RE: ACID
- From: "Goulet, Richard" <Richard.Goulet@xxxxxxxxxxx>
- To: "Laimutis.Nedzinskas@xxxxxx" <Laimutis.Nedzinskas@xxxxxx>, "oracle-l@xxxxxxxxxxxxx" <oracle-l@xxxxxxxxxxxxx>
- Date: Wed, 24 Aug 2011 14:30:55 +0000
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@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx] On
Behalf Of Laimutis.Nedzinskas@xxxxxx
Sent: Wednesday, August 24, 2011 6:04 AM
To: oracle-l@xxxxxxxxxxxxx
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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