Re: Clarification about HOT

On 11/2/07, Heikki Linnakangas <heikki(at)enterprisedb(dot)com> wrote:
>
> Gokulakannan Somasundaram wrote:
> > I understand that if you have to Vacuum a tuple, it has to satisfy the
> > necessary snapshot requirements. i will never be able to reduce the
> chain to
> > just one, because the there is always a indirection at the top of HOT. I
>
> > understood this.
> >
> > My question was is it the only reason for the decision to stop HOT
> across
> > pages.
>
> Another reason is that it avoids the whole problem of updating multiple
> pages atomically, without deadlocks.

Thanks Heikki. I am still not getting what you said. In the case of HOT,
you need to update the top pointer to point to some other tuple in some
other page. That's one update. what's the other one?

say currently the top of heap chain points to (2,3) . Imagine we are making
the HOT chain through the pages. there might be a situation it should start
pointing to (4,5) after the tuple at (2,3) gets ready to be Vacuumed. We
should just lock the page where the top of HOT chain resides and update it
to point to (4,5). What else we should do atomically?

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