 decisions involved in
   <TT
CLASS="FILENAME"
>src/backend/access/nbtree/README</TT
> and
   <TT
CLASS="FILENAME"
>src/backend/access/hash/README</TT
>.
  </P
><P
>   Aside from the index's own internal consistency requirements, concurrent
   updates create issues about consistency between the parent table (the
   <I
CLASS="FIRSTTERM"
>heap</I
>) and the index.  Because
   <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> separates accesses
   and updates of the heap from those of the index, there are windows 