In previous article we have gone through architecture of Oracle Dataguard and redo apply and sql apply architecture. A main role of any DR server is to protect Production Server’s critical data from any natural and unnatural disasters. Oracle Data Guard have different flavors to provide protection to Production’s critical data. That we can see as Protection Modes in Data Guard.
There are three types of Protection Modes in Dataguard .
- Maximum Availability
- Maximum Performance
- Maximum Protection.
Maximum Availability :
It provides highest level of protection of data without compromising availability of database. In this protection mode primary database’s transaction does not commit until that redo is transferred to one of synchronized database and acknowledged from standby process of redo data arrival.
Once transaction’s redo data is transferred and written to standby redo log files then RFS process sent a acknowledgement to primary database and then that transaction commits at primary database.
If the primary database cannot write its redo stream to at least one synchronized standby database, it operates as if it were in maximum performance mode to preserve primary database availability until it is again able to write its redo stream to a synchronized standby database.
Maximum Performance :
As its name says it provides maximum level of data protection that a database can have without compromising performance of database.
This is default Protection mode in dataguard.
Unlike Maximum Availability Protection mode, this mode allows transactions to commit as soon as all redo data generated by those transactions are written to online redo log files. Here , redo data is transferred to standby database in asynchronous way , so it doesn’t affect primary database’s performance.
This mode offers less data protection than Maximum Availability mode as there is no concept of acknowledgment of redo data written to standby redo log file at standby database.
But as the primary database is unaffected by this delay , it offers maximum performance.
Maximum Protection :
This protection mode ensures zero data loss if primary database fails.
We have seen in Maximum Availability protection mode that if it cannot write to one of synchronized standby database it works as if it were in Maximum Performance mode But here in Maximum Protection mode , if database can not write to one of synchronized standby database , Primary database will shut down as this prioritize protection of primary database than availability of data.
Note : Oracle recommends when you use this mode of protection , you should keep at least two standby database that runs in maximum protection mode to prevent a single standby database failure from causing the primary database to shut down.
Stay tuned for More articles on Oracle DataGuard
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