| Oracle FAQ | Your Portal to the Oracle Knowledge Grid | |
 |
 | |||
| Oracle FAQ | Your Portal to the Oracle Knowledge Grid | |
|
| |||
Home -> Community -> Mailing Lists -> Oracle-L -> RE: why does oracle recovery redo before undo?
Chip - Thanks for mentioning these manuals. I am reading the 10g Concepts
manual right now, but I had overlooked this particular material, so that was
very helpful. With this size of manual it is easy to overlook some important
stuff.
As near as I can tell, the B&R architecture stuff is now moved to the Backup and Recovery Basics manual in 10g. If I am wrong, please let me know. Thanks.
Dennis Williams
DBA
Lifetouch, Inc.
dwilliams_at_lifetouch.com
-----Original Message-----
From: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org]On Behalf Of Chip
Sent: Monday, April 19, 2004 10:43 PM
To: oracle-l_at_freelists.org
Subject: Re: why does oracle recovery redo before undo?
"Optimal" recovery steps depend on the database architecture. By design, Oracle has implemented a multi-versioning read and write concurrency architecture to maximize data availability for many simultaneous database users. In contrast, other database architectural approaches block read access to data when an update is occuring - data is not available for other users to read until the transaction is complete.
Chapter 1 of the Oracle Concepts documents the "Data Concurrency and Consistency" design. The Oracle Backup and Recovery Concepts documents the "Redo Application During Recovery" which includes a couple potential problems that can result if an instance failure occurs. Due to these potential problems, Oracle's cache recovery (roll forward) and transaction recovery (roll back) steps are "optimal" for the Oracle database architecture.
Have Fun :)
Ryan wrote:
>I know how it works. I know that it works. I can't find 'why'? I'm taking a
university database class and my professor says the optimal way to recover
is with undo before redo and so does my book.
>Anyone know why Oracle does it the other way?
>
>
-- Archives are at http://www.freelists.org/archives/oracle-l/ FAQ is at http://www.freelists.org/help/fom-serve/cache/1.html ----------------------------------------------------------------- ---------------------------------------------------------------- Please see the official ORACLE-L FAQ: http://www.orafaq.com ---------------------------------------------------------------- To unsubscribe send email to: oracle-l-request_at_freelists.org put 'unsubscribe' in the subject line. -- Archives are at http://www.freelists.org/archives/oracle-l/ FAQ is at http://www.freelists.org/help/fom-serve/cache/1.html -----------------------------------------------------------------Received on Tue Apr 20 2004 - 11:47:06 CDT
 |
 |