What is the difference between Oracle Streams and Change Data Capture?

Question

There are several similar Oracle technologies - Oracle Streams, Oracle Change Data Capture and Database Change Notification.

What are the differences between these?

Are they related to Oracle Advanced Queueing?

Answer 1

Oracle CDC is all about capturing changes in DB tables and the changes are stored in special Oracle tables. There are two modes of CDC operation: asynchronous (based on Java) or synchronous (based on DB triggers, more performance overhead).

Oracle Streams sits on top of Oracle CDC and it's a full transport mechanism (over e.g. HTTP) for data synchronization between 2 servers. It's based on Oracle Advanced Queues technology and it's designed for high performance and reliability.

Both Oracle CDC and Streams are generally used for data synchronization between Oracle DB servers... With Oracle CDC, you don't have to use Oracle Streams for, e.g. you could write your own data export routines which create flat files for the purpose of synchronization between 2 DB servers, whereas with Streams you must have a network link between the 2 servers.

Database Change Notification is something else again, it's not used for server-to-server synch but instead more for server notification of resultset changes to clients, mostly in the context of data caches on the client side.

Answer 2

I would add that for synchronizing between systems, you can achieve asynchronous mode by combining Streams and the CDC publishing mechanism. If you choose not to use Streams for this purpose, you would end up using a synchronous mode (I think it's via triggers) putting a little extra overhead on each transaction.