创建存放块跟踪文件目录
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1. [oracle@host01 ~]$ cd /u01/app
2. [oracle@host01 app]$ mkdir BCT
3. [oracle@host01 app]$ ls
4. BCT oracle oraInventory
启用块跟踪
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1. SQL> alter database enable block change tracking using file '/u01/app/BCT/rman.bct';
显示块跟踪文件位置、块跟踪状态（启用/停用）、该文件大小（单位字节）
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1. SQL> col filename for a22
2. SQL> select filename, status, bytes from v$block_change_tracking;
4. FILENAME STATUS BYTES
5. ---------------------- ---------- ----------
6. /u01/app/BCT/rman.bct ENABLED 11599872
通过查询视图来判断减少增量备份I/O，查看PCT_FOR_BACKUP字段，值比较高表明RMAN在备份期间，从数据文件读取非常多的块，那么可以适当的减少增量备份的时间间隔来降低这个比率
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1. SQL> select file#,AVG(datafile_blocks),avg(blocks_read),avg(blocks_read/datafile_blocks) * 100 as pct_read_for_backup, avg(blocks) from v$backup_datafile where used_change_tracking = 'YES' and incremental_level >0 group by file#;
3. FILE# AVG(DATAFILE_BLOCKS) AVG(BLOCKS_READ) PCT_READ_FOR_BACKUP AVG(BLOCKS)
4. ---------- -------------------- ---------------- ------------------- -----------
5. 1 96000 1 .001041667 1
6. 2 66560 1 .001502404 1
7. 5 40080 1 .00249501 1
8. 4 640 1 .15625 1
9. 3 11520 1 .008680556 1
停用块跟踪
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1. SQL> alter database disable block change tracking;
3. Database altered.
5. SQL> !ls /u01/app/BCT
7. SQL> select filename,status,bytes from v$block_change_tracking;
10. FILENAME STATUS BYTES
11. -------------------- ---------- ----------
12. DISABLED

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启用块跟踪

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