RE: ACID
Date: Wed, 24 Aug 2011 14:30:55 +0000
Message-ID: <7642C3D639A75E4284658CAA38BF60A4022A17_at_US-BOS-VEX001.eu.pxl.int>
I think your confusing apples with oranges. Redo is used to create a data record that is as of a point in time so that you get that read consistent view of the data. Logging is there so that you can recreate the changes to the data files during a recover operation. Using WAL for the log records falls into line with Oracle's ideas on write as little as possible as infrequently as possible for performance enhancement. Redo gives you the ability to show an existing query what the data looked like when it started without regard to if the change is permanent or not. They serve very different purposes.
Richard Goulet
Senior Oracle DBA/Na Team Leader
-----Original Message-----
From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Laimutis.Nedzinskas_at_seb.lt
Sent: Wednesday, August 24, 2011 6:04 AM
To: oracle-l_at_freelists.org
Subject: Re: ACID
Implementation of durability by Oracle deserves some discussion.
The term REDO is may be fine but now days there exists a better term: Write-ahead logging. Three words tell the essence: write to log ahead of modifications.
Obviously for some reasons (a few of them can be named actually) oracle implemented the commit command using Write-after logging. One wonders what about rollback ? For me, Rollback seems to be fine even with write-after logic.
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Received on Wed Aug 24 2011 - 09:30:55 CDT