[tor-bugs] #24681 [Core Tor/Tor]: Make the default fallback weight in Tor 10.0

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#24681: Make the default fallback weight in Tor 10.0
-------------------------------------------------+-------------------------
 Reporter:  teor                                 |          Owner:  teor
     Type:  enhancement                          |         Status:
                                                 |  needs_review
 Priority:  Medium                               |      Milestone:  Tor:
                                                 |  0.3.3.x-final
Component:  Core Tor/Tor                         |        Version:  Tor:
                                                 |  0.2.8.1-alpha
 Severity:  Normal                               |     Resolution:
 Keywords:  fallback, easy, intro, 032           |  Actual Points:  0.1
  -backport-maybe, 031-backport-maybe, 030       |
  -backport-maybe, 029-backport-maybe, 028       |
  -backport-maybe                                |
Parent ID:  #22271                               |         Points:  0.1
 Reviewer:                                       |        Sponsor:
                                                 |  Sponsor8-can
-------------------------------------------------+-------------------------
Changes (by teor):

 * status:  assigned => needs_review
 * version:   => Tor: 0.2.8.1-alpha
 * actualpoints:   => 0.1
 * keywords:  fallback, 032-backport-maybe, easy, intro =>
     fallback, easy, intro, 032-backport-maybe, 031-backport-maybe, 030
     -backport-maybe, 029-backport-maybe, 028-backport-maybe
 * points:   => 0.1


Old description:

> This is a follow-up to #24679.
>
> * update the default weight in parse_dir_fallback_line() to 50.0
> * update the man page to reflect the new default
>
> (50.0 gives us about 1 in 1000 clients bootstrapping off an authority
> when all fallbacks are up.)

New description:

 This is a follow-up to #24679.

 * update the default weight in parse_dir_fallback_line() to 10.0
 * update the man page to reflect the new default

 10.0 gives us:
 * 0.5% clients bootstrapping off an authority when all fallbacks are up, *
 2% when 25% are down (our replacement threshold)
 * 7% when 40% are down (our worst case scenario)

--

Comment:

 Please see my branch ticket24681_028, which is based on maint-0.2.8, just
 in case we decide to backport that far.

 I actually ended up changing DirAuthorityFallbackRate to 0.1, which is a
 one-line config change. (The comment and the man page change are longer.)

 Given how simple the patch is, I think we should backport it all the way
 back to whatever versions we plan to release with the new fallback list.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/24681#comment:4>
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