source:  http://dbatrainer.com/difference-between-physical-standby-and-logical-standby-database/

Data Guard Apply process in standby database can apply redo information directly and in that case it willbe called physical standby.

OR

It can apply SQL and in that case it will be called Logical standby.

Physical Standby: –

In this case standby database is an exact, block-by-block, physical replica of the primary database.The change vectors received by RFS process are directly applied to the standby database by using mediarecovery.so here the apply process read data blocks, assemble redo changes from mappings, and thenapply redo changes to data blocks directly.

Physical Standby is the best choice for disaster recovery (DR) based upon their simplicity, transparency,high performance, and good data protection.

Logical Standby: –

In this case standby database uses SQL Apply method to “mine” the redo by converting it to logical change records, and then building SQLtransactions and applying SQL to the standby database.

As this process of replaying the workload is more complex than the Physical Standby’s process, so itrequires more memory, CPU, and I/O.

One good advantage here is that a logical standby database can be opened read-write while SQL Apply isactive which means you can update (create/insert/delete etc) local tables and schemas in the logical standby database.

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