Oracle-L: RE: Shutdown abort

From: DENNIS WILLIAMS <DWILLIAMS_at_LIFETOUCH.COM>
Date: Fri, 09 Aug 2002 11:38:36 -0800
Message-ID: <F001.004B0EB5.20020809113836@fatcity.com>

Stefan - It is in the Oracle Student Guide for Backup & Recovery. Here is what it says:

Deferred Transaction Rollback
Deferred rollback was introduced in Oracle7.3.1. It enables a database to be opened as
soon as the roll forward using the redo log files is completed. The rollback of any
uncommitted transactions is done after opening the database to users. The rollback could be done in one of the following ways: * By SMON, which periodically scans all the rollback segments and rolls back aborted transactions as needed.
* By user processes, whereby a user process encounters a row lock held by a dead
transaction and recovers the transaction, which frees the row lock, after which the
user process continues processing.
Prior to Oracle8i
Deferred rollback could take a long time when parallel transactions are terminated by
a system crash, because rollback is predominantly a serial operation. For example, a
parallel update transaction with a degree of parallelism of 6 runs for 10 minutes, but
fails due to a system crash. Rolling back this transaction serially by SMON could take
one hour or more.
With Oracle8i
Fast start parallel rollback in Oracle8i enables a SMON to use parallel query slaves to
complete the rollback operation. Parallel rollback is automatically started when
SMON determines that the dead transaction had generated a large number of rollback
blocks. The current threshold for determining whether a transaction is large is 100
rollback blocks.

-----Original Message-----
Sent: Friday, August 09, 2002 2:53 AM
To: Multiple recipients of list ORACLE-L

Hi Dennis

Thanks you. Were did you find this information ? I seem to be unable to do a correct search on the documentation (I'm on 9.2 though).

Regards,

Stefan Jahnke
Consultant
BOV Aktiengesellschaft
Voice: +49 201 - 4513-298
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mailto:stefan.jahnke_at_bov.de

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-----Ursprüngliche Nachricht-----
Von: DENNIS WILLIAMS [mailto:DWILLIAMS_at_LIFETOUCH.COM] Gesendet: Donnerstag, 8. August 2002 16:48 An: Multiple recipients of list ORACLE-L Betreff: RE: Shutdown abort

Stefan

Well, I finally found a good reason for studying for OCP! I would not have known this answer without being forced to study.

It depends on your Oracle version. The Oracle 8i answer is: On startup, Oracle performs recovery, including rolling forward all transactions. Oracle then opens the database for production use. In the background, SMON continues to roll back transactions that were not committed when the database shut down. If a process needs a block that was involved in an uncommitted transaction, then SMON goes ahead and rolls back that transaction so the process doesn't have to wait.

Dennis Williams
DBA
Lifetouch, Inc.
dwilliams_at_lifetouch.com

-----Original Message-----
Sent: Thursday, August 08, 2002 7:58 AM
To: Multiple recipients of list ORACLE-L

Hi list

stupid one: In case of a shutdown abort and startup, are the rollback activities discontinued after startup and the rollback segs are available again ? or not ?

regards,
Stefan

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Author: Stefan Jahnke
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Author: DENNIS WILLIAMS
INET: DWILLIAMS_at_LIFETOUCH.COM

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Author: Stefan Jahnke
INET: Stefan.Jahnke_at_bov.de

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