Re: log buffer space vs. redo log space requests

Thanks, for the input guys! Here is some more information...

My log buffer is at 2Megs when I was observing these waits.

There are 4 groups of online redo logs of 20 megs each. When the app was running under a regular load I noticed that the logs were switching at around 45 seconds. So I have since bumped by log files up to 200Megs each and waiting to see what this will give. I was thinking that the log switches were causing the LGWR to fall behind.

If this fails I will try increasing my log buffer again.

What do you think about decreasing the checkpoint timeout/ interval so there is less work to do once a log switch does come around.

Thanks,
scott.

"Mark J. Bobak" <mark.NOSPAM_at_bobak.net> wrote in message news:20010530.203754.1244316437.24699_at_bobak.net...
> In article <9f3b7i0cci_at_drn.newsguy.com>, "Thomas Kyte"
> <tkyte_at_us.oracle.com> wrote:
>
> > In article <ip7R6.748$m76.424872_at_news20.bellglobal.com>, "Scott says...
> >>
> >>I am a little confused as to the values I am getting from these two
> >>statistics.
> >>
> >>log buffer space in V$SYSTEM_EVENT shows a value for waits which leads
> >>me to believe that the log buffer is not large enough however the redo
> >>log space requests from V$SYSSTAT shows a value of zero.
> >>
> >>Therefore one stat tells me there is not enough space while the other
> >>tells me everything is ok. I think I am misinterpreting these
> >>statistics. Can someone set me straight.
> >>
> >>Oracle 8.1.6 running on solaris.
> >>
> >>thanks,
> >>Scott.
> >>
> >>
> >>
> >>
> >>
> > log buffer space is a wait for space in the redo log buffer (in the
> > SGA). you'll get this when your log buffer is too small or LGWR is not
> > able to empty it fast enough (slow IO)
> >
> > redo log space is a wait for space in the physical online redo log file
> > (on disk). you might get this on a "checkpoint not complete".
> >
> > The are somewhat un-related.
> >
> > Thomas Kyte (tkyte_at_us.oracle.com) Oracle Service Industries Howtos and
> > such: http://asktom.oracle.com/ http://asktom.oracle.com/~tkyte/ Oracle
> > Magazine: http://www.oracle.com/oramag Opinions are mine and do not
> > necessarily reflect those of Oracle Corp
> >
>
> In addition to what Tom said, if you have log buffer space waits,
> this could be due to excessive log switches, which cause a backlog
> in the log buffer.
>
> How big are your log files?
> How big is your log buffer?
> How often are you seeing log switches?
>
> Also, Steve Adams has some good info on log buffer and log file
> tuning, check out http://www.ixora.com.au/
>
> Hope that helps,
>
> -Mark
Received on Wed May 30 2001 - 22:17:29 CDT