[tor-bugs] #27047 [Core Tor/Tor]: Authorities should keep recent consensuses, votes, and bandwidth files

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#27047: Authorities should keep recent consensuses, votes, and bandwidth files
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 Reporter:  teor                                 |          Owner:  (none)
     Type:  enhancement                          |         Status:  new
 Priority:  Medium                               |      Milestone:  Tor:
                                                 |  unspecified
Component:  Core Tor/Tor                         |        Version:
 Severity:  Normal                               |     Resolution:
 Keywords:  tor-bwauth, tor-dirauth, needs-      |  Actual Points:
  design                                         |
Parent ID:  #25925                               |         Points:
 Reviewer:                                       |        Sponsor:
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Changes (by teor):

 * keywords:  tor-bwauth, tor-dirauth => tor-bwauth, tor-dirauth, needs-
               design
 * cc: irl (added)


Comment:

 irl, let's design the "recent" URLs in dir-spec.txt when you have time.

 Here's some background:

 The documents that are used form a tree (strictly, a DAG):
 * every consensus contains a vote-digest for the votes used to create it
 * after #26698, every vote will contain a bandwidth-file-digest for the
 bandwidth file used to create it

 So we need a design to:
 * get recent consensuses by consensus period
 * get (unused) votes by consensus period
 * (unused bandwidth files aren't relevant, because each bandwidth file is
 tied to a vote)

 Normally, there is 1 consensus per hour, but during a consensus failure,
 authorities attempt to produce 2 consensuses per hour:
 https://gitweb.torproject.org/torspec.git/tree/dir-spec.txt#n1575

 Directory caches (and authorities) store 72 hours of recent consensus
 diffs by default:
 https://gitweb.torproject.org/torspec.git/tree/dir-spec.txt#n1961

 So we should probably try to keep 72 hours of votes and bandwidth files as
 well.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/27047#comment:1>
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