Oracle 18c新特性-PDB快照轮播(Snapshot Carousel)

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Oracle 18c推出的一个新功能就是PDB快照轮播，最多可以创建8个pdb的快照，而这8个构成的一组快照就被称作快照轮播。当达到第8个快照限制时，新的快照就会覆盖最旧的快照，就像redo log一样。PDB的快照主要作用是当出现了问题可以闪回到快照的时间点，另一个功能是基于快照来查询历史数据。

SQL> SELECT r.CON_ID, p.PDB_NAME, PROPERTY_NAME,
    PROPERTY_VALUE AS value, DESCRIPTION
    FROM  CDB_PROPERTIES r, CDB_PDBS p
    WHERE r.CON_ID = p.CON_ID
    AND  PROPERTY_NAME LIKE 'MAX_PDB%'
    AND  description like 'maximum%'
    ORDER BY PROPERTY_NAME;

  CON_ID PDB_NAME       PROPERTY_NAME    VALUE        DESCRIPTION
---------- -------------------- -------------------- -------------------- ----------------------------------------------------------------------
     3 ORCLPDB1       MAX_PDB_SNAPSHOTS            
maximum number of snapshots for a given PDB

默认情况下是手动创建快照，我们可以把它改成自动创建。

SQL> select snapshot_mode,snapshot_interval/60 from dba_pdbs;
SNAPSH SNAPSHOT_INTERVAL/60
------ --------------------
MANUAL
SQL> alter pluggable database snapshot mode every 4 hours;
Pluggable database altered.
SQL> select snapshot_mode,snapshot_interval/60 from dba_pdbs;
SNAPSH SNAPSHOT_INTERVAL/60
------ --------------------
AUTO  
4

要返回手动模式，输入mode manual即可。

SQL> alter pluggable database snapshot mode manual;
Pluggable database altered.
SQL> alter pluggable database snapshot;
Pluggable database altered.

手动创建快照，可以自己指定名字，也可以使用系统自动生成的名字。通过查看DBA_PDB_SNAPSHOTS视图，可以找到快照存放的路径及创建快照的SCN号。

SQL> SELECT CON_ID, CON_NAME, SNAPSHOT_NAME, SNAPSHOT_SCN AS snap_scn, FULL_SNAPSHOT_PATH FROM DBA_PDB_SNAPSHOTS ORDER BY SNAP_SCN;
  CON_ID CON_NAME       SNAPSHOT_NAME        SNAP_SCN FULL_SNAPSHOT_PATH
---------- -------------------- ------------------------- ---------- ---------------------------------------------------------------------------
     3 ORCLPDB1       SNAP_2953839490_989014667  2821702 /opt/oracle/oradata/ORCLCDB/ORCLPDB1/snap_2953839490_2821702.pdb
     3 ORCLPDB1       PDB_SNAP           2823303 /opt/oracle/oradata/ORCLCDB/ORCLPDB1/snap_2953839490_2823303.pdb
     3 ORCLPDB1       SNAP_2953839490_989015970  2823679 /opt/oracle/oradata/ORCLCDB/ORCLPDB1/snap_2953839490_2823679.pdb
[oracle@oracle-18c-vagrant ORCLPDB1]$ ls -lsh
total 1.3G
4.0K drwxr-x---. 8 oracle oinstall 4.0K Oct 8 22:39 ORCLCDB
171M -rw-r--r--. 1 oracle oinstall 171M Oct 8 22:18 snap_2953839490_2821702.pdb
171M -rw-r--r--. 1 oracle oinstall 171M Oct 8 22:38 snap_2953839490_2823303.pdb
171M -rw-r--r--. 1 oracle oinstall 171M Oct 8 22:40 snap_2953839490_2823679.pdb
371M -rw-r-----. 1 oracle oinstall 371M Oct 8 22:39 sysaux01.dbf
271M -rw-r-----. 1 oracle oinstall 271M Oct 8 22:39 system01.dbf
 56K -rw-r-----. 1 oracle oinstall 63M Oct 1 23:21 temp01.dbf
101M -rw-r-----. 1 oracle oinstall 101M Oct 8 22:39 undotbs01.dbf
5.1M -rw-r-----. 1 oracle oinstall 5.1M Oct 8 22:39 users01.dbf

如果要删除快照，则有两种方法，第一种就是使用alter pluggable database删除，第二种是修改max_pdb_snapshots参数，当max_pdb_snapshots参数设置成0时，将删除全部快照。

SQL> alter pluggable database drop snapshot SNAP_2953839490_989015970;
Pluggable database altered.
SQL> SELECT CON_ID, CON_NAME, SNAPSHOT_NAME, SNAPSHOT_SCN AS snap_scn, SNAPSHOT_TIME, FULL_SNAPSHOT_PATH FROM DBA_PDB_SNAPSHOTS ORDER BY SNAP_SCN;
  CON_ID CON_NAME       SNAPSHOT_NAME        SNAP_SCN SNAPSHOT_TIME FULL_SNAPSHOT_PATH
---------- -------------------- ------------------------- ---------- ------------- ---------------------------------------------------------------------------
     3 ORCLPDB1       SNAP_2953839490_989014667  2821702  1539008272 /opt/oracle/oradata/ORCLCDB/ORCLPDB1/snap_2953839490_2821702.pdb
     3 ORCLPDB1       PDB_SNAP           2823303  1539009503 /opt/oracle/oradata/ORCLCDB/ORCLPDB1/snap_2953839490_2823303.pdb
SQL> alter pluggable database set max_pdb_snapshots=0;
Pluggable database altered.
SQL> SELECT CON_ID, CON_NAME, SNAPSHOT_NAME, SNAPSHOT_SCN AS snap_scn, SNAPSHOT_TIME, FULL_SNAPSHOT_PATH FROM DBA_PDB_SNAPSHOTS ORDER BY SNAP_SCN;
no rows selected

演示了上述功能之后，还有一个功能，就是我们可以根据快照创建pdb。

SQL> alter pluggable database set max_pdb_snapshots=8;
Pluggable database altered
SQL> alter pluggable database snapshot pdb_snap;
Pluggable database altered.
SQL> SELECT CON_ID, CON_NAME, SNAPSHOT_NAME, SNAPSHOT_SCN AS snap_scn, SNAPSHOT_TIME, FULL_SNAPSHOT_PATH FROM DBA_PDB_SNAPSHOTS ORDER BY SNAP_SCN;
  CON_ID CON_NAME       SNAPSHOT_NAME        SNAP_SCN SNAPSHOT_TIME FULL_SNAPSHOT_PATH
---------- -------------------- ------------------------- ---------- ------------- ---------------------------------------------------------------------------
     3 ORCLPDB1       PDB_SNAP           2825283  1539010328 /opt/oracle/oradata/ORCLCDB/ORCLPDB1/snap_2953839490_2825283.pdb
SQL> !
[oracle@oracle-18c-vagrant ~]$ mkdir -p /opt/oracle/oradata/ORCLCDB/ORCLPDB2
SQL> create pluggable database ORCLPDB2 from ORCLPDB1 using snapshot PDB_SNAP create_file_dest='/opt/oracle/oradata/ORCLCDB/ORCLPDB2'; 
create pluggable database ORCLPDB2 from ORCLPDB1 using snapshot PDB_SNAP create_file_dest='/opt/oracle/oradata/ORCLCDB/ORCLPDB2'
*
ERROR at line 1:
ORA-65040: operation not allowed from within a pluggable database    
SQL> alter session set container=CDB$ROOT;
Session altered.
SQL> create pluggable database ORCLPDB2 from ORCLPDB1 using snapshot PDB_SNAP create_file_dest='/opt/oracle/oradata/ORCLCDB/ORCLPDB2'; 
Pluggable database created.
SQL> show pdbs;
  CON_ID CON_NAME            OPEN MODE RESTRICTED
---------- ------------------------------ ---------- ----------
     2 PDB$SEED            READ ONLY NO
     3 ORCLPDB1            READ WRITE NO
     5 ORCLPDB2            MOUNTED
SQL> alter pluggable database ORCLPDB2 open; 
Pluggable database altered.

这样我们就根据快照创建了一个新的PDB，假设当前PDB出现了数据覆盖，我们就可以使用这个历史快照的PDB来恢复数据。

当然还有一个很好用的功能就是我们在创建pdb的过程中把他设置成15分钟产生一个快照。当然配置这个功能有一个先决条件：CDB必须处于本地undo模式.

SQL> create pluggable database ORCLPDB3 from ORCLPDB1 file_name_convert=('ORCLPDB1','ORCLPDB3') snapshot mode every 5 minutes;
Pluggable database created.

可以看到每隔5分钟自动创建一个快照

[oracle@oracle-18c-vagrant ORCLPDB3]$ ls -lrt snap*
-rw-r--r--. 1 oracle oinstall 179134736 Oct 8 23:13 snap_2091710291_2830531.pdb
-rw-r--r--. 1 oracle oinstall 179167158 Oct 8 23:18 snap_2091710291_2832545.pdb
-rw-r--r--. 1 oracle oinstall 179285979 Oct 8 23:23 snap_2091710291_2833104.pdb
-rw-r--r--. 1 oracle oinstall 179284365 Oct 8 23:28 snap_2091710291_2833687.pdb
-rw-r--r--. 1 oracle oinstall 179302205 Oct 8 23:33 snap_2091710291_2834965.pdb
-rw-r--r--. 1 oracle oinstall 179315484 Oct 8 23:38 snap_2091710291_2836695.pdb
-rw-r--r--. 1 oracle oinstall 115724288 Oct 8 23:43 snap_2091710291_2837222.pdb

我们可以做个实验测试一下。在生成快照之前创建一个表插入点数据，这里上一次快照是23:43分。

SQL> alter session set container=ORCLPDB3;
Session altered.
SQL> create table a1 as select * from dba_objects;
Table created.
SQL> select count(1) from a1;
 COUNT(1)
----------
   72897
[oracle@oracle-18c-vagrant ORCLPDB3]$ ls -lrt snap*
-rw-r--r--. 1 oracle oinstall 179134736 Oct 8 23:13 snap_2091710291_2830531.pdb
-rw-r--r--. 1 oracle oinstall 179167158 Oct 8 23:18 snap_2091710291_2832545.pdb
-rw-r--r--. 1 oracle oinstall 179285979 Oct 8 23:23 snap_2091710291_2833104.pdb
-rw-r--r--. 1 oracle oinstall 179284365 Oct 8 23:28 snap_2091710291_2833687.pdb
-rw-r--r--. 1 oracle oinstall 179302205 Oct 8 23:33 snap_2091710291_2834965.pdb
-rw-r--r--. 1 oracle oinstall 179315484 Oct 8 23:38 snap_2091710291_2836695.pdb
-rw-r--r--. 1 oracle oinstall 179353508 Oct 8 23:43 snap_2091710291_2837222.pdb
-rw-r--r--. 1 oracle oinstall  5767168 Oct 8 23:48 snap_2091710291_2839217.pdb
SQL> SELECT CON_ID, CON_NAME, SNAPSHOT_NAME, SNAPSHOT_SCN AS snap_scn, SNAPSHOT_TIME, FULL_SNAPSHOT_PATH FROM DBA_PDB_SNAPSHOTS ORDER BY SNAP_SCN;
  CON_ID CON_NAME       SNAPSHOT_NAME        SNAP_SCN SNAPSHOT_TIME FULL_SNAPSHOT_PATH
---------- -------------------- ------------------------- ---------- ------------- ---------------------------------------------------------------------------
     7 ORCLPDB3       SNAP_2091710291_989017984  2830531  1539011592 /opt/oracle/oradata/ORCLCDB/ORCLPDB3/snap_2091710291_2830531.pdb
     7 ORCLPDB3       SNAP_2091710291_989018284  2832545  1539011887 /opt/oracle/oradata/ORCLCDB/ORCLPDB3/snap_2091710291_2832545.pdb
     7 ORCLPDB3       SNAP_2091710291_989018584  2833104  1539012188 /opt/oracle/oradata/ORCLCDB/ORCLPDB3/snap_2091710291_2833104.pdb
     7 ORCLPDB3       SNAP_2091710291_989018884  2833687  1539012489 /opt/oracle/oradata/ORCLCDB/ORCLPDB3/snap_2091710291_2833687.pdb
     7 ORCLPDB3       SNAP_2091710291_989019184  2834965  1539012787 /opt/oracle/oradata/ORCLCDB/ORCLPDB3/snap_2091710291_2834965.pdb
     7 ORCLPDB3       SNAP_2091710291_989019484  2836695  1539013087 /opt/oracle/oradata/ORCLCDB/ORCLPDB3/snap_2091710291_2836695.pdb
     7 ORCLPDB3       SNAP_2091710291_989019784  2837222  1539013386 /opt/oracle/oradata/ORCLCDB/ORCLPDB3/snap_2091710291_2837222.pdb
     7 ORCLPDB3       SNAP_2091710291_989020084  2839217  1539013686 /opt/oracle/oradata/ORCLCDB/ORCLPDB3/snap_2091710291_2839217.pdb

23点48分产生了新的快照，此时我们使用新的快照做一个克隆，登陆到ORCLPDB4数据库后，我们会发现是有数据的。

SQL> alter session set container=CDB$ROOT;
Session altered.
SQL> create pluggable database ORCLPDB4 from ORCLPDB3 using snapshot SNAP_2091710291_989020084 create_file_dest='/opt/oracle/oradata/ORCLCDB/ORCLPDB4';
Pluggable database created
SQL> alter pluggable database ORCLPDB4 open;
Pluggable database altered.
SQL> alter session set container=ORCLPDB4;
Session altered.
SQL> select count(1) from a1;
 COUNT(1)
----------
   72897

这个功能对于测试人员非常有用，例如移动电信现在有BCV环境，专门用于经分抽数及测试，而这个BCV环境是底层同步的一个克隆。使用18c数据库，我们就可以直接创建快照，然后使用快照克隆一个新数据库形成BCV环境给经分抽数及测试使用了。

以上所述是小编给大家介绍的Oracle 18c新特性-PDB快照轮播（Snapshot Carousel），希望对大家有所帮助，如果大家有任何疑问请给我留言，小编会及时回复大家的。在此也非常感谢大家对脚本之家网站的支持！

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