Re: DML on dual?

I'm sure I saw this problem with SELECT 1 FROM DUAL FOR UPDATE NOWAIT on an older version of Oracle a few years ago. If I recall correctly, we traced it to an internal Oracle process... either the OCI interface or DBMS_PIPE or ??? I just can't remember for sure which one it was. We eventually realized it was some internal application's lame way of making sure that there was only one instance of a certain process running at any point in time.

I realize that's not much to go on, but maybe it will trigger someone else's memory... Tim

On 4/12/07, John Darrah <darrah.john_at_gmail.com> wrote:
>
> 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
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