ORACLE Primary Background process

Table 5-4 Oracle Database Background Processes

Process Name	Description
Database writer (DBWN)	The database writer writes modified blocks from the Database buffer cache to the data files. Oracle database allows a maximum of the database writer processes (DBW0-DBW9 and DBWA-DBWJ). The db_writer_processes  initialization parameter specifies the number of Dbwn processes. The database selects an appropriate default setting for this initialization parameter or adjusts a user-specified setting Based on the number of CPUs and the number of processor groups. For more information about setting The db_writer_processes  initialization parameter, see The oracle Database performance Tuning guide .
log writer (LGWR)	The Log writer Process writes redo log entries to disk. Redo log entries is generated in the Redo log buffer of the system global Area (SGA). LGWR writes the redo log entries sequentially into a redo log file. If the database has a multiplexed redo log, then LGWR writes the redo log entries to a group of redo log files. See chapter, "Managing the Redo Log"  for information about the log writer process.
checkpoint (CKPT)	at specific times, All modified database buffers in the system global area is written to the data files by Dbwn. This event is called a checkpoint. The checkpoint process is responsible for signalling Dbwn at checkpoints and updating all the DA TA files and control files of the database to indicate the most recent checkpoint.
system Monitor (Smon)	The System Monitor performs recovery when a failed instance starts up again. In a Oracle Real application Clusters database, the Smon process of one instance can perform instance recovery for other Instances that has failed. Smon also cleans up temporary segments that is no longer in use and recovers terminated transactions skipped during Syste m failure and instance recovery because of file-read or offline errors. These transactions was eventually recovered by Smon when the tablespace or file was brought back online.
process Monitor (Pmon)	The Process Monitor performs process recovery when a user process fails. Pmon is responsible for cleaning up the cache and freeing resources, the process was using. Pmon also checks on the dispatcher processes (described later in this table) and server processes and restarts them if the Y has failed.
archiver (Arcn)	one or more Archiver Processes copy the redo log files to archival storage when they is full or a log switch occurs. Archiver processes is the subject of chapter, "Managing archived Redo Logs".
recoverer (RECO)	the recoverer process is used to resolve distributed transactions This is pending because of a network or system failure In a distributed database. At timed intervals, the local RECO attempts to connect to remote databases and automatically complete the commit or Rollba CK of the local portion of any pending distributed transactions. For information approx. this process and how to start it, See chapter, "Managing Distributed Transactions".
Dispatcher (Dnnn)	Dispatchers is optional background processes, present if the shared server configuration is used. Shared server was discussed previously in "Configuring Oracle Database for Shared server".

"From:http://docs.oracle.com/cd/E11882_01/server.112/e25494/manproc.htm#ADMIN11186"

ORACLE Primary Background process