Oracle Database Discussions

My Undo retention is : 900 sec
Retention Guarantee enabled

From the OEM - My undo system activity is :

Selected Analysis Time Period Jul 20, 2011 1:00:00 PM IDT To Jul 27, 2011 1:00:00 PM IDT
Longest Running Query (minutes) 18.0
Average Undo Generation Rate (KB/minute) 74.0
Maximum Undo Generation Rate (KB/minute) 482.0
Queries failed due to low Retention 0
Transactions failed due to small Undo Tablespace 0

And the OEM Analysis Results :

Selected Analysis Time Period Jul 20, 2011 1:00:00 PM IDT To Jul 27, 2011 1:00:00 PM IDT
Minimum Required Undo Tablespace Size (MB) 68
Recommended Undo Tablespace Size (MB) 101

What calculation Oracle used in order to achieve these numbers (68 and 101 MB) ?
I tried to calculate those values based on v$undostat tablespace and received different numbers

1 SELECT &retention *
2 (SELECT (SUM(undoblks))/ SUM ((end_time - begin_time) * 24*60*60)
3* FROM v$undostat) MB FROM dual
SYS@orcl> /
Enter value for retention: 900
old 1: SELECT &retention *
new 1: SELECT 900 *

MB
----------
143.344832

Thank you

Edited by: Jerry on Jul 27, 2011 2:43 AM

Edited by: Jerry on Jul 27, 2011 2:44 AM