An unexpected find that freed 20GB of unused index space in PostgreSQL(hakibenita.com)

    create table purchase_order (
        id int primary key,
        ordered_on timestamptz not null,
        customer_id int not null references customer,
        canceled_on timestamptz
    );

    create table purchase_order (
        id int primary key,
        ordered_on timestamptz not null,
        customer_id int not null references customer
    );

    create table order_cancelation (
        order_id int primary key references purchase_order,
        canceled_on timestamptz not null
    );