Martijn van Oosterhout wrote:
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?
No, you'd still have the the number of attributes (t_natts) in the header.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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