Re: Another idea for dealing with cmin/cmax - Mailing list pgsql-hackers

On Fri, Sep 29, 2006 at 10:59:13AM +0100, Heikki Linnakangas wrote:
> Martijn van Oosterhout wrote:
> >On Fri, Sep 29, 2006 at 09:35:31AM +0100, Heikki Linnakangas wrote:
> >>We could get rid of t_hoff, because we should always be able to
> >>calculate the header size. Then we're down to 18 bytes.
> >
> >Without t_hoff, how do you know the size of the null bitmap? You could
> >probably do it only if you assume the null bitmap, if present, always
> >covers all the columns...
>
> I think we assume that already. heap_form_tuple reserves space for the
> bitmap like this:
>
>    if (hasnull)
>        len += BITMAPLEN(numberOfAttributes);

Ok, now we do an ALTER TABLE blah ADD COLUMN ..., and we have to expand
the bitmaps for the entire table?

Have a nice day,
--
Martijn van Oosterhout   <kleptog@svana.org>   http://svana.org/kleptog/
> From each according to his ability. To each according to his ability to litigate.