About Change Capture with a Synchronous Capture

Instead of asynchronously mining the redo log, a synchronous capture uses an internal mechanism to capture data manipulation language (DML) changes when they are made to tables. A single DML change can result in changes to one or more rows in the table. A synchronous capture captures each row change, converts it into a row logical change record (LCR), and enqueues it.

A synchronous capture is always associated with a single queue, and it enqueues row LCRs into this queue only. Synchronous capture always enqueues row LCRs into the persistent queue. The persistent queue is the portion of a queue that stores messages on hard disk in a queue table, not in memory.

It is usually best to use synchronous capture in a replication environment that captures changes to a relatively small number of tables. If you must capture changes to many tables, to an entire schema, or to an entire database, then you should use a capture process instead of a synchronous capture.

Figure: Synchronous Capture shows how a synchronous capture works.