Oracle 18c新特性-PDB快照輪播(Snapshot Carousel)
阿新 • • 發佈：2020-01-09
Oracle 18c推出的一個新功能就是PDB快照輪播，最多可以建立8個pdb的快照，而這8個構成的一組快照就被稱作快照輪播。當達到第8個快照限制時，新的快照就會覆蓋最舊的快照，就像redo log一樣。PDB的快照主要作用是當出現了問題可以閃回到快照的時間點，另一個功能是基於快照來查詢歷史資料。
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預設情況下是手動建立快照，我們可以把它改成自動建立。
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
要返回手動模式，輸入mode manual即可。
SQL> alter pluggable database snapshot mode manual; Pluggable database altered. SQL> alter pluggable database snapshot; Pluggable database altered.
手動建立快照，可以自己指定名字，也可以使用系統自動生成的名字。通過檢視DBA_PDB_SNAPSHOTS檢視，可以找到快照存放的路徑及建立快照的SCN號。
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如果要刪除快照，則有兩種方法，第一種就是使用alter pluggable database刪除，第二種是修改max_pdb_snapshots引數，當max_pdb_snapshots引數設定成0時，將刪除全部快照。
SQL> alter pluggable database drop snapshot SNAP_2953839490_989015970;
Pluggable database altered.
SQL> SELECT CON_ID,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,FULL_SNAPSHOT_PATH FROM DBA_PDB_SNAPSHOTS ORDER BY SNAP_SCN;
no rows selected
演示了上述功能之後，還有一個功能，就是我們可以根據快照建立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,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.
這樣我們就根據快照建立了一個新的PDB，假設當前PDB出現了資料覆蓋，我們就可以使用這個歷史快照的PDB來恢復資料。
當然還有一個很好用的功能就是我們在建立pdb的過程中把他設定成15分鐘產生一個快照。當然配置這個功能有一個先決條件：CDB必須處於本地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分鐘自動建立一個快照
[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
我們可以做個實驗測試一下。在生成快照之前建立一個表插入點資料，這裡上一次快照是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,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點48分產生了新的快照，此時我們使用新的快照做一個克隆，登陸到ORCLPDB4資料庫後，我們會發現是有資料的。
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
這個功能對於測試人員非常有用，例如移動電信現在有BCV環境，專門用於經分抽數及測試，而這個BCV環境是底層同步的一個克隆。使用18c資料庫，我們就可以直接建立快照，然後使用快照克隆一個新資料庫形成BCV環境給經分抽數及測試使用了。
總結
以上所述是小編給大家介紹的Oracle 18c新特性-PDB快照輪播（Snapshot Carousel），希望對大家有所幫助，如果大家有任何疑問請給我留言，小編會及時回覆大家的。在此也非常感謝大家對我們網站的支援！