How to determine which data blocks are changed in Oracle Incremental Backup

We all know that Oracle 8.0 implements incremental Oracle backup only when relevant recovery management is introduced. Before RMAN, the output of the Oracle database can also be incrementally increased. However, once any part of a table changes, the entire table needs to be overwritten. RMAN Incremental Backup only needs to re-write the modified part in the given data file, which greatly saves space.

However, before the 10 GB version, Oracle Incremental backup needs to scan the entire data file to determine which data blocks have changed. For large databases, although space is saved, the time complexity is not much better than full backup.

Oracle 8.0 introduced recovery management RMAN), the first implementation of a real Incremental backup. Before RMAN, the database output can also be incremental, but once any part of a table changes, the entire table needs to be overwritten. RMAN Incremental Backup only needs to re-write the modified part in the given data file, which greatly saves space.

However, before the 10 GB version, Incremental backup needs to scan the entire data file to determine which data blocks have changed. For large databases, although space is saved, the time complexity is not much better than full backup.

Change tracking technology, also known as block change tracking technology, solves the above problem by recording changed data blocks in an independent tracking file, these changes are written to files by a background process in real time.

The initial incremental Oracle backup still requires a complete scan. After that, you can directly access the block to be backed up by referring to the change tracking file during Backup.

To create and activate change tracking files, first make sure that the DATABASE is open or accessible, and then run the following DATABASE change alter database command:

 
 

  
  
ALTER DATABASE   
  
  
ENABLE BLOCK CHANGE TRACKING   
  
  
USING FILE ;   
 
 

To change the storage location of the tracking file in the operating system. If you have activated the Oracle management file, the USING clause is optional. The change tracking file is created in the DB_CREATE_FILE_DEST directory .)

No matter where the file path is located, the initial size is 10 MB, and the size is increased by 10 MB each time as needed.

Using change tracking will affect system performance, so unless you need to use the RMAN Incremental backup function, you 'd better set it to the default setting for unavailability ).
 

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