Dir auths should choose Fast and Guard flags by consensus weight if they don't measure
In #8435 (moved) we made directory-authorities-that-run-bwauths stop voting Fast or Guard for relays they hadn't measured yet.
But as I pointed out in https://trac.torproject.org/projects/tor/ticket/8435#comment:13, since only a minority of dir auths run bwauths, the majority of dir auths are still voting Fast and Guard based on descriptor bandwidths.
So while the title of ticket #8435 (moved) says "Ignore advertised bandwidths for flags once we have enough measured bandwidths", the ChangeLog entry is more accurate:
- Directory authorities that have more than a threshold number of relays with measured bandwidths now treat relays with unmeasured bandwidths as having bandwidth 0. Resolves ticket 8435.
We should at some point actually do the original goal, which is to give Fast to the 7/8s of relays whose consensus weights are highest, and Guard to the 1/2 of relays whose consensus weights are highest and who match the other guard constraints.