I have not seen this situation, but I have a thought on it. At one site, a
client had all their sequences with a cache size 0 to "enforce" a nogap
policy which obviously didn't work instead it caused a sql loader job to run
extremly slow. After tracing the session I saw a ton of recursive sql on the
internal sequnence tables which is a serial operation (to prevent duplicate
sequence values) using locks.
While the sql loader job does not, afaik, select from dual the lock might be
caused by underlying sequence refreshing its values too often.
On Behalf Of Kerber, Andrew W.
Sent: Thursday, April 12, 2007 11:07 AM
To: Dave.Herring_at_acxiom.com; oracle-l_at_freelists.org
Subject: RE: DML on dual?
Is perhaps doing a select from dual to bump a sequence as part of a
transaction? I suppose that might get a lock...
On Behalf Of Herring Dave - dherri
Sent: Thursday, April 12, 2007 9:42 AM
Subject: DML on dual?
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
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 220.127.116.11, on Tru64 5.1b, 10 x 40GB GS1280 server.
David C. Herring, DBA | A c x i o m Delivery Center Organization
630-944-4762 office | 630-430-5988 wireless | 630-944-4989 fax
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