Oracle recommends that Change Data Capture (CDC) is configured and started before the Initial Load. This enables "change synchronization" to keep track of ongoing transactional changes while the load is being applied—a very useful feature when you cannot afford for your source system to be taken offline. In fact GoldenGate can manage and combine the online transactional changes plus the initial data extract with ease, ensuring no data loss or down-time.
So let's take a look at the steps required to configure and start CDC.
As stated in Chapter 1, the Extract process extracts only committed transactions from the database's redologs. The first task, therefore, is to create the Extract process.