The difference between physical standby database in a Data Guard and Active Data Guard is as bit confusing. Few DBAs assumes that active Data Guard need different configuration and implementation plan. Few thinks both are same. As a DBA it is very focal to understand the difference, as active Data Guard involves license cost. In this article I take a quick tour to make you all understand the overall difference of physical standby database in a Data Guard and Active Data Guard.
Data Guard
Data Guard provides the management, monitoring, and automation software to create and maintain one or more synchronized copies of a production database to protect Oracle data from failures, disasters, human error, and data corruptions while providing high availability for mission critical applications. Data Guard is included with Oracle Database Enterprise Edition. Oracle Data Guard forms an extension to the Oracle RDBMS. It aids in establishing and maintaining secondary “standby databases” as alternative/supplementary repositories to production “primary databases”.
Data Guard supports both physical standby and logical standby sites. Oracle Corporation makes Data Guard available only as a bundled feature included within its “Enterprise Edition” of the Oracle RDBMS.
Active Data Guard
Active Data Guard is an option license for Oracle Database Enterprise Edition. Active Data Guard enables advanced capabilities that that extend basic Data Guard functionality. These include:
- Real-Time Query – offload read-only workloads to an up-to-date standby database.
- Automatic Block Repair – automatic repair of physical corruption transparent to the user.
- Far Sync – zero data loss protection across any distance.
- Standby Block Change Tracking – enable incremental backups on an active standby.
- Active Data Guard Rolling Upgrade – make it simple to reduce planned downtime.
- Global Database Services – load balancing and service management across replicated databases.
- Application Continuity – make outages transparent to users.
If a physical standby database in a Data Guard configuration has any of the above features enabled, then the Active Data Guard option must be licensed for every such physical standby, and also for the primary database. Yes, what you read is right “must be licensed for every such physical standby, and also for the primary database”.
Below are the commands can give you more insight for DBA to understand on Physical database in the Data Guard and Active Data Guard
How to start physical standby database in a Data Guard
- Bring Database in Mount State.
- Put database in recovery mode.
Commands:
SQL> startup mount
SQL> alter database recover managed standby database using current logfile disconnect from session; – (11G and lesser version)
SQL alter database recover managed standby database disconnect from session; – Note: USING CURRENT LOGFILE is already deprecated for start command Real-Time Apply on Oracle Database 12c (12.1).
How to start Active Data Guard database in a Data Guard
- Start the database in open mode.
- Put database in recovery mode.
Commands:
SQL> startup open;
SQL> alter database recover managed standby database using current logfile disconnect from session; -(11G and lesser version)
SQL> alter database recover managed standby database disconnect from session; – Note: USING CURRENT LOGFILE is already deprecated for start command Real-Time Apply on Oracle Database 12c (12.1).
Conversion from Physical standby to Active Data Guard
We can convert the physical standby into active Data Guard standby . Below are the steps
- Stop Apply Services.
- Shut the database.
- Start the database in open mode.
- Put database in recovery mode.
SQL> alter database recover managed standby database cancel;
SQL> shut immediate;
SQL> startup open;
SQL> alter database recover managed standby database using current logfile disconnect from session; -(11G and lesser version)
SQL> alter database recover managed standby database disconnect from session; – Note: USING CURRENT LOGFILE is already deprecated for start command Real-Time Apply on Oracle Database 12c (12.1).
It enables us to have a physical standby read only open, while redo apply is still done in the background.
How to Check if Active Data Guard is Enabled or Not
Use the following query to confirm that Data Guard is in active mode:
From standby database
SQL> select open_mode,controlfile_type from v$database;
OPEN_MODE CONTROLFILE
READ ONLY WITH APPLY STANDBY
This means Active Data Guard is enabled
SQL> select open_mode,controlfile_type from v$database;
OPEN_MODE CONTROLFILE
Mounted STANDBY
This means Active Data Guard is not enabled
In short physical standby database in Data Guard will be in mount mode and Active Data Guard will be in READ ONLY WITH APPLY mode.
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