[tor-bugs] #18828 [Core Tor/Tor]: Regenerate fallback list for 0.2.9

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#18828: Regenerate fallback list for 0.2.9
---------------------------------------------+-----------------------------
 Reporter:  teor                             |          Owner:  teor
     Type:  enhancement                      |         Status:
                                             |  needs_revision
 Priority:  Medium                           |      Milestone:  Tor:
                                             |  0.2.9.x-final
Component:  Core Tor/Tor                     |        Version:
 Severity:  Normal                           |     Resolution:
 Keywords:  TorCoreTeam201612, 029-accepted  |  Actual Points:
Parent ID:  #20172                           |         Points:  3
 Reviewer:                                   |        Sponsor:  SponsorU-
                                             |  can
---------------------------------------------+-----------------------------

Comment (by teor):

 > * restore the 120 day stability period and 99% uptime requirement that
 were reduced in 0.2.8 due to #18050

 I initially tried 183 days stability and 99% uptime, but that excluded too
 many good relays.
 Instead, I am switching it back to 120 days (4 months) and 98%.

 120 days is a compromise between the 6-monthly major tor release cycle,
 and actual relay stability.

 98% still gives us `(0.98)^3 = 94%` of clients bootstrapping in the first
 5 seconds, before contacting an authority.
 `8/(200*10 + 8) * 3 = 1.2%` of clients try an authority in their first 3
 attempts anyway, as the authorities are also in the fallback list (but
 with lower weight).

 This works with 0.2.8, which has:
 Fallback 0, 1, 5, 16, ...
 Authority 6, 17, ...
 https://gitweb.torproject.org/tor.git/tree/src/or/config.c#n550
 (The schedules are delays, which are additive.)

 And 0.2.9 and later, which have:
 Fallback 0, 2, 5, 13, 33, ...
 Authority 6, 11, 27, ...
 https://trac.torproject.org/projects/tor/ticket/20534#comment:19

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/18828#comment:26>
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