Re: why undo_management=auto

From: DA Morgan <damorgan_at_psoug.org>
Date: Thu, 21 Dec 2006 14:56:12 -0800
Message-ID: <1166741771.312409@bubbleator.drizzle.com>

Charles Hooper wrote:
> DA Morgan wrote:

>> aman.oracle.dba wrote:
>>> Hello ALL,
>>>
>>> according to
>>> http://www.lc.leidenuniv.nl/awcourse/oracle/server.920/a96521/undo.htm#9114
>>> the use of rollback segments for managing undo space will be deprecated
>>> in a future release.
>>> WHY....................
>>> what are the main advantages to keep separate undo_tablespace in
>>> database, when I can make one separate tablespace for rollback segments
>>> also.
>> Not that far into the future ... as of 10g they are gone.
>>
>> Why?
>>
>> Partially to put an end to ORA-01555, partially because DBAs have proven
>> themselves incapable of managing rollback segments, and partially
>> because the new algorithm improves many aspects of database existance
>> and makes possible some aspects of flashback technology.
>>
>> It would seem that Oracle has taken the same attitude toward rollback as
>> they have taken toward temp ... we can do it better than you can. <g>
>> --
>> Daniel A. Morgan
>> University of Washington
>> damorgan_at_x.washington.edu
>> (replace x with u to respond)
>> Puget Sound Oracle Users Group
>> www.psoug.org

>
> Are you sure that they are gone?
>
> Oracle Database Administrator's Guide 10g Release 2, Page xlv:
> "Deprecation of use of rollback segments (manual undo management mode)
> Manual undo management mode has been deprecated and is no longer
> documented in this book. Use an undo tablespace and automatic undo
> management instead.
> See Chapter 10, Managing the Undo Tablespace"
>
> Page 10-2
> "You set the UNDO_MANAGEMENT initialization parameter to AUTO to enable
> automatic
> undo management. A default undo tablespace is then created at database
> creation. An
> undo tablespace can also be created explicitly. The methods of creating
> an undo
> tablespace are explained in "Creating an Undo Tablespace" on page
> 10-6."
>
> "UNDO_MANAGEMENT If AUTO, use automatic undo management. The default is
> MANUAL."
>
> It appears that in 10g R2, rollback segments are deprecated, no longer
> documented in the Administrator's Guide, yet are still the default
> based on the default value of UNDO_MANAGEMENT. Did I read something
> wrong?
>
> Charles Hooper
> PC Support Specialist
> K&M Machine-Fabricating, Inc.

Well I know there is still one rollback segment in the system tablespace (10.2.0.2):

desc dba_rollback_segs

SELECT segment_name, owner, tablespace_name FROM dba_rollback_segs;

So perhaps I should have been more precise and stated they are deprecated. But it would seem a DBA heck-bent on making a mess of things probably still can.

I just went into the docs:
http://download-west.oracle.com/docs/cd/B19306_01/server.102/b14231/create.htm#sthref413 and found an error I just reported. Where what is written is: "By default, this parameter is set to MANUAL."

-- 
Daniel A. Morgan
University of Washington
damorgan_at_x.washington.edu
(replace x with u to respond)
Puget Sound Oracle Users Group
www.psoug.org

Received on Thu Dec 21 2006 - 16:56:12 CST