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【DataGuard】DG系列

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Jun 07, 2016 pm 04:50 PM

在Oracle 11g以前的物理备库，备库是可以只读方式打开，但是这时Media Recovery（redo Apply）过程就停止了。如果备库处于恢复过

一、物理备库的新特点

1、物理备库可实时查询

在Oracle 11g以前的物理备库，备库是可以只读方式打开，，但是这时Media Recovery（redo Apply）过程就停止了。如果备库处于恢复过程，那么备库就不能打开。Oracle 11g解决了这个矛盾，在恢复的同时也可以打开数据库。

2、加快备库备份的速度

在oracle10g引入了Block Tracking技术，来监控那些数据库是上次增量以来修改的，这样可以加快增量备份的速度，但是这个功能只能在主库上有效，oracle11g解决了这个矛盾，备库的备份也支持Block Tracking，这样用户可以再备库上面快速执行备份，减轻主库负载。

3、快照备库（oracle10g已经有了）

就是允许物理备库以读写模式打开，但是同时没有破坏它作为备库的功能，这个特性可以用来的物理备库上面执行某些测试，待测试完成，把数据库再置为物理备库。当然在备库以读写方式打开的时候它只能接受主库传过来的redo，但是不能应用这些redo。实际上就是因为在备库上使用了Flashback技术来实现这个功能。

4、提高redo apply的性能

oracle11g可以利用并行技术来进行redo apply，提高恢复的速度。

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相关参考:

Oracle Data Guard 重要配置参数

基于同一主机配置 Oracle 11g Data Guard

探索Oracle之11g DataGuard

Oracle Data Guard （RAC+DG) 归档删除策略及脚本

Oracle Data Guard 的角色转换

Oracle Data Guard的日志FAL gap问题

Oracle 11g Data Guard Error 16143 Heartbeat failed to connect to standby 处理方法

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二、逻辑备库的新特点

1、支持更多的数据类型

XMLType data type（CLOB存储）

2、支持下面的oracle包和数据加密

DBMS_FGA(Fine Grained Auditing)

DBMS_RLS(Virtual Private Database)

实际上就是支持在逻辑备库上面支持精细的审计功能和虚拟数据库功能。

Transparent Data Encryption(TDE)的支持

备库上面支持并行DDL

3、Fast-Start Failover

更快速执行失败切换，更精细控制触发failover的事件，比如可以根据某个ora的错误号来发出切换。

三、其他改进

1、重做压缩

将归档日志从主库发送到备库服务器，再将它们应用到数据库上，这一过程是data guard的前提。主备库间时间差的一个重要部分是传输归档日志的时间。如果对重做流进行压缩，可以将这一过程加快。在oracle11g中，可以使用SQL*Net将压缩参数设为真。从而压缩传输至备库服务器的重做流。这一过程之适用在Gap Resolution间传输的日志。一下命令可以用来启用压缩：

SQL>alter system set log_archive_dest_2='service=DG_ORCLSTD LGWR ASYNC valid_for=(ONLINE_LOGFILES,PRIMARY_ROLE) db_unique_name=ORCLSTD compression=enable';

2、网络超时

Data guard环境的工具原理是：连接备库服务器的数据库实例，向备库服务器发送重做数据。如果实例没有及时响应，日志传输服务将等待指定的超时值，然后放弃。可以在Oracle数据库中使用net_timeout参数设置超时值。在最大限度的保护模式下，日志传输服务将尝试20次后放弃。但首先要知道日志传输中当前的延迟。新视图v$redo_dest_resp_histogram以直方图形式表示了该时间值。该视图在给定圆柱中间显示了传输花费时间中的次数。如果运行几天后再查看此视图，可以清楚要设置的超时时间。然后可以使用以下命令设置超时时间：

SQL>alter system set log_archive_dest_2='service=DG_ORCLSTD LGWR ASYNC valid_for=(ONLINE_LOGFILES,PRIMARY_ROLE) db_unique_name=ORCLSTD compression=enable net_timeout=20';

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