Oracle ADG vs DG

其实ADG的实验自己早已做过，就是不知道是DG的升级版而已。

ADG: Active Data Guard

DG: Data Guard

What is the difference between DG and ADG ? 

From the docs: 
Oracle Data Guard ensures high availability, dataprotection, and disaster recovery for enterprise data. Oracle Data Guardprovides a comprehensive set of services that create, maintain, manage, andmonitor one or more standby databases to enable production Oracle databases tosurvive disasters and data corruptions. Oracle Data Guard maintains thesestandby databases as copies of the production database. Then, if the productiondatabase becomes unavailable because of a planned or an unplanned outage, OracleData Guard can switch any standby database to the production role, minimizingthe downtime associated with the outage. Oracle Data Guard can be used withtraditional backup, restoration, and cluster techniques to provide a high levelof data protection and data availability. 
Oracle dg保证高可用性、数据保护、企业数据的灾难恢复。Oracle dg提供一系列的综合性服务，如一个或多个备库的创建、维护、管理和监控，使得生产库从灾难、数据崩溃中得以恢复。Oracle dg维护这些备库作为生产库的副本。如果生产库因计划或非计划的中断，dg可切换任何一个备库当人生产库的角色，最小化因中断造成的宕机时间。DG也可用作传统的备份、恢复、提供数据高可用和保护的集群技术。
So both DG and ADG provide those additional copiesof the database. Early DG versions provided that facility solely for disasterrecovery. Nowadays, there are many other things you can use DG for, eg, youcould backup the DG copy rather than the production database to ease resourceconsumption etc. 
因此DG和ADG都提供数据库的附加复制。早期版本的DG只提供数据的灾难恢复。现在你通过DG有很多其他的东西可以使用，如你可备份DG库而不是生产库来达到降低资源消耗的目的。
Where ADG offers more is that you can have thedatabase open for read-only (eg reports) whilst it is still being kept in syncwith your primary database. With normal DG, if you want it open read-only, youmust pause the sync process. 

ADG能提供更多的就是你能使DG库以只读状态打开，同时DG库保持和主库的同步。对于普通的DG，你以只读形式打开DG库，必须暂停同步进程。

What is the difference betweenADG and GoldenGate ? 

ADG maintains a physical copy of yourprimary database (that can be read by queries). You are100% positive that it and the primary are the same.

Goldengate replicates *changes* from yourprimary database to a secondary but quite separate copy of your database. This second copy might be a subset, or superset, or simply bedivergent from your primary. The advantage is that this secondarydatabase can be read-write...its really a *different* database into whichchanges are being pushed.