This is one of the most frequently asked question.There are basically 9
Processes but in a general system we need to mention the first five
background processes.They do the house keeping activities for the
Oracle and are common in any system.
The various background processes in oracle are
a) Data Base Writer(DBWR) :: Data Base Writer Writes Modified blocks
from Database buffer cache to Data Files.This is required since the
data is not written whenever a transaction is commited.
b)LogWriter(LGWR) :: LogWriter writes the redo log entries to disk.
Redo Log data is generated in redo log buffer of SGA. As transaction
commits and log buffer fills, LGWR writes log entries into a online redo
log file.
c) System Monitor(SMON) :: The System Monitor performs instance
recovery at instance startup.This is useful for recovery from system
failure
d)Process Monitor(PMON) :: The Process Monitor peforms process
recovery when user Process fails. Pmon Clears and Frees resources
that process was using.
e) CheckPoint(CKPT) :: At Specified times, all modified database buffers
in SGA are written to data files by DBWR at Checkpoints and Updating
all data files and control files of database to indicate the most recent
checkpoint
f)Archieves(ARCH) :: The Archiver copies online redo log files to
archival storal when they are busy.
g) Recoveror(RECO) :: The Recoveror is used to resolve the distributed
transaction in network
h) Dispatcher (Dnnn) :: The Dispatcher is useful in Multi Threaded
Architecture
i) Lckn :: We can have upto 10 lock processes for inter instance locking
in parallel sql.