Oracle in Action - Oracle 10g Database Administration Concepts and Implementation Made Simple - page 122

Things to Remember Before Moving Ahead
1) Figure 5-1: Background processes of Oracle Instance.
Oracle Instance running under Shared Server Mode is
shown. Oracle two modes of operations: Shared Server,
Dedicated Server. Utilizing Shared Server mode you can
have least Idle Time but performance would not be as
that of Dedicated Server mode. If system resources are
not a problem keeping in mind the connected users, then
always go with dedicated server mode. Software
application (e.g. MS Word) has GUI whereas a Software
Process is independent of GUI and requires no user
interaction (e.g. LGWR). Depends on the way you
program a Process, usually a process runs when certain
event happens and re-runs if the event happens again.
DBWR writes the dirty buffers from Database Buffer
Cache to the data files. LGWR writes the redo log
buffers from Redo Log Cache to the redo files. Log
Switch happens whenever LGWR process finishes
writing one Redo Log file and moves to the next one.
LGWR process will start new ARCn process whenever
ARCn gets overloaded. PMON frees up the resources
from a failed user process. SMON is responsible for
Instance recovery, if necessary.
2) Figure 5-3: Background processes of Oracle Instance.
Oracle Instance running under Dedicated Server Mode
is shown. Oracle running under Dedicated Server mode
works the same as Shared Server mode except that a new
server process gets created to serve the new logged in
user. Idle Time of Server process(es) will be more
compared to Shared Server environment. For unlimited
resources, always go with Dedicated Server Mode
otherwise stick with Shared Server Mode.