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)
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
Any comments about the onlining of segments welcomed...