18c Database : Logging Enhancements for nologging blocks for standby

Hi,

We all aware of, when a table has attribute set with nologging option , those redo will be missed (although redo information there, the data will be missed) and standby will not apply those changes, and this will problematic when you do a switchover or failover unless you use force logging mode.

To address this in 18c, we have three different logging modes to ensure nologged blocks are also captured and send to standby depends on requirement of performance and availability perspective.

Of course, we can use FORCE LOGGING at primary database to ensure all modifications are captured, however this has an performance impact where in which you are doing a bulk load and this has to be captured in redo logs may slow down your load process.

To overcome this, we have two new Logging modes available at primary database,

ALTER DATABASE SET STANDBY NOLOGGING FOR DATA AVAILABILITY;

This  mode causes the load operation to send the loaded data to each standby through its own connection to the standby. Means the data availability is critical so it has to delay the commit on primary side to ensure all non logged blocks also shipped and applied by MRP

ALTER DATABASE SET STANDBY NOLOGGING FOR LOAD PERFORMANCE;

This mode  is similar to the above one except that the loading process can stop sending the data to the standbys if the network cannot keep up with the speed at which data is being loaded to the primary. Standby may miss the data but eventually it fetches the non logged blocks during recover process by MRP process.

Suresh