[tor-bugs] #27338 [Core Tor/sbws]: How long should sbws keep measured and observed bandwidths?

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#27338: How long should sbws keep measured and observed bandwidths?
---------------------------+-------------------------------------
 Reporter:  teor           |          Owner:  (none)
     Type:  task           |         Status:  new
 Priority:  Medium         |      Milestone:  sbws 1.0 (MVP must)
Component:  Core Tor/sbws  |        Version:
 Severity:  Normal         |     Resolution:
 Keywords:                 |  Actual Points:
Parent ID:  #27108         |         Points:
 Reviewer:                 |        Sponsor:
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Comment (by juga):

 Replying to [comment:4 teor]:

 > The minimum viable product must:
 > * Use the latest descriptor bandwidth limit, because:
 >   - the latest descriptor contains the limit that the operator has asked
 for
 > * Use at least 2 sbws measured bandwidths over at least 2 days, because:
 >   - tor relay usage varies on a daily cycle
 >   - each sbws measurement depends on the time of day
 > * Use at least 2 descriptor observed bandwidths over at least 2 days,
 because:
 >   - a single download by a single client can increase the observed
 bandwidth
 >   - for security, we want results that don't depend on a single client's
 behaviour

 Currently, it's possible that after 2 (or more) days we didn't collected
 less than 2 measurements and descriptor observed bandwidths for some
 relays.
 It's possible that prioritization might need some changes, which i think
 might be related to https://github.com/pastly/simple-bw-
 scanner/issues/136.
 If prioritization can't change that, it might be the case that is not
 possible to obtain 2 measurements in the last 2 days.

 > * Don't keep bandwidths for more than 1 week
 >   - old bandwidths do not help us work out current relay capacity

 For bandwidth files, that's the default. Raw measurements are keep 90 days
 by default
 >
 > What do you think?
 > Can you implement something based on these suggestions?

 Yes, except for the comments above

 >
 > If you want, I can write or review patches, or write a detailed spec.

 I've already the code except for the comments above (need to clean a bit
 commits). Reviews and spec would help.

 > Do you mean 1, 2, 3 on the last 3 lines?

 Yes, sorry, distracted copy & paste...

 >
 > The descriptor has:
 > {{{
 > "bandwidth" bandwidth-avg bandwidth-burst bandwidth-observed NL
 > }}}
 >
 > Torflow does:
 > {{{
 > bw_observed = min(bandwidth-avg, bandwidth-burst, bandwidth-observed)
 > }}}
 > https://gitweb.torproject.org/pytorctl.git/tree/TorCtl.py#n459
 >
 > But that's redundant, because tor relays do:
 > {{{
 > "bandwidth" min(RelayBandwidthRate, RelayBandwidthBust, BandwidthRate,
 BandwidthBurst, MaxAdvertisedBandwidth) min(RelayBandwidthBust,
 BandwidthBurst) bandwidth-observed NL
 > }}}
 > See get_effective_bwrate() and get_effective_bwburst().

 i've been collecting and documenting all these possible values and the
 different names they could have so i don't get confused.
 I've just not put that notes online somewhere yet but intend to do so.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/27338#comment:5>
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