Re: Log file I/O throughput

mccmx_at_hotmail.com (Matt) wrote in message news:<cfee5bcf.0308130306.72bacefe_at_posting.google.com>...
> Thanks very much for your response.
>
> The fact that the wait count is so high but the OS I/O is not
> bottlenecked must mean that the commit rate is much too high.
>
> I will speak to the app provider about increasing the commit
> interval....
>
> Matt
>
> Stephan Bressler <agadir_at_web.de> wrote in message news:<3F378225.5000101_at_web.de>...
> > > By far the most significant waits occuring in the database are for
> > > 'log file sync' and 'log file parallel write'.
> ... snip
> > > The reason I am hesitating is that the Unix Sys Admin (HP-UX) has run
> > > some I/O diagnostics on the server (sar, glance, and iostat) and we
> > > can see that there
> > > is no bottleneck at the operating system level. However I know for
> > > sure that Oracle is generating at least 100 x 80Mb redo log files
> > > every day.
> .. snip
> > > Any ideas....?
> > Hi,
> >
> > your redo writing is fast? Still have waits?
> > That usually indicates that your session are doing many short
> > transactions. A session has to wait on every commit for the lgwr to
> > flush the redo log buffer. Even on very fast disks this take 5-10msec,
> > exspecially if you configure several log groups.
> > So go and check the number of user commits and the relation of "redo
> > writes" (=background writes) and "redo synch writes" (=forced writes).
> > I believe the only working solution in your case to lower the commit rate.
> >
> > Regards
> > Stephan

enable write-back caching on the RAID conroller, if one is used.

cautions:
you best have a battery backup on the RAID conroller cache (that you recharge annually)
UPS required on server.
shutdown immediate of instance configured in the event that UPS is in use and has n minutes left.
shutdown abort of instance configured in the event that UPS is in use and has less than n minutes left.
sync of filesystem and controller cache configured so that you are certain that filesystem is flushed to disk shutdown of server configured so that you are certain that filesystem is flushed to disk

write-back caching is great at reducing events due to writes. it sucks if you lose what is in the cache, meaning, a corrupt database.

hth.

Pd Received on Wed Aug 13 2003 - 15:24:24 CDT