19. Oracle Processes

Processes

Oracle uses many small (focused) processes to manage and control the Oracle instance. This allows for optimum execution on multi-processor systems using multi-core and multi-threaded technology.

Some of these processes include:

PMON - Process Monitor

SMON - System Monitor

ARCn - Redo Log Archiver

LGWR - Redo Log Writer

DBWn - Database Writer

CKPT - Checkpoint process

RECO - Recoverer

CJQn - Job Queue Coordinator

QMNn - Queue-monitor processes

Dnnn - Dispatcher Processes (multiplex server-processes on behalf of users)

Snnn - Shared server processes (serve client-requests)

MMAN - Internal process (used for internal database tasks)

LSP0 - Logical standby coordinator process (controls Data Guard log-application)

MRP - Media-recovery process (detached recovery-server process)

MMON - Memory-monitor process

MMNL - Memory monitor light (gathers and stores AWR statistics)

PSP0 - Process-spawner (spawns Oracle processes)

RFS - Remote file server process (archive to a remote site)

DBRM - DB resource manager (new in 11g)

DIAGn - Diagnosability process (new in 11g)

FBDA - Flashback data archiver process (new in 11g)

VKTM - Virtual Timekeeper (new in 11g)

Wnnn - Space Management Co-ordination process (new in 11g)

SMCn - Space Manager process (new in 11g)

An instance can mount and open one and only one database.
A database can normally only be mounted and opened by one instance. However, when using Real Application Clusters (RAC) a database can be mounted and opened by many instances.