Re: Background Processes and I/O

From: Ana C. Dent <anacedent_at_hotmail.com>
Date: Sat, 20 Dec 2003 20:33:55 -0800
Message-ID: <To9Fb.33100$BQ5.17333@fed1read03>

Michael J. Moore wrote:

> "Ana C. Dent" <anacedent_at_hotmail.com> wrote in message
> news:8t8Fb.32649$BQ5.21787_at_fed1read03...
> 

>>Michael J. Moore wrote:
>>
>>>Okay, but why would CKPT be any more true than SMON? Does not SMON also
>>>perform I/O?
>>>
>>>
>>>"Ana C. Dent" <anacedent_at_hotmail.com> wrote in message
>>>news:ZK6Fb.32237$BQ5.9627_at_fed1read03...
>>>
>>>
>>>>Michael J. Moore wrote:
>>>>
>>>>>From 9i Self Test ...
>>>>
>>>>>Which 4 background processes perform I/O? (Choose 4)
>>>>>
>>>>>* DBWn
>>>>>* ARCn
>>>>>* PMON
>>>>>* SMON
>>>>>* CKPT
>>>>>* LGWR
>>>>>-----------------
>>>>>I thought they all did, except CKPT which tells DBWn to do it, and PMON
>>>>>which only works with memory structures.
>>>>>
>>>>>Their answer was all except SMON and PMON. In reality, none of them do
>>>
>>>I/O
>>>
>>>
>>>>>because they call OS library routines to do the actual I/O. This is

> 
> why
> 


>>>I

>>>

>>>

>>>>>don't have a chance in hell of passing this test, because too many

>>>

>>>answers

>>>

>>>

>>>>>depend on how you consider the question. ;-)

>>>>>

>>>>>Any comments?

>>>>

>>>>I agree with "their" answer.
>>>>Which process writes to the control files?
>>
>>
>>Top posting is rude!
>>
>>DBW - does I/O to datafiles
>>ARC - Does I/O when archiving redo logfiles
>>CKPT- Updates control files.
>>LGWR- Writes redo logfiles.
>>To which file(s) does SMON read & write?
>>

> 
> 
> Sorry, I didn't know that top posting is rude.
> 
> SMON performs instance recovery, so it must read from redo logs. The manuals
> I have read are not clear on how SMON does this, but if it does read, then
> that counts as I/O, right? SMON also cleans up temporary segments anc
> coalesces free extents. Can it do this without performing I/O?

SMON might to I/O at instance startup; also to the rollback segments for uncommitted "transactions" (which I'll stipulate is an oxymoron).

I agree that the OCP test questions leave a lot to be desired. Received on Sat Dec 20 2003 - 22:33:55 CST