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see ORA-12699
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INSERT versus CTAS

Alexander Gorbachev

2004-12-11

Replies:
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
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http://www.freelists.org/webpage/oracle-l