Database Software

Hi,

I'm currently testing the benefits of Oracle 11g OLTP Compression. While everthing works great (like space savings of 50%, faster table scans), it is "updates" that made things go for a toss.
Observations:
I have a table with around 400,000 records. If I issue update on fewer records say 2000 or 3000, things are fine. But if I issue update on the entire column, things go worse. The size of the table is increased dramatically. What is the reason behind this? Is it just because data is written in uncompressed form and future inserts would kick in compression?
I dont think its ROW-CHAINING issue here, as I'm not inserting data. ROW-MIGRATION is definite case but as per the ORACLE documents, Migrated rows are compressed.

Pls shed some light on this. I need to know why the size of the table increases on BULK UPDATES.


Thank You.