[tor-bugs] #31071 [Metrics/ExoneraTor]: Add a notice if we're missing data for a lookup

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#31071: Add a notice if we're missing data for a lookup
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 Reporter:  karsten             |          Owner:  metrics-team
     Type:  enhancement         |         Status:  needs_review
 Priority:  Medium              |      Milestone:
Component:  Metrics/ExoneraTor  |        Version:
 Severity:  Normal              |     Resolution:
 Keywords:                      |  Actual Points:
Parent ID:                      |         Points:
 Reviewer:  irl                 |        Sponsor:
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Changes (by karsten):

 * status:  assigned => needs_review


Comment:

 I finished a first implementation of this feature. It's pretty much as
 described in my previous comment, with the following exceptions:

  - I extended the view to missing statuses. That means if the directory
 authorities do not produce a consensus for an extended time, we'll put out
 a warning, too. This case is much less likely than a failing exit scanner,
 but it seemed related enough to include this case here.

  - I did not restrict the warning to cases when we're missing consecutive
 18 hours of statuses or exit lists, but for cases when we're missing any
 18 hours in the 3 or 4 days we're looking at. This was slightly easier to
 implement, but it's probably also slightly more robust, because it also
 addresses cases where the scanner dies, comes back shortly, and dies
 again.

  - I updated `src/main/sql/exonerator2.sql` rather than creating a new
 file `src/main/sql/exonerator3.sql`, because the changes did not affect
 any tables or views, just a single function. Let's be honest, the whole
 update is going to be a manual process anyway, and one needs to know
 exactly what one is doing. That's why I kept this simple.

 Please take a look at the attached screenshot with examples how this new
 warning would look like. It's the "However, the database..." part. We
 could of course make this more visible and clearer. Maybe that's a UX team
 mission, though.

 [[Image(task-31071-note.png, 700px)]]

 Regarding code, please take a look at
 [https://gitweb.torproject.org/user/karsten/exonerator.git/commit/?h=task-31071&id=b0165cb03138e933a337ddc8400c3a8bbe889b3d
 commit b0165cb in my task-31071 branch].

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/31071#comment:7>
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