Re: TOAST performance (was Re: [GENERAL] Delete Performance)

Tom Lane wrote:
> 
> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> > What bothers me about this is that we have the original page with the
> > old data.  It would be nice if we could write the new page in a
> > different location, make the new page active and recycle the old page at
> > some later time.
> 
> I don't see how that reduces the total amount of disk traffic?
> 
> It's also kind of unclear how to do it without doubling (or worse) the
> amount of table space used in many common scenarios.  I doubt many
> people will be happy if "DELETE FROM foo" requires transient space equal
> to twice the original size of foo.

IIRC the double space requrement is what has kept us from implementing 
DROP COLUMN.

-----------
Hannu