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Re: I/O activity during HOT backups

From: Eric Lansu <eric.lansu_at_quicknet.nl>
Date: Tue, 20 Jun 2000 13:55:32 +0200
Message-Id: <10534.109829@fatcity.com>


Am I wrong, or am I wrong?

But as far as I know you have to do a log-switch BEFORE starting the HOT-backup, and one AFTER the HOT-backup. The tape containing the database-files should also contain the archive-log-files created between the log-switches. This way you can roll-forward (recover) the database to the point-in-time after completion of the backup, and thus bringing it all in a consistent state. ( yes, yes, not from a book.... )

Still the question remains; how can the OS make a copy of a datafile if Oracle is still writing in it? Better, how does Oracle know what to update after recovery?

Eric Lansu

> Wow! your explanation is wonderful.
>
> Thanks Rachel.
>
>
> Bhat
>
> -----Original Message-----
> Sent: Tuesday, June 20, 2000 4:19 AM
> To: Multiple recipients of list ORACLE-L
>
>
> Lisa,
>
> I'm sorry but you are wrong. Writes to the datafiles continue during hot
> backup.....
>
> take a hypothetical situation:
>
> you have 3 redo logs
> you have put every tablespace in your database into hot backup mode
> you do a LARGE dataload (enough to cycle through all your redo logs
several
> times)
>
>
> so... if Oracle does NOT write to the datafiles, then the changes you have
> been making to the blocks get overwritten in the redo logs after the logs
> are archived. Once you take the tablespaces out of backup mode, given your
> thinking, Oracle would have to then write all the blocks to the database
> files at once. But where would it get them from? The archived redo logs
are
> NOT re-read, nor are the redo logs.
>
> So...... writing continues to the database files.
>
> Rachel
>
> >From: Lisa_Koivu_at_gelco.com
> >Reply-To: ORACLE-L_at_fatcity.com
> >To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>
> >Subject: Re: I/O activity during HOT backups
> >Date: Mon, 19 Jun 2000 11:50:37 -0800
> >
> >No! The command below stops all writes to the datafiles in the
tablespace
> >for
> >the duration of the backup, to ensure consistency.
> >
> >The i/o overload I see during backups is the data being copied out to our
> >backup
> >server. And it is usually very high: like 80% of all current activity.
> >
> >Lisa
> >
> >
> >
> >
> >
> >Dan.Hubler_at_midata.com on 06/19/2000 01:18:14 PM
> >
> >Please respond to ORACLE-L_at_fatcity.com
> >
> >To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>
> >cc: (bcc: Lisa Koivu/GELCO)
> >
> >
> >
> >
> >
> >Please settle a discussion amongst our DBA team:
> >
> >Is there ANY I/O that takes place to the database files (*.DBF)
> >during a HOT backup? (That is, ALTER TABLESPACE BEGIN BACKUP).
> >
> >If not, how does the process work?
> >
> >Thanks.
> >
> >
> >
> >
> >???
> >
> >
> >--
> >Author:
> > INET: Dan.Hubler_at_midata.com
> >
> >Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051
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> >
> >
> >
> >
> >
> >
> >--
> >Author:
> > INET: Lisa_Koivu_at_gelco.com
> >
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> --
> Author: Rachel Carmichael
> INET: carmichr_at_hotmail.com
>
> Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051
> San Diego, California -- Public Internet access / Mailing Lists
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> Author:
> INET: LBhat_at_LEVI.com
>
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Received on Tue Jun 20 2000 - 06:55:32 CDT

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