Oracle Background Process

 Oracle Background Process

 

In Oracle Database, background processes are essential components that handle various tasks to support the functioning and performance of the database system. These processes run in the background and perform critical activities such as memory management, I/O operations, recovery, and monitoring. Here are some important background processes in Oracle:

1. System Monitor (SMON): SMON is responsible for instance recovery, which ensures the database is in a consistent state after an instance crash or failure. It recovers the database by applying undo and redo logs to roll forward or roll back transactions.

2. Process Monitor (PMON): PMON is responsible for process cleanup and process recovery. It detects and resolves failed and terminated processes, releasing system resources associated with them. PMON also performs process recovery during instance recovery.

3. Database Writer (DBWn): DBWn processes (DBW0, DBW1, etc.) are responsible for writing modified database buffers from the database buffer cache to data files on disk. They ensure that dirty buffers are periodically written to disk, reducing the risk of data loss during a system failure.

4. Log Writer (LGWR): LGWR writes redo log buffers to the redo log files on disk. It ensures that changes made to the database are durably stored in the redo logs before committing transactions. LGWR plays a crucial role in database recovery and maintaining data integrity.

5. Checkpoint (CKPT): CKPT is responsible for signaling the DBWn processes to perform a checkpoint. A checkpoint flushes modified database buffers to disk and updates the control file and data file headers. It helps in reducing the instance recovery time during a crash or failure.

6. Archiver (ARCn): The archiver process (ARCn) copies online redo log files to archive destinations for backup and recovery purposes. It ensures the availability of redo logs beyond the point of online log switching and enables point-in-time recovery.

7. Dispatcher (Dnnn): Dispatchers are used in Shared Server configurations, where multiple client connections are served by a smaller number of dedicated server processes. Dispatchers receive client requests and direct them to the appropriate dedicated server process.

8. Job Queue Processes (CJQn): Job Queue processes manage and execute scheduled jobs in the database. They handle tasks such as running stored procedures, executing PL/SQL blocks, or launching external programs as part of scheduled jobs.

These are some of the important background processes in Oracle Database. Each process plays a critical role in maintaining the integrity, availability, and performance of the database system.