2 Replies Latest reply: Dec 26, 2012 6:37 AM by Osama_Mustafa RSS

    read only tablespace

    user10389461
      Hi DBA gurus,

      I wanted to know what happens to the datafiles when we put a tablespace in read only/offline/begin-backup mode . I have read many links and now I am confused.

      Thanks in advance.
        • 1. Re: read only tablespace
          Niket Kumar
          begin backup mode
          When you place a tablespace in backup mode, the Oracle instance notes that a backup is being performed and internally compensates for it. As you know, it is impossible to make an authentic copy of a database file that is being written to. On receipt of the command to begin the backup, however, Oracle ceases to make direct changes to the database file. It uses a complex combination of rollback segments, buffers, redo logs, and archive logs to store the data until the end backup command is received and the database files are brought back in sync. Simplifying a hot backup in this way is tantamount to classifying the USS Nimitz as a boat. The complexity of the actions taken by the Oracle RDBMS under a hot backup could consume an entire chapter and is beyond the scope of this book. What you should understand is the trade-off for taking a hot backup is increased use of rollback segments, redo logs, archive logs, and internal buffer areas within the SGA.
          read only tablespace
          Making a tablespace read-only prevents write operations on the datafiles in the tablespace. The primary purpose of read-only tablespaces is to eliminate the need to perform backup and recovery of large, static portions of a database. Read-only tablespaces also provide a way to protecting historical data so that users cannot modify it. Making a tablespace read-only prevents updates on all tables in the tablespace, regardless of a user's update privilege level.
          offline tablespace
          http://abiliusta.blogspot.in/2010/03/offline-datafiles-and-offline.html
          • 2. Re: read only tablespace
            Osama_Mustafa
            user10389461 wrote:
            Hi DBA gurus,

            I wanted to know what happens to the datafiles when we put a tablespace in read only/offline/begin-backup mode . I have read many links and now I am confused.

            Thanks in advance.
            Making a tablespace read-only prevents write operations on the datafiles in the tablespace. The primary purpose of read-only tablespaces is to eliminate the need to perform backup and recovery of large, static portions of a database. Read-only tablespaces also provide a way to protecting historical data so that users cannot modify it. Making a tablespace read-only prevents updates on all tables in the tablespace, regardless of a user's update privilege level.

            Refer to
            http://docs.oracle.com/cd/B28359_01/server.111/b28310/tspaces006.htm