Sunday, December 25, 2011

Oracle background processes.

An Oracle instance consists of many background processes; not all the processes running all the time; only mandatory process is running continuously and other processes may spawn on demand or the configuration of Oracle instance. With each release oracle had some new background process added with some new features.
You can view the background processes running on your system by issuing the following SQL query

SELECT * FROM V$BGPROCESS
WHERE PADDR != '00'
ORDER BY NAME;

The common background processes in an Oracle instance include the following:

Mandatory
· Database Writer (DBWR)
· Log Writer (LGWR)
· Checkpoint (CKPT)
· System Monitor (SMON)
· Process Monitor (PMON)
Optional
· Archiver (ARCn)
· Recoverer (RECO)
· Queue Time Manager Process (QMNn)
· Dispatcher (Dnnn) (Present when MST/Shared Server configuration is used.)
· shared server processe (Snnn)
· Coordinator Job Queue Process (CJQ)
· Parallel Query Slaves(Pnnn)
· Wakeup Monitor process(WMON)
· File Mapping Process (FMON) (FMON is a background process started by Oracle file_mapping is set to TRUE)
· Trace writer (TRWR)
· Input/output Slaves(Innn)
· Job queue process (Jnnn)
· event monitor coordinator(EMNC)
· Block server Process (BSPn)


Oracle10g introduced new background processes.
· Manageability Monitor (MMON also called as Memory Monitor).
· Manageability Monitor Light (MMNL)
· Memory Manager (MMAN)
· Recovery Writer process (RVWR)
· Change Tracking Writer (CTWR)
· MMON background slave (m000) processes
.

Data guard/stream related Background processes
· Data Guard Broker process ( DMON).
· Managed recovery process(MRP)
· Remote File Server process(RFS)
· Queue Monitor Process (QMNC) (monitors message queue and used by oracle stream advance queueing)
· Logical standby process (LSP)
· DR Resource Manager Process(RSMn)
· DR Server NetSlave or dataguard Net server Process(
NSVn)
· DR Partner Process (DRCn) (Partner process of NSV process at standby)
· The snapshot process (SNP) (obsolete in 10g and above).
· communicates with the Automatic Storage Management instance (OSMB).
· data extent rebalance in an Automatic Storage Management instance (ORBn).

Oracle ASM related background process.
· Re-balancer (RBAL)
· Re-balancer child (ARBx)
· ASM Bridge process (ASMB)


Oracle RAC related background process
· Diagnosability Daemon (DIAG)
· process manages the global enqueue requests and the cross-instance broadcast (LCKx)
· Global Enqueue Service Monitor (LMON)
· Global Enqueue Service Daemon (LMDx)
· Global Cache Service Processes (LMSx)
· Global transaction processes(GT
X0-j) (provide transparent support for XA global transactions in an Oracle RAC environment)
· atomic control file to memory service(ACMS)

Oracle11g introduced new background processes.
Oracle 11g introduced about 56 bg processes, some mandatory processes are
· DB resource manager(DBRM)
· Virtual Timekeeper (VKTM)
· Flashback data archiver process(FBDA)
· Diagnosability process (DIA0)
· Space Management Co-ordination process (w000)
· Space Management coordinator process (SMCO)


Next we will discuss the working of these processes…..

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