Re: student question: incremental backups (level 0 and level 1)
Date: Wed, 25 Jun 2008 13:15:40 -0700 (PDT)
On Jun 25, 10:02 am, Holger Baer <baer_at_dont_ask.com> wrote:
> fitzjarr..._at_cox.net schrieb:
> > Comments embedded.
> > On Jun 25, 4:58 am, pellicleund..._at_hotmail.com (obakesan) wrote:
> >> Hi
> >> so far my oracle experience has been on 8i with only PL/SQL development on 9
> >> and later.
> >> I'm just going through some questions in preparation for a 10g Admin 1 exam
> >> and find (among others) a question for which the answer seems to be less than
> >> right. Of course I can simply memorize the answer, but in the interests of
> >> developing knowledge (rather than simply passing exams) I thought I'd seek
> >> some suggestions here.
> >> The question poses: You perform differential incremental level 1 backups of
> >> your database on each working day and level 0 backups on Sundays. which two
> >> statements are true about the differential incremental backups.
> >> the answer I have issue with is: the backup performed on sundays contains all
> >> the blocks that have everbeen used in the database.
> >> I would have thought that it is possible for blocks to be used and then become
> >> free, these blocks should then not need backing up ... no??
> > No. They are below the HWM so they do get backed up. Any block below
> > the HWM has the potential to contain data. Thus, all blocks below the
> > HWM are backed up.
> >> I'd have thought
> >> it was also possible that eventually (despite being used and freed) this could
> >> eventually encompas every block in a datafile.
> > It could. And the issue with that is?
> >> thus the word EVER seems to be making this a wrong answer (which it is not
> >> according to my review software).
> > It's wrong only in your mind. It's correct in terms of the concepts
> > and functionality of RMAN.
> >> I'd be happy to learn what I've overlooked on this ... thanks :-)
> >> See Ya
> >> (when bandwidth gets better ;-)
> >> Chris Eastwood
> >> Photographer, Programmer Motorcyclist and dingbat
> >> blog:http://cjeastwd.blogspot.com/
> >> please remove undies for reply
> > David Fitzjarrell
> The documentation is a little bit clearer (http://download.oracle.com/docs/cd/B19306_01/backup.102/b14191/rcmcon...
> Multilevel Incremental Backups
> RMAN can create multilevel incremental backups. Each incremental level is denoted by a value of 0 or 1. A level 0 incremental backup, which is the base for
> subsequent incremental backups, copies all blocks containing data.
> The only difference between a level 0 incremental backup and a full backup is that a full backup is never included in an incremental strategy.
> The important point to note:
> - a level 0 incremental backup copies all blocks containing data
> This does not mean all blocks that *ever* contained data, think of truncate table for example. So the OP is right to express his doubts about the wording,
> even if it's not in the sense he originally meant. Another example: drop a table/index/partition and you're likely to to have lots of blocks that once contained
> data but now don't. They shouldn't (and to the best of my knowledge don't) get backed up.
Playing a bit of semantics games here, but if a block is no longer
under the high water mark, I'm thinking it is not considered ever to
have been used... then there's
I think the OP is correct, this is an example of the kind of crap questions OCP engenders, specifically antithetical to the kind of thinking a DBA needs to do, someone who actually knows how this works could get it wrong.
-- @home.com is bogus. Lies. Damn Lies. Statistics. Correlation. http://www.wired.com/science/discoveries/magazine/16-07/pb_theoryReceived on Wed Jun 25 2008 - 15:15:40 CDT