如何在Oracle 10gR2中设定指定的恢复点实现轻松闪回

    作者:课课家更新于: 2015-11-03 09:00:50

    关于数据库的知识数不胜数,今天,小编为大家带来了新的关于数据库的内容。Oracle 9i引入的闪回查询功能显示前一个时间点的查询结果。但是,表本身并没有改变。Oracle 10g增强了闪回功能,可以永久闪回一个表格。现在Oracle 10g第二版通过增加指定的恢复点,使这一过程更加方便。
    通常,你为FLASHBACK TABLE语句提供一个时间标签或系统改变号(SCN),表明你希望闪回多远。(闪回次数仅限于系统存储撤销的次数。)问题在于,中国期刊全文数据库时间标签只是一个近似值,而了解准确的SCN需要查明一个特别的事务。在开始更新前,你可混沌与秩序数据库 应用DBMS_FLASHBACK中的GET_SYSTEM_CHANGE_NUMBER进程来显示当前的SCN,但你必须记住它。
    应用恢复点不必知道准确的SCN。恢复点建立后,它即恢复当前SCN。因此,外文文献数据库使用恢复点名称等同于使用对应的SCN。
    CREATE RESTORE POINT(创建恢复点)命令的语法很简单:
    CREATE RESTORE POINT restore_point_name;
    FLASHBACK ANY TABLE或SELECT ANY DICTIONARY权限需要建立一个正常(无保证)的恢复点。一旦恢复点不再需要,对应的DROP RESTORE POINT命令就将它删除。
    列表A显示向OE模式提供的正确许可,建立一个恢复点,然后在一个错过正确WHERE子句的错误UPDATE后建立一个FLASHBACK TABLE。

    SQL> CONNECT / AS SYSDBA
    Connected.
    SQL> GRANT SELECT ANY DICTIONARY TO oe;
    Grant succeeded.
    SQL> CONNECT OE/OE
    Connected.
    SQL> -- Tables must have row movement enabled to flash back
    SQL> ALTER TABLE warehouses 2 ENABLE ROW MOVEMENT;
    Table altered.
    SQL> CREATE RESTORE POINT my_update;
    Restore point created.
    SQL> COLUMN name FORMAT a25
    SQL> COLUMN time FORMAT a32
    SQL>
    SQL> SELECT name, scn, time,
    guarantee_flashback_database 2 FROMv$restore_point;
    NAME SCN TIME GUA
    ------------------------- ---------- ------------------------------
    MY_UPDATE 734934 10-AUG-06 03.32.29.000000000 PM NO
    SQL> UPDATE warehouses 2 SET warehouse_name = 'Bellevue, WA';
    9 rows updated.
    SQL> COMMIT;
    Commit complete.
    SQL> SELECT warehouse_id, warehouse_name 2 FROM warehouses;
    WAREHOUSE_ID WAREHOUSE_NAME
    ------------ -----------------------------------
    1 Bellevue, WA 2 Bellevue, WA 3 Bellevue, WA 4 Bellevue,
    WA 5 Bellevue, WA 6 Bellevue, WA 7 Bellevue, WA 8 Bellevue,
    WA 9 Bellevue, WA 9 rows selected.SQL> CONNECT / AS SYSDBA Connected.
    SQL> GRANT SELECT ANY DICTIONARY TO oe;
    Grant succeeded.
    SQL> CONNECT OE/OE
    Connected.
    SQL> -- Tables must have row movement enabled to flash back
    SQL> ALTER TABLE warehouses 2 ENABLE ROW MOVEMENT;
    Table altered.
    SQL> CREATE RESTORE POINT my_update;
    Restore point created.
    SQL> COLUMN name FORMAT a25
    SQL> COLUMN time FORMAT a32
    SQL>
    SQL> SELECT name, scn, time,
    guarantee_flashback_database 2 FROMv$restore_point;
    NAME SCN TIME GUA
    ------------------------- ---------- -------------------------------
    MY_UPDATE 734934 10-AUG-06 03.32.29.000000000 PM NO
    SQL> UPDATE warehouses 2 SET warehouse_name = 'Bellevue, WA';
    9 rows updated.
    SQL> COMMIT;
    Commit complete.
    SQL> SELECT warehouse_id, warehouse_name 2 FROM warehouses;
    WAREHOUSE_ID WAREHOUSE_NAME
    ------------ -----------------------------------
    1 Bellevue, WA 2 Bellevue, WA 3 Bellevue,
    WA 4 Bellevue, WA 5 Bellevue, WA 6 Bellevue, WA 7 Bellevue,
    WA 8 Bellevue, WA 9 Bellevue, WA 9 rows selected.
    SQL> FLASHBACK TABLE warehouses 2 TO RESTORE POINT my_update;
    Flashback complete.
    SQL> SELECT warehouse_id, warehouse_name 2 FROM warehouses;
    WAREHOUSE_ID WAREHOUSE_NAME
    ------------ -----------------------------------
    1 Southlake, Texas 2 San Francisco 3 New Jersey 4 Seattle,
    Washington 5 Toronto 6 Sydney 7 Mexico City 8 Beijing 9 Bombay
    9 rows selected.

    SQL> FLASHBACK TABLE warehouses 2 TO RESTORE POINT my_update;
    Flashback complete.
    SQL> SELECT warehouse_id, warehouse_name 2 FROM warehouses;
    WAREHOUSE_ID WAREHOUSE_NAME
    ------------ -----------------------------------
    1 Southlake, Texas 2 San Francisco 3 New Jersey 4 Seattle,
    Washington 5 Toronto 6 Sydney 7 Mexico City 8 Beijing 9 Bombay
    9 rows selected.

    列表A
    恢复点存储在控制文件中,所以即使数据库关闭(安装好,但未开),它们仍然有效。这意味着你还可在内存数据库 FLASHBACK DATABASE命令中使用它们。
    作者:Bob Watkins(OCP、MCDBA、MCSE、MCT)是一位有25年经验的计算机专业人士,从事过技术培训师、顾问与数据库管理员等职。更多详情请咨询课课家官网,了解更多内容.


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