希望减少Redo Log生成的思路无非是：Redo Log生成量少了，这样在LGWR写入的量就少了，从而带来的物理IO和日志切换动作就少了。但是，随着带来的问题是：日志少了真的没有问题吗？
Oracle Redo Log是数据库的重要对象，原始提出Redo Log的目的在于“日志在先，数据恢复”。从宏观上看，Redo Log是保证数据库事务一致性的手段。但更重要的是，Redo Log是数据库内部一致性、数据库完全恢复和高可用性组件（DG、OGG）的重要技术基础。
Redo Log是描述数据块变化的记录信息，其中包括逻辑变化和物理变化。本篇就通过实验来确定Append+Nologging给备份还原带来的问题。
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1、环境准备和备份
我们选择Oracle 11gR2进行测试。为了保证一致性，我们首先进行一次热备份动作。
RMAN> backup database plus archivelog delete all input;
Starting backup at 10-DEC-13
current log archived
allocated channel: ORA_DISK_1
channel ORA_DISK_1: SID=38 device type=DISK
（篇幅原因，有省略……）
Starting Control File and SPFILE Autobackup at 10-DEC-13
piece handle=/u01/flash_recovery_area/WILSON/autobackup/2013_12_10/o1_mf_s_833787521_9bdo43ol_.bkp comment=NONE
Finished Control File and SPFILE Autobackup at 10-DEC-13
此时，配合归档模式，我们是可以实现完全恢复的。
RMAN> list backup;
List of Backup Sets
===================
BS Key Type LV Size Device Type Elapsed Time Completion Time
------- ---- -- ---------- ----------- ------------ ---------------
130 Full 1.31G DISK 00:01:55 10-DEC-13
BP Key: 130 Status: AVAILABLE Compressed: NO Tag: TAG20131210T073642
Piece Name: /u01/flash_recovery_area/WILSON/backupset/2013_12_10/o1_mf_nnndf_TAG20131210T073642_9bdo0djj_.bkp
List of Datafiles in backup set 130
（篇幅原因，有省略……）
SPFILE Included: Modification time: 10-DEC-13
SPFILE db_unique_name: WILSON
Control File Included: Ckp SCN: 5260073 Ckp time: 10-DEC-13
2、一次append+nologging动作
我们创建一张数据表T，将其nologging属性设置为Y。
SQL> create table t as select * from dba_objects where 1=0;
Table created
SQL> alter table t nologging;
Table altered
使用insert append插入数据。
SQL> insert /*+append*/ into t select * from dba_objects;
72768 rows inserted
SQL> commit;
Commit complete
3、启动恢复过程
如果此时发生系统故障，数据丢失，需要进行数据恢复动作。试图使用RMAN来进行完全恢复。
SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> conn / as sysdba
Connected to an idle instance.
SQL> startup mount;
ORACLE instance started.
Total System Global Area 849530880 bytes
Fixed Size 1339824 bytes
Variable Size 511708752 bytes
Database Buffers 331350016 bytes
Redo Buffers 5132288 bytes
Database mounted.
启用RMAN恢复过程。
--Restore过程
RMAN> restore database;
Starting restore at 10-DEC-13
allocated channel: ORA_DISK_1
channel ORA_DISK_1: SID=18 device type=DISK
channel ORA_DISK_1: starting datafile backup set restore
channel ORA_DISK_1: specifying datafile(s) to restore from backup set
channel ORA_DISK_1: restoring datafile 00001 to
（篇幅原因，有省略……）
channel ORA_DISK_1: piece handle=/u01/flash_recovery_area/WILSON/backupset/2013_12_10/o1_mf_nnndf_TAG20131210T073642_9bdo0djj_.bkp tag=TAG20131210T073642
channel ORA_DISK_1: restored backup piece 1
channel ORA_DISK_1: restore complete, elapsed time: 00:07:05
Finished restore at 10-DEC-13
--Recover应用Redo Log
RMAN> recover database;
Starting recover at 10-DEC-13
using channel ORA_DISK_1
starting media recovery
media recovery complete, elapsed time: 00:00:12
Finished recover at 10-DEC-13
RMAN>
恢复过程没有明显的错误标志，恢复似乎是成功了。之后打开数据库。
RMAN> alter database open;
database opened