Re: Fwd: Clarification about HOT

On 11/5/07, Heikki Linnakangas <heikki(at)enterprisedb(dot)com> wrote:
>
> Gokulakannan Somasundaram wrote:
> > I think pointer swinging is still about maintaining the HOT chain within
> a
> > page. Actually i am thinking about continuing the HOT chain across
> pages.
>
> AFAICS, pointer-swinging would be exactly the same on cross-page HOT
> chains as same-page chains.

When i read pointer-swinging, it talks a lot about in-page updates, pointing
to the latest tuple instead of oldest tuple and circular pointers etc.
Maybe, if i am missing the post, which you are referring to, please correct
me on the steps i am talking about.

This scheme, if implemented would avoid the use of HOT stub and avoids the
need to go to index, even if some other indexes are getting updated/ even if
the updated new tuple goes into a new page

a) Whenever we update, we will update only those indexes whose attributes
are updated. So the index will point to the top of the HOT chain.
b) Whenever we Vacuum the index, we take a list of tids and check whether
there are any index tuples pointing to it. If the Vacuumed tuple is a start
of the HOT chain, then we will carry the next in-line HOT tuple when we goto
Vacuum the index. If the next in-line also satisfies the Vacuum, it will
carry with it the next in-line HOT tuple-id.

In this way, we will make sure the Index points to a live tuple after the
Vacuum.

This will remove the in-page pruning exercises, but as i said already the
cost of updates will go down a lot with normal indexes.

Can you please tell, what are the disadvantages of the above mentioned
approach?

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