Database Changes

The source database is the where the Data Manipulation Language (DML) and the Data Definition Language (DDL) changes occur through database transactional activity. DML statements make changes to the data in the table through insert, update, and delete SQL statements. The table data rows are affected by DML statements. In contrast, the DDL statements make changes to the table definition or table structures. These changes are shared with the destination database. This process is called database replication.

The replicated configuration, in which changes occur on only one database and the remote database merely receives the changes is called One-Way Replication. When both of the participating databases make changes and those changes are shared with the other database, the configuration is called Two-Way Replication. When more than two databases participate, it is known as Multi-Way replication. Streams Replication allows all of these replication configuration types.

Source and Destination Database

The source database is where transaction changes are recorded into the redo log files.  The Streams process then captures those changes and propagates them to the destination database. The Streams Capture and Propagation processes run primarily on the source database.

The Oracle background process, which acts as the Capture process, is the main means of extracting the changes from the redo log files and converting them into Logical Change Record (LCR) events. Such events are enqueued into a queue.