Oracle Replication Introduction

What is Replication ?
Replication is the process of copying and maintaining database objects, such as tables, in multiple databases that make up a distributed database system. However, Streams is the preferred way to set up Replication in Oracle databases. Following are the replication types

Multi-Master Replication: Multi-Master replication comprises of multiple master sites equally participating in an update-anywhere model. Updates made to an individual master site are propagated (sent) to all other participating master sites using database links.

Materialized View Replication: Materialized View Replication allows complete or partial replicas of tables on the source database (called the master site) to be created on one or more destination databases (called materialized view sites). Materialized view replication have two subtypes:

I) Read-only materialized views
A master table is copied to one or more databases. Changes in the master table are reflected in the snapshot tables whenever the snapshot refreshes. The snapshot site determines the frequency of the refreshes; data is pulled.

II) Updateable materialized views
Maintains an updateable replica of a subset of data on a scheduled basis. Similar to read-only snapshots, except that the snapshot sites are able to modify the data and send their changes back to the master. The snapshot site determines the frequency of the refreshes and the frequency with which updates are sent back to the master.

Procedural replication: A call to a packaged procedure or function is replicated to one or more databases.

Error Transactions
These are the deferred transactions from another master site or materialized view site that could not be applied successfully at the current master site. User can remove, retry or see the details of the error in the error transaction page.

Deferred Transactions
These are the data manipulation language (DML) changes on a table which are stored in a queue in an asynchronous replication environment. The deferred transactions are propagated to the target destinations at scheduled intervals or on-demand. User can remove, push the transaction manually, or see the details of the transaction in Deferred transaction page.

Scheduled Links
A scheduled link is a database link with a user-defined schedule to push deferred transactions. It determines how a master site propagates its deferred transactions to another master site, or how a materialized view site propagates its deferred transactions to its master site. User can schedule each link and also set the additional options like propagation, stop on error s on the Scheduled link page.