"Konstantin Andreev" <plafcow4odno@datatech.ru> wrote in message
news:e8h6o7$s5g$1@dns.comcor.ru...
> Recently I was engaged in the database optimization for one big commercial
> application. During this business I was greatly astound by the fact that
> it's impossible in DB2 to get the accurate size of a table. Indeed, the
> disk space occupied by a table is composed from three parts:
>
> # part size information @
> - ------------------ ------------------
> 1) data (except LOBs) syscat.tables: (npages,fpages) - exact info
> 2) indexes syscat.indexes: nleafs - partial info
> 3) LOBs (no information available)
>
> Only the first of the three parts (1: data) can be counted accurate. For
> part 2 (indexes) we do not know the count of non-leafs pages, and for part
> 3 (LOBS) we know nothing about their amount.
>
> There is merely the oblique way, proposed in this conference by "P.
> Saint-Jacques" in 1998
> (http://groups.google.ru/group/comp.d...ba45720fd38bfc)
> for estimation of LOBs size for a whole database.
>
> The thorough investigation of the Table:'Estimate size' action in the
> modern DB2 Control Center (NT, 8.2.3) uncovers that nothing changed since
> 1998. The proposed list of numbers is just the direct reflection of parts
> 1 and 2 information sources, indicated above.
>
> Please, contradict if I am wrong. Maybe some of IBM gurus here could
> comment this topic ?
>
> Cheers,
> --
> Konstantin Andreev.

Yes, it is a bit difficult to precise estimate the size of a database,
especially if you considering the amount of data versus the amount of space
allocated. But a precise estimate of db size has nothing to do with
"database optimization." For that, you only need rough estimates, and a lot
of skill and experience in optimization and performance tuning.