Problem with timestamp

Hello,

I try to check the time needed by a function.
I would like to :. select current_timestamp,. execute 5000 times a function. select the current_timestamp and return
theinterval.
 
Problem : the interval is always '00:00', the two timestamps have always 
the same value.
Could you help me ? have you any suggestions for testing sql functions 
speed?
Thank you in advance,
Béatrice


create function test_function() returns interval
as '
declare   j integer;   t1 timestamp;   t2 timestamp;   t3 interval;   x integer;
begin   select into t1 now();   FOR j in 0..5000 loop       select into x get_function_to_test();   end loop;   select
intot2 now();   t3 := t2 - t1;   RAISE NOTICE '' from % to % = %'',t2,t1,t3;   return t3;
 

end;
' language 'plpgsql';