20090918_oralce 042 试题27 关于 Flashback Transaction query
27. Which two statements about Flashback Query are true? (Choose two.)
A) It is generated by using the redo log files.
B) It helps in row-level recovery from user errors.
C) It can be performed to recover ALTER TABLE statements
D) It fails when undo data pertaining to the transaction is overwritten.
E) The database has to be opened with the resetlogs option after performing Flashback Query.
例子如下:
从9i简单的flashback query到10G的flashback database、flashback drop、flashback version query 、flashback transaction query。oracle一直在完善flashback。尤其是flashback transaction query可以用来恢复一个事务。要想完成这个工作,必须通过两步实现:
1、通过flashback version query 技术查看某张表过去某个时刻发生的事务的XID;
2、根据事务ID,再在flashback_transaction_query视图中找过需要undo的sql,回滚事务;
必须注意:flashback query、flashback transaction query都依赖于undo,如果undo过期或者被覆盖,乃么这个恢复也将最终以失败告终.看操作
SQL> connect mayp/mayp
Connected.
SQL> select table_name from user_tables;
Connected.
SQL> select table_name from user_tables;
TABLE_NAME
————————————————————
P
T
TEST
TEST1
TEST2
SQL> desc t
Name Null? Type
—————————————————————————————————————– ——– —————————————————————————-
NAME VARCHAR2(10)
AGE NUMBER
SEX NUMBER
————————————————————
P
T
TEST
TEST1
TEST2
SQL> desc t
Name Null? Type
—————————————————————————————————————– ——– —————————————————————————-
NAME VARCHAR2(10)
AGE NUMBER
SEX NUMBER
SQL> select name,versions_xid,versions_starttime,versions_endtime,versions_operation from t versions between timestamp minvalue and maxvalue;
NAME VERSIONS_XID VERSIONS_STARTTIME VERSIONS_ENDTIME VE
——————– —————- ————————————————————————— ————————————————————————— –
AAA
bbb
ccc
——————– —————- ————————————————————————— ————————————————————————— –
AAA
bbb
ccc
目前表t上没有发生的事务信息,下面做一个事务:
SQL> insert into t values(’4545′,4,5);
SQL> insert into t values(’4545′,4,5);
SQL> insert into t values(’4545′,4,5);
SQL> insert into t values(’4545′,4,5);
SQL> commit;
SQL> set feedback on
SQL> select name,versions_xid,versions_starttime,versions_endtime,versions_operation from t versions between timestamp minvalue and maxvalue;
SQL> select name,versions_xid,versions_starttime,versions_endtime,versions_operation from t versions between timestamp minvalue and maxvalue;
NAME VERSIONS_XID VERSIONS_STARTTIME VERSIONS_ENDTIME VE
——————– —————- ————————————————————————— ————————————————————————— –
4545 06000C00B3C10000 08-JUL-08 04.16.43 PM I
454554 06000C00B3C10000 08-JUL-08 04.16.43 PM I
454554 06000C00B3C10000 08-JUL-08 04.16.43 PM I
454554 06000C00B3C10000 08-JUL-08 04.16.43 PM I
AAA
bbb
ccc
——————– —————- ————————————————————————— ————————————————————————— –
4545 06000C00B3C10000 08-JUL-08 04.16.43 PM I
454554 06000C00B3C10000 08-JUL-08 04.16.43 PM I
454554 06000C00B3C10000 08-JUL-08 04.16.43 PM I
454554 06000C00B3C10000 08-JUL-08 04.16.43 PM I
AAA
bbb
ccc
7 rows selected.
可以发现最近发生的事务.
SQL> insert into t values(’dfdd’,3,2);
1 row created.
SQL> commit;
Commit complete.
SQL> select name,versions_xid,versions_starttime,versions_endtime,versions_operation from t versions between timestamp minvalue and maxvalue;
NAME VERSIONS_XID VERSIONS_STARTTIME VERSIONS_ENDTIME VE
——————– —————- ————————————————————————— ————————————————————————— –
dfdd 01001200E4EA0000 08-JUL-08 04.17.22 PM I
4545 06000C00B3C10000 08-JUL-08 04.16.43 PM I
454554 06000C00B3C10000 08-JUL-08 04.16.43 PM I
454554 06000C00B3C10000 08-JUL-08 04.16.43 PM I
454554 06000C00B3C10000 08-JUL-08 04.16.43 PM I
AAA
bbb
ccc
——————– —————- ————————————————————————— ————————————————————————— –
dfdd 01001200E4EA0000 08-JUL-08 04.17.22 PM I
4545 06000C00B3C10000 08-JUL-08 04.16.43 PM I
454554 06000C00B3C10000 08-JUL-08 04.16.43 PM I
454554 06000C00B3C10000 08-JUL-08 04.16.43 PM I
454554 06000C00B3C10000 08-JUL-08 04.16.43 PM I
AAA
bbb
ccc
8 rows selected.
现在发现了两笔事务,是否是同一个事务,根据VERSIONS_XID 判断。
现在需要回滚XID=06000C00B3C10000 的事务;通过查询FLASHBACK_TRANSACTION_QUERY视图获取undo sql
SQL> desc flashback_transaction_query
Name Null? Type
—————————————————————————————————————– ——– —————————————————————————-
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
Name Null? Type
—————————————————————————————————————– ——– —————————————————————————-
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
SQL> select undo_sql from flashback_transaction_query where xid=hextoraw(’06000C00B3C10000′);
UNDO_SQL
—————————————————————————————————-
delete from "MAYP"."T" where ROWID = ‘AAAiqrAANAAAAUcAAG’;
delete from "MAYP"."T" where ROWID = ‘AAAiqrAANAAAAUcAAF’;
delete from "MAYP"."T" where ROWID = ‘AAAiqrAANAAAAUcAAE’;
delete from "MAYP"."T" where ROWID = ‘AAAiqrAANAAAAUcAAD’;
—————————————————————————————————-
delete from "MAYP"."T" where ROWID = ‘AAAiqrAANAAAAUcAAG’;
delete from "MAYP"."T" where ROWID = ‘AAAiqrAANAAAAUcAAF’;
delete from "MAYP"."T" where ROWID = ‘AAAiqrAANAAAAUcAAE’;
delete from "MAYP"."T" where ROWID = ‘AAAiqrAANAAAAUcAAD’;
可以插入的4条insert可以用4条delete来undo.
flashback transaction query 演示到此结束.
其他参考： http://www.wangchao.net.cn/bbsdetail_1776485.html
http://space.itpub.net/111631/viewspace-607506
http://www.cnblogs.com/gkl0818/archive/2009/02/08/1386513.html