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Re: I/O activity during HOT backups

From: Ruth Gramolini <rgramolini_at_tax.state.vt.us>
Date: Wed, 21 Jun 2000 13:06:25 -0400
Message-Id: <10535.110027@fatcity.com>


Thanks a million! RBG
----- Original Message -----
From: Vidya Kalyanaraman <kvidya13_at_hotmail.com> To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com> Sent: Wednesday, June 21, 2000 12:12 PM
Subject: Re: I/O activity during HOT backups

> Hi Ruth,
> Here it goes again...
> www.wolfenet.com/~jeremiah/hot-backup.html
>
> Thanks
> Vidya
>
>
> Reply-To: ORACLE-L_at_fatcity.com
> To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>
> Date: Wed, 21 Jun 2000 06:58:11 -0800
>
> Could you post the link again. I have been looking for it and I can't find
> it. Thanks!
> Ruth
> ----- Original Message -----
> To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>
> Sent: Tuesday, June 20, 2000 11:07 AM
>
>
> > William,
> > That book you are refering has erroneous descriptions of hot backup.
> > Pls read this article by Jeremiah...I have already posted this link to
> > list....
> > This article talks mainly about "Oracle Unleashed...." book and its
> > misleading hot backup concepts.
> > Thanks
> > Vidya
> >
> >
> >
> > Reply-To: ORACLE-L_at_fatcity.com
> > To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>
> > Date: Tue, 20 Jun 2000 05:57:30 -0800
> >
> > The following is a quote from my favorite Oracle reference boot titled
> > "Oracle Unleashed, Edition 2" by SAMS Publishing.
> >
> > When you place a tablespace in backup mode, the Oracle instance notes
> that
> a
> > backup is being performed and internally compensates for it. As you
know,
> it
> > is impossible to make an authentic copy of a database file that is
being
> > written to. Upon receipt of the command to begin the backup, however,
> Oracle
> > ceases to make direct changes to the database file. It uses a complex
> > combination of rollback segments, buffers, redo logs, and archive logs
to
> > store the data until the end backup command is received and the
database
> > files are brought back to sync. .... What you should understand is that
> the
> > trade-off for taking a hot backup is increased use of rollback
segments,
> > redo logs, archive logs, and internal buffers within the SGA.
> >
> > You must be running the database in Archive mode to perform a hot
backup.
> > Archive logs assure data consistency when backing up only pieces of a
> > database at a time.
> >
> > >>> "Eric Lansu" <eric.lansu_at_quicknet.nl> 06/20/00 09:11AM >>>
> > 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
> >
> > ----- Original Message -----
> > To: "Multiple recipients of list ORACLE-L" <ORACLE-L_at_fatcity.com>
> > Sent: Tuesday, 20 June 2000 11:03
> >
> >
> > > 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
> > > >San Diego, California -- Public Internet access / Mailing
> Lists
> > >
>--------------------------------------------------------------------
> > > >To REMOVE yourself from this mailing list, send an E-Mail message
> > > >to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in
> > > >the message BODY, include a line containing: UNSUB ORACLE-L
> > > >(or the name of mailing list you want to be removed from). You may
> > > >also send the HELP command for other information (like
subscribing).
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >--
> > > >Author:
> > > > INET: Lisa_Koivu_at_gelco.com
> > > >
> > > >Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051
> > > >San Diego, California -- Public Internet access / Mailing
> Lists
> > >
>--------------------------------------------------------------------
> > > >To REMOVE yourself from this mailing list, send an E-Mail message
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> > >
> > >
> ________________________________________________________________________
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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
> > > --------------------------------------------------------------------
> > > To REMOVE yourself from this mailing list, send an E-Mail message
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> > > the message BODY, include a line containing: UNSUB ORACLE-L
> > > (or the name of mailing list you want to be removed from). You may
> > > also send the HELP command for other information (like subscribing).
> > > --
> > > Author:
> > > INET: LBhat_at_LEVI.com
> > >
> > > Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051
> > > San Diego, California -- Public Internet access / Mailing
Lists
> > > --------------------------------------------------------------------
> > > To REMOVE yourself from this mailing list, send an E-Mail message
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> > > (or the name of mailing list you want to be removed from). You may
> > > also send the HELP command for other information (like subscribing).
> >
> > --
> > Author: Eric Lansu
> > INET: eric.lansu_at_quicknet.nl
> >
> > Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051
> > San Diego, California -- Public Internet access / Mailing Lists
> > --------------------------------------------------------------------
> > To REMOVE yourself from this mailing list, send an E-Mail message
> > to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in
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> > also send the HELP command for other information (like subscribing).
> > --
> > Author: William Beilstein
> > INET: BeilstWH_at_obg.com
> >
> > Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051
> > San Diego, California -- Public Internet access / Mailing Lists
> > --------------------------------------------------------------------
> > To REMOVE yourself from this mailing list, send an E-Mail message
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> >
> >



> > Get Your Private, Free E-mail from MSN Hotmail at
http://www.hotmail.com
> >
> > --
> > Author: Vidya Kalyanaraman
> > INET: kvidya13_at_hotmail.com
> >
> > Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051
> > San Diego, California -- Public Internet access / Mailing Lists
> > --------------------------------------------------------------------
> > To REMOVE yourself from this mailing list, send an E-Mail message
> > to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in
> > the message BODY, include a line containing: UNSUB ORACLE-L
> > (or the name of mailing list you want to be removed from). You may
> > also send the HELP command for other information (like subscribing).
> >
>
> --
> Author: Ruth Gramolini
> INET: rgramolini_at_tax.state.vt.us
>
> Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051
> San Diego, California -- Public Internet access / Mailing Lists
> --------------------------------------------------------------------
> To REMOVE yourself from this mailing list, send an E-Mail message
> to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in
> the message BODY, include a line containing: UNSUB ORACLE-L
> (or the name of mailing list you want to be removed from). You may
> also send the HELP command for other information (like subscribing).
>
> ________________________________________________________________________
> Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com
>
> --
> Author: Vidya Kalyanaraman
> INET: kvidya13_at_hotmail.com
>
> Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051
> San Diego, California -- Public Internet access / Mailing Lists
> --------------------------------------------------------------------
> To REMOVE yourself from this mailing list, send an E-Mail message
Received on Wed Jun 21 2000 - 12:06:25 CDT

Original text of this message

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