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Oracle Streams — flexible data replication

Oracle Streams is a built-in feature that offers an extremely flexible way to replicate data at no additional licence cost. With asynchronous downstream capture it does so without consuming resources on the primary database.

A note on currency: Oracle Streams was deprecated with Oracle Database 12c Release 1. Oracle Database 18c was the terminal release for Streams support, and the feature was removed from 19c onwards. Oracle GoldenGate is the strategic replication solution for new work. This page remains as a reference for existing systems — we support you in running them and in moving off them.

Overview

Oracle Streams is a fast and flexible way to replicate data. A capture mechanism reads data from the redo logs of the source system and an apply mechanism applies it to the target database. Both DML and DDL statements can be streamed. For minimal impact on the source system, downstream capture is the recommended approach.

Downstream capture

With downstream capture, the redo log information in the log files on the target machine is translated into logical change records (LCRs) by one or more capture processes.

Architecture of a downstream capture process in Oracle Streams

The following kinds of downstream capture are distinguished:

Downstream capture
The source database sends online and archived redo logs to the downstream capture process on the target database.
Real-time downstream capture
The source database sends online and archived redo logs to the downstream capture process on the target database, and the online redo information can be transferred synchronously or asynchronously. The log apply service on the source database transfers the log information to the remote file server of the target database. The behaviour is controlled through the parameters LGWR SYNC or LGWR ASYNC for LOG_ARCHIVE_DEST_n.
Archived-log downstream capture
Only the archived logs are transferred, so the target side is updated only after a log switch.

Asynchronous real-time downstream capture gives you good protection against data loss and requires no additional resources on the source database. Because this is logical replication, structures such as partitions may differ between source and target. Historical data can, for instance, be retained longer on the target system after it has already been deleted on the source.

GoldenGate

GoldenGate is Oracle's licensed add-on for replication. It offers several advantages over Streams:

  • configuration through configuration files, which is considerably simpler than Streams
  • support for heterogeneous systems and databases
  • straightforward configuration of transformations
  • better performance than Streams under certain conditions

Oracle itself calls GoldenGate its strategic replication solution. As long as that remains the case, no significant further development of Streams is to be expected, although Oracle has committed to continuing support.