Did a search prior to posting, ran across some older threads I didn't think needed resurfacing, so I'm posting a new one.

I'm interested in discussing the way in which Oracle allocates initial and additional Undo segments. I've found on Metalink the following.

Note: 135090.1 Managing Rollback/Undo Segments

1. When creating an UNDO tablespace, these are automatically created:
* n undo segments (based on SESSIONS parameter value)
* named as _SYSSMUn$
* owned by PUBLIC (usable for OPS configuration)
* not manually manageable

In the Oracle 9.2 documentation:

When the instance starts up, it brings online a number of rollback segments as determined by either of the following:

The ROLLBACK_SEGMENTS initialization parameter
The TRANSACTIONS and TRANSACTIONS_PER_ROLLBACK_SEGMENT initialization parameters (Anyway, this only releates to PUBLIC rollabck segments anyway)

I have the parameters


And yet 10 Rollback segments were onlined *scratches head*. I'm not sure how 9.2.0. arrived at on-lining 10 segments.

Undo Segment 1 Onlined
Undo Segment 2 Onlined
Undo Segment 3 Onlined
Undo Segment 4 Onlined
Undo Segment 5 Onlined
Undo Segment 6 Onlined
Undo Segment 7 Onlined
Undo Segment 8 Onlined
Undo Segment 9 Onlined
Undo Segment 10 Onlined

Also, I found the followig information for when additional UNDO segments are onlined (Metalink: Rowena Serna)

"It will online them as needed in this matter:
* Any new txn created will attempt to bind to an undo segment with NO current active txns
* When all online undo segments have active txns, then offlined undos will be onlined
* If all offlined undo segs have been onlined, then more undo segs
will be dynamically created.
* When no more undo segs can be created (not enough space in the
tablespace) then existing segments will allow multiple active
txns "

Any comments about the onlining of segments welcomed...