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Home -> Community -> Mailing Lists -> Oracle-L -> RE: redo logs
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
> --
> Author: <bulbultyagi_at_now-india.net.in
> INET: bulbultyagi_at_now-india.net.in
>
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> Author: DENNIS WILLIAMS
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-- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: <bulbultyagi_at_now-india.net.in INET: bulbultyagi_at_now-india.net.in Fat City Network Services -- 858-538-5051 http://www.fatcity.com San Diego, California -- Mailing list and web hosting services --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing). -- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: DENNIS WILLIAMS INET: DWILLIAMS_at_LIFETOUCH.COM Fat City Network Services -- 858-538-5051 http://www.fatcity.com San Diego, California -- Mailing list and web hosting services --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing). -- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: INET: Jared.Still_at_radisys.com Fat City Network Services -- 858-538-5051 http://www.fatcity.com San Diego, California -- Mailing list and web hosting services --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing). -- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: DENNIS WILLIAMS INET: DWILLIAMS_at_LIFETOUCH.COM Fat City Network Services -- 858-538-5051 http://www.fatcity.com San Diego, California -- Mailing list and web hosting services --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).Received on Tue May 20 2003 - 08:52:00 CDT
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