[tor-bugs] #9670 [Tor]: Disable exploratory client circuit builds (set cbtdisabled to 1 and cbtmincircs to 1)

["Tor Bug Tracker & Wiki" <blackhole@xxxxxxxxxxxxxx>]

#9670: Disable exploratory client circuit builds (set cbtdisabled to 1 and
cbtmincircs to 1)
----------------------+------------------------------------
 Reporter:  arma      |          Owner:
     Type:  task      |         Status:  new
 Priority:  normal    |      Milestone:  Tor: 0.2.5.x-final
Component:  Tor       |        Version:
 Keywords:  tor-auth  |  Actual Points:
Parent ID:  #9657     |         Points:
----------------------+------------------------------------
 When clients find that they're failing a lot of circuits, they back off
 from their computed cbt value, which puts them in the "launch a bunch of
 test circuits so we can get a better estimate of our cbt" phase. By
 default they launch 100 circuits, one per second, from
 circuit_build_needed_circs() which calls circuit_predict_and_launch_new()
 which does
 {{{
   if (num < MAX_UNUSED_OPEN_CIRCUITS-2 &&
       get_options()->LearnCircuitBuildTimeout &&
       circuit_build_times_needs_circuits_now(&circ_times)) {
     flags = CIRCLAUNCH_NEED_CAPACITY;
     log_info(LD_CIRC,
              "Have %d clean circs need another buildtime test circ.",
 num);
     circuit_launch(CIRCUIT_PURPOSE_C_GENERAL, flags);
 }}}

 I think while our network is overloaded (#9657), we should turn this
 behavior off.

 To do it, we need to set
 {{{
   cbtdisabled=1
   cbtmincircs=1
 }}}
 in our consensus params.

 (We need to set both because there's a bug where it doesn't look at
 cbtdisabled when making the decision. But I'll open that as a separate
 ticket.)

-- 
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/9670>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
The Tor Project: anonymity online
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