When do I use Active Data Guard and GoldenGate Together

When do I use Active Data Guard and GoldenGate Together

Active Data Guard and GoldenGate are not mutually exclusive. The following examples of high availability architectures that include the simultaneous use of both technologies:

• An Active Data Guard standby is utilized for disaster protection and database rolling upgrades for a mission critical OLTP database. GoldenGate is used to extract data from the Data Guard primary database (or from the standby database using GoldenGate ALO mode) for ETL update of an enterprise data warehouse.
• GoldenGate subset replication is used extract, transforms, and aggregate data from numerous data sources into a central operational data store (ODS). The ODS supports mission critical application systems that generate significant revenue for the company. An Active Data Guard standby database is used to protect the ODS, providing optimal data protection and availability.
• GoldenGate multi-master replication is utilized to synchronize several databases, each located in different geographies. Each GoldenGate copy has its own local synchronous Data Guard standby database that enables zero data loss failover should an outage occur. GoldenGate capture and apply processes are easily restarted on the new primary database following a failover since primary and standby are an exact, up-to-date replica of each other.
• Reducing planned downtime for various planned maintenance activities not supported by Data Guard – such as cross-endian platform migration or application upgrades that modify back-end database objects. In many cases customers wish to isolate a current mission critical production environment having a Data Guard primary and standby database from being impacted by the maintenance activity. A parallel environment (new primary and standby) is deployed on the new release or new platform and GoldenGate one-way or bi-directional replication is used to keep old and new environments synchronized. Production is moved to the new environment once sufficiently tested. GoldenGate can continue to replicate to the previous environment for fast fall-back until the stability of the new version is no longer in question, at which time the old environment can be de-commissioned.

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Data Guard Configurations

Data Guard Configurations

A Data Guard configuration consists of one production database and one or more standby databases. The databases in a Data Guard configuration are connected by Oracle Net and may be dispersed geographically. There are no restrictions on where the databases are located, provided they can communicate with each other. For example, you can have a standby database on the same system as the production database, along with two standby databases on other systems at remote locations.
You 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.

1.1.1 Primary Database

A Data Guard configuration contains one production database, also referred to as the primary database, that functions in the primary role. This is the database that is accessed by most of your applications.
The primary database can be either a single-instance Oracle database or an Oracle Real Application Clusters (Oracle RAC) database.

1.1.2 Standby Databases

A standby database is a transactionally consistent copy of the primary database. Using a backup copy of the primary database, you can create up to thirty standby databases and incorporate them in a Data Guard configuration. Once created, Data Guard automatically maintains each standby database by transmitting redo data from the primary database and then applying the redo to the standby database.
Similar to a primary database, a standby database can be either a single-instance Oracle database or an Oracle RAC database.
The types of standby databases are as follows:

• 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. A physical standby database is 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.
  As of Oracle Database 11g release 1 (11.1), a physical standby database can receive and apply redo while it is open for read-only access. A physical standby database can therefore be used concurrently for data protection and reporting.
  
• Logical standby database
  Contains the same logical information as the production database, although the physical organization and structure of the data can be different. The 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 for other business purposes in addition to disaster recovery requirements. This allows users to access a logical standby database for queries and reporting purposes at any time. Also, using a logical standby database, you can upgrade Oracle Database software and patch sets with almost no downtime. Thus, a logical standby database can be used concurrently for data protection, reporting, and database upgrades.
  
• Snapshot Standby Database
  A snapshot standby database is a fully updatable standby database.
  Like a physical or logical standby database, a snapshot standby database receives and archives redo data from a primary database. Unlike a physical or logical standby database, a snapshot standby database does not apply the redo data that it receives. The redo data received by a snapshot standby database is not applied until the snapshot standby is converted back into a physical standby database, after first discarding any local updates made to the snapshot standby database.
  A snapshot standby database is best used in scenarios that require a temporary, updatable snapshot of a physical standby database. Note that because redo data received by a snapshot standby database is not applied until it is converted back into a physical standby, the time needed to recover from a primary database failure is directly proportional to the amount of redo data that needs to be applied.
  

1.1.3 Configuration Example

Figure 1-1 shows a typical Data Guard configuration that contains a primary database that transmits redo data to a standby database. The standby database is remotely located from the primary database for disaster recovery and backup operations. You can configure the standby database at the same location as the primary database. However, for disaster recovery purposes, Oracle recommends you configure standby databases at remote locations.

Figure 1-1 Typical Data Guard Configuration

This illustration shows a Data Guard configuration consisting of a primary database and a physical standby database.
From the primary database, redo is being transmitted and applied to the standby database. Log apply services apply the redo out of the standby redo log files to the standby database.