[tor-bugs] #21758 [Core Tor/Tor]: Improve compression estimators for directory spooling

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#21758: Improve compression estimators for directory spooling
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     Reporter:  nickm         |      Owner:
         Type:  enhancement   |     Status:  new
     Priority:  Low           |  Milestone:  Tor: 0.3.1.x-final
    Component:  Core Tor/Tor  |    Version:
     Severity:  Normal        |   Keywords:  prop278
Actual Points:                |  Parent ID:  #21662
       Points:  .5            |   Reviewer:
      Sponsor:  Sponsor4      |
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 Once we have zstd compression in place, we should improve the estimated
 ratio in estimate_compression_ratio().  We could also do well to have that
 function consider the _size_ of the input data, since bigger data sets
 compress better.

 (I'm deliberately only saying zstd here, not lzma2:  We should never do
 lzma2 compression on the fly, so we shouldn't need to estimate the size of
 the output for spooling purposes.)

 Calling this "low" priority because "0.5" isn't that bad of an estimate.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/21758>
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