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Oracle background processes

Oracle Background processes:

A multi processes Oracle system uses background processes to maximize the performance.

Background processes are run behind or in background of the system, are used to do deal with abnormal conditions and maintenance activities.

Background processes gets invoked automatically when an instance is started.

Oracle system involves the following background processes-
1) Database Writer Process (DBWn)
2) Log Writer Process (LGWR)
3) System Monitor Process (SMON)
4) Process Monitor Process (PMON)
5) Recoverer Process (RECO)
6) Job Queue Processes
7) Archiver Processes (ARCn)
8)Queue Monitor Processes (QMNn)
9) Other Background Processes.

1) Database Writer Process (DBWn)-
Writes the contents from databuffer cache to the data files asynchronously.

2) Log Writer Process (LGWR)-
Writes the content from redo log buffers to the redo log files.

3) System Monitor Process (SMON)-
Recovers the crashed instance into the next instance.

4) Recoverer Process (RECO)-
The RECO process is used by the Oracle distributed transaction facility to recover from failures involving distributed transactions by:
  • Connecting to other databases involved in the distributed transaction.
  • Removing rows corresponding to any in-doubt transaction from each database's transaction table.

5) Job Queue Processes-
Job Queue processes can be viewed as a scheduler service that is used for batch processing. Job queue process allowed clients to use more job queue processes when required.

6) Archiver Processes (ARCn)-

When database in ARCHIVELOG mode, ARCn processes copies redo log files to a specific storage device after a log switch occurred.