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

版权声明:本文为Buddy Yuan原创文章,未经允许不得转载。原文地址:Oracle 18c新特性-PDB快照轮播(Snapshot Carousel)
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,
  2      PROPERTY_VALUE AS value, DESCRIPTION
  3      FROM   CDB_PROPERTIES r, CDB_PDBS p
  4      WHERE  r.CON_ID = p.CON_ID
  5      AND    PROPERTY_NAME LIKE 'MAX_PDB%'
  6      AND    description like 'maximum%'
  7      ORDER BY PROPERTY_NAME;

    CON_ID PDB_NAME             PROPERTY_NAME        VALUE                DESCRIPTION
---------- -------------------- -------------------- -------------------- ----------------------------------------------------------------------
         3 ORCLPDB1             MAX_PDB_SNAPSHOTS    8                    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。

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