[metrics-bugs] #25264 [Metrics/Website]: Decide what graph to display when there's no data to graph

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#25264: Decide what graph to display when there's no data to graph
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     Reporter:  karsten          |      Owner:  metrics-team
         Type:  enhancement      |     Status:  new
     Priority:  Medium           |  Milestone:
    Component:  Metrics/Website  |    Version:
     Severity:  Normal           |   Keywords:
Actual Points:                   |  Parent ID:
       Points:                   |   Reviewer:
      Sponsor:                   |
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 While looking through the Rserve logs, I found that we sometimes attempt
 to graph data that cannot be graphed in a reasonable way. Examples:
  - Data from the CSV file ends on 2018-02-13. We try to graph 2018-02-13
 to 2018-02-14. A line needs at least 2 points, so we're showing an almost
 empty graph.
  - Data from the CSV file ends on 2018-02-13. We try to graph 2018-02-14
 to 2018-02-15. We don't have a single data point to graph, so we're not
 showing anything at all.

 I could imagine we do the following things, if we can't display a single
 data point or line segment:
  - Display a "No Data Available" placeholder like Relay Search.
    - Note that we might need this for other cases, too, when users pass
 parameters that we cannot process.
    - We might as well not display anything, which is what we do right now.
 Might be less usable, though.
  - Display an empty graph with all requested dates on the x axis and no
 data points.
    - Note that if we want to do this, we need to decide when to "trim" the
 graph to the available dates and when to show all requested dates from
 start to end. Example: Try to draw a graph from 2000-01-01 to 2001-01-01,
 and then try to draw another graph from 2000-01-01 to 2018-01-01. Should
 both graphs display the full requested time period, or should just the
 second graph be trimmed to available data?

 Thoughts?

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/25264>
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