Re: quick hot backup question...

Comments Embedded Forgot in the previous Post.

Thanks Howard for all the help.

regards,
Ganesh R

"Howard J. Rogers" <dba_at_hjrdba.com> wrote in message news:<a7rpfh$p5$1_at_lust.ihug.co.nz>...
> Comments embedded.
> HJR
> --
> ------------------------------------------
> Resources for Oracle : www.hjrdba.com
> ============================
>
> "Ganesh Raja" <ganesh_at_gtfs-gulf.com> wrote in message
> news:a8aed4.0203262202.7123b846_at_posting.google.com...
> > Howard,
> >
> > A Question on The same lines...
> >
> > Is it really mandatory that you do Alter system Archive Log Current or
> > Alter System Switch Logfile after the End Backup Command or after the
> > entire script is done ?
> >
>
> It's not mandatory, no. The reason they recommend that you force a
> checkpoint (which either of those commands will do) is that until a new
> checkpoint is issued, the SCN in the header of the datafile(s) just come out
> of hot backup mode is still behind that of the rest of the database (having
> been locked that way by the begin backup command). If you were then to have
> an Instance failure, the database would not be openable, because not all
> datafiles appear synchronised when SMON checks the file headers at startup
> time.
>
> Now, if the failure had happened *during* the hot backup, you also wouldn't
> be allowed to open the database -but you could fix that up with a quick
> 'alter database datafile X end backup'. In this scenario, that won't work
> because the thing's already come *out* of hot backup mode. You would
> therefore be forced to perform media recovery (as well as the Instance
> recovery of course) -which isn't necessarily a pain, but since it's totally
> unnecessary, it just makes getting the Instance up and running longer than
> it should do.
>
> Personally, with redundant power supplies and UPSes, and a half-decent
> operating system(!), I think the chances of an Instance failure remote
> enough that I never issue the recommended log switch. Another checkpoint
> will come along soon enough anyway, and I'd rather not be issuing extra
> checkpoints of my own.
>
> > Yeah i know that u need to take a Backup of the Log that Has the Alter
> > Tablespace End Backup command. I am doing that now in all my backup
> > scripts but my feelings is that it is not mandatory that it be done.
> > Am i right ???
> >
> > I Feel that if u dont have the End Backup Command archived and all
> > your redo and archives after the Backup got thrashed you can say
> > <<Alter database Datafile <filename> end backup>>. So it does not make
> > any difference you have the logs or not.

This Command is not working it is saying that the datafile is inconsistent.. So now how do i go about restoring the file and bringing the database online. I dont have the Redo Logs and Archives that have been taken after the end Backup.

> > Anyways u have lost your data and u just need to move the datafile back out > > of the backup mode and
> > anyways you will be saying open resetlogs.
> >
> > Am i right in this assumption.
> >
>
> I think so, but I can't be sure as I got a bit lost with what scenario you
> were thinking of towards the end there! If you've lost redo and archives
> after the time of the backup, then yes, you're looking at an incomplete
> recovery, and that will require a resetlogs.
>
> But the recommended log switch/checkpoint after the 'end backup' command
> really has nothing to do with getting the 'End Backup' command archived,
> since it's not a piece of DML and doesn't get into the redo stream in the
> first place. What begin and end backup do is to set or reset a bit in the
> Control File which tells the Checkpoint Process not to update the header of
> the datafiles associated with that tablespace. It's SMON stumbling across a
> very old SCN in one datafile's header on Instance startup that prompts the
> demand for media recovery -even though *we* know that the contents of the
> file are bang up to date and require no such recovery, and that it's just
> the header SCN that's artificially wrong.
>
> So no, it's not mandatory, and I never bother with it. But for the sake of
> quick Instance startup and minimal fiddling around with the database
> unavailable, yes, it's probably sensible.
>
> Regards
> HJR
>
>
>
>
> > Your comments on this are valuable.
> >
> > Thanks.
> >
> > Best Regards,
> > Ganesh R
> >
> > "Glen A Stromquist" <gstromquist_at_nospamyahoo.com> wrote in message
> news:<FpNn8.17155$mR1.434250_at_news2.telusplanet.net>...
> > > Thanks Howard
> > >
> > > The reason for all this was I am just brushing up for an exam (finally)
> and
> > > the oracle tutorial I was running through said that a logfile switch
> and
> > > forced checkpoint should be done before a hot backup. I was pretty sure
> the
> > > checkpoint was done when the file was put in backup mode, but you
> confirmed
> > > it.
> > >
> > > I've had this discussion with you before regarding doing a log switch
> after
> > > the datafiles are copied then copying the archive log generated during
> the
> > > backup, and in the past went to great pains writing my script to do just
> > > that. However after I "restored" a database to another location (clone)
> from
> > > a set of hotbackup files and applied all the archive logs to it, I
> realized
> > > that what I was doing was ok, but not really necessary, like you said.
> > >
> > > End result is that I don't bother anymore, and writing the dynamic
> backup
> > > scripts is a whole lot easier.
> > >
> > >
> > > "Howard J. Rogers" <dba_at_hjrdba.com> wrote in message
> > > news:a7o4ju$vfn$1_at_lust.ihug.co.nz...
> > > > If you're doing O/S online backups, then there's no need for a
> preliminary
> > > > checkpoint, because that's precisely what the 'begin backup' command
> forces
> > > > (at least for the datafiles of the tablespace involved).
> > > >
> > > > The one about a preliminary log switch (presumably because you are
> about
> to
> > > > copy the archives) is always a curious one. Lots of people do it, and
> I've
> > > > never really understood why. Usually the justification is that
> without
> it,
> > > > you are short of the current redo log, so you may lose data. There's
> > > > something to that, I suppose. But it's also usually (so I find)
> because
> > > > people view a backup as an isolated event, whereas the truth of the
> matter
> > > > is, of course, that what you don't backup tonight you will backup
> tomorrow.
> > > > So if there's a bit of current redo left unbacked up, who cares??
> You'll
> > > > get it when tomorrow's backup is performed, and in the meantime
> there's no
> > > > possible risk of data loss because you've multiplexed your online redo
> logs,
> > > > and then mirrored them with hardware RAID. Haven't you?? ;-)
> > > >
> > > > The other thing that mystifies me about forcing a log switch in order
> to
> get
> > > > an archive of the current log is that it only makes another log the
> current
> > > > log. So you can *never* really be completely and utterly up-to-date
> with
> > > > redo copies, unless you stop all your users doing things: there'll
> always
> be
> > > > a new piece of current redo which you haven't backed up today. Hence
> cold
> > > > backups, of course.
> > > >
> > > > That said, a log switch does no real harm -except induce a
> > > > performance-hitting checkpoint.
> > > >
> > > > Regards
> > > > HJR
> > > > --
> > > > ------------------------------------------
> > > > Resources for Oracle : www.hjrdba.com
> > > > ============================
> > > >
> > > > "Glen A Stromquist" <gstromquist_at_nospamyahoo.com> wrote in message
> > > > news:jpMn8.11561$EV.366849_at_news1.telusplanet.net...
> > > > > In my online backup scripts I don't do a logfile switch or force a
> > > > > checkpoint before copying the datafiles.
> > > > >
> > > > > Is this recommended by Oracle?
> > > > >
> > > > > I'm wondering if I overlooked something when writing my scripts, I
> have
> used
> > > > > my online backups on occasion to create a clone db, so I know they
> "work"
> > > > > the way I'm doing it now, but I guess it can't hurt to build in a
> logfile
> > > > > switch and/or force a checkpoint as part of the script as well.
> > > > >
> > > > > Curious to hear what others do regarding this....
> > > > >
> > > > >
> > > > > cheers!
> > > > >
> > > > >
> > > >
> > > >
Received on Wed Mar 27 2002 - 06:34:30 CST