[tor-project] Analyzing bwauth disagreements

Tom Ritter tom at ritter.vg
Fri Oct 6 20:40:50 UTC 2017

In which I pretend to know how to do statistics or data analysis; but
really hope I spur people to point out what I'm doing wrong =)


1) Run two bwauths on the same box
2) Collect votes (and raw bwauth votes where available) for a month
from all bwauths (including the duplicate one)
3) Stick the tuple (vote timestamp, relayid, bwauthid, bw value) into a database
4) Measure the percent difference in bandwidth for the same relay at
the same vote time between two bwauths as (abs(r1.bw - r2.bw) /
((r1.bw + r2.bw) / 2)
5) Average that value for all relays for a given vote time to get the
overall percent difference for that vote time
6) Graph it for multiple bwauth pairs
7) Get a slight flavor difference of the above value by limiting it to
relays with a bandwidth value of at least 100, to see if there are any

Download and archive votes and raw bwauth votes:
cron it up, run it every hour at 15 minutes after the hour.

MySQL Database schema:

Process the files and put them in the database:

Run the last query to get the data:

Plot it: https://github.com/tomrittervg/bwauth-tools/blob/master/plot_data.py
Optionally run something like grep -v
"\\\\N,\\\\N,\\\\N,\\\\N,\\\\N,\\\\N,\\\\N,\\\\N" query.csv >
non-blank-lines.csv, or change non-blank-lines.csv to query.csv

~ One month of data is 29,194,717  rows or ~4GB of data, and you want
to run the query and the plotting overnight.


The data!! https://raw.githubusercontent.com/tomrittervg/bwauth-tools/master/data.png
x axis: unix epoch of the vote time
y axis: percent disagreement between maatuska's bwauth and the indicated bwauth

The two bwauths run from maatuska agree quite consistently. However
they have the only instance of DISagreement between the 'all' set of
relays and the '>100' set.

maatuska and moria agree eerily closely.

two bwauths agree with each other to the same amount consistently over
time, although how much they agree depends on the two bwauths being

the 'base' agreement, how much two identical bwauths will agree, is around 35%

there is not much difference between 'all relays' and 'relays > 100'

Follow Up:

Is my data correct? maatuska and moria being that close together is suspicious.

Compare moria<->longclaw, moria<->faravahar, and longclaw<->faravahar

Change the bandwidth limit to >1000 and see if they produces more or
less disagreement

I can start applying bwauth patches, and run the new bwauth code, from
the same vantage point and use this methodology to determine if new
code has altered the results.
IF it has altered the results: are they better results or worse? Don't know!

I should measure the disagreements between bwauths when grouping
relays by country.

Because I have raw vote data from maatuska and moria, I can test the
hypothesis that relays fall between gaps in scanners. Maybe. I could
probably get positive proof this occurs but maybe not proof it
_doesn't_ occur.


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