Synchronizing Master and Standby
Instances 
Use
When a new standby instance is initialized, the memory management system copies the complete content of the master instance in a consistent state – for example, the state at the last savepoint - to the data area of the standby instance.
Thereafter, the standby instance regularly updates its data area by importing the redo log entries of the master instance up to a certain point in time from the shared log area and redoing the corresponding transactions.
By contrast, with a standby database, it is log backups that are imported.
Thus the data area of the standby instance, with some delay, always corresponds to the data area of the master instance.
Activities
Master and standby instances use the same database parameters. To change a database parameter, change it in the master instance. The system then automatically transfers the changes to the standby instances.
At regular intervals, the master instance informs the standby instances of the position in the log area up to which it has written new redo log entries in the shared log area. To configure this time interval, use the special database parameter HS_SYNC_INTERVAL.
To configure the time interval at which the standby instances import the redo log entries of the master instance and redo the corresponding transactions, use the special database parameter HS_DELAY_TIME.
See also: