postgres locking (re http://dba.stackexchange.com/a/15442/1396)

test.sql

set role dba;
create role stack;
grant stack to dba;
create schema authorization stack;
set role stack;
--
create table film(film_id integer primary key, release_year integer not null);
create table film_actor(actor_id integer, film_id integer references film, primary key (actor_id, film_id));
insert into film(film_id, release_year) values(1,2004);
begin;
insert into film_actor(actor_id, film_id) values(1,1);
--in session 2: update film set release_year=2005 where film_id=1;
commit;
--
drop schema stack cascade;
set role dba;
drop role stack;