From: | Martijn van Oosterhout <kleptog(at)svana(dot)org> |
---|---|
To: | Heikki Linnakangas <heikki(at)enterprisedb(dot)com> |
Cc: | ITAGAKI Takahiro <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp>, "Jim C(dot) Nasby" <jim(at)nasby(dot)net>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: Another idea for dealing with cmin/cmax |
Date: | 2006-09-29 10:05:15 |
Message-ID: | 20060929100515.GB8702@svana.org |
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Lists: | 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(at)svana(dot)org> http://svana.org/kleptog/
> From each according to his ability. To each according to his ability to litigate.
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