Re: quick hot backup question...

> Lots of people do it, and I've never really understood why.

maybe they want to differentiate between the two types of redo that can be written? just a guess...

however sometimes in a system where user activity stops at close of business hours then it would be really easy to recover to that log seq num knowing it contains the last business tx's, but no overnight stuff like batch etc etc...

it is also very handy to refresh a test system from this without the need for time based or scn based recovery, again knowing its a capture of the data at close of play.

> 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.

agreed, but it can be used as an easy marker and/or punting it off to the standby server if thats the setup, there's a stack more reasons why you may want to do it but i won't bore you with them...

:O)

--
Regards,

Daniel.


"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!

> >

> >

>

>