William,
This goes to prove that not everyone who writes a book know what
the heck they are talking about. There is so much wrong
information out there and the idea of a list such as ours, is to
get the facts, shut out the noise and confront the technical
issues head on. It gets even worse in the area of "performance
tuning", there is even more "voodoo" out there and reading it
sometimes makes my blood boil. Well, I just tell myself
"serenity now", take a few deep breaths and move on with life.
Best Regards,
Gaja.
- William Beilstein <BeilstWH_at_obg.com> wrote:
> 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
> > >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
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> subscribing).
> >
> >
>
> > Get Your Private, Free E-mail from MSN Hotmail at
> http://www.hotmail.com
> >
> > --
> > 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
> > 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
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> > --
> > 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
> > 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: 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
> 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: 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
> 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).
Received on Tue Jun 20 2000 - 10:12:50 CDT
