[tor-bugs] #33421 [Metrics/Onionperf]: Track which Guard is used for experimental measurements

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#33421: Track which Guard is used for experimental measurements
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 Reporter:  acute                      |          Owner:  metrics-team
     Type:  enhancement                |         Status:  new
 Priority:  Medium                     |      Milestone:
Component:  Metrics/Onionperf          |        Version:
 Severity:  Normal                     |     Resolution:
 Keywords:  metrics-team-roadmap-2020  |  Actual Points:
Parent ID:  #33321                     |         Points:  3
 Reviewer:                             |        Sponsor:  Sponsor59-must
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Comment (by karsten):

 I'm afraid I don't fully understand what this ticket is about. Can you
 flesh this out a bit more to make it clear what needs to be done?

 Replying to [ticket:33421 acute]:
 > Sometimes tor uses Guards other than its main one;

 Does this refer to a setup with `UseEntryGuards 1` and `NumEntryGuards 1`?
 How often and when does it happen that tor uses another guard than its
 main one? Does Tor really pick a random other guard for a single circuit
 and drop it as a guard right after, or does it give up on a guard and pick
 a new one? Is this related to the type of circuit being built?

 > we need to differentiate this in the Onionperf results from measurement
 rotation events.

 We already store which guards are being used as part of circuit paths. We
 do not store which relays we picked as our guards at the time of building
 circuits, however. What exactly is it that we're currently missing in
 OnionPerf results? What do you refer to by ''measurement rotation event''?

 Thanks!

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/33421#comment:4>
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