ring, which can
   dramatically reduce the number of random I/Os needed for non-ordered data
   sets. For well-ordered data sets the benefit is smaller or non-existent,
   because only a small number of pages receive new tuples at a time, and
   those pages fit in cache even if the index as whole does not.
  </P
><P
>   However, buffering index build needs to call the <CODE
CLASS="FUNCTION"
>penalty</CODE
>
   function more often, which consumes some extra CPU resources. Also, the
   buffers used in the buf