[tor-bugs] #24248 [Core Tor/Torflow]: bwauth goes crazy in test network with no measured nodes

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#24248: bwauth goes crazy in test network with no measured nodes
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 Reporter:  Sebastian         |          Owner:  tom
     Type:  defect            |         Status:  new
 Priority:  Medium            |      Milestone:
Component:  Core Tor/Torflow  |        Version:
 Severity:  Normal            |     Resolution:
 Keywords:                    |  Actual Points:
Parent ID:                    |         Points:
 Reviewer:                    |        Sponsor:
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Comment (by teor):

 There are 8 scanners that partition the networ' between them by bandwidth
 percentile (and one scanner for unmeasured nodes).
 This makes it likely that one of those 8 partitions has 0 or 1 relays in
 it.
 I have a local patch that is probably hiding this issue, because it cuts
 down the number of scanners to 2 (one scanner for all nodes, and one
 scanner for unmeasured nodes).

 There are a few ways we can fix this issue:
 * configure 1 or 2 scanners in small networks - this isn't great, because
 it hides bugs in the default config
 * make scanners sleep when they can't find enoug nodes, like the
 unmeasured scanner - this may lead to small networks not getting scanned,
 because none of their scanners have enough nodes
 * when percentile restrictions result in not having enough nodes, remove
 the lower restriction (include higher-bandwidth nodes), then the lower
 restriction - this seems the best strategy for small networks

 Making relays report bandwidths earlier (#16386) might also help get the
 percentiles right on short-lived networks, but we would need to be
 careful, because this information can be used to identify client guards
 (#23856).

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/24248#comment:1>
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