Performance issue with cross table updates

Hi all

I am no database wizard so I am hoping someone may be able to assist me :)

I get a daily CSV file of 6.5 million records. I create a temporary
table and COPY them in. On completion I create an index on the mdnid
column. This column is also indexed in table 2. This part is very
fast. I had some 'checkpoint too often' issues, but that I have
resolved.

I then use the following procedure to update all the records, and if a
record does not exist, insert it instead:

declare
    v_update e_lookup_load%ROWTYPE;

begin

for v_update in select * from e_lookup_load loop

update e_lookup set
       cur_balance = v_update.cur_balance,
       last_usage = v_update.last_usage,
       b_code = v_update.b_code,
       u_date = v_update.u_date,
       date_of_insert = v_update.date_of_insert
       where mdnid = v_update.mdnid;

if NOT FOUND then
    begin
    insert into e_lookup(mdnid,cur_balance,last_usage,b_code,u_date,date_of_insert)
values
    (v_update.mdnid,
    v_update.cur_balance,
    v_update.last_usage,
    v_update.b_code,
    v_update.u_date,
    v_date_of_insert);
    end;
end if;
end loop;

end;

From my understanding, a for loop is encapsulated in a cursor anyway
so no need to do that. Am I fundamentally doing something wrong as the
operation is slow as molasses? Maybe there is a better way altogether
that I have not thought of? The bottom line is that at no point can
the e_lookup table be unavailable to clients, else I would have just
done a simple drop and rename post the COPY.

Kind Regards
Craig