Wednesday, 28 December 2016

Oracle Data Guard Concept

Hi Friends,
Today, we will discuss about DataGuard. We will see as why we need Dataguard? We will also check the Advantages and Disadvantage.

Now, what is DataGuard?

A DataGuard provide us following as high availability, data protection, and disaster recovery for enterprise data. It provides a comprehensive set of services that create, maintain, manage, and monitor one or more standby databases to enable production Oracle databases to survive disasters and data corruptions. And also, it maintains these standby databases as copies of the production database.

It means, suppose the production database becomes unavailable because of a planned (if there is any maintenance) or an unplanned (like disaster, network issue etc.) outage. So, Data Guard can switch any standby database to the production role, and it will minimize the downtime associated with the outage. It can be used with traditional backup, restoration, and cluster techniques to provide a high level of data protection and data availability.


* Data Guard provides us below following below points:
* It helps in Data protection, high availability for a database system.
* Human intervention will be less in case of failover and failback switchover.
* By the using standby redo log files Data guard can minimize loss of data.
* It is simple management and centralized.
* It also supports in heterogeneous configurations where the primary and standby systems may have different CPU architectures, operating.


Suppose, if the network links connecting primary and standby is over-subscribed, and the redo logs are not shipped in chronological order, then this can result in large gaps appearing in the available of redo at the standby. Such a condition results in the standby being behind the primary.
Here, the same release of Oracle Database Enterprise Edition must be installed on the primary database and all standby databases also, except during rolling database upgrades using logical standby databases. Oracle Data Guard is available only as a feature of Oracle Database Enterprise Edition.

Data Guard Configurations Details:

A Data Guard configuration consists of one production database and one or more standby databases.
Here, we can manage primary and standby databases using the SQL command-line interfaces or the Data Guard broker interfaces, including a command-line interface (DGMGRL) and a graphical user interface that is integrated in Oracle Enterprise Manager.

Primary Database:
A Data Guard configuration contains one production database, which called as the primary database that functions in the primary role. And this is the database that is accessed by most of our applications.
This primary database can be either a single-instance Oracle database or an Oracle Real Application Clusters(RAC) database.

Standby Database:
DataGuard contain a standby database as transactionally consistent copies of the production or primary database. Once standby database created from production database backup copies, Data Guard can automatically maintains each standby database by transmitting the redo data from the production or primary database and then applying the redo to the standby database.

Standby database can also be either a single-instance Oracle database or an Oracle RACdatabase like Primary database.

There are two type of Standby database Physical Standby Database and Logical Standby Database.

A physical Standby Database provides a physically identical copy of the primary database, with on disk database structures that are identical to the primary database on a block-for-block basis. The database schema, including indexes, are the same. It always kept synchronized with the primary database, through Redo Apply, which recovers the redo data received from the primary database and applies the redo to the physical standby database.

A logical Standby Database is kept synchronized with the primary database through SQL Apply, which transforms the data in the redo received from the primary database into SQL statements and then executes the SQL statements on the standby database. A logical standby database can be used concurrently for data protection, reporting, and database upgrade with almost no downtime. 

As above discussion, we can see a simple and important difference between Physical and Logical Standby Database is that, In physical standby database is synchronizing through Redo Apply and In Logical Standby Database is synchronizing though SQL Apply. 


Hope these above details and concepts will be useful and helpful. In next update we will update for DataGuard setup.


Some more useful link:

Interviews Q & A

RAC concepts in Oracle

R12.1 Vs R12.2

R12.2 Architecture & Concepts

Please write to us for any more details and concepts which is not clear. Always remember, we like to hear from you. Contact us



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    1. Dear User,

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      Thanks & Regards,
      ora-data Team.

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    1. Dear User,

      Thank you for your feedback.

      ora-data Team


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