Re: rman compression

Howard J. Rogers wrote:
>
> If they are below the high water mark, they'd be included in your level 0
> backup, but if they *remain* empty, subsequent incrementals will skip them.
>
> Regards
> HJR
>
> "Ted Chyn" <tedchyn_at_yahoo.com> wrote in message
> news:44a19320.0108300953.46d35b97_at_posting.google.com...
> > howard, thnx for the reply. If I have a table with 500mb under hwm
> > 500mb will be backup by rman even when most records were deleted ?
> >
> > thnx again.
> >
> >
> > "Howard J. Rogers" <howardjr_at_www.com> wrote in message
> news:<3b8e22a3$1_at_news.iprimus.com.au>...
> > > The Backup and Recovery Course not being quite so popular as it used to
> be
> > > (and can't you just tell from some of the posts here of late?!), I may
> be a
> > > bit out of touch with RMAN... but here goes for nothing...
> > >
> > > RMAN doesn't "compress" backups, if by "compression" you're thinking of
> > > anything like WinZip or gzip.
> > >
> > > Being an Oracle utility, however, it is intelligent enough to realise
> when a
> > > block on disk has never been used (ie, is above a high watermark
> somewhere),
> > > and will not include such blocks in the output backup sets. That
> contrasts,
> > > of course, with O/S backups which, not having a clue what they are
> actually
> > > copying, take a byte for byte copy of the physical datafile, unused
> blocks
> > > and all. Net result: RMAN backup sets are significantly smaller than a
> > > physical backup simply using O/S copy commands would be.
> > >
> > > RMAN makes things even smaller when you do incremental level backups:
> again,
> > > because it understands Oracle blocks and data structures, it can tell
> > > whether a block has changed since the last backup... if it has, it gets
> > > included in the backup set. If not, it doesn't -and once again, such
> > > omission makes the resultant backup set much smaller than it otherwise
> would
> > > be.
> > >
> > > If there is actually an RMAN command to compress a backup set a la
> WinZip,
> > > I'm not aware of it, and frankly I'd be gobsmacked ...Oracle generally
> takes
> > > the view that you play around with compression utilities at your peril.
> > > It's valuable data, after all.
> > >
> > > Regards
> > > HJR
> > >
> > >
> > >
> > > "Ted Chyn" <ericis6_at_home.com> wrote in message
> > > news:Bhlj7.139845$oh1.55982353_at_news2.rdc2.tx.home.com...
> > > > sir, Can anybody shed light on how rman compress the datafile during
> > > backup
> > > > ?
> > > > thnx ted chyn
> > > >
> > > >

altough most tape devices will compress the stuff beyong high water mark to virtually nil anyway.

Signed
Cynical Bastard :-)

-- 
==============================
Connor McDonald

http://www.oracledba.co.uk

"Some days you're the pigeon, some days you're the statue..."