What triggers Undo Size Oracle Advisories?
What does it mean and how can the issue be fixed?
Encountering errors "ORA-30036: unable to extend segment by string in undo tablespace" or "ORA-01555: Snapshot Too Old" indicates that undo size should be tuned.
Tuning undo size includes setting the "undo_retention" parameter to an optimal value and allocating the proper size for the undo tablespace.
The V$UNDOSTAT view provides statistics about undo space consumption, transaction concurrency and length of queries executed in the instance.
The following metrics should be taken into consideration during the tuning process
To guarantee the success of long-running queries you can enable "retention guarantee" and then Oracle never overwrites unexpired undo data even if it means that transactions fail due to lack of space in the undo tablespace. This option is disabled by default and should be used with caution.
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