[tor-bugs] #8240 [Tor]: Raise our guard rotation period

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#8240: Raise our guard rotation period
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 Reporter:  arma                                    |          Owner:                    
     Type:  defect                                  |         Status:  needs_review      
 Priority:  major                                   |      Milestone:  Tor: 0.2.4.x-final
Component:  Tor                                     |        Version:                    
 Keywords:  tor-client needs-proposal 023-backport  |         Parent:                    
   Points:                                          |   Actualpoints:                    
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Comment(by mikeperry):

 Replying to [comment:7 arma]:
 > Replying to [comment:6 mikeperry]:
 > > One way to improve this balancing problem might to adjust the Wxx
 weights such that the guard ones are dependent on how long you've had the
 guard flag vs this rotation parameter. If we had a curve to model the
 migration rate and metadata to record the Guard flag age to create points
 on this curve, this might not be too hard to do. I suppose a uniform
 migration rate might be as good an assumption as any...
 >
 > I agree that a uniform migration rate is as good as any (I assume by
 migration you mean from clients with the old behavior to clients with the
 new behavior). But further, don't forget that another factor here is new
 users showing up and picking guards. I guess we could assume that those
 are negligible (not true but hey, maybe it's close enough).

 Actually no, I mean migration rate in terms of how quickly new guards can
 expect to accumulate their proper fraction of clients actually using them
 as a Guard node. The problem I'm describing is that giving new relays a
 Guard flag means the weights from
 https://gitweb.torproject.org/torspec.git/blob/master:/path-spec.txt#l206
 cause fresh guards get substantially less clients until people migrate.
 Increasing the rotation period would exacerbate this problem. Hence, we
 might want to use an additional computation on the Wg* and W*g weights.

 In fact there may be two rates at work here: the natural rate of migration
 of clients to your new Guard node, and then later, the fraction of Guard
 flagged nodes who are of a certain age. Both of these will require some
 kind of annotation or record keeping on the authority side to compute, as
 they are likely best represented as points along the (0, 9.5mo] domain of
 two different curves.

 > I like the notion of changing the weights, but I feel like inflating the
 Bandwidth= weight is the wrong way to do it. I increasingly think we need
 a per-relay thing to say "how much of a guard it is".

 Correct, this would be a change to the authority consensus process that
 computes these weights:
 https://gitweb.torproject.org/torspec.git/blob/HEAD:/dir-spec.txt#l1482

-- 
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/8240#comment:9>
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