[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):

 I think there's some confusion in the comments about dirreq-share lines
 and how clients on different Tor major versions use different weights for
 picking a directory mirror.  This is all irrelevant here!  Our current
 user number estimate is based on estimated written directory bytes, not on
 probabilities for clients to pick directory mirrors.  These estimated
 directory byte histories are, in theory, far more reliable and useful for
 adding up the observations from multiple directories than the dirreq-share
 values that we used before.

 The suspected reason why our estimated user numbers have some false values
 in the past few months is that our directory bytes estimate is slightly
 broken.  We're estimating directory bytes based on the difference between
 written and read total bytes.  This approach worked okay when developing
 the user number estimate, but apparently it's not fail-safe.  We're using
 this estimate as opposed to extrapolating the recently introduced
 directory byte metric, because we have bandwidth data for the past few
 years.  Even if we switched to the reported directory bytes now, we'd only
 have user numbers for the past few months.

 I'm going to re-run the comparison of extrapolated directory bytes and our
 estimate based on the difference between written and read total bytes.

 Also, I was wrong that relays need to upgrade to 0.2.2.x to report
 directory stats by default.  It's 0.2.3.x that they need to upgrade to.
 Relays on 0.2.2.x would have to add `DirReqStatistics 1` and
 `ExtraInfoStatistics 1` to their torrc to report directory stats.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/3338#comment:13>
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