INSERT versus CTAS

Hi,

What are the differencies between "create ... table as select" and "create table" + "insert /*+ parallel(...) append(...) */ into" from performance point of view?
I am interested in various tables:
- non-partitioned

• partitioned
• non pratitioned IOT
• partitioned IOT

Currently, I use create + insert with parallel append hints. It works reasonable fast for us - we are able to fill 100+ Gb of data within 1,5 hour.
However, inserting in partitioned IOT's is quite different. There are few problems:
- slow

• append doesn't work (and, consequently, parallel).
• lot's of redo (coz no append).
• lot's of undo (I guess because no append as well, since with append you need only revert HWM) and, consequently, ora-1555.
• lot's of temporary space required.

We are able to overcome some problems iterating through each partition, but it's not a clean solution and performance is still far from what we target.

I want to change INSERT to CTAS, but it requires some efforts to amend the script. I assume that CTAS would be more performant for IOT since it will create index as temporary segment in table's tablespace and then just amend dictionary (object definition + hwm). So I expect to eleminate UNDO generation, reduce temporary space requirements, reduce redo, and.... well, boost performance.

Any comments/links are appreciated.

It's 9.2.0.5 on 64 bit HP-UX.

Thanks in advance.
Alex

-- 
Best regards,
Alex Gorbachev
--
http://www.freelists.org/webpage/oracle-l