student question: incremental backups (level 0 and level 1)
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From: obakesan on 25 Jun 2008 05:58 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?? I'd have thought it was also possible that eventually (despite being used and freed) this could eventually encompas every block in a datafile. thus the word EVER seems to be making this a wrong answer (which it is not according to my review software). 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
From: fitzjarrell on 25 Jun 2008 08:54 Comments embedded. On Jun 25, 4:58 am, pellicleund...(a)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
From: obakesan on 25 Jun 2008 10:36 David In article <7edbdd2f-d37a-4079-bb80-6c03d1d5d6da(a)j22g2000hsf.googlegroups.com>, "fitzjarrell(a)cox.net" <oratune(a)msn.com> wrote: > >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. Hmm ... but I thought that only used blocks were backed up in an incremental backup. Does this mean that it can't determine if a block is used or not used? >It's wrong only in your mind. It's correct in terms of the concepts >and functionality of RMAN. well, of course everything only ever exists in my mind. All of this will cease to exist when that stops ;-) See Ya (when bandwidth gets better ;-) Chris Eastwood Photographer, Programmer Motorcyclist and dingbat blog: http://cjeastwd.blogspot.com/ please remove undies for reply
From: fitzjarrell on 25 Jun 2008 11:27 On Jun 25, 9:36 am, pellicleund...(a)hotmail.com (obakesan) wrote: > David > > In article > <7edbdd2f-d37a-4079-bb80-6c03d1d5d...(a)j22g2000hsf.googlegroups.com>, > > "fitzjarr...(a)cox.net" <orat...(a)msn.com> wrote: > > >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. > > Hmm ... but I thought that only used blocks were backed up in an incremental > backup. Does this mean that it can't determine if a block is used or not used? > > >It's wrong only in your mind. It's correct in terms of the concepts > >and functionality of RMAN. > > well, of course everything only ever exists in my mind. All of this will cease > to exist when that stops ;-) > > See Ya > (when bandwidth gets better ;-) > > Chris Eastwood > Photographer, Programmer Motorcyclist and dingbat > blog:http://cjeastwd.blogspot.com/ > > please remove undies for reply 'Used' blocks are backed up in a level 1 or level 2 incremental; a level 0 incremental is about as close to a full backup as you can get and still keep an incremental strategy. David Fitzjarrell
From: Holger Baer on 25 Jun 2008 13:02
fitzjarrell(a)cox.net schrieb: > Comments embedded. > On Jun 25, 4:58 am, pellicleund...(a)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/rcmconc1005.htm#sthref241): <quote> 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. </quote> 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. Cheers Holger |