> > > Sorry, that's what I meant ... why should marking a column as 'deleted'
> > > and running a 'vacuum' to clean up the physical table be any less
> > > crash-safe?
> >
> > It is not. The only downside is 2x disk space to make new versions of
> > the tuple.
>
> huh? vacuum moves/cleans up tuples, as well as compresses them, so that
> the end result is a smaller table then what it started with, at/with very
> little increase in the total size/space needed to perform the vacuum ...
>
> if we reduced vacuum such that it compressed at the field level vs tuple,
> we could move a few tuples to the end of the table (crash safe) and then
> move N+1 to position 1 minus that extra field. If we mark the column as
> being deleted, then if the system crashes part way through, it should be
> possible to continue after the system is brought up, no?
If it crashes in the middle, some rows have the column removed, and some
do not.
-- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610)
853-3000+ If your life is a hard drive, | 830 Blythe Avenue + Christ can be your backup. | Drexel Hill,
Pennsylvania19026