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    • Tom Lane's avatar
      Fix misuse of Lossy Counting (LC) algorithm in compute_tsvector_stats(). · bc0f0809
      Tom Lane authored
      We must filter out hashtable entries with frequencies less than those
      specified by the algorithm, else we risk emitting junk entries whose
      actual frequency is much less than other lexemes that did not get
      tabulated.  This is bad enough by itself, but even worse is that
      tsquerysel() believes that the minimum frequency seen in pg_statistic is a
      hard upper bound for lexemes not included, and was thus underestimating
      the frequency of non-MCEs.
      
      Also, set the threshold frequency to something with a little bit of theory
      behind it, to wit assume that the input distribution is approximately
      Zipfian.  This might need adjustment in future, but some preliminary
      experiments suggest that it's not too unreasonable.
      
      Back-patch to 8.4, where this code was introduced.
      
      Jan Urbanski, with some editorialization by Tom
      bc0f0809