Oracle 12c R2新特性: PDB级闪回（Flashback PDB）

闪回数据库在10G版本时引入，当数据产生逻辑错误或升级失败时，用于闪回数据库到指定时间点，在12C 多租户结构中增加了PDB概念，在恢复时通常为了节约时间和一致性做最小粒度的恢复，在12.1版本如果对Flashback database需要创建辅助实例和CDB(只能是CDB级)，有些像表空间的基于时间点的恢复 ,在12C r2版本新特性引入了PDB级别的flashback，更加快速方便， 可以使用RMAN和SQL两种方式实现， 且闪回后原PDB的备份仍然有效。
PDB闪回有几个基本的前提条件：
1，enable local undo
2，enable archivelog mode
3，enable flashback database;

QL> startup upgrade
SQL> show parameter db_reco
PARAMETER_NAME                     TYPE        VALUE
---------------------------------- ----------- --------------
db_recovery_file_dest              string
db_recovery_file_dest_size         big integer 0
SQL> show parameter flashback
PARAMETER_NAME                     TYPE        VALUE
---------------------------------- ----------- --------------
db_flashback_retention_target      integer     1440
SQL> alter system set db_recovery_file_dest_size=1G;
System altered.
SQL> alter system set db_recovery_file_dest='/u01/arch_anbob';
System altered.
SQL> alter database flashback on;
Database altered.
SQL> alter database local undo on;
Database altered.
SQL> archive log list
Database log mode              Archive Mode
Automatic archival             Enabled
Archive destination            USE_DB_RECOVERY_FILE_DEST
Oldest online log sequence     15
Next log sequence to archive   17
Current log sequence           17
SQL> shutdown immediate;
SQL> startup
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Note:
flashback database, local undo ,archivelog这些属性都是CDB级别的， 所以不允许在部分PDB级修改。
Create （还原点）restore point
restore point就是用户创建一个自定义名称与scn相关的时间点，信息存储在control file中，目前分3种restore point: Normal Restore Point,Guaranteed Restore Point,Clean Restore Point.  其中Clean resotre point只用于使用shared undo模式时如12.1中没有local undo;  而Normal 和Guaranteed 的区别是Guaranteed 可以保证restore point后的闪回日志不会被自动删除除非手动明确删除，而nomal可能会因为flashback retention时间而age out.
 

SQL> show pdbs
    CON_ID CON_NAME                       OPEN MODE  RESTRICTED
---------- ------------------------------ ---------- ----------
         2 PDB$SEED                       READ ONLY  NO
         3 PDBANBOB                       MOUNTED
         5 PDBTEST2_PROXY                 MOUNTED
         6 PDBWEEJAR                      MOUNTED
		 
SQL> alter pluggable database pdbanbob open;
Pluggable database altered.
SQL> show pdbs
    CON_ID CON_NAME                       OPEN MODE  RESTRICTED
---------- ------------------------------ ---------- ----------
         2 PDB$SEED                       READ ONLY  NO
         3 PDBANBOB                       READ WRITE NO
         5 PDBTEST2_PROXY                 MOUNTED
         6 PDBWEEJAR                      MOUNTED
		 
SQL> alter session set container=pdbanbob;
Session altered.
SQL> select sysdate from dual;
SYSDATE
-------------------
2017-03-21 15:58:13
SQL> create restore point pdbanbob_201703211800;
Restore point created.
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Note:
首先创建还原点,如果恢复到之前创建的还原点，前提是保证还原点之后的闪回日志的完整性。还原点可以在CDB或PDB级创建只是PDB作用域不同， 以上是创建在PDB级。 还原点也可以创建为GUARANTEE,语法如下:

create restore point pdbanbob_201703211800 GUARANTEE FLASHBACK DATABASE;

创建测试数据

SQL> alter session set container=pdbanbob;
SQL> create table anbob.t16(id int, v date);
Table created.
SQL> insert into anbob.t16 values(1,sysdate);
1 row created.
SQL> commit;
Commit complete.
SQL> select * from anbob.t16;
        ID V
---------- -------------------
         1 2017-03-21 16:12:12
SQL> insert into anbob.t16 values(1,sysdate);
1 row created.
SQL> commit;
Commit complete.
SQL> select * from anbob.t16;
        ID V
---------- -------------------
         1 2017-03-21 16:12:12
         1 2017-03-21 16:13:37
SQL> col name for a30
SQL> select SCN,to_char(time,'mm-dd hh24:mi') time,NAME,CLEAN_PDB_RESTORE_POINT IS_CLEAN,CON_ID from v$restore_point;
       SCN TIME        NAME                           IS_     CON_ID
---------- ----------- ------------------------------ --- ----------
   3469597 03-21 15:59 PDBANBOB_201703211800          NO           3
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还原到第一条记录insert后的时间
flashback backup在12.2中有rman和SQL两种方式闪回， 当使用shared undo里需要使用rman，前提需要在pdb close immediate后创建clean resotre point, 过程中会自动创建辅助实例CDB和PDB PITR； 使用local undo时,就可以使用SQL命令更佳快速，而且只是pdb 数据文件原位置闪回，并应用undo，在做之前创建任意一种restore point都可以，也不需要辅助实例。

SQL> alter pluggable database pdbanbob close;
Pluggable database altered.
SQL> FLASHBACK PLUGGABLE DATABASE pdbanbob TO TIMESTAMP to_timestamp('2017-03-21 16:13:01','yyyy-mm-dd hh24:mi:ss');
Flashback complete.
SQL> alter pluggable database pdbanbob open resetlogs;
Pluggable database altered.
SQL>  select * from anbob.t16;
        ID V
---------- -------------------
         1 2017-03-21 16:12:12
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还原到还原点(restore point)

SQL> alter pluggable database pdbanbob close;
Pluggable database altered.
SQL> FLASHBACK PLUGGABLE DATABASE pdbanbob TO RESTORE POINT PDBANBOB_201703211800;
Flashback complete.
SQL> alter pluggable database pdbanbob open resetlogs;
Pluggable database altered.
SQL> select * from anbob.t16;
select * from anbob.t16
                    *
ERROR at line 1:
ORA-00942: table or view does not exist
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NOTE:
只能还原到还原点和open resetlogs之间的时间，也就是只能向前还原。如果向后还原同样会提示下面的错误

SQL>  alter pluggable database pdbanbob close;
Pluggable database altered.
SQL> FLASHBACK PLUGGABLE DATABASE pdbanbob TO TIMESTAMP to_timestamp('2017-03-21 16:14:01','yyyy-mm-dd hh24:mi:ss');
FLASHBACK PLUGGABLE DATABASE pdbanbob TO TIMESTAMP to_timestamp('2017-03-21 16:14:01','yyyy-mm-dd hh24:mi:ss')
*
ERROR at line 1:
ORA-39889: Specified System Change Number (SCN) or timestamp is in the middle of a previous PDB RESETLOGS operation.
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check db incarnation

SQL> select INCARNATION#,RESETLOGS_TIME from v$database_incarnation;
INCARNATION# RESETLOGS_TIME
------------ -------------------
           1 2016-12-09 20:42:51
           2 2017-01-18 21:27:59
SQL>  select DB_INCARNATION#,PDB_INCARNATION#,INCARNATION_TIME,con_id from v$pdb_incarnation order by 3;
DB_INCARNATION# PDB_INCARNATION# INCARNATION_TIME        CON_ID
--------------- ---------------- ------------------- ----------
              1                0 2016-12-09 20:42:51          1
              1                0 2016-12-09 20:42:51          5
              1                0 2016-12-09 20:42:51          6
              1                0 2016-12-09 20:42:51          2
              2                0 2017-01-18 21:27:59          5
              2                0 2017-01-18 21:27:59          2
              2                0 2017-01-18 21:27:59          1
              2                0 2017-01-18 21:27:59          3
              2                0 2017-01-18 21:27:59          6
              2                2 2017-03-21 15:59:13          3
              2                1 2017-03-21 16:13:06          3
11 rows selected.
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Note:
PDB级别的闪回，并没有改变整个数据库的INCARNATION， 从新增加的v$pdb_incarnation视图可以确认刚才的闪回操作只是在PDB（con_id is 3）增加了对应的2条记录。