[tor-bugs] #24022 [Core Tor/Tor]: Make clients avoid retrying slow exits when they time out (was: Make clients avoid retrying the same exit when it times out)

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#24022: Make clients avoid retrying slow exits when they time out
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 Reporter:  teor                                 |          Owner:  (none)
     Type:  defect                               |         Status:  new
 Priority:  Medium                               |      Milestone:  Tor:
                                                 |  0.3.3.x-final
Component:  Core Tor/Tor                         |        Version:
 Severity:  Normal                               |     Resolution:
 Keywords:  tbb-performance, tbb-usability,      |  Actual Points:
  performance, tbb-needs                         |
Parent ID:  #21394                               |         Points:
 Reviewer:                                       |        Sponsor:
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Old description:

> In #21394, we discovered that Tor clients sometimes retry the same exit,
> even when it is timing out.
> Can we retry fewer times, but still have an acceptable risk of clients
> encountering a bad exit?

New description:

 In #21394, we discovered that Tor clients sometimes ~~retry the same exit,
 even when it is timing out.
 Can we retry fewer times, but still have an acceptable risk of clients
 encountering a bad exit?~~
 experience a lot of exit timeouts when trying to connect to a website via
 DNS.

--

Comment (by teor):

 Oh, I see. Those were attempts to random exits that timed out before
 completing.
 Maybe we could fix that at the client level by keeping an exit failure
 cache?
 But the client would still need to experience some timeouts before it
 could skip failed exits.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/24022#comment:2>
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