Re: Backup questions

"George Wang" <wang.jianhua_at_att.net> wrote in message news:Jb5v6.3524$0e1.271151_at_bgtnsc05-news.ops.worldnet.att.net...
>
> Howard J. Rogers <howardjr_at_www.com> wrote in message
> news:3ab9c390_at_news.iprimus.com.au...
> >
> > <vikasa_at_despammed.com> wrote in message
> > news:sl2ibt4pm54th4q8ig5be9jlcghs3luppb_at_4ax.com...
> > > Would appreciate help with the following backup/recovery related
> > > issues:
> > >

 [Snip]
> > >
> > > 3. If I need to recover only a few datafiles and not the entire
> > > database, I would do RECOVER DATAFILE <datafile>. What happens in this
> > > case? Does Oracle ignore the redo entries which pertain to the other
> > > datafiles?
> > >
> >
> > Yes. But Oracle ignores the other datafiles anyway when they are not in
> > need of recovery. Use 'recover datafile' to recover single files in
 need
 of
> > recovery, and use 'recover database' when two or more files are in need
 of
> > recovery. At the end of the day, both will work -but if two files are
 down,
> > you will have to issue two 'recover datafile' commands before the
 database
> > can be opened.
> >
> Compare to run 'recover datafile' twice with 'recover database', which way
> may be quicker?
>

[snip]

You'll have to test that out for yourself. Theoretically, there's a possibility that if your database consisted of several hundred datafiles, you'd want to avoid a recover database at all costs, and a two-phase 'recover datafile' would be much faster. But I don't have such a database to hand to test that out, so I can't be categorical.

My own experience in the classroom, on a thoroughly simple and lightweight database (ie, 12 datafiles), is that there is no distinguishable speed difference between the two options. But that's a pretty unrepresentative test.

Remember that at the point of discovering a file is missing, v$recover_file shows you exactly what data files are in need of recovery -so it's not as if Oracle is flying blind on these matters, and I doubt that it would dumbly try and apply redo to every file in the database just on the off-chance that it might need it! It *does* know where to apply the stuff, before you apply it.

Regards
HJR Received on Sat Mar 24 2001 - 14:07:42 CST