Re: why does oracle recovery redo before undo?
- From: Chip <ocp-dba@xxxxxxxxxxxxx>
- To: oracle-l@xxxxxxxxxxxxx
- Date: Mon, 19 Apr 2004 21:42:36 -0600
"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?
>
>
----------------------------------------------------------------
Please see the official ORACLE-L FAQ: http://www.orafaq.com
----------------------------------------------------------------
To unsubscribe send email to: oracle-l-request@xxxxxxxxxxxxx
put 'unsubscribe' in the subject line.
--
Archives are at //www.freelists.org/archives/oracle-l/
FAQ is at //www.freelists.org/help/fom-serve/cache/1.html
-----------------------------------------------------------------
Other related posts:
