[tor-bugs] #4294 [Tor Relay]: Add percentiles of bridge descriptor downloads by fingerprint to served-descs-stats

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#4294: Add percentiles of bridge descriptor downloads by fingerprint to served-
descs-stats
-------------------------+--------------------------------------------------
 Reporter:  karsten      |          Owner:  Sebastian
     Type:  enhancement  |         Status:  new      
 Priority:  normal       |      Milestone:           
Component:  Tor Relay    |        Version:           
 Keywords:               |         Parent:           
   Points:               |   Actualpoints:           
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 Sebastian and I discussed Tonga's statistics about served bridge
 descriptors:

 {{{
 served-descs-stats-end 2011-10-23 23:03:31 (86400 s) total=515010
 unique=3766
 }}}

 We suspect that Tonga also serves and counts relay descriptors here.
 There are only 1665 unique bridge fingerprints in descriptors published
 since 2011-10-20, so these can't just be bridge descriptors.  Also, the
 total number of 515K descriptor fetches is much higher than expected.

 Sebastian works on a patch to exclude fetches for relay descriptors to
 only count bridge descriptors.  But we wonder if two numbers are enough to
 explain what's going on.

 I suggest to include a few percentiles of downloaded descriptors per
 unique bridge fingerprint in the statistics.  The output could be (example
 data):

 {{{
 served-descs-stats-end 2011-10-23 23:03:31 (86400 s) total=515010
 unique=3766 max=12095 q3=1752 md=498 q1=112 min=5
 }}}

 There are two necessary changes to the implementation:

  1. The digestmap needs to store a pointer to an integer counting the
 downloaded descriptors by bridge fingerprint.

  2. When formatting the server descriptor stats, we need to add all
 counters to a (smart?)list, sort the list, and write list[0],
 list[length/4], list[length/2], list[3*length/4], and list[length-1] to
 the output string.

-- 
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/4294>
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