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    • Tom Lane's avatar
      New cost model for planning, incorporating a penalty for random page · b1577a7c
      Tom Lane authored
      accesses versus sequential accesses, a (very crude) estimate of the
      effects of caching on random page accesses, and cost to evaluate WHERE-
      clause expressions.  Export critical parameters for this model as SET
      variables.  Also, create SET variables for the planner's enable flags
      (enable_seqscan, enable_indexscan, etc) so that these can be controlled
      more conveniently than via PGOPTIONS.
      
      Planner now estimates both startup cost (cost before retrieving
      first tuple) and total cost of each path, so it can optimize queries
      with LIMIT on a reasonable basis by interpolating between these costs.
      Same facility is a win for EXISTS(...) subqueries and some other cases.
      
      Redesign pathkey representation to achieve a major speedup in planning
      (I saw as much as 5X on a 10-way join); also minor changes in planner
      to reduce memory consumption by recycling discarded Path nodes and
      not constructing unnecessary lists.
      
      Minor cleanups to display more-plausible costs in some cases in
      EXPLAIN output.
      
      Initdb forced by change in interface to index cost estimation
      functions.
      b1577a7c
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