Re: Visibility map thoughts

On Nov 6, 2007 4:33 PM, Heikki Linnakangas <heikki(at)enterprisedb(dot)com> wrote:
> Gokulakannan Somasundaram wrote:
> > Just one more thought on the same. This implementation also assumes
> > that there won't be any update chains across pages, which is the
> > current stage.
>
> No, it doesn't assume that.

Say, if there is a tuple, which is visible to everyone, the Vacuum
process might have marked that block as visible. But the new update
which has happened, which is linked to the index tuple through the
head of the update chain might not be visible to everyone. How do you
think this design takes care of it?

>
> > Heikki,
> > Is it planned as a optional feature? (I support the optional
> > feature model)
>
> I'm not planning it. Clearly you are :-).

If you are planning it as a non-optional feature, you do realize that
there might be tables which don't need this index only scan and still
incur the extra overhead of maintaining the Visibility map.

--
Thanks,
Gokul.
CertoSQL Project,
Allied Solution Group.
(www.alliedgroups.com)