"Paul Mathews" <plm@netspace.net.au> writes:
  

Despite the existence of the index, postgresql is determined to full table
scan when given.
  SELECT 
    postcode
  WHERE
    boundary @> point 'x,y';
    

polygon @> point isn't an indexable operator.  The indexable operators
for a gist index on polygon are

 <<(polygon,polygon)
 &<(polygon,polygon)
 &&(polygon,polygon)
 &>(polygon,polygon)
 >>(polygon,polygon)
 ~=(polygon,polygon)
 @>(polygon,polygon)
 <@(polygon,polygon)
 &<|(polygon,polygon)
 <<|(polygon,polygon)
 |>>(polygon,polygon)
 |&>(polygon,polygon)
 ~(polygon,polygon)
 @(polygon,polygon)

So it looks like you need to convert the point to a one-point polygon.

			regards, tom lane