RE: I/O activity during HOT backups

Lisa,

the begin backup DOES NOT stop writes to the datafiles. in fact data is written to the datafiles as usual with the following exceptions:

• the file headers are not updated (they like to use the word "frozen")
• dml on the file being backed up generates excessive redo (redo block copies of deltas)

once the backup completes, oracle updates the file headers with the latest checkpoint/scn information.
up until 7.3, if your dB crashed during a hot backup, one had to go thru media recovery.
in newer releases they have some .. alter datafile .. end backup command, which simply updates the file headers with the correct info. As a result, no unneccesary recovery is required as the all ur data is there anyway.
(assuming ur disks are still intact:))

deepAk

-----Original Message-----
From: Lisa_Koivu_at_gelco.com [mailto:Lisa_Koivu_at_gelco.com] Sent: Monday, June 19, 2000 12:51 PM
To: Multiple recipients of list ORACLE-L Subject: Re: I/O activity during HOT backups

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.

???

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