[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:
-------------------------------------------+-------------------------------

Comment (by teor):

 Here's how the latest version works, with the next delay in [1, delay*5]
 (multiplier 4), except when delay is 0, when the next delay is in [1,2].
 This time, I'm using ranges and averages:

 {{{
 0, 1.5 [1-2], 4.3 [2-10], 11 [3-50], 28 [4-250], 71 [5-1250], ...
 6, 19 [7-30], 47 [8-150], 117 [9-750], 294 [10-3750], ...
 1200, 3601 [1201-6000], 9002 [1202-30000], 22505 [1203-150000], ...
 }}}

 Ok, so that multiplier is going to be terrible (in rare cases) for
 clients, let's try delay*4 (multiplier 3):

 {{{
 0, 1.5 [1-2], 5 [2-8], 11 [3-32], 22 [4-128], 44 [5-256], 88 [6-512], ...
 6, 16 [7-24], 32 [8-96], 64 [9-384], 128 [10-1536], ...
 1200, 3001 [1201-4800], 6002 [1202-19200], 12004 [1203-76800], ...
 }}}

 And delay*3 (multiplier 2):

 {{{
 0, 1.5 [1-2], 4 [2-6], 6.5 [3-18], 10 [4-54], 16 [5-162], 24 [6-486], 37
 [7-1458], 56 [8-4374], 85 [9-13122], ...
 6, 13 [7-18], 19 [8-54], 29 [9-162], 45 [10-486], ...
 1200, 2400 [1201-3600], 3601 [1202-10800], 5402 [1203-32400], ...
 }}}

 So a multiplier of 2 is too fast, 3 seems just about right.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/20534#comment:16>
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