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Oracle Instance Management


An Oracle database server consists of an Oracle database and an Oracle instance. An Oracle instance is made up of memory structures, known as the System Global Area (SGA), and background processes that handle much of the behind-the-scenes work involved in running an instance. The most common background processes are the following:

System Monitor (SMON): Performs crash recovery when the instance is started following a failure

Process Monitor (PMON):
Performs process cleanup when a user process fails

Database Writer (DBWn):
Writes modified blocks from the database buffer cache to the data files on the disk

Checkpoint (CKPT):
Updates all the data files and control files of the database to indicate the most recent checkpoint

LogWriter (LGWR):
Writes redo log entries to the disk

Archiver (ARCn):
Copies redo log files to the archival storage when a log switch occurs