This section lists views that are useful for viewing information about undo space in the automatic undo management mode and provides some examples. In addition to views listed here, you can obtain information from the views available for viewing tablespace and datafile information.
Oracle Database also provides proactive help in managing tablespace disk space use by alerting you when tablespaces run low on available space.
In addition to the proactive undo space alerts, Oracle Database also provides alerts if your system has long-running queries that cause SNAPSHOT TOO OLD errors. To prevent excessive alerts, the long query alert is issued at most once every 24 hours. When the alert is generated, you can check the Undo Advisor Page of Enterprise Manager to get more information about the undo tablespace.
The following dynamic performance views are useful for obtaining space information about the undo tablespace:
The V$UNDOSTAT view is useful for monitoring the effects of transaction execution on undo space in the current instance. Statistics are available for undo space consumption, transaction concurrency, the tuning of undo retention, and the length and SQL ID of long-running queries in the instance.
Each row in the view contains statistics collected in the instance for a ten-minute interval. The rows are in descending order by the BEGIN_TIME column value. Each row belongs to the time interval marked by (BEGIN_TIME, END_TIME). Each column represents the data collected for the particular statistic in that time interval. The first row of the view contains statistics for the (partial) current time period. The view contains a total of 1008 rows, spanning a 7 day cycle.
The following example shows the results of a query on the V$UNDOSTAT view.
The preceding example shows how undo space is consumed in the system for the previous 24 hours from the time 14:35:12 on 10/27/2003.
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