SPI_execp is the same as
   SPI_execute_plan, with the latter's
   read_only parameter always taken as
   false.
  
      prepared statement (returned by SPI_prepare)
     
An array of actual parameter values. Must have same length as the statement's number of arguments.
An array describing which parameters are null. Must have same length as the statement's number of arguments.
      If nulls is NULL then
      SPI_execp assumes that no parameters
      are null.  Otherwise, each entry of the nulls
      array should be ' ' if the corresponding parameter
      value is non-null, or 'n' if the corresponding parameter
      value is null.  (In the latter case, the actual value in the
      corresponding values entry doesn't matter.)  Note
      that nulls is not a text string, just an array:
      it does not need a '\0' terminator.
     
maximum number of rows to return, or 0 for no limit