Oracle 18C新特性之PDB snapshot Carousel--PDB快照轮播

时间 2021-04-16

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Oracle 18C新特性之PDB snapshot Carousel(快照轮播)

| 关于PDB快照 Carousel数据库

Oracle18c新特新 pdb snapshot Carousel（ PDB快照轮播（Snapshot Carousel））提供了在pdb级别下手工或者自动生成快照的功能，为开发测试用例提供了便捷。CDB为local undo和归档模式下，指定MAX_PDB_SNAPSHOTS控制pdb最多生成快照的数量，当快照超过最大数量时，会覆盖最旧的快照。session

在Oracle 18c数据库中，建立PDB时能够同时为PDB建立快照，完整的保存快照建立时间点的PDB数据。PDB快照主要有两个做用：oracle

经过闪回恢复数据到快照时间点app

使用快照PDB查询历史数据less

每一个PDB快照都会关联一个快照名称，能够在建立时定义也能够由系统自动生成。同时，每一个快照也会关联建立时的时间戳和SCN。每一个PDB容许保存的最大PDB快照数量由MAX_PDB_SNAPSHOTS属性控制，最大和默认值均为8。当建立的PDB快照数量超过定义时，最早建立的PDB快照将会被删除。使用alter database命令能够修改最大容许的PDB快照数量，若是将限制设为0，则会删除全部的PDB快照。ide

以下图：pdb1_prod为生产PDB,而后建立refresh PDB pdb1_test_master，让refreshPDB pdb1_test_master天天生成快照。当你须要测试用例时，那么你能够指定snapshot建立PDB。测试

一个通用的策略是天天在同一时间生成PDB快照。另外一种策略是在数据加载以前手动抓取快照。在这两种状况下，均可以从snapshot Carousel中使用任何可用的快照恢复PDB。ui

1. PDB快照Carousel是如何工做的

数据库按需或自动建立carousel中的连续副本。当达到快照限制时，数据库将覆盖旧的快照。PDB快照的文件存放在文件系统上的物理文件。其不包含数据库归档文件archive log。默认存放在PDB的数据文件相同的目录中。系统自动生成的snapshot以snap_开始，惟一标示结尾的命名规则，包含了快照当前的SCN，而且扩展名为.PDB。this

相关视图：MAX_PDB_SNAPSHOTS、DBA_PDB_SNAPSHOTS、DBA_PDBSspa

PDB建立时默认开始快照功能，能够经过两种方式对PDB快照进行定义：

1. 手工方式

建立或修改PDB是指定snapshot mode manual字句，这是PDB建立时的默认行为

create pluggable database pdb1 snapshot mode manual;

2. 定义一个自动建立的时间周期

alter pluggable database pdb1 snapshot mode every 24 hours;

当时间量以分钟表示时，指定值必须小于3000；当时间量以小时表示时，指定值不能超过2000。

PDB快照建立完成后，能够利用其建立新的PDB。使用的PDB快照可经过快照名称、快照SCN或者快照时间戳来指定。

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>;

在出现用户错误或其余极端状况时，PDB快照还可用于对PDB的闪回。实施步骤以下：

关闭PDB1
从指定PDB快照建立新的PDB
删除PDB1
重命名新的PDB为PDB1
打开PDB1

| 设置PDB快照的最大数量

使用MAX_PDB_SNAPSHOTS参数设置PDB快照最大快照数，首先登陆到须要设置的PDB中，经过视图CDB_PROPERTIES查询当前MAX_PDB_SNAPSHOT值，可使用alter pluggabledatabase/alter database更改MAX_PDB_SNAPSHOTS值。

以下为设置PDB snapshot的例子

SET LINESIZE 1500

COL CON_ID FORMAT 99999

COL PROPERTY_NAME FORMAT a17

COL PDB_NAME FORMAT a9

COL VALUE FORMAT a12

COL DESCRIPTION FORMAT a90

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%'

ORDER BY PROPERTY_NAME;

CON_ID PDB_NAME PROPERTY_NAME VALUE DESCRIPTION

----- --------- ----------------- --------- ---------------------------------------------------------------

3 ORCLPDB MAX_PDB_SNAPSHOTS 7 maximum number of snapshots for a given PDB

3 ORCLPDB MAX_PDB_STORAGE UNLIMITED Maximum Space Usage of Datafiles and Local Tempfiles in Container

下面语句将当前pdb的快照数设置为7

进入PDB

YAO.CHONG> alter session set container = ORCLPDB;

Session altered.

Elapsed: 00:00:00.01

YAO.CHONG> ALTER PLUGGABLE DATABASE SET MAX_PDB_SNAPSHOTS=7;

Pluggable database altered.

想要删除全部的快照，咱们只须要执行下面一条命令便可。

ALTER PLUGGABLE DATABASE SET MAX_PDB_SNAPSHOTS=0;

SET LINESIZE 150

COL CON_NAME FORMAT a10

COL SNAPSHOT_NAME FORMAT a25

COL SNAP_SCN FORMAT 9999999

COL FULL_SNAPSHOT_PATH FORMAT a45

SELECT CON_ID,CON_NAME,SNAPSHOT_NAME,SNAPSHOT_SCN AS snap_scn, FULL_SNAPSHOT_PATH

FROM DBA_PDB_SNAPSHOTS

ORDER BY SNAP_SCN;

##都没了

| 配置自动生成PDB快照

默认状况下都是手动生成快照，使用SNAPSHOT MODE EVERY子句自动产生PDB快照。

SELECT SNAPSHOT_MODE "S_MODE" , SNAPSHOT_INTERVAL/60 "SNAP_INT_HRS" FROM DBA_PDBS;

S_MODE SNAP_INT_HRS

------ ------------

MANUAL

更改自动建立模式为每24小时自动生成PDB快照

进入PDB里面去执行

YAO.CHONG > alter session set container = ORCLPDB;

Session altered.

Elapsed: 00:00:00.01

YAO.CHONG> ALTER PLUGGABLE DATABASE SNAPSHOT MODE EVERY 24 HOURS;

Pluggable database altered.

Elapsed: 00:00:00.17

#确认自动生成快照的时间间隔

SELECT SNAPSHOT_MODE "S_MODE" , SNAPSHOT_INTERVAL/60 "SNAP_INT_HRS" FROM DBA_PDBS;

S_MODE SNAP_INT_HRS

------ ------------

AUTO 24

下面是每2小时生成快照的例子

首先登陆到CDB根目录。如下语句从名为cdb1_pdb1的现有PDB建立cdb1_pdb3，并将其配置为每2小时自动获取快照：

CREATE PLUGGABLE DATABASE cdb1_pdb3 FROM cdb1_pdb1

FILE_NAME_CONVERT=( 'cdb1_pdb1' , 'cdb1_pdb3' )

SNAPSHOT MODE EVERY 120 MINUTES;

| 手工建立PDB快照

使用ALTER PLUGGABLE DATABASE/CREATE PLUGGABLE DATABASE手动生成快照。使用ALTER PLUGGABLE DATABASE SNAPSHOT语句须要知足的要求。

CDB必须是LOCAL UNDO模式
用户必须有权限建立和删除PDB

YAO.CHONG> ALTER PLUGGABLE DATABASE SNAPSHOT test_snapshot;

Pluggable database altered.

Elapsed: 00:03:15.66/快照大小481M，3分钟，

下面查询出当前PDB的快照

SET LINESIZE 150

COL CON_NAME FORMAT a10

COL SNAPSHOT_NAME FORMAT a30

COL SNAP_SCN FORMAT 9999999

COL FULL_SNAPSHOT_PATH FORMAT a70

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 CDB1_PDB1 CDB1_PDB1_B4WEDLOAD 2962078 /disk1/oracle/dbs/snap_3489077498_2962078.pdb

3 CDB1_PDB1 CDB1_PDB1_AFWEDLOAD 2962938 /disk1/oracle/dbs/snap_3489077498_2962938.pdb

若是你不指定快照名，系统自动生成惟一名称的快照，下面即为不指定名字建立快照

ALTER PLUGGABLE DATABASE SNAPSHOT;

SET LINESIZE 150

COL CON_NAME FORMAT a10

COL SNAPSHOT_NAME FORMAT a25

COL SNAP_SCN FORMAT 9999999

COL FULL_SNAPSHOT_PATH FORMAT a45

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 ORCLPDB SNAP_3034367141_987737800 2995234 /home/oradata/ORCL/orclpdb/snap_3034367141_2995234.pdb

| 删除PDB快照

将MAX_PDB_SNAPSHOTS设置为0，即删除全部PDB快照，同时也关闭此功能。一样也可使用ALTER PLUGGABLE DATABASE删除当前的快照。

SET LINESIZE 150

COL CON_NAME FORMAT a10

COL SNAPSHOT_NAME FORMAT a25

COL SNAP_SCN FORMAT 9999999

COL FULL_SNAPSHOT_PATH FORMAT a45

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 ORCLPDB CDB_CNDBA_20180813151200 2970060 /home/oradata/ORCL/orclpdb/snap_3034367141_2970060.pdb

3 ORCLPDB SNAP_3034367141_987737800 2995234 /home/oradata/ORCL/orclpdb/snap_3034367141_2995234.pdb

ALTER PLUGGABLE DATABASE DROP SNAPSHOT CDB_CNDBA_20180813151200;

再次查询PDB快照已经被删除

CON_ID CON_NAME SNAPSHOT_NAME SNAP_SCN FULL_SNAPSHOT_PATH

---------- ---------- ------------------------- -------- ---------------------------------------------------

3 ORCLPDB SNAP_3034367141_987737800 2995234 /home/oradata/ORCL/orclpdb/snap_3034367141_2995234.pdb

| 从snapshot建立PDB

alter system set db_create_file_dest = '/home/oradata/ORCL/orclpdb' ;

conn / as sysdba

YAO.CHONG> create pluggable database pdb_snap_test from orclpdb using snapshot test_snapshot;

Pluggable database created.

Elapsed: 00:00:39.13

YAO.CHONG> show pdbs;

CON_ID CON_NAME OPEN MODE RESTRICTED

---------- ------------------------------ ---------- ----------

2 PDB$SEED READ ONLY NO

3 ORCLPDB READ WRITE NO

4 PDB_SNAP_TEST MOUNTED

YAO.CHONG> alter pluggable database PDB_SNAP_TEST open ;

Pluggable database altered.

Elapsed: 00:00:09.28

YAO.CHONG> alter pluggable database PDB_SNAP_TEST close ;

Pluggable database altered.

Elapsed: 00:00:01.11

YAO.CHONG> drop pluggable database PDB_SNAP_TEST including datafiles;

Pluggable database dropped.

Elapsed: 00:00:00.67

| 基于SCN或时间点生产快照库

在阅读官方文档时，看到生成PDB能够基于SCN，我心中不由暗喜，当再仔细查阅一番则否则，简直万念俱寂、黯然销魂。提供的基于SCN生成的快照库只能是基于当前生成快照时间点的SCN，彷佛有些鸡肋。

1	create pluggable database pdb_snap_test from orclpdb using snapshot at SCN 3620951;

与recover database until scn指定scn方式打开数据库不一样，pdb snapshot Carousel指定scn生成的PDB只能是建立snapshot时的固定scn，而且生成快照与snapshot生成pdb的过程当中占据了大量的物理空间与IO资源。

那么问题来了,说了这么多关于PDB snapshot Carousel的优点与好处,是否就说明已经找到了最佳的解决方案呢?

Hold on.

凡事有利也有弊,一样PDB snapshot Carousel也不能幸免。

快照数量受限

虽然可以作到Carousel轮转,但毕竟数量有限,较为死板。在用户的实际测试环境中条件复杂多变,会限制测试环境的搭建.

占据大量物理空间与IO资源

对于当前用户动辄几十T的数据量，在生成snapshot与snapshot建立pdb的过程当中，消耗的时间和占据的物理资源是巨大的。

拘泥固定时间点

对于PDBsnapshot Carouse而言,只能基于固定时间，即快照点建立，没法根据测试须要灵活指定时间点。面对不断变化的测试需求，如此死板的模式明显是不可能知足要求的。

版本受限

最后是客观条件的限制,利用新特性须要知足是在18C的环境下且启用了PDB功能,但目前不少用户依然是10G\11G\12C的环境,所以也仅仅只能远观而没法上手,对于实际工做很难产生推进做用。

说到这,是否还有更好的解决办法呢?

答案是必须有!

16 Administering a PDB Snapshot Carousel

您能够为指定的PDB配置一个PDB快照库，手动或自动建立快照，并设置快照的最大数量。

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 the SNAPSHOT clause of CREATE PLUGGABLE DATABASE (or ALTER PLUGGABLE DATABASE ), or automatically using the EVERY interval clause. 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 the SNAPSHOT MODE EVERY clause when creating or altering a PDB.
Creating PDB Snapshots Manually
To create a PDB snapshot manually, specify the SNAPSHOT snapshot_name clause in ALTER PLUGGABLE DATABASE or CREATE PLUGGABLE DATABASE .
Dropping a PDB Snapshot
You can drop a PDB snapshot by running an ALTER PLUGGABLE DATABASE statement with the DROP SNAPSHOT clause.

Parent topic: Administering a Multitenant Environment

16.1 About PDB Snapshot Carousel

PDB快照是PDB的时间点副本。您可使用create PLUGGABLE DATABASE(或ALTER PLUGGABLE DATABASE)的SNAPSHOT子句手动建立快照，也可使用each interval子句自动建立快照

. A PDB snapshot carousel 快照库.

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
The SNAPSHOT MODE clause 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快照库是维护最近的PDB副本库以便进行时间点恢复和克隆的一种有用方法。
克隆用于开发和测试的PDBs

在一个典型的开发用例中，您克隆一个产品PDB来进行测试。当CDB处于ARCHIVELOG模式和本地撤销模式时，源生产PDB能够以读/写模式打开，并在操做过程当中充分发挥功能。这种技术被称为热克隆。当SCN完成时，热克隆在事务上与源PDB一致of the ALTER PLUGGABLE DATABASE ... OPEN statement.

例如，当名为pdb1_prod的生产PDB处于打开状态并正在使用时，您将建立一个名为pdb1_test_master的可刷新克隆。而后配置pdb1_test_master来天天建立自动快照。当您须要新的PDBs进行测试时，请建立任何快照的完整克隆，而后使用 CREATE PLUGGABLE DATABASE ... SNAPSHOT COPY .

下图显示了从4月5日拍摄的PDB快照建立的克隆pdb1_test_full1。图中显示了从pdb1_test_full1建立的三个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快照库进行时间点恢复

典型的策略是天天在同一时间对PDB进行快照。另外一种策略是在数据加载以前手动进行快照。在这两种状况下，PDB快照库都容许您使用任何可用快照恢复PDB。

例如，名为pdb1_prod的销售历史记录PDB天天在12:01生成一个自动快照。在4/9周一下午的daily data load中，您意外加载了错误的数据，损坏了PDB。您能够基于Monday 4/9快照建立一个新的生产PDB，删除损坏的PDB，而后重试数据加载。

Figure 16-2 Restore a Production PDB Using a Snapshot

Description of "Figure 16-2 Restore a Production PDB Using a Snapshot"

See Also:

" About Cloning a PDB "
Oracle Database SQL Language Reference for CREATE PLUGGABLE DATABASE syntax and semantics

Parent topic: About PDB Snapshot Carousel

16.1.2 How PDB Snapshot Carousel Works

The carousel 对于特定的PDB，是该PDB的一个循环复制库。

数据库根据须要或自动地在库中建立连续的副本。当达到快照限制时，数据库将重写最旧的快照。

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快照的数据文件驻留在文件系统上的归档文件中。
不包括存档的重作日志文件。一般，归档文件存储在与PDB的数据文件相同的目录中。对于系统生成的快照名称，snap_以唯一标识符为前缀，该标识符包含快照SCN。该归档文件的扩展名是.pdb。

数据库使用隐式的using snapshot子句获取快照。在使用建立可插入数据库快照获取快照时，不能指定快照复制子句。

Note:

使用USING snapshot子句建立的PDB快照和使用snapshot copy子句建立的快照复制PDB是两种不一样类型的快照，它们不该该混淆。USING SNAPSHOT子句建立一个不须要物化的完整PDB。快照复制子句建立了一个稀疏的PDB，若是您想删除它所基于的PDB快照，就必须将其物化。

虽然PDB快照carousel中的快照始终是完整的PDB，可是您能够在carousel中获取快照的快照副本。在这种状况下，快照副本是一个稀疏克隆。

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快照库是一个PDB的全部现有快照的集合。
max_pdb_snapshot属性指定库中容许的最大快照数量。当前设置在CDB_PROPERTIES视图中是可见的。

下图显示了cdb1_pdb1的库。在本例中，数据库每24小时自动获取一个快照，维护一组8个快照。建立了前8个快照以后，每一个新快照都会替换旧快照。例如，星期二4/10快照替换星期一4/2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

要为PDB设置快照模式，请在快照模式中使用如下值之一 clause of ALTER PLUGGABLE DATABASE or CREATE PLUGGABLE DATABASE :

MANUAL
This clause, which is the default, enables the creation of manual snapshots of the PDB. To create a snapshot on demand, specify the SNAPSHOT snapshot_name clause in an ALTER PLUGGABLE DATABASE or CREATE PLUGGABLE DATABASE statement.
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 EVERY is specified.
- The minutes value must be less than 3000 .
- The hours value must be less than 2000 .
NONE
This clause disables snapshot creation for the PDB.

See Also:

" About Point-in-Time Cloning of PDB Snapshots "
Oracle Database SQL Language Reference for the syntax and semantics of the SNAPSHOT clause

MAX_PDB_SNAPSHOTS Database Property

要设置PDB的最大快照数量，请在ALTER PLUGGABLE DATABASE或CREATE PLUGGABLE DATABASE中指定max_pdb_snapshot属性。属性的默认值是8，这也是最大值。当建立了容许的最大快照数量时，数据库将清除最旧的快照。CDB_PROPERTIES视图显示了max_pdb_snapshot的设置。

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_SNAPSHOTS view metadata about the snapshots, including name, creation SCN, creation time, and file name.
The DBA_PDBS view has a SNAPSHOT_MODE and SNAPSHOT_INTERVAL column.

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数据库属性设置PDB快照旋转***中每一个PDB的最大快照数量。默认最大值是8。不能将属性设置为大于8的数字。

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_PROPERTIES for the current setting of the SET MAX_PDB_SNAPSHOTS property.
Run an ALTER PLUGGABLE DATABASE or ALTER DATABASE statement with the SET MAX_PDB_SNAPSHOTS clause.

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时，经过使用快照模式EVERY子句为自动快照配置PDB。
默认状况下，PDB是为手动快照配置的。

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_PDBS to determine the current snapshot mode.
Run ALTER PLUGGABLE DATABASE with the SNAPSHOT MODE EVERY interval clause, specifying either MINUTES or HOURS .

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_PDBS to determine the current snapshot mode.
Run CREATE PLUGGABLE DATABASE with the SNAPSHOT MODE EVERY interval clause, specifying either MINUTES or HOURS .

Example 16-3 为现有PDB天天配置一个自动快照

本例假设您已登陆到要更改其快照模式的PDB。查询数据字典，确认PDB目前处于手动模式(包括示例输出):

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:

" Creating a Point-in-Time Clone of a PDB Snapshot: Example "
" Configuring a CDB to Use Local Undo Mode "

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_PDBS to confirm that the snapshot mode is not set to NONE .
Run an ALTER PLUGGABLE DATABASE statement with the SNAPSHOT clause.

Example 16-5 Creating a Snapshot with a User-Specified Name

如下SQL语句建立两个cdb1_pdb1的PDB快照，一个在周三数据加载以前，一个在周三数据加载以后:

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 建立具备系统指定名称的快照

下面的SQL语句建立一个快照，但没有指定名称:

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:

" About Container Access in a CDB "
" Configuring a CDB to Use Local Undo Mode "

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 DATABASE statement with the DROP SNAPSHOT clause.

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快照轮播（SNAPSHOT CAROUSEL）

版权声明：本文为Buddy Yuan原创文章，未经容许不得转载。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，最多能够建立8个pdb的快照，而这8个构成的一组快照就被称做快照轮播。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同样。PDB的快照主要做用是当出现了问题能够闪回到快照的时间点，另外一个功能是基于快照来查询历史数据。

<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>

默认状况下是手动建立快照，咱们能够把它改为自动建立。

<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>

要返回手动模式，输入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>

手动建立快照，能够本身指定名字，也可使用系统自动生成的名字。经过查看DBA_PDB_SNAPSHOTS视图，能够找到快照存放的路径及建立快照的SCN号。

<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>

演示了上述功能以后，还有一个功能，就是咱们能够根据快照建立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>

这样咱们就根据快照建立了一个新的PDB，假设当前PDB出现了数据覆盖，咱们就可使用这个历史快照的PDB来恢复数据。
固然还有一个很好用的功能就是咱们在建立pdb的过程当中把他设置成15分钟产生一个快照。固然配置这个功能有一个先决条件：CDB必须处于本地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>

能够看到每隔5分钟自动建立一个快照

<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>

咱们能够作个实验测试一下。在生成快照以前建立一个表插入点数据，这里上一次快照是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点48分产生了新的快照，此时咱们使用新的快照作一个克隆，登录到ORCLPDB4数据库后，咱们会发现是有数据的。

<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>

这个功能对于测试人员很是有用，例如移动电信如今有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，咱们就能够直接建立快照，而后使用快照克隆一个新数据库造成BCV环境给经分抽数及测试使用了。