RE: "snapshot too old" and undo

From: Hallas, John, Tech Dev <John.Hallas_at_gb.vodafone.co.uk>
Date: Fri, 30 Sep 2005 08:04:30 +0100
Message-ID: <1C6E45ADB2EC324F9553E468ABFE0F63030F0EF3@UKWMXM04>

If it is a huge table then it does not really matter how accurate the statistics are so why bother gathering them. Estimate them instead.

dbms_stats.set_table_stats( user, 'TABLE', numrows => 50000, numblks
=> 10000 );

dbms_stats.set_column_stats( user, 'TABLE', 'COLUMN', distcnt => 15000 );

I think space is the only issue with a large undo_rention area. However do you really want a job to be running for 36 hours

Is the table not partitioned? If so then use the partition option of dbms_stats and break the job down into smaller sections

HTH John

From: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Roger Xu Sent: 29 September 2005 22:33
To: Oracle-L_at_Freelists. Org (E-mail)
Subject: "snapshot too old" and undo_retention

Hi List,

Background: Oracle 9.2.0 w/ Auto Undo Management

We have a huge table and it takes more than 24 hours to collect its statistics.

But the undo_retention is set to 864000 i.e. 24 hours. As a result we see the following a lot.

"ORA-01555: snapshot too old: rollback segment number 11 with name "_SYSSMU11$" too small"

Since we have lots of space in the undo tablespace, I am thinking of increasing undo_retention to 36 hours

via "ALTER SYSTEM SET UNDO_RETENTION = 129600;"

Is this my only choice?

What are the drawbacks to have a large undo_retention value assuming we never run out undo tablespace?

Thanks,

Roger Xu

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Received on Fri Sep 30 2005 - 02:12:51 CDT

RE: "snapshot too old" and undo_retention