Oracle Active Data Guard and Oracle Golden Gate are strategic capabilities within Oracle's software portfolio. While they generally fall into the category of replication technologies, each has a very different area of focus.

When do I use Oracle Active Data Guard?

Use Active Data Guard for data protection, high availability, and disaster recovery. Active Data Guard is Oracle's standard recommendation for these requirements due to the following advantages it offers over logical replication:

• Secure physical replica, impossible to modify data independent of primary transactions
• Native redo-based replication for all data-types and Oracle features. Supports all applications, no restrictions
• Management simplicity; simple one-way replication of the entire database
• Choice of asynchronous or synchronous (zero data loss) protection
• Replication of changes directly from memory (log buffer) for lowest possible replication latency and no I/O overhead. No capture processing on the primary database
• Fast, predictable performance - both for OLTP and batch loads
• No apply tuning required, automatically configured based on server configuration
• All recovery actions are completely inter-changeable between primary and standby
• Detect silent corruptions due to lost-writes that can impact either primary or standby
• Automatically repair corrupt blocks on the primary or standby transparent to the user
• A single command will dual-purpose a physical standby database as test system
• Automatic failure detection and database failover - no manual intervention required
• Integrated client and database failover – quickly and automatically redirect users to production copy
• Offload read-only workload from the primary database to a synchronized Active Data Guard standby open read-only.
• Implement query-lag SLA's for Active standby queries, with sub-second accuracy, automatically monitored
• Offload fast incremental backups to physical standby database, use to recover either primary or standby
• Minimize planned downtime by implementing database upgrades, system and site maintenance, or technology refresh, in rolling fashion across primary and standby databases. See My Oracle Support Note 413484.1 for information on supported mixed platform Data Guard configurations.

When do I use Oracle GoldenGate?

GoldenGate is an advanced logical replication product that supports multi-master replication, hub and spoke deployment and data transformation, providing customers very flexible options to address the complete range of replication requirements. GoldenGate also supports replication between a broad range of heterogeneous hardware platforms and database management systems. Unlike Active Data Guard, GoldenGate captures primary database changes by reading redo records from disk, transforming those records into a platform independent trail file format, and transmitting the trail file to the target database. GoldenGate maintains a logical replica by converting the trail file into SQL and applying SQL to the target database. The target database is open read-write while synchronization occurs.  While this provides substantial flexibility as a replication solution when compared to Data Guard, care must be taken to insure that the target database is not modified independent of the source, unless it is explicitly desired to do so.

GoldenGate is most often used for traditional data distribution and data integration requirements. It may also be used as an alternative to Data Guard for requirements where GoldenGate advantages outweigh  Data Guard's specialized capabilities for data protection, high availability, and disaster recovery, and when all prerequisites and additional implementation considerations for logical replication can be satisfied. Such requirements would include:

• If read-write access to the target database is required, either to implement multi-master replication, or to offload packaged reporting applications that require read-write access to the target database
• For planned maintenance or migrations in heterogeneous environments not supported by Data Guard
• To maintain availability through application upgrades that modify back-end database objects
• For additional flexibility during planned maintenance to replicate downward from a new Oracle Database or application version to the previous version, for fast switchback should unforeseen problems arise,

Complementary Technologies

Data Guard and GoldenGate are not mutually exclusive technologies. Many customers use GoldenGate for data integration and data distribution while the same Oracle Databases are protected by Data Guard. In other cases, customers who have standardized on Data Guard for data protection also use GoldenGate to facilitate planned maintenance, upgrades, and migrations. The following is an example that depicts the complementary use of Active Data Guard and GoldenGate

In the above example, a Data Guard physical standby database is utilized for data protection and to offload read-only workload from the primary database. GoldenGate is also used for heterogeneous replication of different subsets of the production database to multiple target databases. Rather than host GoldenGate replication on the production database, multiple GoldenGate capture processes can be offloaded to the physical standby database (using GoldenGate ALO mode). GoldenGate is able to captures changes from the standby database archive log files, eliminating any overhead of GoldenGate processing from the production system.
 

GoldenGate can also be used in a Data Guard configuration for any planned maintenance that is not supported by a Data Guard rolling upgrade (e.g. migrating to a different hardware architecture and operating system, or application upgrades that modifies database objects). In a second example of using both technologies in a complementary fashion, GoldenGate and Data Guard are utilized to isolate the production database from the tasks required to perform such maintenance while providing maximum availability and complete data protection at all times. The following describes this use-case:

• The process begins with the current environment having a primary database and a Data Guard physical standby database.
• A new copy of the production database is then instantiated on the new platform. Depending upon the type of migration planned, instantiating the new version of the production database may be as simple as restoring a backup of the existing standby database. For more complex migrations it may be necessary to use other Oracle technologies to instantiate the new primary database, such as Oracle Transportable Technologies or Oracle Data Pump. 
• Once instantiated, all required maintenance is implemented on the new production system.
• When all changes have been implemented, a new Data Guard physical standby is created for the new production system to provide continuous data protection after cutover.
• GoldenGate heterogeneous replication (previously configured using the original production database as the source and the new production database as the target), is then used to synchronize the new database with all transactions that had occurred while the new environment was being implemented.
• When synchronization is complete, production is ready for cutover to the new environment.
• There is also the option of using GoldenGate heterogeneous replication after the cutover to keep the old environment synchronized with the new production system for a period of time - to provide a fast fall back option should any unanticipated problems arise.