I started working with Oracle 6.0. Back then, the BHR was one of THE
standard ways of looking at performance issues, and even all the Oracle
books back then recommended it. Low BHR, increase db_block_buffers. This
was what was followed. I admit, I did it too. Then came Oracle 7.3 and
Oracle 8 where a DBA could look at wait events. And then the works of Gurus
like Craig Shallahamer showed that this was not the right way. These works
convey to me that a BHR of 99% does not mean a highly efficient database.
Vice Versa, a BHR 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. Thats all I read into it. It does not mean
in any way that I should now ignore PIO's and start tuning LIO's. It also
does not mean that if the BHR is 99%, I have an LIO problem.
I must admit that I do sometimes tend to use the BHR, like Mladen. It can
be an indicator that theres something wrong with the database. I have this
database performing well, the users are happy, the BHR is mostly at 90%,
and now it suddenly shoots down to 70%. Someone's sneaked in a query he
should not.
What you infer from the BHR is what counts.
Moi 0.02$
Raj
"Gogala,
Mladen" To: Multiple recipients of list ORACLE-L
<[EMAIL PROTECTED]>
<MGogala@oxhp cc:
.com> Subject: RE: missed Anjo's webcast..
Sent by:
root@fatcity.
com
August 08,
2002 04:31 PM
Please
respond to
ORACLE-L
Well, I guess that I disagree. Buffer hit radio does matter as one of the
performance indicators, but
certainly not the only one. Your and Mr. Milsap thesis is that LIO also is
very expensive and its cost
is far from being negligible, so having gazillion of LIOs instead of 100
times smaller number of PIOs will
not make our system run faster. BHR alone cannot be used to judge to
overall health of the system, but
thebn again, there is no such thing as the "overall health of the system".
It's the users of the system who
will say whether the performance is satisfactory or not, and I'm usually
tuning an application, not an
imaginary "overall system". Low cache hit ratio usually tells me that I do
have a hog who is using lots
of PIOs. By my experience, it usually is a very good indicator that
something is wrong, at least on an OLTP
system. So, after all, I do find BHR a useful indicator, but by no means
the only one or the most important
one. Event 10046, SQL_TRACE (level 1 of 10046), explain plan and
v$session_event still are the tools
I need most, but I still do need BHR as an indicator.
Mladen Gogala
Oracle DBA
Phone: (203) 459-6855
Email: [EMAIL PROTECTED]
-----Original Message-----
From: Anjo Kolk [mailto:[EMAIL PROTECTED]]
Sent: Thursday, August 08, 2002 1:05 PM
To: Multiple recipients of list ORACLE-L
Subject: Re: missed Anjo's webcast..
Moi wrong ;-) Jeeh, human after all
To summarize the webcast:
db-block-buffers do mattter. Too many LIO do matter. Too many PIO do
matter. But Buffer Cache Hit ratio doesn't matter ....... End user
satisfaction does matter.
I am always willing to clarify any points that I made, you just have to
ask me l ....
Anjo.
----- Original Message -----
From: [EMAIL PROTECTED]
To: Multiple recipients of list ORACLE-L
Sent: Thursday, August 08, 2002 5:43 PM
Subject: RE: missed Anjo's webcast..
Guys,
I had this dream that I missed the webcast - which I did. However,
someone said it wasn't very interesting but the conversation of the people
(gurus) left over was very interesting as there was good solid evidence
that he was incorrect and db_block_buffers do matter. Kind of inline with
the discussion about redos yesterday and my indexing/partition issues -
hmmm.
-----Original Message-----
From: Mladen Gogala [mailto:[EMAIL PROTECTED]]
Sent: Thursday, August 08, 2002 1:38 AM
To: Multiple recipients of list ORACLE-L
Subject: Re: missed Anjo's webcast..
Www.precise.com, go to Events->webcasts...
On 2002.08.08 00:53 Madhusudhanan Sampath wrote:
> Are transcript documents available anywhere?
>
> Regards
> Madhusudhanan S
--
Mladen Gogala
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