Performance hit of a check constraint in Postgres

gistfile1.sql

begin; 
set role dba;
create role stack;
grant stack to dba;
create schema authorization stack;
set role stack;
--
create table foo(id integer check (id>0));
create table bar(id integer);
\timing on
insert into foo(id) select generate_series(1, 1000000);
insert into bar(id) select generate_series(1, 1000000);
\timing off
--
rollback;