{"id":52597,"date":"2022-10-05T18:19:47","date_gmt":"2022-10-05T18:19:47","guid":{"rendered":"https:\/\/dbtut.com\/?p=52597"},"modified":"2022-10-05T18:20:44","modified_gmt":"2022-10-05T18:20:44","slug":"what-is-change-block-tracking","status":"publish","type":"post","link":"https:\/\/dbtut.com\/index.php\/2022\/10\/05\/what-is-change-block-tracking\/","title":{"rendered":"What Is Change Block Tracking"},"content":{"rendered":"

In a system where Incremental Backup is included in the Backup Strategies, it is a very troublesome task to find which blocks have changed by scanning the full datafiles each time.<\/p>\n

Instead, knowing the changed blocks and taking a backup just by reading them will provide us an incredible benefit in terms of time.<\/p>\n

Oracle provides this solution with BLOCK CHANGE TRACKING.<\/p>\n

\u2022 Block Change Tracking is enabled in the database, and only the information of the changed blocks is written to a BINARY file. RMAN reads this file during backup and takes backup of those blocks.<\/p>\n

\u2022 This file is created to the location specified in the DB_CREATE_FILE_DEST parameter.<\/p>\n

\u2022 Initially, its size is 10MB. When it is full, an increase of 10 MB is provided. The control is completely in Oracle. The DBA does not need any intervention.<\/p>\n

\u2022 If we want to change the name then we can intervene. Its name can be changed while in MOUNT mode.<\/p>\n

\u2022 It is turned off in Default.<\/p>\n

\u2022 The working logic is as follows:<\/p>\n

\u25cb When DML operations are performed, the data is brought to the Database Buffer Cache from the physical data blocks on the disk and changed there.<\/p>\n

These changed dirty blocks are written to the Change Tracking File with the CTWR process activated when block change tracking is enabled. This file is also read during backup.<\/p>\n

BLOCK CHANGE TRACKING is ENABLED as follows.<\/p>\n

1. First of all, the status of block change tracking is checked.<\/p>\n[Primary-1 & Standby-1]\n

SQL> column filename format a10\r\nSQL> SELECT status, filename FROM V$BLOCK_CHANGE_TRACKING;\r\n\r\nSTATUS     FILENAME\r\n---------- ----------\r\nDISABLED\r\n<\/pre>\n
2. Enabled.<\/p>\n[Primary-1 & Standby-1]\n
SQL> ALTER DATABASE ENABLE BLOCK CHANGE TRACKING;\r\n\r\nDatabase altered.\r\n<\/pre>\n
3. The status is checked again.<\/p>\n[Primary-1 & Standby-1]\n
SQL> set linesize 500\r\nSQL> column filename format a60\r\nSQL> SELECT status, filename, trunc(bytes\/1024\/1024) FROM V$BLOCK_CHANGE_TRACKING;\r\n\r\nSTATUS     FILENAME                                                     TRUNC(BYTES\/1024\/1024)\r\n---------- ------------------------------------------------------------ ----------------------\r\nENABLED    +DATA\/primary\/changetracking\/ctf.273.932464389                                   11\r\n<\/pre>\n
4. We can see the return of Block Change Tracking in Incremental Backup as follows.<\/p>\n
\tSELECT file#, avg(datafile_blocks),\r\n\tavg(blocks_read),\r\n\tavg(blocks_read\/datafile_blocks)\r\n\t* 100 AS PCT_READ_FOR_BACKUP,\r\n\tavg(blocks)\r\n\tFROM v$backup_datafile\r\n\tWHERE used_change_tracking = 'YES'\r\n\tAND incremental_level > 0\r\n\tGROUP BY file#;\r\n<\/pre>\n
\"\"<\/p>\n
In this output, the PCT_READ_FOR_BACKUP column shows us how many % of the blocks in the datafile will be read during backup.<\/p>\n
For example, it provides tremendous performance by reading 7% of datafile #1.<\/p>\n
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In a system where Incremental Backup is included in the Backup Strategies, it is a very troublesome task to find which blocks have changed by scanning the full datafiles each time. Instead, knowing the changed blocks and taking a backup just by reading them will provide us an incredible benefit in terms of time. Oracle …<\/p>\n
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<\/div>\n","protected":false},"author":484,"featured_media":52602,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"om_disable_all_campaigns":false,"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"_uf_show_specific_survey":0,"_uf_disable_surveys":false,"footnotes":""},"categories":[4],"tags":[],"class_list":["post-52597","post","type-post","status-publish","format-standard","has-post-thumbnail","","category-oracle"],"aioseo_notices":[],"yoast_head":"\nWhat Is Change Block Tracking - Database Tutorials<\/title>\n<meta name=\"description\" content=\"Scanning full datafiles every time in a system that includes Incremental Backup in Backup Strategies is a very laborious task.\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/dbtut.com\/index.php\/2022\/10\/05\/what-is-change-block-tracking\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"What Is Change Block Tracking - 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