flashback六大技术之flashback transaction query 和flashback table
环境：
15:25:40 hr@ORCL (^ω^) select * from v$version where rownum=1; BANNER ------------------------------------------------------------------------------- Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Prod
Ⅰ）flashback transaction query
flashback transaction query是基于flashback version query的“恢复”,因为在flashback version query中，有个伪列versions_xid，这是这两类query的“红线”，视图flashback_transaction_query进行的是全表扫描，要注意代价的评估。
14:17:18 sys@ORCL (^ω^) desc flashback_transaction_query 名称 是否为空? 类型 ----------------------------------------- -------- ---------------------------- XID RAW(8) START_SCN NUMBER START_TIMESTAMP DATE COMMIT_SCN NUMBER COMMIT_TIMESTAMP DATE LOGON_USER VARCHAR2(30) UNDO_CHANGE# NUMBER OPERATION VARCHAR2(32) TABLE_NAME VARCHAR2(256) TABLE_OWNER VARCHAR2(32) ROW_ID VARCHAR2(19) UNDO_SQL VARCHAR2(4000)
实验：
select operation,undo_sql
from flashback_transaction_query q where q.xid in (
select versions_xid from t1 versions between scn 4198407 and 4198441)
/
15:34:17 hr@ORCL (^ω^) select dbms_flashback.get_system_change_number from dual;
GET_SYSTEM_CHANGE_NUMBER
------------------------
4197364
15:34:22 hr@ORCL (^ω^) delete test where rownum=1;
已删除 1 行。
15:34:41 hr@ORCL (^ω^) commit;
提交完成。
15:35:08 hr@ORCL (^ω^) select dbms_flashback.get_system_change_number from dual;
GET_SYSTEM_CHANGE_NUMBER
------------------------
4197405
15:35:25 hr@ORCL (^ω^) select xid,commit_scn,operation,undo_sql
15:36:16 2 from flashback_transaction_query q where q.xid in (
15:36:16 3 select versions_xid from test versions between scn 4197364 and 4197405)
15:36:18 4 /
XID COMMIT_SCN
---------------- ----------
OPERATION
----------------------------------------------------------------
UNDO_SQL
--------------------------------------------------------------------------------
06002000F4040000 4197376
DELETE
insert into "HR"."TEST"("ID1","ID2") values ('2281','2283');
06002000F4040000 4197376
***************************************************我是分隔线哦********************************************************************
Ⅱ）flashback table
由于flashback table使用了DML(注意：不能将表恢复到改变表结构的DDL操作之前)操作去恢复数据，不能保证rowid不变，所以在flashback table之前需要启用row movement特性。
15:57:19 hr@ORCL (^ω^) select row_movement from user_tables where table_name='T1';
ROW_MOVEMENT
----------------
DISABLED
16:20:38 hr@ORCL (^ω^) alter table t1 enable row movement;
表已更改。
16:21:04 hr@ORCL (^ω^) select row_movement from user_tables where table_name='T1';
ROW_MOVEMENT
----------------
ENABLED
16:21:09 hr@ORCL (^ω^) select dbms_flashback.get_system_change_number from dual;
GET_SYSTEM_CHANGE_NUMBER
------------------------
4199918
16:22:52 hr@ORCL (^ω^) select count(*) from t1;
COUNT(*)
----------
8
16:23:22 hr@ORCL (^ω^) delete t1 where rownum=1;
已删除 1 行。
16:23:31 hr@ORCL (^ω^) commit;
提交完成。
16:23:36 hr@ORCL (^ω^) flashback table t1 to scn 4199918;
闪回完成。
16:24:19 hr@ORCL (^ω^) select count(*) from t1;
COUNT(*)
----------
8