In Oracle Data Guard , you can check whether the standby database is in sync with the primary database by monitoring the apply lag. The apply lag represents the time delay between when a redo log is generated on the primary database and when it is applied on the standby database. A zero or low apply lag indicates that the standby is relatively up-to-date with the primary, while a high apply lag suggests a potential synchronization delay. Here are some methods to check whether the standby database is in sync with the primary: 1. Data Guard Broker If you are using the Data Guard Broker, you can use the DGMGRL command-line interface or Enterprise Manager (Grid Control) to check the status of the Data Guard configuration and monitor the apply lag. For example, using DGMGRL: DGMGRL> SHOW DATABASE 'standby_database_name' APPLY_LAG; DGMGRL > SHOW DATABASE 'standby_database_name' APPLY_LAG ; 2. V$DATAGUARD_STATS View On the primary datab...