2 Replies Latest reply on Jan 24, 2013 11:12 PM by TSharma-Oracle

    Logical Standby databases


      When we say "Logical Standby Databases are logically identical to primary databases although the physical organization and structure of the data can be different." what does it exactly means?

      Does it mean that in logical standby tablespace name, schema name, table name, column names etc can be different and still has the same data as primary?

      Does it mean that we can exclude indexes and constraints as present in primary?

      Only the data should match with primary word by word, value by value?

      I am asking this as i have never worked in a logical standby database but i seriously want to know.

      Please answer.

        • 1. Re: Logical Standby databases
          Peter Häusler
          a logical Standby database means that it applies his data with sql statment instead of do a recovery. When you make a sql apply, a table name should be the same. If it does not be the same then also a sql apply could not work. Also a create tablespace command would be apply on such database, or a create table which depends on this tablespace.

          But a logical standby (except the new feature active standby) can be read only, which means you can query this database for example reporting queries. So there are some possibilities to do some changes on a logical standby database to have a better performance for reporting as long it does not stop the sql apply.

          hope this helps
          • 2. Re: Logical Standby databases
            Physical standby differs from logical standby:

            Physical standby schema matches exactly the source database.
            Archived redo logs and FTP'ed directly to the standby database which is always running in "recover" mode. Upon arrival, the archived redo logs are applied directly to the standby database.

            Logical standby is different from physical standby:

            Logical standby database does not have to match the schema structure of the source database.

            Logical standby uses LogMiner techniques to transform the archived redo logs into native DML statements (insert, update, delete). This DML is transported and applied to the standby database.

            Logical standby tables can be open for SQL queries (read only), and all other standby tables can be open for updates.

            Logical standby database can have additional materialized views and indexes added for faster performance.

            Installing Physical standbys offers these benefits:

            An identical physical copy of the primary database

            Disaster recovery and high availability

            High Data protection

            Reduction in primary database workload

            Performance Faster

            Installing Logical standbys offer:

            Simultaneous use for reporting, summations and queries

            Efficient use of standby hardware resources

            Reduction in primary database workload

            Some limitations on the use of certain datatypes