UDB: Backup Image Size & Used Pages Size

[Anurag]

Hi,
I posted this on other user-groups.
Hardly got any responses. Here goes the question:

PLATFORM = DB2 UDB 8.2+ on AIX 5.x, DPF

Two Topics broadly:
(A) I wish to find out a rough correlation between the size
of Used Pages in the database and its backup image size
(Have to do some space calculation).
(B) How many partitions should be backed up in parallel to
gain the most optimum performance?

Specifically, the questions / observations on Topic A are
(Assuming Used Pages Size is fixed):
(1) Backup Image Size changes with number of buffers
specified in the backup command.
(2) Is backup image size related to number of partitions
even when the used pages are same?
(3) Does datatype have an impact on backup size?
OR
If the used pages add upto 1G, approx how much would be the
size of uncompressed backup image?

All answers / hints / experience-sharing are appreciated.

Regards,
Anurag

[Shashi Mannepalli]

Your USED PAGES in a database is always not correct. It depends on the
activity on database.
For example if u delete lot of records in a table and if there is no
REORG done it may not show up the correct usage of the USED PAGES.

But generally if your database is well maintained this USED PAGES is
the good indicator of how much space your tablespaces have used.

Where as your BACKUP image of the database contains everything.

As far as tuning the performance of BACKUP process is concerned please
explore the PARALLESIM ...etc options
you can check them in the DB2 ADMIN GUIDE.

cheers...
Shashi Mannepalli

[Knut Stolze]

Shashi Mannepalli wrote:

Your USED PAGES in a database is always not correct. It depends on the
activity on database.
The used pages indicator _is_ correct. It shows how many pages are
allocated in a tablespace. It is not intended to show on how much pages
the data in the DB would fit if it were optimally stored and not
fragmented.
But generally if your database is well maintained this USED PAGES is
the good indicator of how much space your tablespaces have used.
Even if it is not well maintained. ;-)
Where as your BACKUP image of the database contains everything.

Unless you are doing an incremental backup.

--
Knut Stolze
DB2 Information Integration Development
IBM Germany

[Shashi Mannepalli]

Sorry....i was referring to the HIGH WATER MARK usage...some
times....it may show higher than the intended
if u don't do REORG...etc

Knut Stolze is correct.