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Re: automatic undo management vs rollback segs (9i)

From: Brian Peasland <>
Date: Thu, 1 Apr 2004 22:21:24 GMT
Message-ID: <>

> Apparently 9i has some new version of rollback segments called undo
> management.
> Does anyone have any experience with this and is it worth using.

I use nothing but automated UNDO. I can't imagine going back to the old rollback segments. Undo segments have worked great for me and it is a relief that I don't have to worry about rollback segments any more. I haven't experienced any problems from them either except for the occasional ORA-1555 (snapshot too old) error when my UNDO_RETENTION was not sufficiently high enough.

>I run
> a small DB
> < 3G total not tons of transactions or concurrnet users
> If it is good does the tablespace reside on SYSTEM tablespace and can
> you change that since Oracle has always advised against using SYSTEM
> for anything other than Oracle Stuff.

You have to create a special tablespace called an UNDO tablespace. You create it with the CREATE UNDO TABLESPACE command. Then you set your UNDO_TS parameter to this tablespace name. You also set UNDO_MANAGEMENT to AUTO and set your UNDO_RETENTION.

You cannot use the SYSTEM tablespace for automated undo.

I would highly recommend that you read the Oracle docs on the subject...

> If it not a great new tool do you use the same old methods to create
> Rollback segments as before (8.1.5). ie

I don't use the old rollback segments any more.

> Use the system rollback for early instance and database creation
> then
> create an additional RBS on system and bring online
> run catalog.sql and catproc.sql
> create tablespaces including an RBS tablespace
> create new RB segs and bring system rollback seg offline
> shutdown and restart instance with new parameter file with
> RB1,RB2....RBn uncommented which will bring them all online

When you create a database, the CREATE DATABASE command can also create the UNDO tablespace at the same time. The syntax now allows for this.

> ? has that changed if you decide to use UNDO_MANAGEMENT = MANUAL

If you are using manual undo management, ie. the old rollback segments, then nothing has changed.



Brian Peasland

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Received on Thu Apr 01 2004 - 16:21:24 CST

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