[tor-relays] dynamically adjusting bandwidth

[starlight.2013q4 at binnacle.cx]

>The question is, should I put in an adjustment for
>'MaxAdvertisedBandwidth' during the backup window
>or make any other change to advise remote relays to
>de-prioritize the node for the duration?

Another unanswered question now understood:

As a consequence of a simple parameter tweak,
Vidalia buggily zapped (for the second time)
the relay configuration and turned off relaying.
Quickly restored 'torrc' and restarted the relay,
but noticed that the

   getinfo dir/server/authority

observed bandwidth value (third of three)
was zapped to a low value for about
an hour.  This had the effect of causing
four out of nine authorities to remove
the Guard flag and almost resulted in
a consensus "not Guard" state.

So the answer here is definitely DO NOT
lower 'MaxAdvertisedBandwidth' during
intervals when 'RelayBandwidthRate' is
reduced for events like offsite backups.
Doing so will probably cause the Guard
flag to be removed when it is present.

The only possible exception would be if one
has insane amounts of bandwidth and the
lowered value is still quite high.  Seems
unlikely that 'MaxAdvertisedBandwidth' has
any immediate effect on the selection
algorithm is only averaged into consensus
bandwidth gradually, so probably it's best
to not make temporary reductions.