Automatic Undo Management, UNDO tablspace, and undo_segment count

Question

When I created my UNDO tablespace I was given 10 undo_segments:
SQL> SELECT usn "Rollback Table", GETS, WAITS, xacts "Active Transactions"
2 FROM V$ROLLSTAT;
Rollback Table GETS WAITS Active Transactions
0 1242 0 0
1 88678 8 0
2 83884 2 0
3 82519 9 0
4 85661 17 0
5 80613 14 0
6 82183 0 0
7 92551 9 0
8 78371 14 0
9 89043 1 0
10 75477 5 0
The above statistic indicates I need more undo_segments. Do I need to recreate my UNDO tablespace in order to get the number of segments necessary to prevent waits or will more undo_segments be spawned eventually??
I think I'm suffering Contention? Is there medicine?

Answer 1

Compared to the number of GETS, the number of WAITS is very small. I doubt that you could ever have enough rollback segments to ensure that there were never any waits. Oracle's read consistency mechanism virtually guarantees that you will at least occasionally get waits.
Aside from that, the point of UNDO tablespaces is that Oracle will manage the number and size of rollback segments based on the load. If you are really concerned about this, and if you have statistics indicating that waits for rollback segments are a performance bottleneck (something like a statspack report showing large amounts of time for one of the undo waits), then you can simply add more space to your undo tablespace, and Oracle will likely use it to add additional segmetns if it feels the need.
John