This illustration shows the basic process for online database upgrade or maintenance with Oracle Streams. This illustration shows the following Oracle databases:
The source database contains the following:
The database objects in the database being upgraded or maintained.
The redo log recording changes to the database objects.
The capture database can be the source database, the destination database, or a third database. The capture database contains the following:
A capture process capturing changes from the redo log of the source database. If the capture database and the source database are the same, then a local capture process captures changes in the redo log at the source database. If the capture database is the destination database or a third database, then the source database redo log is shipped to the capture database, and a downstream capture process captures changes in this redo log.
The capture process converts the changes to logical change records (LCRs) and enqueues the LCRs.
If the capture database and the destination database are different databases, then a propagation propagates the LCRs to a queue at the destination database. If the capture database and destination database are the same, then the propagation is not needed.
The destination database contains the following:
The queue that contains LCRs that were captured by the capture process.
An apply process that applies the LCRs as changes to the database objects.