[tor-bugs] #3543 [Tor Relay]: Too many absent v2 networkstatuses means caches can't purge their routerlist

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#3543: Too many absent v2 networkstatuses means caches can't purge their
routerlist
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 Reporter:  nickm      |          Owner:                    
     Type:  defect     |         Status:  new               
 Priority:  normal     |      Milestone:  Tor: 0.2.2.x-final
Component:  Tor Relay  |        Version:                    
 Keywords:             |         Parent:                    
   Points:             |   Actualpoints:                    
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 Reported by frosty_un.

 In routerlist_remove_old_routers, we don't actually purge old unlisted
 routers unless (have_enough_v2 && consensus).  But if enough v2
 authorities are down, have_enough_v2 might never be true on systems where
 !directory_caches_dir_info().  This could lead to OOM conditions on
 directory caches.

 One easy but hackish way to fix this is to remove the "have_enough_v2"
 precondition and instead change the cutoff so that it remains at
 ROUTER_MAX_AGE when have_enough_v2 is true, but becomes (say)
 ROUTER_MAX_AGE*3 when !have_enough_v2.

 A less easy way would be to change the requirement from "we have more than
 half of the v2 networkstatuses" to "for at least half of the v2
 networkstatuses, we have it, or we have tried but failed to download it
 for at least N hours."

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/3543>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
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