On 11/2/07, Heikki Linnakangas <heikki@enterprisedb.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)