create table foo(foo_id int auto_increment primary key, bar_id int);
create unique index bar_id_idx on foo (bar_id);
set autocommit=0;
start transaction;
insert into foo (bar_id) values (1);
delete from foo where foo_id = 1;
insert into foo (bar_id) values (1);
select sleep(20);
commit;
set autocommit=1;