What is a logical standby database?
- Apart from Physical and Snapshot Standby Database, it is another type of Standby Database.
- It is an active database that can be read-write in open mode.
- Reporting and querying can be done. Thus, it can reduce the load of the production database with correct usage.
- Since the Logical Standby is not a Block by block standby database, the Logical Standby does not pass any physical corruption on the Primary database to the Logical Standby.
- Logical standby has the ability to make Switchover and Failover.
- Its most important feature is that it can be used in Oracle Database Software and Patch upgrades.
- Redos in Physical Standby were replicated as Redo-Apply. In Logical Standby, it is replicated as SQL Apply. It performs this with LogMiner Technology.
Reader: Reads redo records from Redo Buffer Cache or Archive redo log files.
Preparer: Converts block level changes to Logical Change Records. The concept of transaction does not yet exist.
Builder: Creates transactions from single LCRs. The concept of transaction now exists.
Analyzer: Groups transactions by analyzing whether there is a dependency between different transactions.
Coordinator: Gives the Logical Standby the commitment to make changes.
Applier: Processes LCRs into database.
- SQL Apply is done by LSP process.