Standby database (also Oracle Data Guard) | Or

Standby database (also Oracle Data Guard)
Stand by database is used as a protection against failure of main production database.

=> Physical stand by

This may be created from last back up taken for the production database and there after applying archived redo log files on it. This is similar to recovering a database. However, for stand by database, this recovery is like a continuous process, because, archived logs (from production database) are continuously being applied on it to make it sync with production database. However, stand by database won’t be available for use until recovery is completed.

=> Logical stand by

Instead of applying archived redo log files, SQL statement is constructed from log files are being applied to stand by database (similar to Log Miner method). The database is available for use during application of SQLs.