Re: Enable Parallel DML or Not?

From: Kellyn Pedersen <kjped1313_at_yahoo.com>
Date: Wed, 7 Oct 2009 15:42:07 -0700 (PDT)
Message-ID: <92220.95979.qm_at_web32005.mail.mud.yahoo.com>

Thank you for the link, but I've gone through every manual I can find, including this one and I also would consider the CTAS, since it's a create table, in a DDL category of parallel processing and I have had your theory as the most likely possibility, but I want to ensure that I'm not missing something here.  I also have read different websites that INCLUDE CTAS in with standard insert, update, merge and deletes as requiring parallel_dml to be enabled to get the full benefit of all parallel hints, but these may be on older versions of Oracle, as I have seen a couple list Oracle 7.3.
 

Kellyn

• On Wed, 10/7/09, Jaromir D.B. Nemec <jaromir_at_db-nemec.com> wrote:

From: Jaromir D.B. Nemec <jaromir_at_db-nemec.com> Subject: Re: Enable Parallel DML or Not? To: kjped1313_at_yahoo.com, "oracle Freelists" <oracle-l_at_freelists.org> Date: Wednesday, October 7, 2009, 4:20 PM

Hi Kellyn,
 

> QUESTION-  Is this just a mistake by some educated folks out there or are CTAS considered a parallel DML statement along with merge, insert, update and delete when > using parallel?
 

from Manual  http://download.oracle.com/docs/cd/B28359_01/server.111/b28313/usingpe.htm#CACFJJGG
 

The session's PARALLEL DML mode does not influence the parallelism of SELECT statements, DDL statements, and the query portions of DML statements.
 

An other argument (though I can't prove it as the 7.3 mauals are no longer on-line) - the parallel CTAS is there around from 7.3 the ENABLE PARALLEL DML  was introduced first in 8 or 8i.  The actual degree of the parallelism of the create table and select depends on several factors and can be limited or suppressed completely.
 

Regards,
 

Jaromir
 

----- Original Message -----

From: Kellyn Pedersen
To: oracle Freelists
Sent: Wednesday, October 07, 2009 5:20 PM Subject: Enable Parallel DML or Not?

I have to say as much as I learn about parallel processing everyday, the more questions I have...:)
 

I have numerous CTAS operations that load tables with large parallel degrees in both the insert as well as the select, (see example below...)
 

create table member_0_ordersum2 compress pctfree 0 tablespace MARTLARGE parallel(degree 16) as SELECT/*+ parallel (i 16) parallel (s 16)*/ o1.ibid

,recency_key
, ROUND(NVL(AVG(o1.nrt_gap_days), 0), 0) AS adbo
, ROUND(NVL(AVG(o1.onl_gap_days), 0), 0) AS adbo_o...

When I view these through OEM, it is not receiving the parallel on the table creation(insert) and is, of course, using a huge amount of temp space for the hash/sort processes, so I'm seeing large waits on direct read and writes to my temp tablespace group, along with sequential reads on the partitions in question, (but I find this to be an actual index from the data dictionary causing it to be a sequential read wait, not the actual partition, BTW.)
 

I've read misleading information view the web on CTAS being a parallel_DML statement, which I didn't think it was and if it is, would require me to enable parallel DML before the create table statement. 
 

QUESTION-  Is this just a mistake by some educated folks out there or are CTAS considered a parallel DML statement along with merge, insert, update and delete when using parallel?
 

Thanks!
Kellyn Pedersen
Multi-Platform DBA
I-Behavior

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Received on Wed Oct 07 2009 - 17:42:07 CDT