Cheaper VACUUMing

A long time ago, in a galaxy far, far away, gsstark@mit.edu (Greg Stark) wrote:
> Dawid Kuroczko <qnex42@gmail.com> 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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