Optimizing further

Hi,

I'm wondering whether I need to do something to further optimize
a query.  My query looks like this:


   select price, date FROM foo
    WHERE date < '2000-07-01 00:29:00+10' and code='UCL'
    ORDER by date DESC, stock DESC
    LIMIT 100;

I've got over 7 million rows in the table, and a btree
index(date, code).  According to "explain", the query will be
executed as follows:

   Limit  (cost=0.00..393.45 rows=100 width=32)
     ->  Index Scan Backward using foo_date_code on trades
                                (cost=0.00..12309.13 rows=3128 width=32)

When I run the query, it takes a really long time (10 seconds)
the first time I execute it, and then returns instantly the
second time.

Is there something I need to do in order to get these running
faster, the *first* time?  I've run "VACUUM ANALYZE" on the
table after all the rows were inserted.

Thanks.

  -Ken