[tor-bugs] #1566 [Tor - Metrics]: Calculate directory request shares from descriptor archives

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#1566: Calculate directory request shares from descriptor archives
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 Reporter:  karsten        |       Owner:  karsten                           
     Type:  task           |      Status:  new                               
 Priority:  normal         |   Milestone:  Calculate directory request shares
Component:  Tor - Metrics  |     Version:                                    
 Keywords:                 |      Parent:                                    
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 We should not rely on the dirreq-v3-share that directory mirrors report,
 but (be able to) calculate directory request shares from the descriptor
 archives. Three possible approaches are:

  1. advertised bandwidth / sum of advertised bandwidth
  2. measured bandwidth / sum of measured bandwidth
  3. weighted measured bandwidth / sum of weighted measured bandwidth

 The first approach is used by 0.2.0.x clients to decide which directory
 mirror to pick for requesting a network status consensus (among other
 things). For every relay with non-zero directory port, the weight is the
 advertised bandwidth (minimum of bandwidth rate and observed bandwidth) as
 reported by the relay in its server descriptor.

 The second approach is used by 0.2.1.x clients and is based on measured
 bandwidths as written to consensuses. (To be precise, the Bandwidth lines
 in consensuses are only ''measured'' bandwidths if at least three votes
 contain Measured lines for relays; otherwise, the Bandwidth lines contain
 the advertised bandwidths as used by 0.2.0.x clients.)

 The third approach is used by 0.2.2.x clients and is based on the measured
 bandwidths ''plus'' bandwidth weights as written to consensuses. Before
 summing up bandwidths, they are weighted depending on a directory's flags:
 Wbg for Guard, Wbe for Exit, Wbd for Guard+Exit, and Wbm for neither Guard
 nor Exit.

 The graphs in the attachment show the calculated directory request shares
 for the first and second approach plus the reported dirreq-v3-shares
 before bandwidth weights were introduced to consensuses. New graphs will
 follow for the third described approach.

 We need to decide if these calculated shares are stable enough to estimate
 user numbers from them. If not, we should find out what causes volatility,
 or rather, what made dirreq-v3-share such a nice stable metrics so far.

-- 
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/1566>
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