Re: Fast ALTER TABLE ... ADD COLUMN ... DEFAULT xxx?

Dmitry Koterov <dmitry@koterov.ru> writes:
> No, I meant that in case of the row (1, NULL, NULL, 2, 3, NULL):
> - the corresponding NULL bitmap is (100110...)
> - the corresponding tuple is (1, 2, 3)
> - t_natts=3 (if I am not wrong here)

You are wrong --- t_natts would be six here.  In general the length of
the null bitmap in a tuple (if it has one at all) is always exactly
equal to its t_natts value.
        regards, tom lane