[yangyang]

I'd be very interested to know more about this too. There is considerable overhead for each row in PostgreSQL (24 byte header, which must be aligned). Obviously you'll save a bit if there are repeated keys higher up, but you'll pay for the foreign key references to those rows in the children.

[ahachete]

It is true that PostgreSQL has such a high row overhead. But the storage savings are significant, in any way. Please see the presentation pointed out earlier.