onion traffic graph says it counts v2+v3 but actually it's missing some v3
Check out this recent big drop in our onion traffic graph:
https://metrics.torproject.org/hidserv-rend-relayed-cells.html?start=2021-01-30&end=2021-11-28
The graph says it is "Onion-service traffic (versions 2 and 3)" but on further investigation, it isn't. Before Tor 0.4.6.1-alpha came out, it was. But after that version, it's gotten more complicated.
According to https://metrics.torproject.org/reproducible-metrics.html#onion-services the graph is using the hidserv-rend-relayed-cells line in the extrainfo descriptors.
Up through Tor 0.4.5, this line represented the sum of all onion service cells the relay had seen (v2 and v3). But in commit 3cbc513a (which went into 0.4.6.1-alpha, tpo/core/tor#23126 (closed)) we split it into v2 and v3 counts. For example here is a recent stanza from an extrainfo descriptor:
hidserv-stats-end 2021-11-24 01:33:38 (86400 s)
hidserv-rend-relayed-cells 2229996 delta_f=2048 epsilon=0.30 bin_size=1024
hidserv-dir-onions-seen 17 delta_f=8 epsilon=0.30 bin_size=8
hidserv-v3-stats-end 2021-11-23 12:00:00 (86400 s)
hidserv-rend-v3-relayed-cells 22916897 delta_f=2048 epsilon=0.30 bin_size=1024
hidserv-dir-v3-onions-seen -72 delta_f=8 epsilon=0.30 bin_size=8tl;dr: our metrics graph of onion service traffic began being wrong when Tor 0.4.6.1-alpha came out, and as time passes it's becoming more wrong.