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)
the null bitmap in a tuple (if it has one at all) is always exactly
equal to its t_natts value.
And so, the real number of values in the tuple - (1, 2, 3) above - is equal to the number of 1-bits in NULL bitmap. And the size of NULL bitmap is held in t_natts. I meant that when I said "thanks to NULL bitmap, adding a new nullable column is cheap". :-) And, of course, thanks to t_natts (HeapTupleHeaderGetNatts macro) - too.
