Block change tracking (BCT) is an oracle feature that improves the performance of incremental backups.<\/p>\n
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Suppose we have a level 0 backup and want to make a level 1 backup. During the level 1 backup, oracle will scan all the blocks from the last level 0 backup and identify those which have been modified. Once this action has been performed, Oracle will save only all of the modified blocks.<\/p>\n
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With Oracle’s Block Change Tracking (BCT) functionality, you no longer need to scan all blocks from a previous incremental backup. Indeed BCT uses a background process called Change Tracking Writer (CTWR). The role of the CTWR is to track all the modified blocks and then identify them in a tracking file. By default, the BCT function is disabled. That means, oracle does not save block change information.<\/p>\n
To check the status of the BCT, please execute the following command :<\/p>\n
SQL> select status from v$block_change_tracking;\r\n\r\n\r\nSTATUS\r\n\r\n----------\r\n\r\nDISABLED<\/pre>\n<\/p>\n
Let’s activate \u00a0block change<\/p>\n
SQL> alter database enable block change tracking using file '+DATA';<\/pre>\nThe “using file” clause specifies the location of the BCT file on the OS. If you omit this clause, the Oracle Managed File (OMF) option will be enabled.<\/p>\n
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To activate the block change using the OMF option, execute the command below:<\/p>\n
SQL> alter database enable block change tracking;<\/pre>\n<\/p>\n
Now, let\u2019s check again the status of the BCT after activation<\/p>\n
SQL> col filename format a46\r\n\r\nSQL> col status format a12\r\n\r\nSQL>\u00a0 select status, filename from v$block_change_tracking;\r\n\r\n\r\n\r\nSTATUS\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 FILENAME\r\n\r\n------------ ----------------------------------------------\r\n\r\nENABLED\u00a0\u00a0\u00a0\u00a0\u00a0 +DATA\/ACHATS\/CHANGETRACKING\/ctf.288.1027782031<\/pre>\n<\/p>\n
To know the size of the BCT, execute the following command:<\/p>\n
SQL> select status, filename, bytes from v$block_change_tracking;\r\n\r\n\r\nSTATUS\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 FILENAME\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0BYTES\r\n\r\n------------ ---------------------------------------------- ----------\r\n\r\nENABLED\u00a0\u00a0\u00a0\u00a0\u00a0 +DATA\/ACHATS\/CHANGETRACKING\/ctf.288.1027782031\u00a0\u00a0 11599872<\/pre>\n<\/p>\n
To deactivate the block change tracking, execute the following command:<\/p>\n
SQL> alter database disable block change tracking;<\/pre>\n<\/p>\n
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Do you want to learn more details about RMAN, then Click this Link and read the articles.<\/span><\/a><\/h4>\n
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