Re: Rollback Segments Question

Tim X wrote:
>
> I have a couple of questions relating to rollback segments I am hoping
> to get some clarification on from this group. The database is 8.1.7 on
> both True64 and Linux boxes.
>
> 1. According to the 8i documentation, you need to create an additional
> rollback segment when creating a new database. I've also seen this
> mentioned in a couple of books with the rationale that this is
> needed in order to create additional tablespaces and rollback
> segments in the db creation script. My problem with this is that I
> have seen databases created and have created databases where I did
> not need to create an additional rollback segment in the system
> tablespace in order to create tablespaces or rollback segments. So,
> what is the story here. Is this something left over from earlier
> Oracle versions and is not a requirement in newer versions (and
> just has not been removed from the documentation) or is there
> something subtle I'm not aware of?
>
> 2. According to the Oracle 8i documentation, if you do not include
> your rollback segments in the rollback_segment parameter in the
> init.ora file, your rollback segments will not be brought back
> on-line when you bring your database up and will need to explicitly
> be brought on-line with a alter statement. THis is in addition to
> the rollback_segments other role relating to public/private rbs and
> parallel servers. I have done some experiments with 8i and this
> does not seem to be the case. If I don't include the RBS in the
> parameter file, they still come up on-line when the db is
> started. Again, is this just old documentation left from an earlier
> Oracle version, a documentation error or am I missing something?
>
> 3. Can you use locally managed tablespaces for rollback segments?
> According to the Oracle 8i documentation, you cannot use the local
> automatic option for LMT if you want to use the tablespace for
> rollback segments. to me, this implies you could do it if you use
> the "local uniform" option instead. However, when I attempt to do
> this, the rollback segment creation fails with the error
>
> ERROR at line 1:
> ORA-01552: cannot use system rollback segment for non-system tablespace 'RBS'
>
> where RBS is my LMT and RBS01 is the name I am giving to the rollback
> segment. If I drop the tablespace and re-create it as a DMT, then
> everything is fine.
>
> Any info or pointers greatly appreciated.
>
> TIA
>
> Tim
> --
> Tim Cross
> The e-mail address on this message is FALSE (obviously!). My real e-mail is
> to a company in Australia called rapttech and my login is tcross - if you
> really need to send mail, you should be able to work it out!

Probably an easy solution to all of this is to use automatic undo (in 9i). But anyway,

1. in most versions of oracle you needed an additional rollback segment in system just for the purposes of initially creating a tablespace for undo and rb segments within it, after which it was not required
2. complicating this fact was that some early 8i versions where the rb tspace was an LMT had a bug where to recover them you needed a dictionary managed rb seg somewhere, which led people to leave the segment from (a) above existing, but typically offline.

hth
connor

-- 
=========================
Connor McDonald
http://www.oracledba.co.uk

"Some days you're the pigeon, some days you're the statue"