RE: why does oracle recovery redo before undo?
- From: DENNIS WILLIAMS <DWILLIAMS@xxxxxxxxxxxxx>
- To: "'oracle-l@xxxxxxxxxxxxx'" <oracle-l@xxxxxxxxxxxxx>
- Date: Tue, 20 Apr 2004 11:49:55 -0500
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@xxxxxxxxxxxxx
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx]On Behalf Of Chip
Sent: Monday, April 19, 2004 10:43 PM
To: oracle-l@xxxxxxxxxxxxx
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?
>
>
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