> Do we want to head for an overwriting storage manager?
>
> Not sure.
>
> Advantages: UPDATE has easy space reuse because usually done
> in-place, no index change on UPDATE unless key is changed.
>
> Disadvantages: Old records have to be stored somewhere for MVCC use.
> Could limit transaction size.
Really? Why is it assumed that we *must* limit size of rollback segments?
We can let them grow without bounds, as we do now keeping old records in
datafiles and letting them eat all of disk space.
> UNDO disadvantages are:
>
> Limit size of transactions to log storage size.
Don't be kidding - in any system transactions size is limitted
by available storage. So we should tell that more disk space
is required for UNDO. From my POV, putting $100 to buy 30Gb
disk is not big deal, keeping in mind that PGSQL requires
$ZERO to be used.
Vadim