[tor-bugs] #23621 [Core Tor/Tor]: prop224: Missing tons of mds over time with a lurking client

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#23621: prop224: Missing tons of mds over time with a lurking client
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     Reporter:  asn           |      Owner:  (none)
         Type:  defect        |     Status:  new
     Priority:  Medium        |  Milestone:  Tor: 0.3.2.x-final
    Component:  Core Tor/Tor  |    Version:  Tor: 0.3.2.1-alpha
     Severity:  Normal        |   Keywords:  prop224
Actual Points:                |  Parent ID:
       Points:                |   Reviewer:
      Sponsor:                |
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 As roger described in comment:1:ticket:23543 tor will slowly expire its
 cached mds. Tor will start fetching again mds when it sees some client
 activity.

 In the case of a prop224 HS client with a single rend circ open (e.g. to
 an ircd, or downloading something) Tor will consider itself inactive and
 will not fetch any mds during that time.

 After 1-2 days of HS client operation, we will be missing about 2000 mds.
 If at that point we need to do another HS operation we will either stall
 if we are missing too many mds:
 {{{
 hs_client_refetch_hsdesc(): Can't fetch descriptor for service
 MUvEXhuYFWdElDqoHOeXPqi8TcKfLxeDKkYUejwLgt0 because we dont have enough
 descriptors. Stalling connection.
 }}}
 or will try to fetch a descriptor with some missing mds. This can result
 in delays and/or reachability issues.

 That's not a problem for v2, since all the info for v2 are in the
 consensus and it does not need any mds to connect to HSes.

 Perhaps it's good for us to periodically keep fetching mds if we have
 long-lasting active rend circs. (Sorta related to #23543 but not exactly).

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/23621>
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