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prepare.c

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    • Tom Lane's avatar
      e6faf910
      Redesign the plancache mechanism for more flexibility and efficiency. · e6faf910
      Tom Lane authored
      Rewrite plancache.c so that a "cached plan" (which is rather a misnomer
      at this point) can support generation of custom, parameter-value-dependent
      plans, and can make an intelligent choice between using custom plans and
      the traditional generic-plan approach.  The specific choice algorithm
      implemented here can probably be improved in future, but this commit is
      all about getting the mechanism in place, not the policy.
      
      In addition, restructure the API to greatly reduce the amount of extraneous
      data copying needed.  The main compromise needed to make that possible was
      to split the initial creation of a CachedPlanSource into two steps.  It's
      worth noting in particular that SPI_saveplan is now deprecated in favor of
      SPI_keepplan, which accomplishes the same end result with zero data
      copying, and no need to then spend even more cycles throwing away the
      original SPIPlan.  The risk of long-term memory leaks while manipulating
      SPIPlans has also been greatly reduced.  Most of this improvement is based
      on use of the recently-added MemoryContextSetParent primitive.
      e6faf910
      History
      Redesign the plancache mechanism for more flexibility and efficiency.
      Tom Lane authored
      Rewrite plancache.c so that a "cached plan" (which is rather a misnomer
      at this point) can support generation of custom, parameter-value-dependent
      plans, and can make an intelligent choice between using custom plans and
      the traditional generic-plan approach.  The specific choice algorithm
      implemented here can probably be improved in future, but this commit is
      all about getting the mechanism in place, not the policy.
      
      In addition, restructure the API to greatly reduce the amount of extraneous
      data copying needed.  The main compromise needed to make that possible was
      to split the initial creation of a CachedPlanSource into two steps.  It's
      worth noting in particular that SPI_saveplan is now deprecated in favor of
      SPI_keepplan, which accomplishes the same end result with zero data
      copying, and no need to then spend even more cycles throwing away the
      original SPIPlan.  The risk of long-term memory leaks while manipulating
      SPIPlans has also been greatly reduced.  Most of this improvement is based
      on use of the recently-added MemoryContextSetParent primitive.
    prepare.c 21.94 KiB