on to check whether index supports index-only scans,
       or zero if none</TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>amcostestimate</TT
></TD
><TD
><TT
CLASS="TYPE"
>regproc</TT
></TD
><TD
><TT
CLASS="LITERAL"
><A
HREF="catalog-pg-proc.html"
><TT
CLASS="STRUCTNAME"
>pg_proc</TT
></A
>.oid</TT
></TD
><TD
>Function to estimate cost of an index scan</TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>amoptions</TT
></TD
><TD
><TT
CLASS="TYPE"
>regproc</TT
></TD
><TD
><TT
CLASS="LITERAL"
><A
HREF="catalog-pg-pro