[tor-relays] relay bangs into rock; falls off cliff; recovers

[starlight.2015q2 at binnacle.cx]

I've seen this about three times, maybe
four.  Anyone have any idea what's going
on?  Version 0.2.6.10 on Linux.  Showed
up in 0.2.5.x and 0.2.4.x earlier.

 1) seems to happen only one time per relay start
    after a few hours up to a couple of days;
    weeks or months between occurrences

 2) might be happening after dynamic config
    change but not certain (did this time,
    one hour later)

 3) might related to / triggered by client
    activity--was simply browsing regular
    Internet at the time

 4) main thread appears to bog-down, but some
    traffic continues

 5) log messages tied to event

:20:26 : Failed to find node for hop 0 of our path. Discarding this circuit.
:20:26 : Tried for 120 seconds to get a connection to [scrubbed]:443. Giving up.
:20:29 : Failed to find node for hop 0 of our path. Discarding this circuit.
:20:32 : Failed to find node for hop 0 of our path. Discarding this circuit.
:20:32 : Tried for 122 seconds to get a connection to [scrubbed]:443. Giving up. (waiting for circuit)
:20:34 : Failed to find node for hop 0 of our path. Discarding this circuit.
:21:06 : last message repeated 14 times
:21:45 : last message repeated 23 times

 6) for several minutes, all outbound client
    connection attempts show <fail> in Vidalia;
    NEWNYM has no effect

 7) (5) and (6) imply a rate-limit by the guard
    but AFIK there was no burst of circuit
    request that would trigger this

 8) client functionality recovers in something
    like five minutes (awhile after relay
    forwarding traffic knotch ends)

 9) no increase in memory consumption, so
    apparently no buffering backlog

10) WAN clean, no glitches

I suppose I should submit a bug report,
but I just finished with a bug-from-hell
and am in no mood to work another one,
especially since the problem is rare
and not fatal.
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