Re: vacuum, performance, and MVCC

On Sat, Jun 24, 2006 at 08:14:10AM -0400, Mark Woodward wrote:
> > On 6/23/2006 3:10 PM, Mark Woodward wrote:
> >
> >> This is NOT an "in-place" update. The whole MVCC strategy of keeping old
> >> versions around doesn't change. The only thing that does change is one
> >> level of indirection. Rather than keep references to all versions of all
> >> rows in indexes, keep only a reference to the first or "key" row of each
> >> row, and have the first version of a row form the head of a linked list
> >> to
> >> subsequent versions of each row. The list will be in decending order.
> >
> > Where exactly do you intend to keep all those links (for a table with N
> > indexes)?
> >
>
> I'm probably mistaken, but aren't there already forward references in
> tuples to later versions? If so, I'm only sugesting reversing the order
> and referencing the latest version.

You can't do that. The links exist so that in READ COMMITTED mode you
can always find the newest version. You would need to add additional
links to go backwards.

Have a nice day,
--
Martijn van Oosterhout <kleptog(at)svana(dot)org> http://svana.org/kleptog/
> From each according to his ability. To each according to his ability to litigate.