Different processes in oracle database

[Aileen_L]

what are the different processes in oracle database and what are the benefits of their existence.Please explain me with detailed information of these process.When I use the command "ALTER SYSTEM SWITCH LOGFILE " It occur some error like "ORA-00470 LGWR found dead - Oracle " what it means and why it showing like this.Can you explain the existence of background processes.

[Praetor]

Processes :

There are so many processes and services is being used by the oracle database.But at this point, we will explore only those processes which are mandatory and used a lot . They are collectively known as background processes . Each process performs its own job to complete the requirement of task.

[Katty]

SMON -

System Monitor process(SMON) is responsible to take care of recovery operation after instance failure.It helps to manage the roll forward and roll back phases.

PMON -
PMON perform the maintain and restarts any failed or dead processes which can be dispatcher or server process.It also removes the row lock which is done due to the changes of particular block in datafile.

[kelfro]

DBWR -
The database writer is a mandatory process of oracle database instance which performs the writing operation after any checkpoint occur.It takes the changes buffer from the buffer cache and write onto the datafile.

LGWR -
Log Writer process is a part of background process which is responsible to take the redo entries from log buffers and writes on the redo log file.

[Zecho]

CKPT –
The checkpoint process is responsible to write the SCN (System change number) on datafile and controlfile respectively.It performs writing operation when the online redo log file is filled-up.It makes balance of synchronization of database.

ARCn-
This ARCn(archive) process keeps the backup of every transaction of database . it takes the redo entries from online redo log file and writes on archive log files.These are archive files which is used to perform the recovery of database.