[metrics-bugs] #22346 [Metrics/Analysis]: Investigate drop in Tor Browser update pings in early 2017, 2018, 2019 and 2020

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#22346: Investigate drop in Tor Browser update pings in early 2017, 2018, 2019 and
2020
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 Reporter:  cypherpunks       |          Owner:  metrics-team
     Type:  task              |         Status:  new
 Priority:  Medium            |      Milestone:
Component:  Metrics/Analysis  |        Version:
 Severity:  Normal            |     Resolution:
 Keywords:                    |  Actual Points:
Parent ID:                    |         Points:
 Reviewer:                    |        Sponsor:
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Changes (by karsten):

 * type:  defect => task


Comment:

 I took another look at the database to see if what we're seeing here is an
 artifact of processing web server request logs.

 First, I looked at requested sites to see if this is in any way related to
 the change from `www.tp.o`/`dist.tp.o` to `aus1.tp.o` that was mentioned 3
 years ago or similar changes after that. Here's a graph:

 [[Image(tbup-site-2020-01-20.png, 700px)]]

 No, this is not the reason. There was just one such switch, and even
 though it coincides with the first drop, there was no other switch after
 that.

 Second, I looked at requested servers to see if this is maybe related to
 web servers being added to or removed from the rotation. For example, it
 could be that some servers do not properly sync their request logs to the
 metrics server. Here's a graph:

 [[Image(tbup-server-2020-01-20.png, 700px)]]

 There have been quite a few web servers over the years, so that this graph
 is a bit harder to read. That's why I included absolute and relative
 numbers. The first drop is a bit confusing, also related to the site
 change, but the other three drops do not show any correlation with server
 changes at start or end of the drop. The second drop had server changes in
 the middle of the drop, but apparently those did not affect numbers much.
 The third and fourth drop did not have any server changes.

 All in all, I don't see a bug in the data processing part, at least not an
 obvious one. It seems to me that these requests are real.

 I'm changing the ticket type to task, because a defect in a Metrics/*
 component implies that there's a bug in our code, and right now I don't
 see that that's the case.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/22346#comment:24>
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