RE: "create table as" statement versus an "insert into" stateme

Heidi,

The CREATE TABLE .. AS SELECT uses temporary segment space to store the data from the original table which is then bulk loaded into the new table. It doesn't use rollback segments and utilizes memory more efficiently. In addition the performance of CREATE TABLE AS SELECT statements can be further improved in two ways :
1) by parallelism (using the PARALLEL hint) so that multiple CPUs can be used to carry out the command
2) using the NOLOGGING clause, which will disable redo log generation for the table creation statement.

Check out the Oracle documentation on parallel execution at :- http://www.sch.bme.hu/misc/oracle8/server/a58227/ch_paral.htm

Regards,
Kieran

-----Original Message-----
From: Heidi_Schmidt_at_gillette.com
To: Multiple recipients of list ORACLE-L Sent: 10/24/00 4:01 AM
Subject: "create table as" statement versus an "insert into" statement
(performance

I could use some help.

Does someone know why a create table as statement would perform better than
a truncate table, and then insert into statement? Gut instinct tells me the create table is cleaner and the insert into has
to find free chunks, but that can't be all of it.

The background is that we have some developers who are executing large data
loads and have to recreate objects every evening as part of a hierarchical
OLAP tool process. They are looking to shave time wherever they can to get
it all into their batch window.

I am not sure where to begin to look for information that would show why one way would perform better than the other. I think it would be under parsing algorithms, which would be cool to learn
if there was a list of them or a chart.

Thanks in advance,

     Heidi

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