[tor-bugs] #30227 [Core Tor/sbws]: Work out why recent_measurements_excluded_few_count=733

Tor Bug Tracker & Wiki blackhole at torproject.org
Thu Apr 18 02:28:12 UTC 2019


#30227: Work out why recent_measurements_excluded_few_count=733
---------------------------+-----------------------------------
 Reporter:  teor           |          Owner:  (none)
     Type:  defect         |         Status:  new
 Priority:  Medium         |      Milestone:  sbws: unspecified
Component:  Core Tor/sbws  |        Version:  sbws: unspecified
 Severity:  Normal         |     Resolution:
 Keywords:                 |  Actual Points:
Parent ID:  #29710         |         Points:
 Reviewer:                 |        Sponsor:
---------------------------+-----------------------------------

Comment (by teor):

 From comment 10 in #29710:
 > The scanner takes around 48h (i was wrong with my 24h estimation) to
 measure unique relays in the consensus

 Let's do some analysis:

 It takes sbws 48 * 60 * 60 = 172800 seconds to measure the network.
 sbws runs 3 measurement threads, so the total measurement time is 3 *
 172800 = 518400.
 So a sbws thread takes 518400 / 7200 = 72 seconds to measure each relay.
 Each relay must have 5 downloads, so each download takes 72 / 5 = 14.4
 seconds.

 But each download should take between 6-10 seconds, so sbws is using
 30-60% of its time not doing useful downloads. I opened #30230 to work out
 why.

 > so it takes 4 days for each relay to have at least 2 measures (and not
 be excluded by `few`) and we're only considering 5.
 > There would be less relays excluded if we take only 1 measurement as
 valid or we consider more days of measurements.

 It's hard to decide what to change, when we don't know why the scanner is
 so inefficient.
 I have opened some child tickets for some things we could try: #30231,
 #30232, #30233.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/30227#comment:1>
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