Oracle 9i 开始支持闪回，Oracle10g开始全面支持闪回功能，Oracle11g有所完善，为大家快速的恢复数据，查询历史数据提供了很大的便捷方法。
本文主要对Oracle常用闪回使用做些详细介绍，其中对于不常用的事务和版本闪回，这里就不做介绍
一、Oracle闪回概述
| 闪回级别 | 闪回场景 | 闪回技术 | 对象依赖 | 影响数据 |
| 数据库 | 表截断、逻辑错误、其他多表意外事件 | 闪回DATABASE | 闪回日志、undo | 是 |
| DROP | 删除表 | 闪回DROP | 回收站(recyclebin) | 是 |
| 表 | 更新、删除、插入记录 | 闪回TABLE | 还原数据,undo | 是 |
| 查询 | 当前数据和历史数据对比 | 闪回QUERY | 还原数据,undo | 否 |
| 版本查询 | 比较行版本 | 闪回Version Query | 还原数据,undo | 否 |
| 事务查询 | 比较 | 闪回Transaction Query | 还原数据,undo | 否 |
| 归档 | DDL、DML | 闪回Archive | 归档日志 | 是 |
二、Oracle闪回使用详解
1、闪回开启
(1)开启闪回必要条件
a.开启归档日志
SQL> archive log list; Database log mode Archive Mode Automatic archival Enabled Archive destination /home/U01/app/oracle/oradata/testdb/arch Oldest online log sequence 844 Next log sequence to archive 846 Current log sequence 846 ##如未开启，在mount状态执行alter database archivelog;
b.设置合理的闪回区
db_recovery_file_dest：指定闪回恢复区的位置
db_recovery_file_dest_size：指定闪回恢复区的可用空间大小
db_flashback_retention_target：指定数据库可以回退的时间，单位为分钟，默认1440分钟(1天),实际取决于闪回区大小
(2)检查是否开启闪回
SQL> select flashback_on from v$database; FLASHBACK_ON ------------------ NO
(3)开启闪回
a.开启归档
mount状态：alter database archivelog;
b.设置闪回区
SQL> alter system set db_recovery_file_dest=‘/home/U01/app/oracle/fast_recovery_area‘ scope=both; System altered. SQL> alter system set db_recovery_file_dest_size=60G scope=both; System altered. SQL> alter system set db_flashback_retention_target=4320 scope=both; System altered.
c.开启flashback (10g在mount开启)
SQL> alter database flashback on; Database altered.
(4)确定闪回开启
SQL> select flashback_on from v$database; FLASHBACK_ON ------------------ YES
(5)关闭闪回
SQL> alter database flashback off; Database altered.
2、闪回使用
(1)闪回查询
闪回查询主要是根据Undo表空间数据进行多版本查询，针对v$和x$动态性能视图无效，但对DBA_、ALL_、USER_是有效的
a.闪回查询
允许用户查询过去某个时间点的数据，用以重构由于意外删除或更改的数据，数据不会变化。
SQL> select * from scott.dept; DEPTNO DNAME LOC ---------- -------------- ------------- 10 ACCOUNTING NEW YORK 20 RESEARCH DALLAS 30 SALES CHICAGO 40 OPERATIONS BOSTON SQL> delete from scott.dept where deptno=40; 1 row deleted. SQL> commit; Commit complete. SQL> select * from scott.dept as of timestamp sysdate-10/1440; DEPTNO DNAME LOC ---------- -------------- ------------- 10 ACCOUNTING NEW YORK 20 RESEARCH DALLAS 30 SALES CHICAGO 40 OPERATIONS BOSTON SQL> select * from scott.dept as of timestamp to_timestamp(‘2017-12-14 16:20:00‘,‘yyyy-mm-dd hh24:mi:ss‘); DEPTNO DNAME LOC ---------- -------------- ------------- 10 ACCOUNTING NEW YORK 20 RESEARCH DALLAS 30 SALES CHICAGO 40 OPERATIONS BOSTON SQL> select * from scott.dept as of scn 16801523; DEPTNO DNAME LOC ---------- -------------- ------------- 10 ACCOUNTING NEW YORK 20 RESEARCH DALLAS 30 SALES CHICAGO 40 OPERATIONS BOSTON
b.闪回版本查询
用于查询行级数据库随时间变化的方法
c.闪回事务查询
用于提供查看事务级别数据库变化的方法
(2)闪回表(update/insert/delete)
闪回表就是对表的数据做回退，回退到之前的某个时间点，其利用的是undo的历史数据，与undo_retention设置有关，默认是14400分钟（1天）
同样，sys用户表空间不支持闪回表,要想表闪回，需要允许表启动行迁移(row movement)
闪回表示例：
SQL> flashback table scott.dept to timestamp to_timestamp(‘2017-12-14 16:20:00‘,‘yyyy-mm-dd hh24:mi:ss‘); flashback table scott.dept to timestamp to_timestamp(‘2017-12-14 16:20:00‘,‘yyyy-mm-dd hh24:mi:ss‘) ERROR at line 1: ORA-08189: cannot flashback the table because row movement is not enabled SQL> select row_movement from dba_tables where table_name=‘DEPT‘ and owner=‘SCOTT‘; ROW_MOVE -------- DISABLED SQL> alter table scott.dept enable row movement; Table altered. SQL> flashback table scott.dept to timestamp to_timestamp(‘2017-12-14 16:20:00‘,‘yyyy-mm-dd hh24:mi:ss‘); Flashback complete. SQL> select * from scott.dept; DEPTNO DNAME LOC ---------- -------------- ------------- 10 ACCOUNTING NEW YORK 20 RESEARCH DALLAS 30 SALES CHICAGO 40 OPERATIONS BOSTON SQL> alter table scott.dept disable row movement; Table altered.
(3)闪回DROP(drop table)
当一个表被drop掉，表会被放入recyclebin回收站，可通过回收站做表的闪回。表上的索引、约束等同样会被恢复
不支持sys/system用户表空间对象，可通过alter system set recyclebin=off;关闭回收站功能
闪回DROP示例：
SQL> select * from t ; ID NAME ---------- --------------------------------------- 1 2 3 4 30 SQL> drop table t; Table dropped. SQL> show recyclebin; ORIGINAL NAME RECYCLEBIN NAME OBJECT TYPE DROP TIME ---------------- ------------------------------ ------------ ------------------- T BIN$YEh2QcvZdJLgUxyAgQpnVQ==$0 TABLE 2017-12-14:15:02:06 SQL> flashback table t to before drop; Flashback complete. SQL> select * from t; ID NAME ---------- ------------------------------------- 1 2 3 4 30
备注：即使不开始flashback，只要开启了recyclebin，那么就可以闪回DROP表。
但如果连续覆盖，就需要指定恢复的表名，如果已经存在表，则需要恢复重命名。
SQL> show recyclebin; ORIGINAL NAME RECYCLEBIN NAME OBJECT TYPE DROP TIME ---------------- ------------------------------ ------------ ------------------- T BIN$YEh2QcvddJLgUxyAgQpnVQ==$0 TABLE 2017-12-14:15:07:54 T BIN$YEh2QcvcdJLgUxyAgQpnVQ==$0 TABLE 2017-12-14:15:07:27 SQL> flashback table "BIN$YEh2QcvcdJLgUxyAgQpnVQ==$0" to before drop ; Flashback complete. SQL> show recyclebin; ORIGINAL NAME RECYCLEBIN NAME OBJECT TYPE DROP TIME ---------------- ------------------------------ ------------ ------------------- T BIN$YEh2QcvddJLgUxyAgQpnVQ==$0 TABLE 2017-12-14:15:07:54 SQL> flashback table t to before drop rename to tt; Flashback complete.
(4)闪回数据库(truncate/多表数据变更)
数据库闪回必须在mounted状态下进行，基于快照的可以再open下进行闪回库
闪回数据库主要是将数据库还原值过去的某个时间点或SCN，用于数据库出现逻辑错误时，需要open database resetlogs
a.全库闪回
数据库闪回示例
SQL> select * from scott.EMP; EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO ---------- ---------- --------- ---------- ------------------- ---------- ---------- ---------- 7369 SMITH CLERK 7902 1980-12-17 00:00:00 800 20 7499 ALLEN SALESMAN 7698 1981-02-20 00:00:00 1600 300 30 7521 WARD SALESMAN 7698 1981-02-22 00:00:00 1250 500 30 7566 JONES MANAGER 7839 1981-04-02 00:00:00 2975 20 7654 MARTIN SALESMAN 7698 1981-09-28 00:00:00 1250 1400 30 7698 BLAKE MANAGER 7839 1981-05-01 00:00:00 2850 30 7782 CLARK MANAGER 7839 1981-06-09 00:00:00 2450 10 7788 SCOTT ANALYST 7566 1987-04-19 00:00:00 3000 20 7839 KING PRESIDENT 1981-11-17 00:00:00 5000 10 7844 TURNER SALESMAN 7698 1981-09-08 00:00:00 1500 0 30 7876 ADAMS CLERK 7788 1987-05-23 00:00:00 1100 20 7900 JAMES CLERK 7698 1981-12-03 00:00:00 950 30 7902 FORD ANALYST 7566 1981-12-03 00:00:00 3000 20 7934 MILLER CLERK 7782 1982-01-23 00:00:00 1300 10 14 rows selected. SQL> truncate table scott.EMP; Table truncated. SQL> shutdown immediate; Database closed. Database dismounted. ORACLE instance shut down. SQL> startup mount; ORACLE instance started. Total System Global Area 9.4067E+10 bytes Fixed Size 2263936 bytes Variable Size 9395242112 bytes Database Buffers 8.4557E+10 bytes Redo Buffers 112766976 bytes Database mounted. SQL> flashback database to timestamp to_timestamp(‘2017-12-14 14:12:46‘,‘yyyy-mm-dd HH24:MI:SS‘); Flashback complete. SQL> alter database open resetlogs; Database altered. SQL> select * from scott.emp; EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO ---------- ---------- --------- ---------- ------------------- ---------- ---------- ---------- 7369 SMITH CLERK 7902 1980-12-17 00:00:00 800 20 7499 ALLEN SALESMAN 7698 1981-02-20 00:00:00 1600 300 30 7521 WARD SALESMAN 7698 1981-02-22 00:00:00 1250 500 30 7566 JONES MANAGER 7839 1981-04-02 00:00:00 2975 20 7654 MARTIN SALESMAN 7698 1981-09-28 00:00:00 1250 1400 30 7698 BLAKE MANAGER 7839 1981-05-01 00:00:00 2850 30 7782 CLARK MANAGER 7839 1981-06-09 00:00:00 2450 10 7788 SCOTT ANALYST 7566 1987-04-19 00:00:00 3000 20 7839 KING PRESIDENT 1981-11-17 00:00:00 5000 10 7844 TURNER SALESMAN 7698 1981-09-08 00:00:00 1500 0 30 7876 ADAMS CLERK 7788 1987-05-23 00:00:00 1100 20 7900 JAMES CLERK 7698 1981-12-03 00:00:00 950 30 7902 FORD ANALYST 7566 1981-12-03 00:00:00 3000 20 7934 MILLER CLERK 7782 1982-01-23 00:00:00 1300 10 14 rows selected.
b.快照闪回
(5)闪回归档(增加、修改、重命名、删除表的列、truncate表、修改表的约束、以及修改分区表的分区规范)
3、闪回注意事项
(1)数据库闪回需要在mounted下进行，并且open时需要使用resetlogs
(2)闪回DROP只能用于非系统表空间和本地管理的表空间，外键约束无法恢复，对方覆盖、重命名需注意
(3)表DROP，对应的物化视图会被彻底删除，物化视图不会存放在recyclebin里
(4)闪回表，如果在做过dml，然后进行了表结构修改、truncate等DDL操作，新增/删除结构无法做闪回
(5)闪回归档，必须在assm管理tablespace和undo auto管理下进行
(6)注意闪回区管理，防止磁盘爆满，闪回区空间不足等
三、备注
1、相关数据字典
V$FLASHBACK_DATABASE_LOG ##查看数据库可闪回的时间点/SCN等信息
V$flashback_database_stat ##查看闪回日志空间记录信息
2、常用查询语句
(1)查看数据库状态
SQL> select NAME,OPEN_MODE ,DATABASE_ROLE,CURRENT_SCN,FLASHBACK_ON from v$database; NAME OPEN_MODE DATABASE_ROLE CURRENT_SCN FLASHBACK_ON ------------- -------------------- ---------------- ----------- ------------------ TESTDB READ WRITE PRIMARY 16812246 YES
(2)获取当前数据库的系统时间和SCN
SQL> select to_char(systimestamp,‘yyyy-mm-dd HH24:MI:SS‘) as sysdt , dbms_flashback.get_system_change_number scn from dual; SYSDT SCN ------------------- ---------- 2017-12-14 14:28:33 16813234
(3)查看数据库可恢复的时间点
SQL> select * from V$FLASHBACK_DATABASE_LOG; OLDEST_FLASHBACK_SCN OLDEST_FLASHBACK_TI RETENTION_TARGET FLASHBACK_SIZE ESTIMATED_FLASHBACK_SIZE -------------------- ------------------- ---------------- -------------- ------------------------ 16801523 2017-12-14 11:35:05 4320 104857600 244113408
(4)查看闪回日志空间情况
SQL> select * from V$flashback_database_stat; BEGIN_TIME END_TIME FLASHBACK_DATA DB_DATA REDO_DATA ESTIMATED_FLASHBACK_SIZE ------------------- ------------------- -------------- ---------- ---------- ------------------------ 2017-12-14 14:34:53 2017-12-14 14:56:43 1703936 9977856 1487872 0
(5)SCN和timestamp装换关系查询
select scn,to_char(time_dp,‘yyyy-mm-dd hh24:mi:ss‘)from sys.smon_scn_time;
(6)闪回语句
a.闪回数据库
FLASHBACK DATABASE TO TIMESTAMP to_timestamp(‘2017-12-14 14:28:33‘,‘yyyy-mm-dd HH24:MI:SS‘);;
flashback database to scn 16813234;
b.闪回DROP
其中table_name可以是删除表名称，也可以是别名
flashback table table_name to before drop;
flashback table table_name to before drop rename to table_name_new;
c.闪回表
flashback table table_name to scn scn_number;
flashback table table_name to timestamp to_timestamp(‘2017-12-14 14:28:33‘,‘yyyy-mm-dd hh24:mi:ss‘);
d.闪回查询
select * from table_name as of timestamp to_timestamp(‘2017-12-14 14:28:33‘,‘yyyy-mm-dd hh24:mi:ss‘);
select * from scott.dept as of scn 16801523;
(7)闪回空间爆满问题处理
请参照我之前的微博：http://blog.itpub.net/27067062/viewspace-2129130/
