Re: DB2 HADB

"Noons" <wizofoz2k_at_yahoo.com.au> wrote in message news:1132955576.566530.88980_at_f14g2000cwb.googlegroups.com...
> I'm still puzzled at why "reorgs" are such a great part of the db2
> universe.
> Quite frankly, something is definitely wrong if it needs them with such
>
> regularity that they must feature in just about every official document
> on recovery/tuning...
>

The main reason is that DB2 has table clustering, which Oracle does not have unless you use an index ordered table (which maintains the data in exact order all of the time like an index, and is can be a bit time-consuming for inserts due to the extra work involved).

DB2 clustering only "tries" to insert the row on the correct page (never rearranges rows on the page like an index), and if the correct page or a nearby page is not available, then it doesn't waste time with page splits (just puts the row anywhere). The area on a page used for inserting new rows is different on Oracle compared to DB2, and a reorg restores the free space percent (as specified when the table is created) on each page for new inserts in when a clustering index is defined.

DB2 table clustering is not "needed", and it is optional, but in many cases it does provide a definite performance enhancement with the extra overhead of an index ordered table in Oracle. Since DB2 has true on-line reorgs, there is no downtime, so I don't know it bothers you so much. Received on Fri Nov 25 2005 - 16:38:01 CST