Re: Database backups

>>Actually the "dreadful advice" comment was made in relation to your
>>assertion that you should aim "to log switch every 15 mins", and had
nothing
>>to do with how you do backups.

a log switch every 15 mins means we're gonna checkpoint aswell, I made no recommendation as to the frequency of checkpoints ie inside the logswitch time.

>> "dreadful advice"

Hmmm is this really neccassary?

Daniel...

"Howard J. Rogers" <dba_at_hjrdba.com> wrote in message news:a7g5no$26s$1_at_lust.ihug.co.nz...
> "daniel" <test_at_test.com> wrote in message
> news:a7g4mb$q7i$1_at_news5.svr.pol.co.uk...
> > firstly i knew some smart arse would write such a reply,,,, my reply was
> > trying to be generic!!!!!!
> >
>
> Generic is fine. Trying is fine. Failing to be generic, however, isn't.
>
> > a cold backup is a consistent backup of a database that has shutdown
> normal
> > (minus online redo logs) thus negating the need to roll forward from
such
> a
> > backup. yes in an archivelog db you could bring back a df from a cold
> backup
> > set and roll forward but my point was u would not normally roll forward
> from
> > a complete consistent cold backup even though you could do....
> >
>
> Rubbish. Just because you are in archivelog mode does not mandate that
you
> do hot backups. Plenty of people do cold backups, and take archives.
> Archives gives you the ability to completely recover your database.
Taking
> backups (hot or cold) gives you something which can be rolled forward.
> There's no other relationship between the two, and there's nothing
"normal"
> or "abnormal" about either type of backup in archivelog mode.
>
> In my experience, about 35-40% of people running in archivelog mode take
> cold backups. What you say is 'not normal' for them to do, they plan to
do
> routinely.
>
> So, whilst I knew the point you were trying to make, it's simply wrong.
>
> > regarding log switch the user states it is an ebusiness environment
> (oltp!)
> > so we are probably putting tx's through it. well as we both know worst
> case
> > scenario is u lose your current online redo log, thus tx's that may have
> not
> > checkpointed (yes i know we can alter the frequency of the checkpoint)
so
> > online redo sized to switch every 15 mins means worst case scenario is
we
> > lose 15 mins of bussiness data....
> >
>
> So, why not checkpoint every second, 'cause that way you only lose 1
second
> of "bussiness [sic] data"? Because checkpoints have an overhead. And
that
> overhead slows down oltp transactional activity. So to come out with a
bald
> "make it 15 minutes" is just meaningless.
>
> Checkpointing should be done at a rate that balances possible transaction
> loss/recovery time with the slowdown in performance that excessive
> checkpointing induces. The appropriate advice is to find some point on
the
> spectrum that you feel comfortable with, not come out with some
meaningless
> specific time interval.
>
> And *that* is generic advice, whereas 'make it 15 mins' is highly
specific,
> highly misleading, and a thoroughly dreadful piece of advice.
>
> > so before we enter into a "my dad's bigger than your dad" argument there
> are
> > 15 billion approches to oracle backups so don't call it "dreadfull
> advice",
> > it's just another way of looking at it.
> >
>
> Actually the "dreadful advice" comment was made in relation to your
> assertion that you should aim "to log switch every 15 mins", and had
nothing
> to do with how you do backups.
>
> HJR
>
>
>
>
> > reagrds,
> >
> > daniel...
> >
> > "Howard J. Rogers" <dba_at_hjrdba.com> wrote in message
> > news:a7el2i$hek$1_at_lust.ihug.co.nz...
> > > Comments below
> > > HJR
> > > --
> > > ----------------------------------------------
> > > Resources for Oracle: http://www.hjrdba.com
> > > ===============================
> > >
> > >
> > > "daniel" <test_at_test.com> wrote in message
> > > news:a7deuk$417$1_at_newsg2.svr.pol.co.uk...
> > > > as a rule of thumb u don't roll forward from a cold backup, (yes, ye
s
> I
> > > know
> > > > you can but lets not get into bad habits)....
> > > >
> > >
> > > That's simply not true, and it's not a bad habit either. Of course
you
> > can
> > > roll forward from a cold backup. And taking cold backups is much
easier
> > > than the hot variety.
> > >
> > > > you can use just hot backups no probs and can recover quicker from
> them
> > > >
> > > > pointers;
> > > >
> > > > have multiple ctl files spanning physical disks
> > > > multiplex your online redo logs across physical disks
> > > > aim to log switch every 15 mins
> > >
> > > Dreadful advice. If you want performance, log switch every 24 hours,
in
> > the
> > > dead of night, when no-one gives a damn about the huge amount of I/O
the
> > > associated checkpoint will induce. If you want Instance Recovery in
ten
> > > seconds, log switch every second or so. Somewhere in between those
two
> > > extremes will be a happy medium for *you*.
> > >
> > > > every time you change the db structure "alter database backup
> > controlfile
> > > to
> > > > trace"
> > >
> > > Equally dodgy advice, I think. Backup to trace should be routine.
> Every
> > > backup should include it.
> > >
> > > > after the hot backup take a copy of the ctlfile and "archive log
> > current"
> > > > and make sure your archive redo logs are protected stream them off
> > > somewhere
> > > > else every 15 mins
> > >
> > > Depends on your log switch rate, of course (see above!!)
> > >
> > > > also when you take the hot backup keep a copy locally if enough
space
> > also
> > > > stream to tape and if recovery time is an issue copy to some network
> > > storage
> > > >
> > >
> > > Agreed. Keep as much on disk as possible.
> > >
> > > Regards
> > > HJR
> > >
> > > > good luck
> > > >
> > > > daniel...
> > > >
> > > >
> > > > "Dale DeRemer" <dderemer_at_agmc.org> wrote in message
> > > > news:a7dcs8$q7u$1_at_malgudi.oar.net...
> > > > We are new the the Oracle world. We want our ebusiness server to be
> > 7x24.
> > > > Never, ever down. Meaning... no cold backups. So, our question is
> this:
> > If
> > > > we use hot backups, (RMAN), and never take a cold backup, will we be
> > able
> > > to
> > > > recover from any failure. Additionally, what is the impact, or
> > difference
> > > in
> > > > recovery time for a system with no cold backups, vs. one with a cold
> > > backup
> > > > done once a week, or once a month?The DB is 75GB and will grow to
> about
> > > > 100GB over the next year. It will be updated in batches from our
> > > mainframe.
> > > > Users will not update it. Thanks for your help.
> > > >
> > > >
> > > >
> > > >
> > >
> > >
> >
> >
>
>
Received on Sat Mar 23 2002 - 06:10:57 CST