最近发现10g的RMAN备份保留REDUNDANCY策略和9i相比发生了改变。
在Oracle9i中，备份保留策略的REDUNDANCY的值，指的是备份冗余的个数。也就是说，如果REDUNDANCY设置为1，那么Oracle会保留2个备份。
但是在10g以后，REDUNDANCY的值，就是最终备份保留的值，手头没有10g的环境，用11g的rman做了一个例子：
solaris*orcl-/home/oracle$ rman target / Recovery Manager: Release 11.2.0.3.0 - Production ON Sun Jul 8 19:04:43 2012 Copyright (c) 1982, 2011, Oracle AND/OR its affiliates. ALL rights reserved. connected TO target DATABASE: ORCL (DBID=1299676637) RMAN> SHOW retention policy; USING target DATABASE control file instead OF recovery catalog RMAN configuration parameters FOR DATABASE WITH db_unique_name ORCL are: CONFIGURE RETENTION POLICY TO REDUNDANCY 1; # DEFAULT RMAN> backup tablespace ts_32k; Starting backup at 08-JUL-12 allocated channel: ORA_DISK_1 channel ORA_DISK_1: SID=180 device TYPE=DISK channel ORA_DISK_1: starting FULL datafile backup SET channel ORA_DISK_1: specifying datafile(s) IN backup SET INPUT datafile file NUMBER=00005 name=/u01/app/oracle/oradata/ORCL/datafile/o1_mf_ts_32k_7w1w3zmb_.dbf channel ORA_DISK_1: starting piece 1 at 08-JUL-12 channel ORA_DISK_1: finished piece 1 at 08-JUL-12 piece handle=/u01/app/oracle/flash_recovery_area/ORCL/backupset/2012_07_08/o1_mf_nnndf_TAG20120708T190559_7zltdqxy_.bkp tag=TAG20120708T190559 comment=NONE channel ORA_DISK_1: backup SET complete, elapsed TIME: 00:00:01 Finished backup at 08-JUL-12 RMAN> backup tablespace ts_32k; Starting backup at 08-JUL-12 USING channel ORA_DISK_1 channel ORA_DISK_1: starting FULL datafile backup SET channel ORA_DISK_1: specifying datafile(s) IN backup SET INPUT datafile file NUMBER=00005 name=/u01/app/oracle/oradata/ORCL/datafile/o1_mf_ts_32k_7w1w3zmb_.dbf channel ORA_DISK_1: starting piece 1 at 08-JUL-12 channel ORA_DISK_1: finished piece 1 at 08-JUL-12 piece handle=/u01/app/oracle/flash_recovery_area/ORCL/backupset/2012_07_08/o1_mf_nnndf_TAG20120708T190609_7zltf22b_.bkp tag=TAG20120708T190609 comment=NONE channel ORA_DISK_1: backup SET complete, elapsed TIME: 00:00:02 Finished backup at 08-JUL-12 RMAN> list backup OF tablespace ts_32k; List OF Backup Sets =================== BS KEY TYPE LV SIZE Device TYPE Elapsed TIME Completion TIME ------- ---- -- ---------- ----------- ------------ --------------- 20 FULL 2.69M DISK 00:00:01 08-JUL-12 BP KEY: 20 STATUS: AVAILABLE Compressed: NO Tag: TAG20120708T190559 Piece Name: /u01/app/oracle/flash_recovery_area/ORCL/backupset/2012_07_08/o1_mf_nnndf_TAG20120708T190559_7zltdqxy_.bkp List OF Datafiles IN backup SET 20 File LV TYPE Ckp SCN Ckp TIME Name ---- -- ---- ---------- --------- ---- 5 FULL 28932281 08-JUL-12 /u01/app/oracle/oradata/ORCL/datafile/o1_mf_ts_32k_7w1w3zmb_.dbf BS KEY TYPE LV SIZE Device TYPE Elapsed TIME Completion TIME ------- ---- -- ---------- ----------- ------------ --------------- 21 FULL 2.69M DISK 00:00:01 08-JUL-12 BP KEY: 21 STATUS: AVAILABLE Compressed: NO Tag: TAG20120708T190609 Piece Name: /u01/app/oracle/flash_recovery_area/ORCL/backupset/2012_07_08/o1_mf_nnndf_TAG20120708T190609_7zltf22b_.bkp List OF Datafiles IN backup SET 21 File LV TYPE Ckp SCN Ckp TIME Name ---- -- ---- ---------- --------- ---- 5 FULL 28932300 08-JUL-12 /u01/app/oracle/oradata/ORCL/datafile/o1_mf_ts_32k_7w1w3zmb_.dbf RMAN> DELETE obsolete; RMAN retention policy will be applied TO the command RMAN retention policy IS SET TO redundancy 1 USING channel ORA_DISK_1 Deleting the following obsolete backups AND copies: TYPE KEY Completion TIME Filename/Handle -------------------- ------ ------------------ -------------------- Backup SET 20 08-JUL-12 Backup Piece 20 08-JUL-12 /u01/app/oracle/flash_recovery_area/ORCL/backupset/2012_07_08/o1_mf_nnndf_TAG20120708T190559_7zltdqxy_.bkp Do you really want TO DELETE the above objects (enter YES OR NO)? yes deleted backup piece backup piece handle=/u01/app/oracle/flash_recovery_area/ORCL/backupset/2012_07_08/o1_mf_nnndf_TAG20120708T190559_7zltdqxy_.bkp RECID=20 STAMP=788123159 Deleted 1 objects |
可以看到，从10g开始设置的REDUNDANCY的值，就是最终备份保留的个数。为了确认这个问题，特意查询了一下9i和10g的官方文档。
9i的说法是：
The REDUNDANCY parameter specifies that any NUMBER OF backups OR copies beyond a specified NUMBER need NOT be retained. |
而10g的文档中，该参数的描述变为：
A redundancy-based backup retention policy determines whether a backup IS obsolete based ON how many backups OF a file are currently ON disk. |
Oracle改变功能的实现很常见，但是没有想到，对于这种细节的定义也会调整。对于熟悉9i备份策略的DBA需要留神，在设置10g以后的RMAN备份保留策略时，需要在9i的基础上增加1。