Suggestion: choosing fast quality exits for measurment

[binnacle]

In one of the SBWS meeting chats the idea of measuring relays by pairing them with picks from a pool of fast relays was floated. I like the idea and have a suggestion:

For the fast measurement exit pool, require that relays also be guard-flagged. Guard+Exit relays are much faster and more reliable than Exit-Only relays. About 400 Guard+Exit relays are present with an average bandwidth of about 15MB/sec. An equal number of Exit-only relays exist with a much lower bandwidth average of 4MB/sec.

[pastly]

I just want to note here that sbws currently picks a second hop like this.

It tries to find a 2nd hop that is 2x as fast, failing that 1.75x as fast, failing that 1.5x as fast, 1.25x as fast, 1x as fast, then finally failing that the fastest relay available.

The 2nd hop we are selecting is not always an exit: if the relay to be measured is an exit, we search for a non-exit.