Oracle 12c Background Processes

In startup order, the processes running on my test Oracle 12c instance are shown below. Those below the "empty" line are not started on my system, but either start later, or are fairly common and are included for completeness.

Process Name Description

PMON Process Monitor Cleans buffer cache and frees resources when processes die/are killed.
Restarts Oracle processes which have died/been killed (unless stopped by Oracle)

PSP0 Process Spawner Instance startup process to spawn other background Oracle processes

VKTM Virtual Keeper of Time Tracks time
a) "wall clock" with one second interval, and
b) high resolution for interval measurement

GEN0 General Task Execution Performs SQL and DML, but I don't yet know for what purpose

MMAN Memory Manager Instance memory management - resizing of memory areas

DIAG Diagnostic Capture Performs diagnostic dumps when requested by other processes

DBRM Database Resource Manager Resource plan management related tasks

DIA0 Diagnostic Detects and resolves hangs and deadlocks

DBW0 Database Writer Writes dirty/modified buffer cache blocks to disk

LGWR Log Writer Uses LGnn to write redo log buffer to disk on every commit,
wakes up every three seconds, and may write when it wakes up
writes redo before DBWx can write an associated dirty block

CKPT Checkpoint Update headers of all datafiles when a checkpoint is performed

SMON System Monitor Perform recovery at instance startup or tablespace being brought online.
Cleans up TEMP segments which have been finished with.
Coalesces contiguous free extents in dictionary managed tablespaces.

RECO Recoverer Tidies up after failed distributed transactions

LREG Listener Registration Registers database information with the listener

MMON Manageability Monitor Maintains AWR (Automatic Workload Repository) data

MMNL Manageability Monitor Lite Write statistics from the SGA ASH buffer to disk

TMON Transport Monitor Rumoured to be related to threading processes in 12c, seems to wake up every three seconds

SMCO Space Management Coordinator Coordinates Wnnn slave processes to reclaim space, and proactively allocate space

AQPC AQ Process Coordinator Admin for Advanced Queueing

CJQ0 Job Queue Coordinator Used for batch processes
- - -

ARC0 Archiver Copies online redo log files to offline storage, including to standby databases

Dnnn Dispatcher Process Performs network communication

FBDA Flashback Data Archive Stores "before change" versions of rows in tracked tables

Jnnn Job Queue Slave Process spawned by CJQ0 to run one or more job(s)

LGnn Log Writer Worker Spawned by LGWR to write redo to the online redo log

Pnnn Parallel Query Slave

Qnnn AQ Server Class Process

QMnn AQ Master Class Process

Snnn Shared Server Process

TTnn Redo Transport Slave Ships redo from current online and standby redo logs to remote standby

Wnnn Space Management Worker Slave process spawned by SMCO to allocate or reclaim space

Process	Name	Description
PMON	Process Monitor	Cleans buffer cache and frees resources when processes die/are killed. Restarts Oracle processes which have died/been killed (unless stopped by Oracle)
PSP0	Process Spawner	Instance startup process to spawn other background Oracle processes
VKTM	Virtual Keeper of Time	Tracks time a) "wall clock" with one second interval, and b) high resolution for interval measurement
GEN0	General Task Execution	Performs SQL and DML, but I don't yet know for what purpose
MMAN	Memory Manager	Instance memory management - resizing of memory areas
DIAG	Diagnostic Capture	Performs diagnostic dumps when requested by other processes
DBRM	Database Resource Manager	Resource plan management related tasks
DIA0	Diagnostic	Detects and resolves hangs and deadlocks
DBW0	Database Writer	Writes dirty/modified buffer cache blocks to disk
LGWR	Log Writer	Uses LGnn to write redo log buffer to disk on every commit, wakes up every three seconds, and may write when it wakes up writes redo before DBWx can write an associated dirty block
CKPT	Checkpoint	Update headers of all datafiles when a checkpoint is performed
SMON	System Monitor	Perform recovery at instance startup or tablespace being brought online. Cleans up TEMP segments which have been finished with. Coalesces contiguous free extents in dictionary managed tablespaces.
RECO	Recoverer	Tidies up after failed distributed transactions
LREG	Listener Registration	Registers database information with the listener
MMON	Manageability Monitor	Maintains AWR (Automatic Workload Repository) data
MMNL	Manageability Monitor Lite	Write statistics from the SGA ASH buffer to disk
TMON	Transport Monitor	Rumoured to be related to threading processes in 12c, seems to wake up every three seconds
SMCO	Space Management Coordinator	Coordinates Wnnn slave processes to reclaim space, and proactively allocate space
AQPC	AQ Process Coordinator	Admin for Advanced Queueing
CJQ0	Job Queue Coordinator	Used for batch processes
-	-	-
ARC0	Archiver	Copies online redo log files to offline storage, including to standby databases
Dnnn	Dispatcher Process	Performs network communication
FBDA	Flashback Data Archive	Stores "before change" versions of rows in tracked tables
Jnnn	Job Queue Slave	Process spawned by CJQ0 to run one or more job(s)
LGnn	Log Writer Worker	Spawned by LGWR to write redo to the online redo log
Pnnn	Parallel Query Slave
Qnnn	AQ Server Class Process
QMnn	AQ Master Class Process
Snnn	Shared Server Process
TTnn	Redo Transport Slave	Ships redo from current online and standby redo logs to remote standby
Wnnn	Space Management Worker	Slave process spawned by SMCO to allocate or reclaim space