Re: Commit -> write to data file immediately???

currently learning ... how to operate my software!. that last sentence should have read

currently learning IIS4 & 5 in the context of web sites that crash too frequently and where the code is undocumented, and I have to do my dba work too.

--
Niall Litchfield
Oracle DBA
Audit Commission UK

mind you currently learning should be a permanent description for any DBA.

"Niall Litchfield" <n-litchfield_at_audit-commission.gov.uk> wrote in message
news:...


> That will teach me to post after a long day (and maybe never to post on

> checkpoints again).

>

> Last try to write something sensible.

>

> Checkpoint = flush dirty buffers to disk. I.E. DBWR writing.

>

> LOG_CHECKPOINT_TIMEOUT - Does exactly as Bruno describes for the purpose

> Bruno describes (read I was wrong sorry)

> LOG_CHECKPOINT_INTERVAL - Similar to the above, but specifies the interval

> in operating system blocks not seconds.

>

> I believe that the documentation says that DBWR only wakes up every 3

> seconds - However there was some posting earlier on saying that physical

> writes were happening every 3 seconds - verified by system monitoring

 tools.


>

> AS an aside it is probably worth taking more or less everything I say at

 the


> moment with a grain of salt. I am currently in the middle of learning

> --

> Niall Litchfield

> Oracle DBA

> Audit Commission UK

> "Bruno Jargot" <bjargot_at_club-internet.fr> wrote in message

> news:lc77ctk9vhctr1d7lpapc3ba70cs876eps_at_4ax.com...

> > On Thu, 29 Mar 2001 17:13:05 +0100, Niall Litchfield wrote:

> >

> > >"Norman Dunbar" <ndunbar_at_lynxfinancialsystems.co.uk> wrote in message

> > >news:F43E6BAE5BB5D411A44C00805FBE740D6DF36B_at_apps.lynx-fsc.co.uk...

> > >> >> Anyway, the most important misunderstanding above is the 3 second

> > >> >> timeout. DBWR will wake up every 3 seconds regardless of anything

> > >> >> else, but won't necessarily write anything at that point.

> > >>

> > >> Interesting. My course notes clearly state that there will be a

> > >> checkpoint 'n' seconds after the last one (but only if

> > >> LOG_CHECKPOINT_TIMEOUT is set to 'n' seconds.

> > >

> > >This sounds like the misuderstanding I was inadvertently responsible

 for


> > >posting to this group a while back.

> > >

> > >DBWR does write every 3 seconds. This is not a checkpoint (in the sense

 of


> > >writing the redo log buffer to disk). The LOG_CHECKPOINT_TIMEOUT

 controls


> > >how often LOG writer writes. (unless of course I've got it all

 terminally


> > >confused again).

> >

> > No.

> >

> > The checkpoint is when the buffer cache is flush in the datafiles and

> > not when the logwriter is writing in the redolog.

> >

> > And the LOG_CHECKPOINT_TIMEOUT controls how often there will be a

> > checkpoint. The goal of this parameter is to avoid, when the redolog

> > is big, having too much data in the redolog that are not written in

> > the datafiles and then reduce the time to recover if the database

> > crash.

>

>