THANKS dmtry for this long explanation ! > what happen if for exemple we increase the width of > one varchar column during the backup ? >bad question.
:( >So, it's like snapshot that you make in time. >For example, Level 0 - each month, level 1 - each week, and level 2 - >each day. yes i understand, but with level 2 each days, it's mean that if i m on days 4 from the level 1 the nbackup will backup the change from the last 4 days .. it's mean more bigger backup file, more IO ... and this when we know that i have already backup the change of des 3 previous days :( On 12/26/2011 1:45 AM, Dmitry Kuzmenko wrote: > > Hello, Vander! > > Sunday, December 25, 2011, 10:57:32 PM, you wrote: > > VCS> for exemple i see that during the backup, the database file is locked > VCS> and all write are done in a separate delta file ... is this can slow > VCS> down the server ? > VCS> especially when the separate file is merge back with > VCS> the database file ? > Sure, because while writes goes to delta is ok, copying or scanning > database for nbackup levels produces additional IO. > > VCS> what happen if for exemple we increase the width of > VCS> one varchar column during the backup ? > bad question. > > VCS> also i not understand the level strategy, in the doc they say we > will > VCS> rarelly go beyong level 3 or 4 but me what i want to do is to > save on a > VCS> daily basis ... so for me it's will be 30 levels min (because every > VCS> month i will reset)... what wrong in this ? > > 30 levels is nonsense. Also I doubt that nbackup can handle > command line with 30 files specified. > Level 0 - full copy of DB. > Level 1 - only pages that was changed from level 0 > Level 2 - only pages that was changed from level 1 > etc. > > So, it's like snapshot that you make in time. > For example, Level 0 - each month, level 1 - each week, and level 2 - > each day. > Thus with only 3 levels (from 0 to 2) you can restore copy of the > database for each day. Levels goes this way: > 0 > -1 > --2 - pages that changed from level 1 > -1 - again, only pages changed from making level 0 > --2 - only pages changed from level 1 > > So, you can combine some level 2 only with level 1 made before it, not > after, of course. > Creating such "a ladder" with 30 levels doesn't make any sense, > because on restore database can be combined with levels down from > highest, i.e. 2+1+0 in that example. > As you plan to make each day 1 level plus, you will need for example > at 15-th day to specify all 15 levels you made. Instead, > you can make level 1 backup each day, and then use level 0+1 to > restore database for particular day starting from the current month. > > Depending of the application activity, each level will have different > size. It is hard to predict level sizes, because applications can > rewrite same data, or different data. > > So, here is IO also. Using 30 levels needs to apply them all, one by > one to the level 0 backup. > > And, remember, that nbackup makes physical copy of the database, > page by page, and it is not interested about data or transaction > numbers, etc. > > You can make level 0 copy of the database if you just stop the > Firebird and copy database to another file. > > VCS> and to finish how nbackup can know what was changed from the last > backup > VCS> ? > > see above. > > VCS> does it's mean that every page in the database file have a version > VCS> number ? > > It starts to have marks after each level of nbackup you make. > That is how nbackup understands what pages was changed from the > last nbackup level made. > > -- > Dmitry Kuzmenko, www.ib-aid.com > > [Non-text portions of this message have been removed]
