For reference, here's the discussion about this that took place on
hackers: http://lnk.nu/archives.postgresql.org/142.php 

On Sun, Jan 23, 2005 at 01:16:20AM -0500, Christopher Browne wrote:
> A long time ago, in a galaxy far, far away, [EMAIL PROTECTED] (Greg Stark) 
> wrote:
> > Dawid Kuroczko <[EMAIL PROTECTED]> writes:
> >
> >> Quick thought -- would it be to possible to implement a 'partial VACUUM'
> >> per analogiam to partial indexes?
> >
> > No.
> >
> > But it gave me another idea. Perhaps equally infeasible, but I don't see 
> > why.
> >
> > What if there were a map of modified pages. So every time any tuple
> > was marked deleted it could be marked in the map as modified. VACUUM
> > would only have to look at these pages. And if it could mark as free
> > every tuple that was marked as deleted then it could unmark the
> > page.
> >
> > The only downside I see is that this could be a source of contention
> > on multi-processor machines running lots of concurrent
> > update/deletes.
> 
> I was thinking the same thing after hearing fairly extensive
> "pooh-poohing" of the notion of vacuuming based on all the pages in
> the shared cache.
> 
> This "hot list page table" would probably need to be a hash table.  It
> rather parallels the FSM, including the way that it would need to be
> limited in size.
> -- 
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-- 
Jim C. Nasby, Database Consultant               [EMAIL PROTECTED] 
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