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Sizing your undo tablespace


It is always a puzzle for a DBA to look into the user's complaint of getting "ORA-01555 Snapshot too old : rollback segment number x with name "_SYSSMUx$" too small " error. You have looked into the database. If your UNDO_MANAGEMENT is set to AUTO, you can not do anything to size the rollback segments manually since it is being managed by oracle. All the associated tables and indexes have been analyzed and statistics are up to date. The undo tabelspace is almost full. You may advise the user that there should be frequent commits (if it is a data loading process) or if there is a long running query and other users change the data that is being selected by the query, this can happen and in that case, if possible, advise the user not to run these two at the same time.

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