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RE: redo logs

From: DENNIS WILLIAMS <DWILLIAMS_at_LIFETOUCH.COM>
Date: Tue, 20 May 2003 05:52:00 -0800
Message-ID: <F001.0059DB20.20030520055200@fatcity.com>


Jared - Yeah, perhaps I wasn't clear. Perhaps a Seussian rhyme will explain it better:

The redo stores undo so the smon is able to undo the disk writes when the system crashed because your parents came home.

Dennis Williams
DBA, 80%OCP, 100% DBA
Lifetouch, Inc.
dwilliams_at_lifetouch.com

-----Original Message-----
Sent: Monday, May 19, 2003 6:52 PM
To: Multiple recipients of list ORACLE-L

Dennis,

He asked about 'undo'. That is in the rollback segments, or the UNDO tablespace.

Jared

DENNIS WILLIAMS <DWILLIAMS_at_LIFETOUCH.COM> Sent by: root_at_fatcity.com
 05/19/2003 03:37 PM
 Please respond to ORACLE-L  

        To:     Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>
        cc: 
        Subject:        RE: redo logs


Yes. Remember that Oracle doesn't wait for a commit before it writes redo. It is even possible for uncommitted data to get written to the data files. This is a real performance boost on a busy system. In case of a crash, Oracle must be able to recreate the "before" image of the data.

   If you become more interested in this, take a look at LogMiner. Once you
see all the details in a redo log, you'll be much more impressed with Oracle's integrity and throughput! And a good time to practice with LogMiner
is when you aren't under pressure.

Dennis Williams
DBA, 80%OCP, 100% DBA
Lifetouch, Inc.
dwilliams_at_lifetouch.com

-----Original Message-----
Sent: Monday, May 19, 2003 4:58 PM
To: Multiple recipients of list ORACLE-L

Dennis , so what you are trying to say is that the redo logs store undo data
also ?

> Not every statement is committed. Some are rolled back. So when the
database
> is recovered, these statements must again be rolled back.
>
> Dennis Williams
> DBA, 80%OCP, 100% DBA
> Lifetouch, Inc.
> dwilliams_at_lifetouch.com
>
>
> -----Original Message-----
> Sent: Saturday, May 17, 2003 9:09 PM
> To: Multiple recipients of list ORACLE-L
>
>
> Hello list
>
> the "backup and recovery concepts" manual says :"Each redo record
contains
> both the old and the new values. Oracle also records the old value to an
> undo block located either in a rollback segment (if running in manual
undo
> management mode) or in a dedicated undo tablespace (if running in
automatic
> undo management mode)."
>
> Does this mean that undo data is stored in both the undo tablespace and
the
> redo
> logs ?
>
> I thought that only statements were stored in the redo log file.
>
> If undo data is stored in the redo logs also, then , do we need the undo
> tablespace during recovery ? shouldn't the redo logs be enough ?
>
> --
> Please see the official ORACLE-L FAQ: http://www.orafaq.net
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> Author: <bulbultyagi_at_now-india.net.in
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  INET: bulbultyagi_at_now-india.net.in

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  INET: DWILLIAMS_at_LIFETOUCH.COM

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Author: 
  INET: Jared.Still_at_radisys.com

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Author: DENNIS WILLIAMS
  INET: DWILLIAMS_at_LIFETOUCH.COM

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Received on Tue May 20 2003 - 08:52:00 CDT

Original text of this message

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