Undo Retention (Oracle 9i)
The minimum amount of time (in secs) that undo data should be retained in undo tablespace to satisfy the read consistency. If the database requires space then the undo data will be over written even if the undo data has not been retained for UNDO_RETENTION duration.
Automatic Undo Retention (Oracle 10g)
If UNDO_MANAGEMENT=AUTO (no matter the setting for UNDO_RETENTION) automatic undo tuning will be used. MMON will calculate the MAXQUERYLEN every 30 sec interval. Based upon the MAXQUERYLEN, MMON decides the TUNED_UNDORETENTION. That means the new UNDO RETENTION will be set to TUNED_UNDORETENTION.
If UNDO_RETENTION is set > 0, the value specified acts as a minimum setting.
Note: Undo information for LOBs are stored in the segment itself and not in the undo tablespace. If space becomes low, the unexpired LOB undo information may be overwritten. Hence Automatic undo retention is not supported for LOBs.
Thanks
The minimum amount of time (in secs) that undo data should be retained in undo tablespace to satisfy the read consistency. If the database requires space then the undo data will be over written even if the undo data has not been retained for UNDO_RETENTION duration.
Automatic Undo Retention (Oracle 10g)
If UNDO_MANAGEMENT=AUTO (no matter the setting for UNDO_RETENTION) automatic undo tuning will be used. MMON will calculate the MAXQUERYLEN every 30 sec interval. Based upon the MAXQUERYLEN, MMON decides the TUNED_UNDORETENTION. That means the new UNDO RETENTION will be set to TUNED_UNDORETENTION.
If UNDO_RETENTION is set > 0, the value specified acts as a minimum setting.
Note: Undo information for LOBs are stored in the segment itself and not in the undo tablespace. If space becomes low, the unexpired LOB undo information may be overwritten. Hence Automatic undo retention is not supported for LOBs.
Thanks
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