Oracle 18C新特性之PDB snapshot Carousel--PDB快照輪播
Oracle 18C新特性之PDB snapshot Carousel(快照輪播)
| 關於PDB快照 Carousel面試
Oracle18c新特新 pdb snapshot Carousel（ PDB快照輪播（Snapshot Carousel） ）提供了在pdb級別下手工或者自動生成快照的功能，爲開發測試用例提供了便捷。CDB爲local undo和歸檔模式下，指定MAX_PDB_SNAPSHOTS控制pdb最多生成快照的數量，當快照超過最大數量時，會覆蓋最舊的快照。sql
在Oracle 18c數據庫中，建立PDB時能夠同時爲PDB建立快照，完整的保存快照建立時間點的PDB數據。PDB快照主要有兩個做用：數據庫
經過閃回恢復數據到快照時間點網絡
使用快照PDB查詢歷史數據session
每一個PDB快照都會關聯一個快照名稱，能夠在建立時定義也能夠由系統自動生成。同時，每一個快照也會關聯建立時的時間戳和SCN。每一個PDB容許保存的最大PDB快照數量由MAX_PDB_SNAPSHOTS屬性控制，最大和默認值均爲8。當建立的PDB快照數量超過定義時，最早建立的PDB快照將會被刪除。使用alter database命令能夠修改最大容許的PDB快照數量，若是將限制設爲0，則會刪除全部的PDB快照。oracle
以下圖：pdb1_prod爲生產PDB,而後建立refresh PDB pdb1_test_master，讓refreshPDB pdb1_test_master天天生成快照。當你須要測試用例時，那麼你能夠指定snapshot建立PDB。app
一個通用的策略是天天在同一時間生成PDB快照。另外一種策略是在數據加載以前手動抓取快照。在這兩種狀況下，均可以從snapshot Carousel中使用任何可用的快照恢復PDB。less
1. PDB快照Carousel是如何工做的
數據庫按需或自動建立carousel中的連續副本。當達到快照限制時，數據庫將覆蓋舊的快照。PDB快照的文件存放在文件系統上的物理文件。其不包含數據庫歸檔文件archive log。默認存放在PDB的數據文件相同的目錄中。系統自動生成的snapshot以snap_開始，惟一標示結尾的命名規則，包含了快照當前的SCN，而且擴展名爲.PDB。ide
相關視圖：MAX_PDB_SNAPSHOTS、DBA_PDB_SNAPSHOTS、DBA_PDBS
PDB建立時默認開始快照功能，能夠經過兩種方式對PDB快照進行定義：
1. 手工方式
建立或修改PDB是指定snapshot mode manual字句，這是PDB建立時的默認行爲
create pluggable database pdb1 snapshot mode manual;
2. 定義一個自動建立的時間週期
alter pluggable database pdb1 snapshot mode every 24 hours;
當時間量以分鐘表示時，指定值必須小於3000；當時間量以小時表示時，指定值不能超過2000。
PDB快照建立完成後，能夠利用其建立新的PDB。使用的PDB快照可經過快照名稱、快照SCN或者快照時間戳來指定。
create pluggable database pdb1_day_1 from pdb1 using snapshot <snapshot_name>;
create pluggable database pdb1_day_2 from pdb1 using snapshot at scn <snapshot_SCN>;
在出現用戶錯誤或其餘極端狀況時，PDB快照還可用於對PDB的閃回。實施步驟以下：
關閉PDB1
從指定PDB快照建立新的PDB
刪除PDB1
重命名新的PDB爲PDB1
打開PDB1
| 設置PDB快照的最大數量
使用MAX_PDB_SNAPSHOTS參數設置PDB快照最大快照數，首先登陸到須要設置的PDB中，經過視圖CDB_PROPERTIES查詢當前MAX_PDB_SNAPSHOT值，可使用alter pluggabledatabase/alter database更改MAX_PDB_SNAPSHOTS值。
以下爲設置PDB snapshot的例子
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下面語句將當前pdb的快照數設置爲7
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想要刪除全部的快照，咱們只須要執行下面一條命令便可。
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| 配置自動生成PDB快照
默認狀況下都是手動生成快照，使用SNAPSHOT MODE EVERY子句自動產生PDB快照。
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更改自動建立模式爲每24小時自動生成PDB快照
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下面是每2小時生成快照的例子
首先登陸到CDB根目錄。如下語句從名爲cdb1_pdb1的現有PDB建立cdb1_pdb3，並將其配置爲每2小時自動獲取快照：
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| 手工建立PDB快照
使用ALTER PLUGGABLE DATABASE/CREATE PLUGGABLE DATABASE手動生成快照。使用ALTER PLUGGABLE DATABASE SNAPSHOT語句須要知足的要求。
CDB必須是LOCAL UNDO模式
用戶必須有權限建立和刪除PDB
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下面查詢出當前PDB的快照
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若是你不指定快照名，系統自動生成惟一名稱的快照，下面即爲不指定名字建立快照
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| 刪除PDB快照
將MAX_PDB_SNAPSHOTS設置爲0，即刪除全部PDB快照，同時也關閉此功能。一樣也可使用ALTER PLUGGABLE DATABASE刪除當前的快照。
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| 從snapshot建立PDB
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| 基於SCN或時間點生產快照庫
在閱讀官方文檔時，看到生成PDB能夠基於SCN，我心中不由暗喜，當再仔細查閱一番則否則，簡直萬念俱寂、黯然銷魂。提供的基於SCN生成的快照庫只能是基於當前生成快照時間點的SCN，彷佛有些雞肋。
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與recover database until scn指定scn方式打開數據庫不一樣，pdb snapshot Carousel指定scn生成的PDB只能是建立snapshot時的固定scn，而且生成快照與snapshot生成pdb的過程當中佔據了大量的物理空間與IO資源。
那麼問題來了,說了這麼多關於PDB snapshot Carousel的優點與好處,是否就說明已經找到了最佳的解決方案呢?
Hold on.
凡事有利也有弊,一樣PDB snapshot Carousel也不能倖免。
快照數量受限
雖然可以作到Carousel輪轉,但畢竟數量有限,較爲死板。在用戶的實際測試環境中條件複雜多變,會限制測試環境的搭建.
佔據大量物理空間與IO資源
對於當前用戶動輒幾十T的數據量，在生成snapshot與snapshot建立pdb的過程當中，消耗的時間和佔據的物理資源是巨大的。
拘泥固定時間點
對於PDBsnapshot Carouse而言,只能基於固定時間，即快照點建立，沒法根據測試須要靈活指定時間點。面對不斷變化的測試需求，如此死板的模式明顯是不可能知足要求的。
版本受限
最後是客觀條件的限制,利用新特性須要知足是在18C的環境下且啓用了PDB功能,但目前不少用戶依然是10G\11G\12C的環境,所以也僅僅只能遠觀而沒法上手,對於實際工做很難產生推進做用。
說到這,是否還有更好的解決辦法呢?
答案是必須有!
16 Administering a PDB Snapshot Carousel
您能夠爲指定的PDB配置一個PDB快照庫，手動或自動建立快照，並設置快照的最大數量。
This section contains the following topics:
- About PDB Snapshot Carousel
A PDB snapshot is a point-in-time copy of a PDB. You can create snapshots manually using theSNAPSHOTclause ofCREATE PLUGGABLE DATABASE(orALTER PLUGGABLE DATABASE), or automatically using theEVERY intervalclause. A PDB snapshot carousel is a library of snapshots. - Setting the Maximum Number of Snapshots in a PDB Snapshot Carousel
You can set the maximum number of PDB snapshots for a PDB. - Configuring Automatic PDB Snapshots
Configure a PDB for automatic snapshots by using theSNAPSHOT MODE EVERYclause when creating or altering a PDB. - Creating PDB Snapshots Manually
To create a PDB snapshot manually, specify theSNAPSHOT snapshot_nameclause inALTER PLUGGABLE DATABASEorCREATE PLUGGABLE DATABASE. - Dropping a PDB Snapshot
You can drop a PDB snapshot by running anALTER PLUGGABLE DATABASEstatement with theDROP SNAPSHOTclause.
Parent topic: Administering a Multitenant Environment
16.1 About PDB Snapshot Carousel
PDB快照是PDB的時間點副本。您可使用create PLUGGABLE DATABASE(或ALTER PLUGGABLE DATABASE)的SNAPSHOT子句手動建立快照，也可使用each interval子句自動建立快照
. A PDB snapshot carousel 快照庫.
This section contains the following topics:
- Purpose of PDB Snapshot Carousel
A PDB snapshot carousel is a useful way of maintaining a library of recent PDB copies for point-in-time recovery and cloning. - How PDB Snapshot Carousel Works
The carousel for a specific PDB is a circular library of copies for this PDB. - User Interface for PDB Snapshot Carousel
TheSNAPSHOT MODEclause controls creation of snapshots, and determines whether creation is manual, automatic, or disabled.
Parent topic: Administering a PDB Snapshot Carousel
16.1.1 Purpose of PDB Snapshot Carousel
PDB快照庫是維護最近的PDB副本庫以便進行時間點恢復和克隆的一種有用方法。
克隆用於開發和測試的PDBs
在一個典型的開發用例中，您克隆一個產品PDB來進行測試。當CDB處於ARCHIVELOG模式和本地撤銷模式時，源生產PDB能夠以讀/寫模式打開，並在操做過程當中充分發揮功能。這種技術被稱爲熱克隆。當SCN完成時，熱克隆在事務上與源PDB一致of the ALTER PLUGGABLE DATABASE ... OPEN statement.
例如，當名爲pdb1_prod的生產PDB處於打開狀態並正在使用時，您將建立一個名爲pdb1_test_master的可刷新克隆。而後配置pdb1_test_master來天天建立自動快照。當您須要新的PDBs進行測試時，請建立任何快照的完整克隆，而後使用 CREATE PLUGGABLE DATABASE ... SNAPSHOT COPY .
下圖顯示了從4月5日拍攝的PDB快照建立的克隆pdb1_test_full1。圖中顯示了從pdb1_test_full1建立的三個PDBs快照副本。
Figure 16-1 Automatic Snapshots of a Refreshable Clone PDB
Description of "Figure 16-1 Automatic Snapshots of a Refreshable Clone PDB"
使用PDB快照庫進行時間點恢復
典型的策略是天天在同一時間對PDB進行快照。另外一種策略是在數據加載以前手動進行快照。在這兩種狀況下，PDB快照庫都容許您使用任何可用快照恢復PDB。
例如，名爲pdb1_prod的銷售歷史記錄PDB天天在12:01生成一個自動快照。在4/9週一下午的daily data load中，您意外加載了錯誤的數據，損壞了PDB。您能夠基於Monday 4/9快照建立一個新的生產PDB，刪除損壞的PDB，而後重試數據加載。
Figure 16-2 Restore a Production PDB Using a Snapshot
Description of "Figure 16-2 Restore a Production PDB Using a Snapshot"
See Also:
Oracle Database SQL Language Reference for
CREATE PLUGGABLE DATABASEsyntax and semantics
Parent topic: About PDB Snapshot Carousel
16.1.2 How PDB Snapshot Carousel Works
The carousel 對於特定的PDB，是該PDB的一個循環複製庫。
數據庫根據須要或自動地在庫中建立連續的副本。當達到快照限制時，數據庫將重寫最舊的快照。
This section includes the following topics:
- Contents of a PDB Snapshot
The data files of the PDB snapshot reside in an archive file on the file system. - Contents of a PDB Snapshot Carousel
The PDB snapshot carousel is the set of all existing snapshots for a PDB.
Parent topic: About PDB Snapshot Carousel
16.1.2.1 Contents of a PDB Snapshot
PDB快照的數據文件駐留在文件系統上的歸檔文件中。
不包括存檔的重作日誌文件。一般，歸檔文件存儲在與PDB的數據文件相同的目錄中。對於系統生成的快照名稱，snap_以唯一標識符爲前綴，該標識符包含快照SCN。該歸檔文件的擴展名是.pdb。
數據庫使用隱式的using snapshot子句獲取快照。在使用建立可插入數據庫快照獲取快照時，不能指定快照複製子句。
Note:
使用USING snapshot子句建立的PDB快照和使用snapshot copy子句建立的快照複製PDB是兩種不一樣類型的快照，它們不該該混淆。USING SNAPSHOT子句建立一個不須要物化的完整PDB。快照複製子句建立了一個稀疏的PDB，若是您想刪除它所基於的PDB快照，就必須將其物化。
雖然PDB快照carousel中的快照始終是完整的PDB，可是您能夠在carousel中獲取快照的快照副本。在這種狀況下，快照副本是一個稀疏克隆。
See Also:
" How a Snapshot Copy PDB Differs from a Standard Clone "
Parent topic: How PDB Snapshot Carousel Works
16.1.2.2 Contents of a PDB Snapshot Carousel
PDB快照庫是一個PDB的全部現有快照的集合。
max_pdb_snapshot屬性指定庫中容許的最大快照數量。當前設置在CDB_PROPERTIES視圖中是可見的。
下圖顯示了cdb1_pdb1的庫。在本例中，數據庫每24小時自動獲取一個快照，維護一組8個快照。建立了前8個快照以後，每一個新快照都會替換舊快照。例如，星期二4/10快照替換星期一4/2快照;星期三4/11快照取代星期二4/3快照;等等。
Figure 16-3 PDB Snapshot Carousel
Description of "Figure 16-3 PDB Snapshot Carousel"
Parent topic: How PDB Snapshot Carousel Works
16.1.3 User Interface for PDB Snapshot Carousel
The SNAPSHOT MODE clause controls creation of snapshots, and determines whether creation is manual, automatic, or disabled.
CREATE PLUGGABLE DATABASE Statement
要爲PDB設置快照模式，請在快照模式中使用如下值之一 clause of ALTER PLUGGABLE DATABASE or CREATE PLUGGABLE DATABASE :
MANUALThis clause, which is the default, enables the creation of manual snapshots of the PDB. To create a snapshot on demand, specify the
SNAPSHOT snapshot_nameclause in anALTER PLUGGABLE DATABASEorCREATE PLUGGABLE DATABASEstatement.EVERY snapshot_interval [MINUTES|HOURS]This clause enables the automatic creation of snapshots after an interval of time. The following restrictions apply to the interval specified:
The database assigns each automatic snapshot a system-generated name. Note that manual snapshots are also supported for the PDB when
EVERYis specified.The minutes value must be less than
3000.The hours value must be less than
2000.
NONEThis clause disables snapshot creation for the PDB.
See Also:
Oracle Database SQL Language Reference for the syntax and semantics of the
SNAPSHOTclause
MAX_PDB_SNAPSHOTS Database Property
要設置PDB的最大快照數量，請在ALTER PLUGGABLE DATABASE或CREATE PLUGGABLE DATABASE中指定max_pdb_snapshot屬性。屬性的默認值是8，這也是最大值。當建立了容許的最大快照數量時，數據庫將清除最舊的快照。CDB_PROPERTIES視圖顯示了max_pdb_snapshot的設置。
See Also:
Oracle Database SQL Language Reference for the syntax of the ALTER PLUGGABLE DATABASE statement
DBA_PDB_SNAPSHOTS and DBA_PDBS
The following data dictionary views provide snapshot information:
The
DBA_PDB_SNAPSHOTSview metadata about the snapshots, including name, creation SCN, creation time, and file name.The
DBA_PDBSview has aSNAPSHOT_MODEandSNAPSHOT_INTERVALcolumn.
See Also:
Oracle Database Reference to learn about DBA_PDB_SNAPSHOTS and DBA_PDBS
Parent topic: About PDB Snapshot Carousel
16.2 Setting the Maximum Number of Snapshots in a PDB Snapshot Carousel
You can set the maximum number of PDB snapshots for a PDB.
max_pdb_snapshot數據庫屬性設置PDB快照旋轉***中每一個PDB的最大快照數量。默認最大值是8。不能將屬性設置爲大於8的數字。
Prerequisites
The PDB must be open in read/write mode.
To set the maximum number of PDB snapshots for a PDB:
In SQL*Plus, ensure that the current container is the PDB for which you want to set the limit.
Optionally, query
CDB_PROPERTIESfor the current setting of theSET MAX_PDB_SNAPSHOTSproperty.Run an
ALTER PLUGGABLE DATABASEorALTER DATABASEstatement with theSET MAX_PDB_SNAPSHOTSclause.
Example 16-1 Setting the Maximum Number of PDB Snapshots for a PDB
The following query shows the maximum in the carousel for cdb1_pdb1 (sample output included):
SET LINESIZE 150COL CON_ID FORMAT 99999COL PROPERTY_NAME FORMAT a17COL PDB_NAME FORMAT a9COL VALUE FORMAT a3COL DESCRIPTION FORMAT a43SELECT r.CON_ID, p.PDB_NAME, PROPERTY_NAME,PROPERTY_VALUE AS value, DESCRIPTIONFROM CDB_PROPERTIES r, CDB_PDBS pWHERE r.CON_ID = p.CON_IDAND PROPERTY_NAME LIKE 'MAX_PDB%' ORDER BY PROPERTY_NAME;CON_ID PDB_NAME PROPERTY_NAME VAL DESCRIPTION------ --------- ----------------- --- -------------------------------------------3 CDB1_PDB1 MAX_PDB_SNAPSHOTS 8 maximum number of snapshots for a given PDB
The following SQL statement sets the maximum number of PDB snapshots for the current PDB to 7:
ALTER PLUGGABLE DATABASE SET MAX_PDB_SNAPSHOTS=7;
Example 16-2 Dropping All Snapshots in a PDB Snapshot Carousel
To drop all snapshots in a PDB snapshot carousel, set the MAX_PDB_SNAPSHOTS database property to (zero), as shown in the following statement:
ALTER PLUGGABLE DATABASE SET MAX_PDB_SNAPSHOTS=0;
This technique is faster than executing ALTER PLUGGABLE DATABASE ... DROP SNAPSHOTsnapshot_name for every snapshot.
See Also:
" About Container Access in a CDB "
Parent topic: Administering a PDB Snapshot Carousel
16.3 Configuring Automatic PDB Snapshots
在建立或更改PDB時，經過使用快照模式EVERY子句爲自動快照配置PDB。
默認狀況下，PDB是爲手動快照配置的。
Prerequisites
Note the following prerequisites for the ALTER PLUGGABLE DATABASE SNAPSHOT statement:
The CDB must be in local undo mode.
The administrator must have the privileges to create a PDB and drop a PDB.
To configure automatic snapshots when altering a PDB:
In SQL*Plus, log in as an administrator to the PDB whose snapshot mode you intend to configure.
Optionally, query
DBA_PDBSto determine the current snapshot mode.Run
ALTER PLUGGABLE DATABASEwith theSNAPSHOT MODE EVERY intervalclause, specifying eitherMINUTESorHOURS.
To configure automatic snapshots when creating a PDB:
In SQL*Plus, log in as an administrator to the CDB root or application root.
Optionally, query
DBA_PDBSto determine the current snapshot mode.Run
CREATE PLUGGABLE DATABASEwith theSNAPSHOT MODE EVERY intervalclause, specifying eitherMINUTESorHOURS.
Example 16-3 爲現有PDB天天配置一個自動快照
本例假設您已登陸到要更改其快照模式的PDB。查詢數據字典，確認PDB目前處於手動模式(包括示例輸出):
SELECT SNAPSHOT_MODE "S_MODE", SNAPSHOT_INTERVAL/60 "SNAP_INT_HRS" FROM DBA_PDBS;S_MODE SNAP_INT_HRS------ ------------MANUAL
Change the snapshot mode to every 24 hours:
ALTER PLUGGABLE DATABASE SNAPSHOT MODE EVERY 24 HOURS;
Confirm the change to automatic mode:
SELECT SNAPSHOT_MODE "S_MODE", SNAPSHOT_INTERVAL/60 "SNAP_INT_HRS" FROM DBA_PDBS;S_MODE SNAP_INT_HRS------ ------------AUTO 24
Example 16-4 Creating a PDB That Takes Snapshots Every Two Hours
This example assumes that you are logged in to the CDB root. The following statement creates cdb1_pdb3 from an existing PDB named cdb1_pdb1 , and configures it to take snapshots automatically every 2 hours:
CREATE PLUGGABLE DATABASE cdb1_pdb3 FROM cdb1_pdb1FILE_NAME_CONVERT=('cdb1_pdb1','cdb1_pdb3')SNAPSHOT MODE EVERY 120 MINUTES;
See Also:
Parent topic: Administering a PDB Snapshot Carousel
16.4 Creating PDB Snapshots Manually
To create a PDB snapshot manually, specify the SNAPSHOT snapshot_name clause in ALTER PLUGGABLE DATABASE or CREATE PLUGGABLE DATABASE .
Prerequisites
Note the following prerequisites for the ALTER PLUGGABLE DATABASE SNAPSHOT statement:
The CDB must be in local undo mode.
The administrator must have the privileges to create a PDB and drop a PDB.
To create a PDB snapshot:
In SQL*Plus, log in as an administrator to the PDB whose snapshot you intend to create.
Optionally, query
DBA_PDBSto confirm that the snapshot mode is not set toNONE.Run an
ALTER PLUGGABLE DATABASEstatement with theSNAPSHOTclause.
Example 16-5 Creating a Snapshot with a User-Specified Name
如下SQL語句建立兩個cdb1_pdb1的PDB快照，一個在週三數據加載以前，一個在週三數據加載以後:
ALTER PLUGGABLE DATABASE SNAPSHOT cdb1_pdb1_b4wedload;-- data loadALTER PLUGGABLE DATABASE SNAPSHOT cdb1_pdb1_afwedload;
The following query of DBA_PDB_SNAPSHOTS shows the locations of two snapshots of the PDB named cdb1_pdb1 (sample output included):
SET LINESIZE 150COL CON_NAME FORMAT a10COL SNAPSHOT_NAME FORMAT a20COL SNAP_SCN FORMAT 9999999COL FULL_SNAPSHOT_PATH FORMAT a45SELECT CON_ID, CON_NAME, SNAPSHOT_NAME,SNAPSHOT_SCN AS snap_scn, FULL_SNAPSHOT_PATHFROM DBA_PDB_SNAPSHOTSORDER BY SNAP_SCN;CON_ID CON_NAME SNAPSHOT_NAME SNAP_SCN FULL_SNAPSHOT_PATH------- ---------- -------------------- -------- ---------------------------------------------3 CDB1_PDB1 CDB1_PDB1_B4WEDLOAD 2962078 /disk1/oracle/dbs/snap_3489077498_2962078.pdb3 CDB1_PDB1 CDB1_PDB1_AFWEDLOAD 2962938 /disk1/oracle/dbs/snap_3489077498_2962938.pdb
If you do not specify a PDB snapshot name, then the database generates a unique name.
Example 16-6 建立具備系統指定名稱的快照
下面的SQL語句建立一個快照，但沒有指定名稱:
ALTER PLUGGABLE DATABASE SNAPSHOT;
The following sample query shows that the database assigned the snapshot a name prefixed with SNAP_ :
SET LINESIZE 150COL CON_NAME FORMAT a10COL SNAPSHOT_NAME FORMAT a25COL SNAP_SCN FORMAT 9999999COL FULL_SNAPSHOT_PATH FORMAT a45SELECT CON_ID, CON_NAME, SNAPSHOT_NAME,SNAPSHOT_SCN AS snap_scn, FULL_SNAPSHOT_PATHFROM DBA_PDB_SNAPSHOTSORDER BY SNAP_SCN;CON_ID CON_NAME SNAPSHOT_NAME SNAP_SCN FULL_SNAPSHOT_PATH------- ---------- ------------------------- -------- ---------------------------------------------3 CDB1_PDB1 CDB1_PDB1_B4WEDLOAD 2962078 /disk1/oracle/dbs/snap_3489077498_2962078.pdb3 CDB1_PDB1 CDB1_PDB1_AFWEDLOAD 2962938 /disk1/oracle/dbs/snap_3489077498_2962938.pdb3 CDB1_PDB1 SNAP_3489077498_960130367 2993525 /disk1/oracle/dbs/snap_3489077498_2993525.pdb
See Also:
Parent topic: Administering a PDB Snapshot Carousel
16.5 Dropping a PDB Snapshot
You can drop a PDB snapshot by running an ALTER PLUGGABLE DATABASE statement with the DROP SNAPSHOT clause.
To drop all PDB snapshots based on a PDB, set the MAX_PDB_SNAPSHOTS property in the PDB to (zero).
To drop a PDB snapshot:
In SQL*Plus, ensure that the current container is the PDB from which you created the PDB snapshot.
Run an
ALTER PLUGGABLE DATABASEstatement with theDROP SNAPSHOTclause.
Example 16-7 Dropping a PDB Snapshot
The following SQL statement drops a PDB snapshot named sales_snap :
ALTER PLUGGABLE DATABASE DROP SNAPSHOT sales_snap;
See Also:
" About Container Access in a CDB "
Parent topic: Administering a PDB Snapshot Carousel
ORACLE 18C新特性-PDB快照輪播（SNAPSHOT CAROUSEL）
版權聲明：本文爲Buddy Yuan原創文章，未經容許不得轉載。原文地址： Oracle 18c新特性-PDB快照輪播（Snapshot Carousel）
Oracle 18c推出的一個新功能就是PDB快照輪播，最多能夠建立8個pdb的快照，而這8個構成的一組快照就被稱做快照輪播。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同樣。PDB的快照主要做用是當出現了問題能夠閃回到快照的時間點，另外一個功能是基於快照來查詢歷史數據。
<span style="color:#444444"><span style="color:#222222">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 </span></span>
默認狀況下是手動建立快照，咱們能夠把它改爲自動建立。
<span style="color:#444444"><span style="color:#222222">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 </span></span>
要返回手動模式，輸入mode manual便可。
<span style="color:#444444"><span style="color:#222222">SQL> alter pluggable database snapshot mode manual; Pluggable database altered. SQL> alter pluggable database snapshot; Pluggable database altered. </span></span>
手動建立快照，能夠本身指定名字，也可使用系統自動生成的名字。經過查看DBA_PDB_SNAPSHOTS視圖，能夠找到快照存放的路徑及建立快照的SCN號。
<span style="color:#444444"><span style="color:#222222">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 </span></span>
若是要刪除快照，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參數，當max_pdb_snapshots參數設置成0時，將刪除所有快照。
<span style="color:#444444"><span style="color:#222222">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 </span></span>
演示了上述功能以後，還有一個功能，就是咱們能夠根據快照建立pdb。
<span style="color:#444444"><span style="color:#222222">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. </span></span>
這樣咱們就根據快照建立了一個新的PDB，假設當前PDB出現了數據覆蓋，咱們就可使用這個歷史快照的PDB來恢復數據。
固然還有一個很好用的功能就是咱們在建立pdb的過程當中把他設置成15分鐘產生一個快照。固然配置這個功能有一個先決條件：CDB必須處於本地undo模式.
<span style="color:#444444"><span style="color:#222222">SQL> create pluggable database ORCLPDB3 from ORCLPDB1 file_name_convert=('ORCLPDB1','ORCLPDB3') snapshot mode every 5 minutes;
Pluggable database created.
</span></span>
能夠看到每隔5分鐘自動建立一個快照
<span style="color:#444444"><span style="color:#222222">[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 </span></span>
咱們能夠作個實驗測試一下。在生成快照以前建立一個表插入點數據，這裏上一次快照是23:43分。
<span style="color:#444444"><span style="color:#222222">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 </span></span>
23點48分產生了新的快照，此時咱們使用新的快照作一個克隆，登錄到ORCLPDB4數據庫後，咱們會發現是有數據的。
<span style="color:#444444"><span style="color:#222222">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 </span></span>
這個功能對於測試人員很是有用，例如移動電信如今有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數據庫，咱們就能夠直接建立快照，而後使用快照克隆一個新數據庫造成BCV環境給經分抽數及測試使用了。
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........................................................................................................................ ● 本文做者：小麥苗，部份內容整理自網絡，如有侵權請聯繫小麥苗刪除 ● 本文在itpub、博客園、CSDN和我的微 信公衆號（ xiaomaimiaolhr ）上有同步更新 ● 本文itpub地址： http://blog.itpub.net/26736162 ● 本文博客園地址： http://www.cnblogs.com/lhrbest ● 本文CSDN地址： https://blog.csdn.net/lihuarongaini ● 本文pdf版、我的簡介及小麥苗雲盤地址： http://blog.itpub.net/26736162/viewspace-1624453/ ● 數據庫筆試面試題庫及解答： http://blog.itpub.net/26736162/viewspace-2134706/ ● DBA寶典今日頭條號地址： http://www.toutiao.com/c/user/6401772890/#mid=1564638659405826 ........................................................................................................................ ● QQ羣號： 230161599 （滿） 、618766405 ● 微 信羣：可加我微 信，我拉你們進羣，非誠勿擾 ● 聯繫我請加QQ好友 （ 646634621 ） ，註明添加原因 ● 於 2019-08-01 06:00 ~ 2019-08-31 24:00 在西安完成 ● 最新修改時間：2019-08-01 06:00 ~ 2019-08-31 24:00 ● 文章內容來源於小麥苗的學習筆記，部分整理自網絡，如有侵權或不當之處還請諒解 ● 版權全部，歡迎分享本文，轉載請保留出處 ........................................................................................................................ ● 小麥苗的微店 ： https://weidian.com/s/793741433?wfr=c&ifr=shopdetail ● 小麥苗出版的數據庫類叢書 ： http://blog.itpub.net/26736162/viewspace-2142121/ ● 小麥苗OCP、OCM、高可用網絡班 ： http://blog.itpub.net/26736162/viewspace-2148098/ ● 小麥苗騰訊課堂主頁 ： https://lhr.ke.qq.com/ ........................................................................................................................ 使用 微 信客戶端 掃描下面的二維碼來關注小麥苗的微 信公衆號（ xiaomaimiaolhr ）及QQ羣（DBA寶典）、添加小麥苗微 信， 學習最實用的數據庫技術。
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- 1. Oracle 18C新特性之PDB snapshot Carousel--PDB快照輪播
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- 5. Oracle12C新特性——cdb與pdb
- 6. ORACLE 12C新特性——CDB與PDB
- 7. Oracle 12.2 新特性: Online PDB relocate (PDB hot move)
- 8. Oracle Database 18c new features 之10大新特性一覽
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- 1. Oracle 18C新特性之PDB snapshot Carousel--PDB快照輪播
- 2. Oracle 18c十大新特性
- 3. 【傳智播客】Oracle 18C新特性介紹
- 4. Oracle 18c新特性詳解-多租戶專題
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- 7. Oracle 12.2 新特性: Online PDB relocate (PDB hot move)
- 8. Oracle Database 18c new features 之10大新特性一覽
- 9. 專家視角 | 小荷的 Oracle Database 18c 新特性快速一瞥
- 10. Oracle 18c創建PDB的幾種方式