Re: HOT documentation README

On 9/12/07, Pavan Deolasee <pavan(dot)deolasee(at)gmail(dot)com> wrote:
>
>
> One change that is worh mentioning
> and discussing is that we don't follow HOT chains while fetching tuples
> during
> autoanalyze and autoanalyze would consider all such tuples as DEAD.
> In the worst case when all the tuples in the table are reachable via
> redirected line pointers, this would confuse autoanalyze since it would
> consider all tuples in the table as DEAD.

This is all crap. I was under the impression that heap_release_fetch()
would never fetch a HOT tuple directly, but thats not true. analyze fetches
all tuples in the chosen block, so it would ultimately fetch the visible
tuple.
A tuple is counted DEAD only if its t_data is set to non-NULL. For
redirected
line pointer heap_release_fetch() will set t_data to NULL and hence these
line pointers are (rightly) not counted as DEAD. This is the right thing to
do
because lazy vacuum can not remove redirected line pointers.

I think we should change this to follow HOT chain in analyze.
>
>
>
We need not follow the chain, but we should check for redirect-dead line
pointers and count them as dead rows.

Thanks,
Pavan

--
Pavan Deolasee
EnterpriseDB http://www.enterprisedb.com