[tor-bugs] #34030 [Metrics/CollecTor]: Indexer ignores a file after moving it away and back shortly after

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#34030: Indexer ignores a file after moving it away and back shortly after
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     Reporter:  karsten            |      Owner:  metrics-team
         Type:  defect             |     Status:  new
     Priority:  Medium             |  Milestone:
    Component:  Metrics/CollecTor  |    Version:
     Severity:  Normal             |   Keywords:
Actual Points:                     |  Parent ID:
       Points:  0.5                |   Reviewer:
      Sponsor:                     |
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 Today I tried to trigger the new Nagios CollecTor check by moving away a
 recent Snowflake file and moving it back a few minutes later.

 The first part of moving the file away worked fine to the effect that it
 was not included in the `index.json` file anymore.

 However, the second part of moving the file back did not cause the indexer
 to include the file in the `index.json` file again.

 What I had to do was touch the file and setting a slightly different last-
 modified timestamp. More precisely, changing the second was not
 sufficient, but changing the minute was.

 I haven't looked at the code yet, but I could imagine that it's related to
 some optimization we did about not indexing files that we had already
 indexed before. Maybe it's also related to the way how we keep files
 available for a certain time after they dropped out of the `index.json`
 file. Or maybe it's caused by both.

 This is not a critical bug, but it's also likely not a complex fix. It
 would be good to fix this, because it would probably confuse another
 CollecTor operator who didn't happen to write the indexer code.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/34030>
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