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探索Oracle11gR2 之 DataGuard_03 三种保护模式

原创 Linux操作系统 作者:wuweilong 时间:2013-08-15 20:57:33 0 删除 编辑

OracleDataGuard技术有三种实现模式,分别是max performancemax availabilitymax protection这三种模式。

以下是来自Oracle文档的摘要信息:
In some situations, a business cannot afford to lose data. In other situations, the availability of the database may be more important than the loss of data. Some applications require maximum database performance and can tolerate some small amount of data loss. The following descriptions summarize the three distinct modes of data protection.

 

Maximum protection This protection mode ensures that no data loss will occur if the primary database fails. To provide this level of protection, the redo data needed to recover each transaction must be written to both the local online redo log and to the standby redo log on at least one standby database before the transaction commits. To ensure data loss cannot occur, the primary database shuts down if a fault prevents it from writing its redo stream to the standby redo log of at least one transactionally consistent standby database.

Maximum availability This protection mode provides the highest level of data protection that is possible without compromising the availability of the primary database. Like maximum protection mode, a transaction will not commit until the redo needed to recover that transaction is written to the local online redo log and to the standby redo log of at least one transactionally consistent standby database. Unlike maximum protection mode, the primary database does not shut down if a fault prevents it from writing its redo stream to a remote standby redo log. Instead, the primary database operates in maximum performance mode until the fault is corrected, and all gaps in redo log files are resolved. When all gaps are resolved, the primary database automatically resumes operating in maximum availability mode.

This mode ensures that no data loss will occur if the primary database fails, but only if a second fault does not prevent a complete set of redo data from being sent from the primary database to at least one standby database.

Maximum performance This protection mode (the default) provides the highest level of data protection that is possible without affecting the performance of the primary database. This is accomplished by allowing a transaction to commit as soon as the redo data needed to recover that transaction is written to the local online redo log. The primary database's redo data stream is also written to at least one standby database, but that redo stream is written asynchronously with respect to the transactions that create the redo data.

When network links with sufficient bandwidth are used, this mode provides a level of data protection that approaches that of maximum availability mode with minimal impact on primary database performance.

The maximum protection and maximum availability modes require that standby redo log files are configured on at least one standby database in the configuration. All three protection modes require that specific log transport attributes be specified on the LOG_ARCHIVE_DEST_n initialization parameter to send redo data to at least one standby database. See Section 5.6 for complete information about the data protection modes.

以下是对以上摘要信息的翻译信息:

在一些情况下,业务不允许丢失数据。在另外一些情况下,数据库的可用性比丢失数据更为重要。一些应用需要最强的数据库性能并且能容忍丢失少量的数据。下面的描述概述了三种不同的数据保护模式。

最大保护模式 -- 这种保护模式确保如果主数据库故障不会发生数据丢失要提供这种级别的保护,恢复每个事务所需的重做数据必须在事务提交之前同时写到本地联机重做日志和至少一个备数据库上的备重做日志。要确保不发生数据丢失,如果故障导致主数据库无法写重做流到至少一个事务一致性备数据库的备重做日志时,主数据库会关闭。

最大可用性模式 -- 这种保护模式提供了可能的最高级别的数据保护,而不用与主数据库的可用性相折衷。与最大保护模式相同,在恢复事务所需的重做写到本地联机重做日志和至少一个事务一致性备数据库上的备重做日志之前,事务将不会提交。与最大保护模式不同的是,如果故障导致主数据库无法写重做流到异地备重做日志时,主数据库不会关闭。替代地,主数据库以最大性能模式运行直到故障消除,并且解决所有重做日志文件中的中断。当所有中断解决之后,主数据库自动继续以最大可用性模式运行。

这种模式确保如果主数据库故障,但是只有当第二次故障没有阻止完整的重做数据集从主数据库发送到至少一个备数据库时,不发生数据丢失。

最大性能模式 -- 这种保护模式(默认)提供了可能的最高级别的数据保护,而不影响主数据库的性能。这是通过允许事务在恢复该事务所需重做数据在写到本地联机重做日志后立即提交而实现的。主数据库的重做数据流也写到至少一个备数据库,但是那个重做流相对于创建重做数据的事务是异步写的。

当所用的网络连接有足够的带宽,这种模式提供了近似于最大可用性模式的数据保护级别,并且对主数据库性能的影响最小。
最大保护和最大可用性模式需要备重做日志文件配置在配置中的至少一个备数据库上。所有三种保护模式需要在LOG_ARCHIVE_DEST_n 初始化参数上指定特定的日志传输属性以发送重做数据到至少一个备数据库。查看5.6 节以获得数据保护模式的完整信息。

 

 

实验过程:

DG在最大性能模式MAXIMUM PERFORMANCE

SQL>  select protection_mode,protection_level from v$database;

 

PROTECTION_MODE      PROTECTION_LEVEL

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

MAXIMUM PERFORMANCE  MAXIMUM PERFORMANCE

 

SQL> select * from tab;

 

TNAME                          TABTYPE  CLUSTERID

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

BONUS                          TABLE

DEPT                           TABLE

EMP                            TABLE

SALGRADE                       TABLE

 

SQL> create table emp001 as select * from emp;    创建了一张表emp001

 

Table created.

 

SQL> select * from tab;

 

TNAME                          TABTYPE  CLUSTERID

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

BONUS                          TABLE

DEPT                           TABLE

EMP                            TABLE

EMP001                         TABLE

SALGRADE                       TABLE

 

去备机上查看,这张表并没有出现:

SQL> select * from tab;

 

TNAME                          TABTYPE  CLUSTERID

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

BONUS                          TABLE

DEPT                           TABLE

EMP                            TABLE

SALGRADE                       TABLE

 

这个时候,我需要在主库上执行一次日志切换:

SQL> alter system switch logfile;

 

System altered.

 

再备库上再次查询,表已经出来:

SQL> /

 

TNAME                          TABTYPE  CLUSTERID

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

BONUS                          TABLE

DEPT                           TABLE

EMP                            TABLE

EMP001                         TABLE    ----在主库新创建的表

SALGRADE                       TABLE

 

 

DG在最大可用性模式 Maximum availability

Primary 端操作

修改初始化参数

SQL> alter system set log_archive_dest_2 ='SERVICE=sty OPTIONAL LGWR SYNC AFFIRM VALID_FOR=(ONLINE_LOGFILES,PRIMARY_ROLE) DB_UNIQUE_NAME=sty';

 

System altered.

 

SQL> show parameter log_archive_dest_2

 

NAME                                 TYPE        VALUE

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

log_archive_dest_2                   string      SERVICE=sty OPTIONAL LGWR SYNC

                                                  AFFIRM VALID_FOR=(ONLINE_LOGF

                                                 ILES,PRIMARY_ROLE) DB_UNIQUE_N

                                                 AME=sty

SQL> startup mount;

ORACLE instance started.

 

Total System Global Area  839282688 bytes

Fixed Size                  2217992 bytes

Variable Size             549455864 bytes

Database Buffers          285212672 bytes

Redo Buffers                2396160 bytes

Database mounted.

 

SQL> alter database set standby database to maximize availability;

 

Database altered.

提示:maximize后可跟{PROTECTION | AVAILABILITY | PERFORMANCE},分别对应最大保护,最高可用性及最高性能。
Down
掉数据库,重新启动

 

SQL> alter database open;

 

Database altered.

 

看一下当前的保护模式    --primary数据库操作

SQL>  select protection_mode,protection_level from v$database;

 

PROTECTION_MODE      PROTECTION_LEVEL

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

MAXIMUM AVAILABILITY MAXIMUM AVAILABILITY

 

SQL>

 

Standby端操作

SQL>  alter system set log_archive_dest_2='SERVICE=pri OPTIONAL LGWR SYNC AFFIRM VALID_FOR=(ONLINE_LOGFILES,PRIMARY_ROLE) DB_UNIQUE_NAME=pri';

 

System altered.

 

SQL> show parameter log_archive_dest_2

 

NAME                                 TYPE        VALUE

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

log_archive_dest_2                   string      SERVICE=pri OPTIONAL LGWR SYNC

                                                  AFFIRM VALID_FOR=(ONLINE_LOGF

                                                 ILES,PRIMARY_ROLE) DB_UNIQUE_N

                                                 AME=pri

 

SQL> select protection_mode,protection_level from v$database;

 

PROTECTION_MODE      PROTECTION_LEVEL

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

MAXIMUM AVAILABILITY MAXIMUM AVAILABILITY

 

SQL>

 

这样就已经配置完成了。

我们现在停掉standby数据库,再看看primary数据库状态

SQL> shutdown immediate

Database closed.

Database dismounted.

ORACLE instance shut down.

 

SQL> select protection_mode,protection_level,name from v$database;

 

PROTECTION_MODE      PROTECTION_LEVEL     NAME

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

MAXIMUM AVAILABILITY RESYNCHRONIZATION    WOO

 

Standby数据库shutdown后,primary数据库保护级别切换为待同步。

 

启备机器后,一会儿就好了:

SQL> startup

ORACLE instance started.

 

Total System Global Area  839282688 bytes

Fixed Size                  2217992 bytes

Variable Size             507512824 bytes

Database Buffers          327155712 bytes

Redo Buffers                2396160 bytes

Database mounted.

Database opened.

SQL> select protection_mode,protection_level,name from v$database;

 

PROTECTION_MODE      PROTECTION_LEVEL     NAME

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

MAXIMUM AVAILABILITY RESYNCHRONIZATION    WOO

 

SQL> select protection_mode,protection_level,name from v$database;

 

PROTECTION_MODE      PROTECTION_LEVEL     NAME

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

MAXIMUM AVAILABILITY MAXIMUM AVAILABILITY WOO

 

SQL>

 

再查看下主库状态:

SQL> select protection_mode,protection_level,name from v$database;

 

PROTECTION_MODE      PROTECTION_LEVEL     NAME

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

MAXIMUM AVAILABILITY MAXIMUM AVAILABILITY WOO

 

测试:

primary 执行创建表

  查看当前表的数量

SQL> select * from tab;

 

TNAME                          TABTYPE  CLUSTERID

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

BONUS                          TABLE

DEPT                           TABLE

EMP                            TABLE

EMP001                         TABLE

EMP003                         TABLE

SALGRADE                       TABLE

 

6 rows selected.

 

删除emp003

SQL> drop table emp003 purge;

 

Table dropped.

 

创建emp004

SQL> create table emp004 as select * from emp001;

 

Table created.

 

查看emp003表已经被删除,emp004表被创建成功。

SQL> select * from tab;

 

TNAME                          TABTYPE  CLUSTERID

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

BONUS                          TABLE

DEPT                           TABLE

EMP                            TABLE

EMP001                         TABLE

EMP004                         TABLE

SALGRADE                       TABLE

 

6 rows selected.

 

备库上数据直接就可以过来了:

查询到数据和第一次pry数据库一致:

SQL> select * from tab;

 

TNAME                          TABTYPE  CLUSTERID

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

BONUS                          TABLE

DEPT                           TABLE

EMP                            TABLE

EMP001                         TABLE

EMP003                         TABLE

SALGRADE                       TABLE

 

6 rows selected.

 

pri端删除emp003后,可以看到在sty端也随即删除。

SQL> select * from tab;

 

TNAME                          TABTYPE  CLUSTERID

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

BONUS                          TABLE

DEPT                           TABLE

EMP                            TABLE

EMP001                         TABLE

SALGRADE                       TABLE

pri端创建emp004后,在sty端也随即实时创建。

SQL> select * from tab;

 

TNAME                          TABTYPE  CLUSTERID

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

BONUS                          TABLE

DEPT                           TABLE

EMP                            TABLE

EMP001                         TABLE

EMP004                         TABLE

SALGRADE                       TABLE

 

6 rows selected.

 

SQL>

 

实验二,在maximum availability 模式下关闭standby端,在主库执行DML操作后起备库,是否会有数据丢失:

1、  关闭standby:

[root@sty ~]# shutdown -h now

 

Broadcast message from root (pts/1) (Tue May 21 02:09:34 2013):

 

The system is going down for system halt NOW!

[root@sty ~]#

 

2、  查看主库这个时候的状态,已经检测到了standby失败

SQL> select name,open_mode,database_role,protection_mode,SWITCHOVER_STATUS  From v$database;

 

NAME                           OPEN_MODE            DATABASE_ROLE    PROTECTION_MODE      SWITCHOVER_STATUS

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

WOO                            READ WRITE           PRIMARY          MAXIMUM AVAILABILITY FAILED DESTINATION

 

SQL>

3、  这个时候我们删除emp004及创建emp005

SQL> select * from tab;

 

TNAME                          TABTYPE  CLUSTERID

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

BONUS                          TABLE

DEPT                           TABLE

EMP                            TABLE

EMP001                         TABLE

EMP004                         TABLE

SALGRADE                       TABLE

 

6 rows selected.

 

SQL> drop table emp004 purge;

 

Table dropped.

 

SQL> create table emp005 as select * from emp001;

 

Table created.

 

SQL> select * from tab;

 

TNAME                          TABTYPE  CLUSTERID

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

BONUS                          TABLE

DEPT                           TABLE

EMP                            TABLE

EMP001                         TABLE

EMP005                         TABLE

SALGRADE                       TABLE

 

6 rows selected.

 

4、  sty服务器启起来,open数据库:

打开备库后,我们可以看到,standby现在正在应用日志:

SQL> select process, status from v$managed_standby;

 

PROCESS   STATUS

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

ARCH      CLOSING

ARCH      CLOSING

ARCH      CONNECTED

ARCH      CLOSING

RFS       IDLE

RFS       IDLE

RFS       IDLE

MRP0      APPLYING_LOG

 

过一会儿,我们再查询,发现standby 端宕机过程中primary端数据库的改变也同样通过日志更新过来了。

SQL> select * from tab;

 

TNAME                          TABTYPE  CLUSTERID

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

BONUS                          TABLE

DEPT                           TABLE

EMP                            TABLE

EMP001                         TABLE

EMP005                         TABLE

SALGRADE                       TABLE

 

6 rows selected.

 

 

 

我们通过这个实验可以看出,将DataGuard配置为Maximum availability模式后,pri数据是实时同步到sty端。

 

 

DG最大保护模式 Maximum protection

1、将主库修改为最大保护模式

  先关闭主库

SQL> shutdown immediate

Database closed.

Database dismounted.

ORACLE instance shut down.

 启动到mount状态

SQL> startup mount;

ORACLE instance started.

 

Total System Global Area  839282688 bytes

Fixed Size                  2217992 bytes

Variable Size             557844472 bytes

Database Buffers          276824064 bytes

Redo Buffers                2396160 bytes

Database mounted.

 

 修改为最大保护模式

SQL> alter database set standby database to maximize protection;

 

Database altered.

 

Open数据库

SQL> alter database open;

 

Database altered.

 

Primary端查询状态:

SQL> select name,open_mode,database_role,protection_mode,SWITCHOVER_STATUS  From v$database;

 

NAME                           OPEN_MODE            DATABASE_ROLE    PROTECTION_MODE      SWITCHOVER_STATUS

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

WOO                            READ WRITE           PRIMARY          MAXIMUM PROTECTION   TO STANDBY

 

Standby端查询状态(切换只需要操作主库,备库不需要动即可)

 

SQL> select name,open_mode,database_role,protection_mode,SWITCHOVER_STATUS  From v$database;

 

NAME      OPEN_MODE            DATABASE_ROLE    PROTECTION_MODE      SWITCHOVER_STATUS

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

WOO       READ ONLY WITH APPLY PHYSICAL STANDBY MAXIMUM PROTECTION   NOT ALLOWED

 

我们现在可以看到,primarystandby端现在都为Maximum protection 最大保护模式。

 

实验

先查看当前的表

SQL> select * from tab;

 

TNAME                          TABTYPE  CLUSTERID

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

BONUS                          TABLE

DEPT                           TABLE

EMP                            TABLE

EMP001                         TABLE

EMP005                         TABLE

SALGRADE                       TABLE

 

6 rows selected.

 

我们删除emp005以及创建emp006

SQL> drop table emp005 purge;

 

Table dropped.

 

SQL> create table emp006 as select * from emp001;

 

Table created.

 

我们可以看到emp005已经被删除,并且emp006表也被创建好了。

SQL> select * from tab;

 

TNAME                          TABTYPE  CLUSTERID

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

BONUS                          TABLE

DEPT                           TABLE

EMP                            TABLE

EMP001                         TABLE

EMP006                         TABLE

SALGRADE                       TABLE

 

6 rows selected.

 

SQL>

 

现在看standby端,我们可以发现如下

两边的表是一样的

SQL> select * from tab;

 

TNAME                          TABTYPE  CLUSTERID

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

BONUS                          TABLE

DEPT                           TABLE

EMP                            TABLE

EMP001                         TABLE

EMP005                         TABLE

SALGRADE                       TABLE

 

6 rows selected.

 

在主库端删除的emp005及新创建的emp006也实时同步过来了

SQL> select * from tab;

 

TNAME                          TABTYPE  CLUSTERID

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

BONUS                          TABLE

DEPT                           TABLE

EMP                            TABLE

EMP001                         TABLE

EMP006                         TABLE

SALGRADE                       TABLE

 

6 rows selected.

 

SQL>

 

我现在关闭sty端服务器:

 

[root@sty ~]# shutdown -h now

 

Broadcast message from root (pts/1) (Tue May 21 03:14:28 2013):

 

The system is going down for system halt NOW!

 

返回来看主库的状态:

  日志传输以及终止了:

Log Transport Services   Error         ORA-16198: LGWR received timedout error from KSR

Log Transport Services   Error         Error 12543 received logging on to the standby

Log Transport Services   Error         LGWR: Error 12543 attaching to RFS for reconnect

Log Transport Services   Error         Error 12543 received logging on to the standby

Log Transport Services   Error         LGWR: Error 12543 attaching to RFS for reconnect

 

  一段时间之后,primary端也宕机了:

SQL> select name,open_mode,database_role,protection_mode,SWITCHOVER_STATUS  From v$database;

 

NAME                                     OPEN_MODE            DATABASE_ROLE    PROTECTION_MODE      SWITCHOVER_STATUS

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

WOO                                      READ WRITE           PRIMARY          MAXIMUM PROTECTION   TO STANDBY

 

SQL> select name,open_mode,database_role,protection_mode,SWITCHOVER_STATUS  From v$database;

select name,open_mode,database_role,protection_mode,SWITCHOVER_STATUS  From v$database

*

ERROR at line 1:

ORA-03135: connection lost contact

Process ID: 8386

Session ID: 39 Serial number: 5

 

这个时候需要把standby端起来,primary端,数据库才能起来。

SQL> startup mount;

ORACLE instance started.

 

Total System Global Area  839282688 bytes

Fixed Size                  2217992 bytes

Variable Size             507512824 bytes

Database Buffers          327155712 bytes

Redo Buffers                2396160 bytes

Database mounted.

 

停止redo应用

SQL>  ALTER DATABASE RECOVER MANAGED STANDBY DATABASE CANCEL;

 

Database altered.

 

Open数据库

SQL> alter database open;

 

Database altered.

 

开启redo应用

SQL> ALTER DATABASE RECOVER MANAGED STANDBY DATABASE DISCONNECT FROM SESSION;

 

Database altered.再启主库

SQL> startup

ORACLE instance started.

 

Total System Global Area  839282688 bytes

Fixed Size                  2217992 bytes

Variable Size             507512824 bytes

Database Buffers          327155712 bytes

Redo Buffers                2396160 bytes

Database mounted.

Database opened.

 

 

最后我们一块来看一个表格,一目了然的清楚DG三种模式的区别:

 

最大保护模式

最大可用

最大性能

进程

LGWR

LGWR

LGWRARCH

网络传输模式

SYNC

SYNC

LGWR时设置SYNC

磁盘写操作

AFFIRM

AFFIRM

NOAFFIRM

备用日志

Yes

Phycal 备库需要

LGWR和物理需要

备用库类型

Phycal mode

Phycal and logical

Phycal and logical

 

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