2649` ).

-- 
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/2649#comment:15>
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