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SCN:system change number and alertlogfile [message #336471] Sun, 27 July 2008 09:58 Go to next message
Messages: 14
Registered: February 2008
Location: india
Junior Member
hi I have following ques:
1.when i start up database, in alert log file following information is displayed:
PMON started with pid=2
DBW0 started with pid=3
LGWR started with pid=4
CKPT started with pid=5
SMON started with pid=6
RECO started with pid=7
CJQ0 started with pid=8
QMN0 started with pid=9

What does it mean?

2.I fired command alter system set log_checkpoints_to_alert=true.
I get this information:
Beginning log switch checkpoint up to RBA [0x27.2.10], SCN: 0x0000.001a7a8b can anyone explain?

3.when the database is mounted,it says database is mounted in exclusive stage.What is exclusive stage means?
Re: SCN:system change number and alertlogfile [message #336472 is a reply to message #336471] Sun, 27 July 2008 10:01 Go to previous messageGo to next message
Messages: 24958
Registered: January 2009
Location: SoCal
Senior Member
Please read & follow Posting Guideline as stated in URL above

The complete Oracle Documentation set can be found at:

I suggest you take the time & effort to read the Concepts Manual.
Re: SCN:system change number and alertlogfile [message #336474 is a reply to message #336471] Sun, 27 July 2008 10:59 Go to previous messageGo to next message
Michel Cadot
Messages: 63911
Registered: March 2007
Location: Nanterre, France, http://...
Senior Member
Account Moderator
1. It means that some processes start.
Database Concepts, all this kind of questions are answered there.

2. Explain what? The detailed of the figures? You seem to not have sufficient knowledge to appreciate the answer. First read Database Concepts.

3. It means that database is mounted by one instance and for one instance only. See Database Concepts.

Re: SCN:system change number and alertlogfile [message #336676 is a reply to message #336474] Mon, 28 July 2008 12:02 Go to previous message
Messages: 506
Registered: March 2005
Senior Member
The below mention 5 are called background process, they are mandatory background process if any one of them is killed than oracle DB will go down

[1]PMON started with pid=2
[2]DBW0 started with pid=3
[3]LGWR started with pid=4
[4]CKPT started with pid=5
[5]SMON started with pid=6


PMON -->cleans user and server process
DBW0 -->Writes from buffer to disk and disk to buffer.
LGWR -->Write changes made to db into log file.
CKPT -->Updates SCN
SMON -->Instance Recovery.

REC0 -->Used in distributed DB
QMN0 -->Advance queueing
CJQ0 -->Co-ordinate Job queing.

Note :- Instance = Background process + Memory(SGA)

When oracle DB starts its maintain its log which is called alert log, if any error occur than that error is loged in alert log and so DBA can rectify and resolve the error.

when we issue alter system set log_checkpoints_to_alert=true.
Alert log is storing information of checkpoints

[Updated on: Mon, 28 July 2008 12:21]

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