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. ;-)
> 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?
> 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?
>>>* 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?
> >>>* 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?
>>>>>* 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.
> > 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.
Well you did straighten me out about CKPT ... thanks. It is interesting that even in the Oracle manuals, their diagrams never show SMON pointing to any of the files, only pointing to the SGA. This leaves me wondering if SMON actually performs it's own I/O or invokes some other process to do it's dirty work. I wish they would give a little more detail.
> > > 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.
> Well you did straighten me out about CKPT ... thanks. It is interesting that > even in the Oracle manuals, their diagrams never show SMON pointing to any > of the files, only pointing to the SGA. This leaves me wondering if SMON > actually performs it's own I/O or invokes some other process to do it's > dirty work. I wish they would give a little more detail.
normally, for a user process, a logon trigger could be used to trace it (event 10046). I've seen text indicating that an instance crash is likely if you trace PMON, but I don't know if that is true for SMON. So lets just leave that at the usual "don't run it against a database that you can't destroy/corrupt". Then again, the trace file might be so cryptic that only an x$_% wizard (fluent in elvish) could read it.
I believe that LGWR can also write to the controlfiles. I've seen a trace file where a controlfile was locked by a backup process (infidels!) and LGWR crashed before CKPT did. Hmmm, does PMON perform any IO when it takes down the instance?
Smon kicks in every 5 minutes to query ts$ to check if any dictionary-managed tablespaces have pctincrease non-zero, and then tries to coalesce them. THere are several other jobs that smon does which are also visible as standard SQL querying, and therefore require normal database read requests.
> > > 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.
> Well you did straighten me out about CKPT ... thanks. It is interesting that > even in the Oracle manuals, their diagrams never show SMON pointing to any > of the files, only pointing to the SGA. This leaves me wondering if SMON > actually performs it's own I/O or invokes some other process to do it's > dirty work. I wish they would give a little more detail.
If pmon is recovering a process, it has to do a rollback on behalf of that process. Consequently it has to read the rollback blocks in reverse order, and the datablocks as required.
For a long-running transaction, many undo blocks and some data blocks are likely to be on disc, so pmon will have to re-read them in the normal fashion.
During testing, I've never seen the database crash on a normal sql_trace=true in the init.ora, and the resulting traces from pmon et. al. have been quite interesting.
> > > > 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.
> > Well you did straighten me out about CKPT ... thanks. It is interesting that > > even in the Oracle manuals, their diagrams never show SMON pointing to any > > of the files, only pointing to the SGA. This leaves me wondering if SMON > > actually performs it's own I/O or invokes some other process to do it's > > dirty work. I wish they would give a little more detail.
> normally, for a user process, a logon trigger could be used to trace > it (event 10046). I've seen text indicating that an instance crash is > likely if you trace PMON, but I don't know if that is true for SMON. > So lets just leave that at the usual "don't run it against a database > that you can't destroy/corrupt". Then again, the trace file might be > so cryptic that only an x$_% wizard (fluent in elvish) could read it.
> I believe that LGWR can also write to the controlfiles. I've seen a > trace file where a controlfile was locked by a backup process > (infidels!) and LGWR crashed before CKPT did. Hmmm, does PMON perform > any IO when it takes down the instance?
> Smon kicks in every 5 minutes to query ts$ to check > if any dictionary-managed tablespaces have pctincrease > non-zero, and then tries to coalesce them. THere are several > other jobs that smon does which are also visible as standard > SQL querying, and therefore require normal database read > requests.
I'm pretty sure, and I don't know how the question was phrased in your test, but at 8i that the which processes do IO question seemed to regard only writes as IO and not reads.
-- Niall Litchfield Oracle DBA Audit Commission UK ***************************************** Please include version and platform and SQL where applicable It makes life easier and increases the likelihood of a good answer ****************************************** "Michael J. Moore" <NOhicamelS...@comcast.net> wrote in message news:vdmFb.12034$VB2.21282@attbi_s51...
> > Smon kicks in every 5 minutes to query ts$ to check > > if any dictionary-managed tablespaces have pctincrease > > non-zero, and then tries to coalesce them. THere are several > > other jobs that smon does which are also visible as standard > > SQL querying, and therefore require normal database read > > requests.
> 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. ;-)
70,781 physical reads. This btw is the 2nd highest i/o process currently on the prod db I pulled these stats from.
Personally I think things like OCP and MSE certifications are worth crap. It is like those arses who think that a penis enlargement means they will be better at sex.
