[tor-bugs] #3338 [Analysis]: Why do our user graphs have these huge spikes?

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#3338: Why do our user graphs have these huge spikes?
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 Reporter:  arma      |          Owner:     
     Type:  task      |         Status:  new
 Priority:  normal    |      Milestone:     
Component:  Analysis  |        Version:     
 Keywords:            |         Parent:     
   Points:            |   Actualpoints:     
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Comment(by karsten):

 We use the directory bytes to decide what fraction of directory requests
 have been reported to us.  If 100 out of 1000 directory mirrors report
 directory request statistics to us, we don't know if these directory
 mirrors saw 10% or 5% or 20% of all directory requests in the network.
 But we can use the directory bytes of a) the directory mirrors reporting
 directory request statistics and b) all directory mirrors in the network
 to estimate what fraction of directory requests we have seen.

 Note that we're talking about '''estimated''' directory bytes here,
 because not all relays report that number to us yet.  We estimate the
 number of written directory bytes by subtracting the total read bytes from
 the total written bytes.  On page 7 of the relevant
 [https://metrics.torproject.org/papers/countingusers-2010-11-30.pdf tech
 report] we write that ''we assume that the difference between total
 written and total read bytes on directory mirrors is to a large extent the
 result of answering small directory requests with large directory objects.
 We observed that relays that don’t mirror the directory write more bytes
 than they read, too, but the difference between written and read bytes is
 much smaller than on directory mirrors. We weight the bytes written by
 directory mirrors with the quotient of read and written bytes on relays
 that don’t mirror the directory in order to account for non-directory
 related factors. We then subtract the num- ber of bytes read by directory
 mirrors and obtain an estimate of directory bytes written by directory
 mirrors.''

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/3338#comment:3>
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