0 Background Process in Oracle Database

An oracle Database instance runs on 2 types of processes
1) Server Process
2) Background Process

--Server process are created to take care of  requests from users connected to instance
--Background process are of two types Mandatory and Optional process

Mandatory Process

1) SystemMonitor(SMON)

The system monitor performs recovery when a failed instance is started again. It also cleans the temporary segments which not useful.This process also know as Instance Crash Recovery(ICR).
Any transaction  which are not updated to database file will be get updated after the reboot of system and this mechanism is called as ROLLFORWARD mechanism
Any transaction is partially got updated in database file that transaction will be rollback and this mechanism is called as ROLLBACK mechanism

2) Database Writer(DBWn)

This process writes the dirty--buffer present in the database-buffer-cache to datafile.DBWn process invokes under the following conditions
--when database shutdown gracefully
--when dirty block reaches to treshold value
--when a log-switch occurs
--when a check point is issued
--every 3sec timed out

3) Log Writer(LGWR)

Logwriter writes data from the redo log -buffers to the redo-log files on disk.This process invokes during these following points
--When a transaction is commit, a system change number (SCN) is generated and attaches to it.Log writer
keeps a  commit record in the redo log-buffer and then writes it to disk.
--Every 3sec
--When  redo log-buffer is one-third full

4) Process Monitor(PMON)

This process monitor performs process recovery when a user process is failed. It will get back to original position(rollback) when the transaction is uncommitted.Process monitor  also checks on the dispatcher process(user process) and server process and restarts again if failed.


Checkpoint invokes during following conditions

--When log-switch happens
--The newest SCN no is updated into datafile
--The newest SCN no is updated into control file
6) Recover(RECO)

The recover  is used to resolve distributed transactions that are not done completely due to some network problem or system failure in a database. 

Optional Processes

There are many optional process we can use depending on their useage.
Those process are listed below
  1. Archiver(ARCn)
  2. Recovery Writer(RVWR)
  3. Lock Monitor(LMON)
  4. Lock Manager Demon(LMDn)
  5. Lock Process(LCKn)
  6. Block Server Process(BSPn)
  7. Queue Monitor(QMN)
  8. Event Monitor(EVMN0)
  9. Shared Server Process(Snnn)
  10. Memory Manager(MMAN)
  11. Parallel Execution Slaves(Pnnn)
  12. Trace Writer(TRWR)
  13. DMON
  14. Dispatcher(Dnnn)
  15. MMON
  16. INPUT/OUTPUT  Slaves(Innn)
  17. Wakeup Monitor Light(WMON)
  18. Memory MonitorLight(MMON)
  19. Job Queue Process
  20. RBAL
  21. ARBx
  22. ASMB
  23. Change Tracking Writer
  24. Job Queue Monitoring

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