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Re: BCHR Tuning

From: <>
Date: Mon, 13 Jan 2003 09:25:27 -0800
Message-ID: <>

I too think the BCHR has its place, as a problem indicator. It can tell me theres something wrong with my database. Say, I have this database performing well, the users are happy, the BHR is mostly at 90%, and now it suddenly shoots down to 70%, or it suddenly increases to 98. Somethings amiss. Its less tasking, to code for scripts that query v$sysstat to indicate me of some problems, rather than querying v$sqlarea. Or I need to code for some intelligent scripts to query v$session_wait or V$system_event. Or I need to look at the statspack reports every hour. The point is when do I look at wait events? When the user calls me up?

All the papers out there, asking us rightly, to look at wait events, trash the BCHR. I think what the authors intended was to tell us that increasing DB_BLOCK_BUFFERS was not the solution to a low BCHR, and that a BCHR of 99% does not mean a highly efficient database. Vice Versa, a BCHR of 50% does not indicate a poorly performing database. Give me a database with a 45% BHR, and I can get it to 99% by running a few queries. Point well understood. It does not mean in any way that I should now ignore PIO's and start tuning LIO's.

I still use BCHR. "What you infer from the BCHR is what counts".


                    Adar"                To:     Multiple recipients of list ORACLE-L <>        
                    <adar76_at_inter        cc:                                                                        
          >             Subject:     Re: BCHR Tuning                                               
                    Sent by:                                                                                        
                    January 13,                                                                                     
                    2003 10:58 AM                                                                                   
                    respond to                                                                                      

Hello Anjo

I just had a tuning session with Dov Hit, from ACS in Israel. He used some of the scripts that you showed him 2 years ago when you did some work for Amdocs.
Anyway, after doing some search on the waits, he checked the BCHR and found out that this database has only 40%. That led us on further checks and we found more offending SQL's.

The BCHR has it's place.
Just do not measure yourself JUST by it.

Yechiel Adar
----- Original Message -----
To: Multiple recipients of list ORACLE-L <> Sent: Monday, January 13, 2003 3:03 AM

> Hmm,
> Lately? That actually started publicly in 1998 as far as I am concerned
> And acutally long before that.
> Anjo.
> ----- Original Message -----
> To: "Multiple recipients of list ORACLE-L" <>
> Sent: Sunday, January 12, 2003 11:43 PM
> > On Friday 10 January 2003 14:48, Mogens Nørgaard wrote:
> > > Obviously, we don't know what we're talking about. I can see there's
> > > presentation by Rich Niemich at IOUG-A where he'll address all those
> > > idiots who are saying you should ignore the Cash Hit Ratio (and who
> > > all just after making big money on their products - I loved that
> > > > Or modify the set up of these tools to take action when BCHR
> falls......
> > > >
> >
> > Here's the session info:
> >
> > Date: Mon, Apr 28, 2003 @ 11:45 AM - 12:15 PM
> > Venue: Southern Hemisphere 2, Walt Disney World
> > Dolphin, Lake Buena Vista, FL
> >
> > Abstract: Lately, there has been a big push to ignore your
> > hit ratio with claims that it is meaningless. This shallow
> > minded view (usually by people who sell a tuning tool) ignores
> > why people look at hit ratios and what they are looking for.
> > This quick tip talk will show you what to look for and why.
> > You will definitely know when, where & why to look at your
> > hit ratio in the future.
> >
> > Show you why your hit ratio matters. How to analyze the
> > hit ratio. Fallacies by those who want to sell you products
> > and tools instead.
> >
> >
> > Shallow Minded ?!
> >
> > Jared
> > --

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Received on Mon Jan 13 2003 - 11:25:27 CST

Original text of this message