Re: Tuning DBWR

In article <85kn0u$v84$1_at_nnrp1.deja.com>,   sandrazil_at_my-deja.com wrote:
> In Disk A
> 1. Redo logs
> 2. System tablespace
> 3. Temporary tablespace
> In Disk B
> 1. All data files and Roll back segments
>
> Thanks,
>
> In article <387DB540.2AE20059_at_adicom.de>,
> Andreas Michler <Andreas.Michler_at_adicom.de> wrote:
> > Please give me the disk partitioning of your oracle files.
> > Were are Redo-Rollback,Datafiles.........
> >
> > sandrazil_at_my-deja.com wrote:
> >
> > > Hi All,
> > > I am having a performance problem whenever there is a log
switch,
> and
> > > when DBWR writes dirty buffer to disk. It takes 2 minutes for DBWR
> to
> > > complete its job, during that time there is a I/O Bottleneck. I am
> > > running Oracle 8.05 on HPUX 11.0 ( 32 bit), i am running 4
DBWR's. I
> > > have performace problem only during this 2 minute interval. Any
> > > Suggestions is highly appreciated,
> > >
> > > Thanks,
> > >
> > > Sandra
> > >

With only a two disk system you do not need 4 database writers. In fact, I do not believe that you should never have more writers than you have disks. One writer should be sufficient with only 2 disks. You probably have disk I/O contention between them.

How big are your redo logs? If you are generating more than 1 log every 5 minutes during peak time then you probably need to increase their size. I like to generate an average of 1 log per hour over a 24 hour day, but that is my preference not a rule. Larger redo logs decrease the number of checkpoints and hence the number of times dbwr must flush the buffer pool for dirty blocks assuming your have init.ora parameter log_checkpoint_interval set larger than your redo log.

Lastly, how many buffer pool database blocks do you have and at what Oracle block size is your system? If the above two items do not fix your problem then you can reduce the number of db buffers so that dbwr will have to write more often.

I think that about does it. Happy tuning. --
Mark D. Powell -- The only advice that counts is the advice that  you follow so follow your own advice --

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Before you buy. Received on Thu Jan 13 2000 - 17:26:42 CST