6 Replies Latest reply: Jun 8, 2010 3:30 PM by Ehtiram Hasanov RSS

    Tablespace backup

    658523
      Hi,

      In an online tablespace backup, i.e. when we put the table space in backup mode while little transactions are going on it. Then during back up what is the mechanism of Oracle to write the change block to tablespace during backup, because as during backup the file header are frozen and no data is to written on it.

      Regards,
      Abbasi
        • 1. Re: Tablespace backup
          sb92075
          because as during backup the file header are frozen and no data is to written on it.
          WRONG & incorrect!
          • 2. Re: Tablespace backup
            658523
            Yes I know that I've little confusion about this concept thats why I'm asking for you people to tell me the rigt concept.

            Regards,

            Abbasi
            • 3. Re: Tablespace backup
              Lubiez Jean-Valentin
              Hello,


              When a Tablespace is in Backup mode the SCN of its Datafiles (which is located on the header of the datafile) is frozen. More over, the redo generation is modified so as to be able to recover from fractured blocks.

              Else, the blocks of the datafile can be modified / written as usual.


              Best regards,
              Jean-Valentin
              • 4. Re: Tablespace backup
                Zekeriya Besiroglu
                Hi

                tablespace backup mode is old method due to excessive redologs

                pls use rman And then backup tablespace online.
                The biggest advantage of RMAN is that it only backup used space in the database. RMAN doesn't put tablespaces in backup mode, saving on redo generation overhead. RMAN will re-read database blocks until it gets a consistent image of it.


                Regards
                Zekeriya
                • 5. Re: Tablespace backup
                  Ehtiram Hasanov
                  yes. additionally as Lubies said, redo log generation changes, in this case redo log generation increases, as instead of change deltas, entire changed block is written to the redo log files.That is why it is strongly recommended to put the tablespaces out of hot backup mode upon finishing the backup- copying usually.
                  • 6. Re: Tablespace backup
                    Zekeriya Besiroglu
                    Hi again

                    does Oracle write to data files in begin/hot backup mode?

                    When a tablespace is in backup mode, Oracle will stop updating its file headers, but will continue to write to the data files.
                    When in backup mode, Oracle will write complete changed blocks to the redo log files. Normally only deltas (change vectors) are logged to the redo logs. This is done to enable reconstruction of a block if only half of it was backed up (split blocks). Because of this, one should notice increased log activity and archiving during on-line backups.
                    To solve this problem, simply switch to RMAN backups.

                    http://www.orafaq.com/wiki/Oracle_database_Backup_and_Recovery_FAQ

                    hope this helps
                    Zekeriya