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Re: Background Processes and I/O

From: Paul Drake <drak0nian_at_yahoo.com>
Date: 21 Dec 2003 09:01:00 -0800
Message-ID: <1ac7c7b3.0312210901.700b593f@posting.google.com>


"Michael J. Moore" <NOhicamelSPAM_at_comcast.net> wrote in message news:<ez9Fb.446468$275.1320599_at_attbi_s53>...
> --- snip---
>
>
> > >
> > > 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?

Pd Received on Sun Dec 21 2003 - 11:01:00 CST

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