Oracle 9i 開始支持閃回，Oracle10g開始全面支持閃回功能，Oracle11g有所完善，為大家快速的恢復(fù)數(shù)據(jù)，查詢歷史數(shù)據(jù)提供了很大的便捷方法。
本文主要對Oracle常用閃回使用做些詳細介紹，其中對于不常用的事務(wù)和版本閃回，這里就不做介紹
一、Oracle閃回概述
| 閃回級別 | 閃回場景 | 閃回技術(shù) | 對象依賴 | 影響數(shù)據(jù) |
| 數(shù)據(jù)庫 | 表截斷、邏輯錯誤、其他多表意外事件 | 閃回DATABASE | 閃回日志、undo | 是 |
| DROP | 刪除表 | 閃回DROP | 回收站(recyclebin) | 是 |
| 表 | 更新、刪除、插入記錄 | 閃回TABLE | 還原數(shù)據(jù),undo | 是 |
| 查詢 | 當(dāng)前數(shù)據(jù)和歷史數(shù)據(jù)對比 | 閃回QUERY | 還原數(shù)據(jù),undo | 否 |
| 版本查詢 | 比較行版本 | 閃回Version Query | 還原數(shù)據(jù),undo | 否 |
| 事務(wù)查詢 | 比較 | 閃回Transaction Query | 還原數(shù)據(jù),undo | 否 |
| 歸檔 | DDL、DML | 閃回Archive | 歸檔日志 | 是 |
二、Oracle閃回使用詳解
1、閃回開啟
(1)開啟閃回必要條件
a.開啟歸檔日志
SQL> archive log list;Database log mode Archive ModeAutomatic archival EnabledArchive destination /home/U01/app/oracle/oradata/testdb/archOldest online log sequence 844Next log sequence to archive 846Current log sequence 846##如未開啟，在mount狀態(tài)執(zhí)行alter database archivelog;
b.設(shè)置合理的閃回區(qū)
db_recovery_file_dest：指定閃回恢復(fù)區(qū)的位置
db_recovery_file_dest_size：指定閃回恢復(fù)區(qū)的可用空間大小
db_flashback_retention_target：指定數(shù)據(jù)庫可以回退的時間，單位為分鐘，默認1440分鐘(1天),實際取決于閃回區(qū)大小
(2)檢查是否開啟閃回
SQL> select flashback_on from v$database;FLASHBACK_ON------------------NO
(3)開啟閃回
a.開啟歸檔
mount狀態(tài)：alter database archivelog;
b.設(shè)置閃回區(qū)
SQL> alter system set db_recovery_file_dest='/home/U01/app/oracle/fast_recovery_area' scope=both;System altered.SQL> alter system set db_recovery_file_dest_size=60G scope=both;System altered.SQL> alter system set db_flashback_retention_target=4320 scope=both;System altered.
c.開啟flashback (10g在mount開啟)
SQL> alter database flashback on;Database altered.
(4)確定閃回開啟
SQL> select flashback_on from v$database;FLASHBACK_ON------------------YES
(5)關(guān)閉閃回
SQL> alter database flashback off;Database altered.
2、閃回使用
(1)閃回查詢
閃回查詢主要是根據(jù)Undo表空間數(shù)據(jù)進行多版本查詢，針對v$和x$動態(tài)性能視圖無效，但對DBA_、ALL_、USER_是有效的
a.閃回查詢
允許用戶查詢過去某個時間點的數(shù)據(jù)，用以重構(gòu)由于意外刪除或更改的數(shù)據(jù)，數(shù)據(jù)不會變化。
SQL> select * from scott.dept;DEPTNO DNAME LOC---------- -------------- -------------ACCOUNTING NEW YORKRESEARCH DALLASSALES CHICAGOOPERATIONS BOSTONSQL> delete from scott.dept where deptno=40;row deleted.SQL> commit;Commit complete.SQL> select * from scott.dept as of timestamp sysdate-10/1440;DEPTNO DNAME LOC---------- -------------- -------------ACCOUNTING NEW YORKRESEARCH DALLASSALES CHICAGOOPERATIONS BOSTONSQL> select * from scott.dept as of timestamp to_timestamp('2017-12-14 16:20:00','yyyy-mm-dd hh24:mi:ss');DEPTNO DNAME LOC---------- -------------- -------------ACCOUNTING NEW YORKRESEARCH DALLASSALES CHICAGOOPERATIONS BOSTONSQL> select * from scott.dept as of scn 16801523;DEPTNO DNAME LOC---------- -------------- -------------ACCOUNTING NEW YORKRESEARCH DALLASSALES CHICAGOOPERATIONS BOSTONb.閃回版本查詢
用于查詢行級數(shù)據(jù)庫隨時間變化的方法
c.閃回事務(wù)查詢
用于提供查看事務(wù)級別數(shù)據(jù)庫變化的方法
(2)閃回表(update/insert/delete)
閃回表就是對表的數(shù)據(jù)做回退，回退到之前的某個時間點，其利用的是undo的歷史數(shù)據(jù)，與undo_retention設(shè)置有關(guān)，默認是14400分鐘（1天）
同樣，sys用戶表空間不支持閃回表,要想表閃回，需要允許表啟動行遷移(row movement)
閃回表示例：
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 enabledSQL> select row_movement from dba_tables where table_name='DEPT' and owner='SCOTT';ROW_MOVE--------DISABLEDSQL> 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---------- -------------- -------------ACCOUNTING NEW YORKRESEARCH DALLASSALES CHICAGOOPERATIONS BOSTON SQL> alter table scott.dept disable row movement;Table altered.(3)閃回DROP(drop table)
當(dāng)一個表被drop掉，表會被放入recyclebin回收站，可通過回收站做表的閃回。表上的索引、約束等同樣會被恢復(fù)
不支持sys/system用戶表空間對象，可通過alter system set recyclebin=off;關(guān)閉回收站功能
閃回DROP示例：
SQL> select * from t ;ID NAME---------- ---------------------------------------24SQL> drop table t;Table dropped.SQL> show recyclebin;ORIGINAL NAME RECYCLEBIN NAME OBJECT TYPE DROP TIME---------------- ------------------------------ ------------ -------------------T BIN$YEh2QcvZdJLgUxyAgQpnVQ==$0 TABLE 2017-12-14:15:02:06SQL> flashback table t to before drop;Flashback complete.SQL> select * from t;ID NAME---------- -------------------------------------24
備注：即使不開始flashback，只要開啟了recyclebin，那么就可以閃回DROP表。
但如果連續(xù)覆蓋，就需要指定恢復(fù)的表名，如果已經(jīng)存在表，則需要恢復(fù)重命名。
SQL> show recyclebin;ORIGINAL NAME RECYCLEBIN NAME OBJECT TYPE DROP TIME---------------- ------------------------------ ------------ -------------------T BIN$YEh2QcvddJLgUxyAgQpnVQ==$0 TABLE 2017-12-14:15:07:54T BIN$YEh2QcvcdJLgUxyAgQpnVQ==$0 TABLE 2017-12-14:15:07:27SQL> flashback table "BIN$YEh2QcvcdJLgUxyAgQpnVQ==$0" to before drop ;Flashback complete.SQL> show recyclebin;ORIGINAL NAME RECYCLEBIN NAME OBJECT TYPE DROP TIME---------------- ------------------------------ ------------ -------------------T BIN$YEh2QcvddJLgUxyAgQpnVQ==$0 TABLE 2017-12-14:15:07:54SQL> flashback table t to before drop rename to tt;Flashback complete.
(4)閃回數(shù)據(jù)庫(truncate/多表數(shù)據(jù)變更)
數(shù)據(jù)庫閃回必須在mounted狀態(tài)下進行，基于快照的可以再open下進行閃回庫
閃回數(shù)據(jù)庫主要是將數(shù)據(jù)庫還原值過去的某個時間點或SCN，用于數(shù)據(jù)庫出現(xiàn)邏輯錯誤時，需要open database resetlogs
a.全庫閃回
數(shù)據(jù)庫閃回示例
SQL> select * from scott.EMP;EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO---------- ---------- --------- ---------- ------------------- ---------- ---------- ----------SMITH CLERK 7902 1980-12-17 00:00:00 800 20ALLEN SALESMAN 7698 1981-02-20 00:00:00 1600 300 30WARD SALESMAN 7698 1981-02-22 00:00:00 1250 500 30JONES MANAGER 7839 1981-04-02 00:00:00 2975 20MARTIN SALESMAN 7698 1981-09-28 00:00:00 1250 1400 30BLAKE MANAGER 7839 1981-05-01 00:00:00 2850 30CLARK MANAGER 7839 1981-06-09 00:00:00 2450 10SCOTT ANALYST 7566 1987-04-19 00:00:00 3000 20KING PRESIDENT 1981-11-17 00:00:00 5000 10TURNER SALESMAN 7698 1981-09-08 00:00:00 1500 0 30ADAMS CLERK 7788 1987-05-23 00:00:00 1100 20JAMES CLERK 7698 1981-12-03 00:00:00 950 30FORD ANALYST 7566 1981-12-03 00:00:00 3000 20MILLER CLERK 7782 1982-01-23 00:00:00 1300 10rows 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 bytesFixed Size 2263936 bytesVariable Size 9395242112 bytesDatabase Buffers 8.4557E+10 bytesRedo Buffers 112766976 bytesDatabase 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---------- ---------- --------- ---------- ------------------- ---------- ---------- ----------SMITH CLERK 7902 1980-12-17 00:00:00 800 20ALLEN SALESMAN 7698 1981-02-20 00:00:00 1600 300 30WARD SALESMAN 7698 1981-02-22 00:00:00 1250 500 30JONES MANAGER 7839 1981-04-02 00:00:00 2975 20MARTIN SALESMAN 7698 1981-09-28 00:00:00 1250 1400 30BLAKE MANAGER 7839 1981-05-01 00:00:00 2850 30CLARK MANAGER 7839 1981-06-09 00:00:00 2450 10SCOTT ANALYST 7566 1987-04-19 00:00:00 3000 20KING PRESIDENT 1981-11-17 00:00:00 5000 10TURNER SALESMAN 7698 1981-09-08 00:00:00 1500 0 30ADAMS CLERK 7788 1987-05-23 00:00:00 1100 20JAMES CLERK 7698 1981-12-03 00:00:00 950 30FORD ANALYST 7566 1981-12-03 00:00:00 3000 20MILLER CLERK 7782 1982-01-23 00:00:00 1300 10rows selected.b.快照閃回
針對主庫和備庫都可以創(chuàng)建閃回快照點，然后恢復(fù)到指定的快照點，但主庫一旦恢復(fù)到快照點，備庫的同步則需要重新同步
SQL> select * from scott.dept; DEPTNO DNAME LOC ADDR---------- -------------- ------------- ------------------------------ACCOUNTING NEW YORKRESEARCH DALLASSALES CHICAGO SQL> create restore point before_201712151111 guarantee flashback database;Restore point created.SQL> create table scott.t as select * from scott.dept;Table created.SQL> truncate table scott.t;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 bytesFixed Size 2263936 bytesVariable Size 9663677568 bytesDatabase Buffers 8.4289E+10 bytesRedo Buffers 112766976 bytesDatabase mounted.SQL> flashback database to restore point before_201712151111;Flashback complete.SQL> alter database open resetlogs;Database altered.此時主庫scott.t已不存在：SQL> select * from scott.t;select * from scott.t *ERROR at line 1:ORA-00942: table or view does not exist此時從庫的scott.依舊存在，主備同步終止解決方案：在主庫創(chuàng)建快照時間點，從庫自動停止應(yīng)用日志，等主庫閃回后，重新應(yīng)用日志即可。如果已經(jīng)做了上述操作，從庫可以選擇重建ALTER DATABASE REGISTER LOGFILE '/xx/xx/archive.dbf';
c.閃回snapshot standby
此功能在11GR2非常實用，可自動創(chuàng)建閃回點、開啟閃回日志，可完成線上數(shù)據(jù)測試后，然后做數(shù)據(jù)庫閃回恢復(fù)主備關(guān)系
select scn, STORAGE_SIZE ,to_char(time,'yyyy-mm-dd hh24:mi:ss') time,NAME from v$restore_point;select database_role,open_mode,db_unique_name,flashback_on from v$database;SQL> set line 200;SQL> set pagesize 2000;SQL> select database_role,open_mode,db_unique_name,flashback_on from v$database;DATABASE_ROLE OPEN_MODE DB_UNIQUE_NAME FLASHBACK_ON---------------- -------------------- ------------------------------ ------------------PHYSICAL STANDBY READ ONLY testdbms NOSQL> ALTER DATABASE CONVERT TO SNAPSHOT STANDBY; Database altered.SQL> select database_role,open_mode,db_unique_name,flashback_on from v$database;DATABASE_ROLE OPEN_MODE DB_UNIQUE_NAME FLASHBACK_ON---------------- -------------------- ------------------------------ ------------------SNAPSHOT STANDBY MOUNTED testdbms RESTORE POINT ONLYSQL> alter database open;Database altered.SQL> select open_mode from v$database;OPEN_MODE--------------------READ WRITE此時備庫操作：SQL> select * from scott.emp; EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO---------- ---------- --------- ---------- ------------------- ---------- ---------- ----------SMITH CLERK 7902 1980-12-17 00:00:00 800 20ALLEN SALESMAN 7698 1981-02-20 00:00:00 1600 300 30WARD SALESMAN 7698 1981-02-22 00:00:00 1250 500 30JONES MANAGER 7839 1981-04-02 00:00:00 2975 20MARTIN SALESMAN 7698 1981-09-28 00:00:00 1250 1400 30BLAKE MANAGER 7839 1981-05-01 00:00:00 2850 30CLARK MANAGER 7839 1981-06-09 00:00:00 2450 10SCOTT ANALYST 7566 1987-04-19 00:00:00 3000 20KING PRESIDENT 1981-11-17 00:00:00 5000 10TURNER SALESMAN 7698 1981-09-08 00:00:00 1500 0 30ADAMS CLERK 7788 1987-05-23 00:00:00 1100 20JAMES CLERK 7698 1981-12-03 00:00:00 950 30FORD ANALYST 7566 1981-12-03 00:00:00 3000 20MILLER CLERK 7782 1982-01-23 00:00:00 1300 10rows selected.SQL> truncate table scott.emp;Table truncated.主庫操作：SQL> create table scott.t as select * from scott.dept;Table created.SQL> select * from scott.t; DEPTNO DNAME LOC ADDR---------- -------------- ------------- ------------------------------ACCOUNTING NEW YORKRESEARCH DALLASSALES CHICAGO備庫恢復(fù)到物理standbySQL> shutdown immediate;Database closed.Database dismounted.ORACLE instance shut down.SQL> startup mount;ORACLE instance started.Total System Global Area 9.4067E+10 bytesFixed Size 2263936 bytesVariable Size 9663677568 bytesDatabase Buffers 8.4289E+10 bytesRedo Buffers 112766976 bytesDatabase mounted.SQL> ALTER DATABASE CONVERT TO PHYSICAL STANDBY; Database altered.SQL> shutdown immediate;ORA-01507: database not mountedORACLE instance shut down.SQL> startup ;ORACLE instance started.Total System Global Area 9.4067E+10 bytesFixed Size 2263936 bytesVariable Size 9663677568 bytesDatabase Buffers 8.4289E+10 bytesRedo Buffers 112766976 bytesDatabase mounted.Database opened.##此時備庫的數(shù)據(jù)已經(jīng)恢復(fù)到轉(zhuǎn)變snapshot standby時間點SQL> select database_role,open_mode,db_unique_name,flashback_on from v$database;DATABASE_ROLE OPEN_MODE DB_UNIQUE_NAME FLASHBACK_ON---------------- -------------------- ------------------------------ ------------------PHYSICAL STANDBY READ ONLY testdbms NOSQL> select * from scott.emp; EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO---------- ---------- --------- ---------- ------------------- ---------- ---------- ----------SMITH CLERK 7902 1980-12-17 00:00:00 800 20ALLEN SALESMAN 7698 1981-02-20 00:00:00 1600 300 30WARD SALESMAN 7698 1981-02-22 00:00:00 1250 500 30JONES MANAGER 7839 1981-04-02 00:00:00 2975 20MARTIN SALESMAN 7698 1981-09-28 00:00:00 1250 1400 30BLAKE MANAGER 7839 1981-05-01 00:00:00 2850 30CLARK MANAGER 7839 1981-06-09 00:00:00 2450 10SCOTT ANALYST 7566 1987-04-19 00:00:00 3000 20KING PRESIDENT 1981-11-17 00:00:00 5000 10TURNER SALESMAN 7698 1981-09-08 00:00:00 1500 0 30ADAMS CLERK 7788 1987-05-23 00:00:00 1100 20JAMES CLERK 7698 1981-12-03 00:00:00 950 30FORD ANALYST 7566 1981-12-03 00:00:00 3000 20MILLER CLERK 7782 1982-01-23 00:00:00 1300 10rows selected.SQL> alter database recover managed standby database using current logfile disconnect;Database altered.SQL> select * from scott.t; DEPTNO DNAME LOC ADDR---------- -------------- ------------- ------------------------------ACCOUNTING NEW YORKRESEARCH DALLASSALES CHICAGO SQL> select database_role,open_mode,db_unique_name,flashback_on from v$database;DATABASE_ROLE OPEN_MODE DB_UNIQUE_NAME FLASHBACK_ON---------------- -------------------- ------------------------------ ------------------PHYSICAL STANDBY READ ONLY WITH APPLY testdbms NO
(5)閃回歸檔(增加、修改、重命名、刪除表的列、truncate表、修改表的約束、以及修改分區(qū)表的分區(qū)規(guī)范)
3、閃回注意事項
(1)數(shù)據(jù)庫閃回需要在mounted下進行，并且open時需要使用resetlogs
(2)閃回DROP只能用于非系統(tǒng)表空間和本地管理的表空間，外鍵約束無法恢復(fù)，對方覆蓋、重命名需注意
(3)表DROP，對應(yīng)的物化視圖會被徹底刪除，物化視圖不會存放在recyclebin里
(4)閃回表，如果在做過dml，然后進行了表結(jié)構(gòu)修改、truncate等DDL操作，新增/刪除結(jié)構(gòu)無法做閃回
(5)閃回歸檔，必須在assm管理tablespace和undo auto管理下進行
(6)注意閃回區(qū)管理，防止磁盤爆滿，閃回區(qū)空間不足等
(7)主庫做庫的閃回，會影響備庫，需要重新同步
(8)snapshot standby 不支持最高保護模式
三、備注
1、相關(guān)數(shù)據(jù)字典
V$FLASHBACK_DATABASE_LOG ##查看數(shù)據(jù)庫可閃回的時間點/SCN等信息 V$flashback_database_stat ##查看閃回日志空間記錄信息
2、常用查詢語句
(1)查看數(shù)據(jù)庫狀態(tài)
SQL> select NAME,OPEN_MODE ,DATABASE_ROLE,CURRENT_SCN,FLASHBACK_ON from v$database;NAME OPEN_MODE DATABASE_ROLE CURRENT_SCN FLASHBACK_ON------------- -------------------- ---------------- ----------- ------------------TESTDB READ WRITE PRIMARY 16812246 YES
(2)獲取當(dāng)前數(shù)據(jù)庫的系統(tǒng)時間和SCN
SQL> select to_char(systimestamp,'yyyy-mm-dd HH24:MI:SS') as sysdt , dbms_flashback.get_system_change_number scn from dual;SYSDT SCN------------------- ----------2017-12-14 14:28:33 16813234
(3)查看數(shù)據(jù)庫可恢復(fù)的時間點
SQL> select * from V$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)查看閃回日志空間情況
SQL> select * from V$flashback_database_stat;BEGIN_TIME END_TIME FLASHBACK_DATA DB_DATA REDO_DATA ESTIMATED_FLASHBACK_SIZE------------------- ------------------- -------------- ---------- ---------- ------------------------2017-12-14 14:34:53 2017-12-14 14:56:43 1703936 9977856 1487872 0
(5)SCN和timestamp裝換關(guān)系查詢
select scn,to_char(time_dp,'yyyy-mm-dd hh24:mi:ss')from sys.smon_scn_time;
(6)查看閃回restore_point
select scn, STORAGE_SIZE ,to_char(time,'yyyy-mm-dd hh24:mi:ss') time,NAME from v$restore_point;
(7)閃回語句
a.閃回數(shù)據(jù)庫
FLASHBACK DATABASE TO TIMESTAMP to_timestamp('2017-12-14 14:28:33','yyyy-mm-dd HH24:MI:SS');;flashback database to scn 16813234;b.閃回DROP
其中table_name可以是刪除表名稱，也可以是別名
flashback table table_name to before drop;flashback table table_name to before drop rename to table_name_new;
c.閃回表
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.閃回查詢
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;e.閃回快照
create restore point before_201712151111 guarantee flashback database;flashback database to restore point before_201712151111;
(7)閃回空間爆滿問題處理
請參照 基于ORA-19815閃回空間爆滿問題的處理方法
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