[tor-bugs] #20534 [Core Tor/Tor]: Revise hard-coded download schedules

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#20534: Revise hard-coded download schedules
-------------------------------------------+-------------------------------
 Reporter:  teor                           |          Owner:
     Type:  defect                         |         Status:  merge_ready
 Priority:  Medium                         |      Milestone:  Tor:
                                           |  0.2.9.x-final
Component:  Core Tor/Tor                   |        Version:  Tor:
                                           |  0.2.9.1-alpha
 Severity:  Normal                         |     Resolution:
 Keywords:  regression, CoreTorTeam201611  |  Actual Points:
Parent ID:  #20499                         |         Points:  0.5
 Reviewer:                                 |        Sponsor:
-------------------------------------------+-------------------------------
Changes (by teor):

 * status:  needs_review => merge_ready


Comment:

 Replying to [comment:10 nickm]:
 > Okay, I've taken a look here in my branch `bug20534_029`. Is that what
 you had in mind?  I've not been able to convince myself 5x is safe, so I
 went with 4x. Let's see if that works out.

 That's fine, I was concerned 5x would lead to too much variance.

 One nitpick: `no more than quadruple.` is wrong, it is `no more than
 quintuple.`, because the increment is added to the existing delay.

 Let me just do my sums for exponent 2.5 (max = 4*delay):

 0, 1, 2.5, 6.3, 15.6, 39.1, 97.7, ...
 6, 15, 37.5, 93.75, ...
 1200, 3000, 7500, 18750, ...

 This would mean:

 * In 0.2.9, almost every tor instance would try to download almost every
 document 6 times in the first minute. In 0.2.8, this was 3-4 times in the
 first minute.
 * In 0.2.9, clients would try authorities 3 times in the first minute (and
 twice in the first 21 seconds). In 0.2.8, this was 2 times in the first
 minute (and twice in the first 21 seconds).
 * In 0.2.9, bridge clients will try to download bridge descriptors 3 times
 in the first 3 hours (the first time after 20 minutes). In 0.2.8, this was
 4 times in the first 3 hours (the first time after 1 hour).

 I think we should document this somewhere, but that should be a separate
 task.
 (I'm sure arma would like to read this analysis, eventually.)

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/20534#comment:12>
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