[metrics-team] Discontinuity on bridge numbers

[David Fifield]

On Mon, Jul 30, 2018 at 05:16:00PM +0000, nusenu wrote:
> Vinicius Fortuna [vee-NEE-see.oos]:
> > I noticed there's some discontinuity on the Bridge number data:
> > https://metrics.torproject.org/bridges-ipv6.html
> > https://metrics.torproject.org/networksize.html
> > 
> > Do you know what happened there?
> 
> the bridge authority got replaced, since this
> wasn't a smooth transition it resulted in a lot of
> lost bridges because they did not upgraded their tor version
> which contains the new bridge authority to pubish to.

I think the new bridge authority is not the whole story, because the
bridge authority change happened on 2018-07-14, but the missing data
begins on 2018-07-07 (and ends on 2018-07-21).

I didn't hear exactly why the bridge authority had to be changed.
https://bugs.torproject.org/26771 says the "old one hasn't been getting
enough maintenance or attention, and now it's stopped sending bridge
descriptors to bridgedb entirely." It could be that 2018-07-07 is when
Bifroest (the old authority) stopped sending descriptors?

I don't understand why the gap extends all the way to 2018-07-21, when
the changeover happened on 2018-07-14. I would have expected it to start
at zero and increase a bridges upgraded. (I looked at the similar
situation in 2016 when the bridge authority changed from Tonga to
Bifroest, but that's a bit different because the graphs include
descriptors from both simultaneously.
https://lists.torproject.org/pipermail/tor-dev/2016-August/011336.html)