Here's some excerpts from oracle document about oracle golden gate:
Robust Modular Architecture
The Oracle GoldenGate software architecture is comprised of three primary components:
Capture, Trail Files, and Delivery. This modular approach allows each component to perform
its tasks independently of the others, accelerating data replication and ensuring data integrity.
Figure 1: Oracle GoldenGate leverages a component-based architecture to optimize real-time
information access and availability.
Oracle GoldenGate’s Capture module resides on the source database and looks for new
transactional activity. The Capture module reads the result of insert, update, and delete
operations by directly accessing the database transaction (redo) logs, and then immediately
captures new and changed data for distribution.
The Capture module only moves committed transactions—filtering out intermediate activities
and rolled-back operations—which not only reduces infrastructure load but also eliminates
potential data inconsistencies. Further optimization is achieved through transaction grouping
and optional compression features.
Oracle GoldenGate 11g can also capture messages from JMS messaging systems to deliver to
heterogeneous databases in real time for scalable and reliable data distribution.
- Trail Files
Oracle GoldenGate’s Trail Files contain the database operations for the changed data in a
transportable, platform-independent data format. Trail Files are a critical component within
Oracle GoldenGate’s optimized queuing mechanism. They reside on the source and/or target
server but exist outside of the database to ensure heterogeneity, improved reliability, and
minimal data loss. This architecture minimizes impact to the source system because no
additional tables or queries to the database are required to support the data capture process.
The Capture module reads once, and then immediately moves the captured data to the external
Trail File for delivery to the target(s).
In the event of an outage at the source and/or target, the Trail Files contain the most-recent
data up to the point of the outage, and the data is applied once the systems are online again.
Oracle GoldenGate’s Delivery module takes the changed data from the latest Trail File and
applies it to the target database using native SQL for the appropriate relational database
management system. Delivery can be made to any open database connectivity–compliant
database. The Delivery module applies each transaction in the same order as it was committed
and within the same transactional context as at the source, enabling consistency and referential
integrity at the target. To enhance IT flexibility, captured data can also be delivered to a Java
Message Service destination or as a flat file using Oracle GoldenGate Application Adapters.
For full documentation, you can refer to the following pdf file: http://www.oracle.com/us/products/middleware/data-integration/goldengate11g-ds-168062.pdf?ssSourceSiteId=otnen