On Mon, Mar 15, 2010 at 10:53 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Greg Smith <greg(at)2ndquadrant(dot)com> writes:
> > VJK wrote:
> >> Since Pg does not use the concept of rollback segments, it is unclear
> >> why deletion produces so much disk IO (4GB).
>
> For an example like this one, you have to keep in mind that the
> toast-table rows for the large bytea value have to be marked deleted,
> too. Also, since I/O happens in units of pages, the I/O volume to
> delete a tuple is just as much as the I/O to create it.
>
That makes sense.
> regards, tom lane
>