[metrics-bugs] #25176 [Metrics/Onionoo]: Combine fixed-time history objects into a single object with an x axis for time

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#25176: Combine fixed-time history objects into a single object with an x axis for
time
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     Reporter:  karsten          |      Owner:  metrics-team
         Type:  enhancement      |     Status:  new
     Priority:  Low              |  Milestone:
    Component:  Metrics/Onionoo  |    Version:
     Severity:  Normal           |   Keywords:
Actual Points:                   |  Parent ID:
       Points:                   |   Reviewer:
      Sponsor:                   |
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 This idea came up when working on #16513 and #24729, though it's not
 strictly related to those.

 We could stop giving out history data for fixed intervals and instead
 provide all data in a single history object along with a normalized x axis
 with timestamps. For example, we could remove the static `"interval"`
 field and add an array `"intervals"` and a factor `"interval_factor"` as
 follows:

 {{{
   "first": "2018-01-13 12:00:00",
   "last": "2018-02-06 12:00:00",
   "intervals": [4, 4, 2, 2, 2, 2, 1, 1, 1, 1, 1, 1, 1, 1],
   "interval_factor": 86400,
   "factor": 5152.109783914505,
   "count": 15,
   "values": [461, 468, 515, 475, 452, 605, 572, 419, 564, 579, 502, 472,
 555, 542, 553]
 }}}

 If we do this, we'll have to teach Relay Search to draw different graphs
 based on this single history object. Basically, it will need to learn how
 to downsample data points that are too detailed for a graph showing a long
 period of time.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/25176>
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