About Change Capture with a Capture Process

A capture process is an optional Oracle Database background process that asynchronously captures changes recorded in the redo log. When a capture process captures a database change, it converts it into a logical change record (LCR) and enqueues the LCR.

A capture process is always associated with a single queue, and it enqueues LCRs into this queue only. For improved performance, captured LCRs are always stored in a buffered queue, which is System Global Area (SGA) memory associated with a queue.

Figure: Capture Process shows how a capture process works.

A capture process can run on the source database or on a remote database. When a capture process runs on the source database, the capture process is called a local capture process. When a capture process runs on a remote database, the capture process is called a downstream capture process.

With downstream capture, redo transport services use the log writer process (LGWR) at the source database to send redo data to the database that runs the downstream capture process. A downstream capture process requires fewer resources at the source database because a different database captures the changes. A local capture process, however, is easier to configure and manage than a downstream capture process. Local capture processes also provide more flexibility in replication environments with different platforms or different versions of Oracle Database.