Data Replication

The need for data replication is evergreen. The use-case may vary from "High Availability" to "Operational Reporting (BI)" to "Real-time Analytics"; whatever may be the case, the need for replicating the data exists in the information systems and solutions.

I try to summarize the evolution of data replication technology from a Oracle Database standpoint in this post.

1. Looking back at the Oracle based data replication technologies the first one is "Database Link". One can create a database link and pull or push the data directly into a remote database starting Oracle 5 or 6. This is the very first method of replication where the application need to push or pull the data from a remote database and apply necessary logic to identify what data has changed and what to do with those changes.....
2. The next improvement in the replication is around Oracle 8 - one can setup a trigger based replication. That means whenever a transaction changes the data in a table one can trigger a function that can handle the replication without changing the application. So, database started giving a method to replicate data using triggers....
3. Then the next improvement has come around 9.2 with streams and log-based replication. The capability is to mine the redo logs and move the committed transactions to the target systems. (DBMS_CDC_PUBLISH and DBMS_CDC_SUBSCRIBE packages were introduced)
4. Oracle Advanced Queuing enhanced the streams to have robust publish and subscribe model replication that has enqueue and dequeue based communication. I was involved in a very large project that set up a custom Changed Data Capture to migrate data from a legacy system into SAP ERP involving large tables having 100Milion records.... 
5. Later the log-mining technology was used for physical and logical standby dataabses and evolved to a Active Data Guard technology......
6. With GoldenGate, the heterogeneous log-based data replication solution is complete from Oracle that has capabilities to extract, replicate, synchronize data in bi-directional movement.  

Depending on the need one should choose the right technology to achieve the needed data replication....