Re: ORA-01555 seems bogus

From: Kellyn Pedersen <kjped1313_at_yahoo.com>
Date: Mon, 8 Feb 2010 10:58:18 -0800 (PST)
Message-ID: <147190.46349.qm_at_web32007.mail.mud.yahoo.com>

Hey Andrew,
Can I ask you why you would adjust your undo retention?� The system will automatically tune the undo retention for you when a process requires a longer one-� it's part of the smon's job to ensure this...�
�

If you look at tuned_undoretention in v$undostat, anything that requires a larger retention time than the one set, should allocate a longer retention time automatically.� I am having a difficult time understanding how adjusting the retention time would correct a problem with the space allocated in the undo tablespace...
�

Please elaborate... thanks!

Kellyn Pedersen
Multi-Platform DBA
I-Behavior Inc.
http://www.linkedin.com/in/kellynpedersen www.dbakevlar.blogspot.com
�

"Go away before I replace you with a very small and�efficient shell script..."

On Mon, 2/8/10, Andrew Kerber <andrew.kerber_at_gmail.com> wrote:

From: Andrew Kerber <andrew.kerber_at_gmail.com> Subject: Re: ORA-01555 seems bogus
To: Richard.Goulet_at_parexel.com
Cc: "Kellyn Pedersen" <kjped1313_at_yahoo.com>, Dave.Herring_at_acxiom.com, oracle-l_at_freelists.org Date: Monday, February 8, 2010, 11:08 AM

You need to locate the long running transaction, and try and make it run in a shorter time frame, failing that, you need to try adjusting the undo retention.� The issue isnt necessarily a shortage of undo, it is simply that the transaction has run longer than undo_retention setting without doing a commit, and this short query is trying to read the data as it was at the start of the long running transaction.

On Mon, Feb 8, 2010 at 11:49 AM, Goulet, Richard <Richard.Goulet_at_parexel.com> wrote:

Kelly,
�
�� OH SH&^, I think we crossed wires.� What I meant by "undo is the very last" is that the last thing you want to do is extend the undo space because the lack of undo is not the problem.� Case in point, an SAP system that was always throwing ORA-01555 error on a specific report that took all day to process.� The UNDO space was 10 times the size of the entire rest of the database because the BASIS Admin was always adding undo space in response to the error, yet the error remained.

�

Dick Goulet
Senior Oracle DBA/NA Team Lead
PAREXEL International
�

From: Kellyn Pedersen [mailto:kjped1313_at_yahoo.com] Sent: Monday, February 08, 2010 12:42 PM To: Dave.Herring_at_acxiom.com; oracle-l_at_freelists.org; Goulet, Richard

Subject: RE: ORA-01555 seems bogus

Now Dick,
I agree that the overall culprit is often exactly what you have detailed below, but I think it is important to see that what you *think* is being used by your statement might be very different in reality when executed in whole-� as part of that one procedure, etc...� I think starting with undo is perfectly acceptable to see what the database has allocated towards the process, then proceed back, into the statement(s) in question to see where the logic is causing the issue or what other processes might be hampering the one that's been identified as the problem... :)

On Mon, 2/8/10, Goulet, Richard <Richard.Goulet_at_parexel.com> wrote:

From: Goulet, Richard <Richard.Goulet_at_parexel.com> Subject: RE: ORA-01555 seems bogus
To: Dave.Herring_at_acxiom.com, oracle-l_at_freelists.org Date: Monday, February 8, 2010, 8:05 AM

Dave,

�� An ORA-01555 is never bogus, but very misleading as you've found out.� OK, so the query in question is part of a package.� Is the package called from some application that's doing a "commit across a cursor", or is the package doing it internally?� Lots of places to look and undo is the very last.

Dick Goulet
Senior Oracle DBA/NA Team Lead
PAREXEL International

-----Original Message-----
From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Herring Dave - dherri Sent: Saturday, February 06, 2010 10:10 PM To: oracle-l_at_freelists.org
Subject: ORA-01555 seems bogus

Folks, I've got a curious situation where we're getting regular ORA-01555 errors yet they don't seem correct.� First a few things on the set up:

4-node RAC (+ 4-node RAC DG)
10.2.0.2
RHEL 8 x 64GB servers

The query returned in the error is doing a full scan of a 3,100 row table, which takes less than 1 sec to complete.� I've tried the same query repeatedly and it always takes less than one second, even when trying it while ORA-01555 errors are being returned saying that query is failing elsewhere.� The query is run 10,000+ times per day, always run from the same node.

The ORA-01555 error lists this query as having a duration of around 12,000 seconds each time, which from what I can tell is impossible.� Again, it's a 3,100 row table, no parallelism, 1 index (which isn't used by this query).� I checked LAST_ANALYZED and the table hasn't been analyzed in 4 days.� I checked DBA_TAB_MODIFICATIONS and it's had around 200 DML's since it was analyzed, but the last of which was 2 days ago.

So is Oracle returning the wrong query?� Is the ORA-01555 bogus?� Checking GV$UNDOSTAT, SSOLDERRCNT matches the # of ORA-01555 we're seeing (87 today, all the same query).� All instances have the same UNDO_RETENTION (3600) and similarly sized undo tablespaces.

Any clues how to catch the trouble making queries?

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Received on Mon Feb 08 2010 - 12:58:18 CST

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