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Home -> Community -> Usenet -> c.d.o.server -> Re: Crazy mistake in "Oracle Unleashed"
It is true: Oracle stops updating file headers durring backup mode.
It is also true: Oracle writes changed blocks to the files durring backup mode.
satar@my-dejanews.com wrote:
OK, I think everyone is confused. According to "Oracle7:Backup and RecoveryReceived on Tue Sep 29 1998 - 17:11:31 CDT
Volume Two * Student Guide" which I obtained durring my DBA Master's program
held by Oracle Corporation, on page 10-13 through page 10-17 it tells you the
following: After you administer BEGIN BACKUP...This action suspends updates
to the header block of each database file belonging to the Tablespace. If a
log switch occures, the sequence number information is updated as shown. A
record is also written to the active redo log file to indicate that an online
backup has begun. END BACKUP...This action will cause the header blocks for
the datafiles belonging to the tablespace to be updated at the next log
switch. If a log switch occures, the sequence number information is updated
as shown. * The time between the ALTER BEGIN and ALTER END commands should be
minimized, as more redo information is generated and written to the redo log
files durring the backup since modified blocks are written to the redo log
files. * Prior to Oracle7 release 7.2, any instance faliur while an online
backup was in progress could cause the subsequent automatic recovery at
startup to fail due to the header on the backed up file being frozen. Oracle7
at startup would then detect that the header was out of sync with the rest of
the files, and startup would fail with the message the file needed recovery.
New to release 7.2, you can allow an online backup to be ended before opening
the database after a system failure, by executing the ALTER DATABASE DATAFILE
END BACKUP command.In article <36118da2.3730684@192.86.155.100>,
tkyte@us.oracle.com wrote:
> A copy of this was sent to John <john@yellowstone.co.uk>
> (if that email address didn't require changing)
> On Mon, 28 Sep 1998 12:40:21 +0100, you wrote:
>
> >I read the quotes from 'unleashed' as meaning that, the datafiles of the
> >tablespaces which had been put into backup mode would not be written to,
which
> >is true, isn't it, even if the other datafiles would be written to ?
> >
>
> No it is not. The datafiles that are being backed up are definitely written
to.
> they are inconsistent, fuzzy and will be in need of recovery in the event they
> are used for recovery.
>
> >>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. On receipt of the command to begin the
> >>backup, however, Oracle ceases to make direct changes to the database
> >>file.
> >
>
> that is an outright mis-statement. it is false. do not believe it.
>
> >Thomas Kyte wrote:
> ><quote>
> >If you are in a situation where your database must be up and running 24 hours
> >a day, 7 days a week, you will need to perform inconsistent whole database
> >backups. A backup of an open database is inconsistent because portions of the
> >database (hence, datafiles in the database) are being modified and written to
> >disk while the backup is progressing. The database must be in ARCHIVELOG
> >mode to be able to perform open backups.
> ></quote>
> >
> >...but not the portions in backup mode ?
>
> Thomas Kyte
> tkyte@us.oracle.com
> Oracle Government
> Herndon VA
>
> --
> http://govt.us.oracle.com/ -- downloadable utilities
>
> ----------------------------------------------------------------------------
> Opinions are mine and do not necessarily reflect those of Oracle Corporation
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Satar Naghshineh
Oracle DBA/ UNIX System Admin
Advanced Enterprise Solutions
(949) 756-0588
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