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

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.