Oracle FAQ Your Portal to the Oracle Knowledge Grid
HOME | ASK QUESTION | ADD INFO | SEARCH | E-MAIL US
 

Home -> Community -> Usenet -> c.d.o.server -> Re: Oracle Myths

Re: Oracle Myths

From: Fraser McCallum <fmcc_at_removetoemail_odbaguru.com>
Date: Wed, 15 May 2002 23:10:01 +1000
Message-ID: <n0tE8.10994$b5.37784@newsfeeds.bigpond.com>


Jeff,

If you check your buffer cache hit ratio in the traditional way the cache misses can include the direct reads which no amount of buffer cache tuning can eliminate. Off the top of my head temporary tablespaces are an example of something that does direct reads. I know that Steve Adams has scripts that take all of this into account somewhere on his web site www.ixora.com.au as well as probably some more in-depth details.

Increasing the shared pool size in response to a bad library hit ratio will create more memory in which the database will create longer free lists and thus ultimately increasing the time taken to scan these lists and making your hit ratio worse. However after you restart the database when their is still lots of free chunks things will appear to have been made better, thus many DBA's fall into a cycle of continuos enlargement.

Kind Regards,

Fraser McCallum
MVP Oracle Administration
www.brainbench.com

"Jeff Traigle" <traigle_at_si.umich.edu> wrote in message news:B907C95A.139FB%traigle_at_si.umich.edu...
> Most of the myths you posted I've not followed anyway. However, these two
I
> would appreciate more info about. The corporate DBAs in my company wrote a
> script that checks some basic performance metrics. Two of the items that
it
> checks are buffer cache hit ratio and library cache hit ratio.
>
>
> On 5/15/02 4:25 AM, in article
> 3ce21b71$0$8510$ed9e5944_at_reading.news.pipex.net, "Niall Litchfield"
> <n-litchfield_at_audit-commission.gov.uk> wrote:
>
> > Suggested list to be added to, deleted from etc
> >
> > Buffer cache hit ratio should be as high as possible preferably greater
than
> > 90%.(from the java tool we use developed in house)
> >
> > Library Cache hit ratio should be greater than 99% if it isn't increase
the
> > size of the shared pool.(ditto!)
>
> --
> Jeff Traigle
> traigle_at_si.umich.edu
> http://www-personal.si.umich.edu/~traigle/
>
Received on Wed May 15 2002 - 08:10:01 CDT

Original text of this message

HOME | ASK QUESTION | ADD INFO | SEARCH | E-MAIL US