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Re: I/O activity during HOT backups

From: Rachel Carmichael <carmichr_at_hotmail.com>
Date: Mon, 19 Jun 2000 19:10:05 GMT
Message-Id: <10533.109754@fatcity.com>


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
>
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>Author:
> INET: Lisa_Koivu_at_gelco.com
>
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Received on Mon Jun 19 2000 - 14:10:05 CDT

Original text of this message

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