[tor-bugs] #23985 [Core Tor/Tor]: If less than 15 missing mds, Tor will delay md download for 10 mins

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#23985: If less than 15 missing mds, Tor will delay md download for 10 mins
---------------------------+-----------------------------------------------
     Reporter:  asn        |      Owner:  (none)
         Type:  defect     |     Status:  new
     Priority:  Medium     |  Milestone:  Tor: 0.3.2.x-final
    Component:  Core       |    Version:  Tor: 0.3.0.6
  Tor/Tor                  |
     Severity:  Normal     |   Keywords:  tor-guard, tor-bridge, tor-client
Actual Points:             |  Parent ID:  #21969
       Points:             |   Reviewer:
      Sponsor:             |
---------------------------+-----------------------------------------------
 In `launch_descriptor_downloads()` if we are missing between 1 to 15 mds
 (`MAX_DL_TO_DELAY`), Tor will delay the md download for 10 mins (or until
 we are missing >= 16 mds). See `TestingClientMaxIntervalWithoutRequest`
 for the 10 min delay.

 This is bad when comboed with #21969 since if one of the 15 missing mds is
 for one of your top two primary guards, tor will hang for 10 mins with
 `missing descriptor for primary guards` before bootstrapping.

 The probability of this happening is small (about 0.004 I think for 6.4k
 mds in total) but given the amount of clients we have this is bound to
 happen for some of them.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/23985>
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