Deduplication in 11g works only in alter/modify?

[PelleFork]

Hi all!

I'm playing around with 11g, especially to evaluate the SecureFiles deduplication mechanisms, which seem incredibly useful.

If I create the table with the DEDUPLICATE storage option and the starts to feed the table with lots of duplicates in the BLOB column, deduplication doesn't seem to take place, according to the DBMS_SPACE package.

create table test_blob (
  id            number(10),
  image_name    varchar2( 400 ),
  image         blob,
  timestamp     date) 
  lob(image) store as securefile 
  ( deduplicate  );
 
 

But, if I issue an

alter table test_blob 
modify lob(image) 
(deduplicate);
 

suddenly it works, reducing my space to one third, which is my calculated goal. Anybody seen this? It's supposed to be application transparent, according to Oracle...

Honestly, it's not really useful if I need to issue DDL statements in production. My db_securefiles parameter is set to PERMITTED which is the default.