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Re: DML on dual?

From: John Darrah <darrah.john_at_gmail.com>
Date: Thu, 12 Apr 2007 12:19:56 -0600
Message-ID: <ec40ac060704121119u67377541g6716790473bb6782@mail.gmail.com>


I've seen several oracle trace files that have the statement "SELECT 1 FROM DUAL FOR UPDATE NOWAIT" I have no idea what the purpose of that statement is but it probably explains what you are seeing.

On 4/12/07, Herring Dave - dherri <Dave.Herring_at_acxiom.com> wrote:
>
> Folks,
>
> I've got an odd problem on our production database where it seems physical
> writes and row lock waits are happening on SYS.DUAL. These are not
> causing any major performance problems, but it concerns me that some sort of
> DML (I'm assuming) is being performed against SYS.DUAL, which in my mind
> should never happen.
>
> I came to the conclusion about DML against SYS.DUAL based on data from
> STATS$SEG_STAT for that segment, where I see physical writes and row lock
> waits, at most 100 or so per day.
>
> I've set auditing on for INSERT, UPDATE, LOCK, DELETE on SYS.DUAL, but
> nothing has shown up. I've search V$SQL for any SQL statement referencing
> DUAL/SYS.DUAL but have found nothing beyond SELECT statements.
>
> Anyone else see this behavior and/or have any clues on how to track what's
> causing this activity?
>
> Database is 9.2.0.6, on Tru64 5.1b, 10 x 40GB GS1280 server.
>
> Thanks.
>
> Dave
> ___________________________________
> David C. Herring, DBA| A c x i o m Delivery Center Organization
> 630-944-4762office |630-430-5988 wireless|630-944-4989 fax
>
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Received on Thu Apr 12 2007 - 13:19:56 CDT

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