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Re: before image vs checkpoint for recovery?

From: Sybrand Bakker <postbus_at_sybrandb.demon.nl>
Date: Mon, 30 May 2005 20:06:25 +0200
Message-ID: <nelm91peahv0mi9227hmii1c2vgt1rb2lv@4ax.com>


On 30 May 2005 10:40:15 -0700, jasonshohet_at_gmail.com wrote:

>I read recently that if a before-image was made before an interruption
>in database processing, you use the before-image dump & simply begin
>processing again from just before the last transaction. Any
>checkpoints are irrelevant.
>
>What I don't understand is, why are checkpoints irrelevant when you did
>a before image dump? Why not begin from the last checkpoint?
>Probably part of my problem is understanding the difference between the
>before image dump and a checkpoint. I know that the checkpoint is a db
>even that suspends processing & writes data to the disk. It represents
>a moment in time when everything is OK in the db. That sounds a lot
>like a before image dump :) Maybe the checkpoint is further back in
>time (?)
>
>Thanks for any clarification
>Jason Shohet

Actually the before image is in a rollback segment (pre 9i) or in the undo tablespace (9i and higher). Rollback segments are protected by the same mechanism as the data tablespaces, which calls in for checkpoints.

--
Sybrand Bakker, Senior Oracle DBA
Received on Mon May 30 2005 - 13:06:25 CDT

Original text of this message

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