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RE: db_block_lru_latches

From: Cary Millsap <cary.millsap_at_hotsos.com>
Date: Wed, 03 Jul 2002 15:13:21 -0800
Message-ID: <F001.0048F87F.20020703151321@fatcity.com>


These numbers are all virtually zero. There have been virtually no sleeps since your instance was last restarted.

Now, what this kind of query DOESN'T show is whether any of those sleeps consumed dozens of seconds of some user's response time. Having an infinitesimally small number of sleeps per get is, I guess, better than having a large number of sleeps per get. But it's impossible from just this ratio to determine whether you have a performance problem or not. (This type of flaw is inherent in virtually *any* ratio query.)

<advice>If you're experiencing system performance problems, analyze the response times of the problem sessions. See www.hotsos.com/dnloads/1/10046a for one way of doing it.</advice>

<advice type="corollary">DON'T start at the inside of your database looking for ratios that may or may not indicate a response time problem. This way takes longer, it's less reliable, and it wastes cash.</advice>

Cary Millsap
Hotsos Enterprises, Ltd.
http://www.hotsos.com

Upcoming events:

- Hotsos Clinic, Jul 9-11 New York City
- Hotsos Clinic, Jul 23-25 Chicago
- 2003 Hotsos Symposium on OracleR System Performance, Feb 9-12 Dallas



-----Original Message-----
Lorraine
Sent: Wednesday, July 03, 2002 5:22 PM
To: Multiple recipients of list ORACLE-L

So this is not good:

CHILD# RATIO
------- -------
16 8.5E-06
15 .000013

14 7.5E-06
13 6.5E-06
12 8.2E-06

11 .00001
10 9.3E-06
9 9.1E-06
8 8.4E-06
7 .000012
6 9.5E-06
5 8.5E-06
4 9.8E-06
3 9.1E-06
2 8.9E-06

1 .000008
16 rows selected.

Enter value for child_latch_number: 16

old 3: WHERE lo_setid <= &&child_latch_number
new 3: WHERE lo_setid <= 16
old 4: AND hi_setid >= &&child_latch_number
new 4: AND hi_setid >= 16

NAME

KEEP
RECYCLE
DEFAULT At 01:07 PM 7/3/2002 -0800, Jared.Still_at_radisys.com wrote:
>If you aren't experiencing performance problems, the best thing to do
>is nothing.
>
> >From the docs ( Designing and Tuning for Performance )
>
>To determine whether your system is experiencing latch contention,
begin
>by determining whether there is LRU latch contention for any individual
>latch.
>
>SELECT CHILD#, SLEEPS / GETS RATIO
>FROM V$LATCH_CHILDREN
>WHERE NAME = 'cache buffers lru chain';
>
>
>The miss ratio for each LRU latch should be less than 3%. A ratio above
3%
>for any particular latch is indicative of LRU latch contention and
should
>be addressed.
>You can determine the buffer pool to which the latch is associated as
>follows:
>
>SELECT NAME
>FROM V$BUFFER_POOL
>WHERE lo_setid <= child_latch_number
>AND hi_setid >= child_latch_number;
>
>Jared
>
>
>
>
>
>
>Hamid Alavi <hamid.alavi_at_quovadx.com>
>Sent by: root_at_fatcity.com
>07/03/2002 08:58 AM
>Please respond to ORACLE-L
>
>
> To: Multiple recipients of list ORACLE-L
<ORACLE-L_at_fatcity.com>
> cc:
> Subject: db_block_lru_latches
>
>
>List,
>
>I have a question regarding db_block_lru_latches, I have read in some
>book(can't remember) which the best number for this parameter is
(number
>of
>CPU)*6 or db_block_buffers/50.
>But these two result is diffrent,anybody have any idea what's the best
>configuration for this parameter.
>In my configuration it has been set to 1 as default and I have two CPU
so
>it
>means it should be 6*2 = 12?is it right?
>Thanks allot for your recommendation.
>
>
>
>
>
>Hamid Alavi
>Office 818 737-0526
>Cell 818 402-1987
>
>
>
>
>
>
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>--
>Please see the official ORACLE-L FAQ: http://www.orafaq.com
>--
>Author: Hamid Alavi
> INET: hamid.alavi_at_quovadx.com
>
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-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.com
-- 
Author: Deborah Lorraine
  INET: dlorraine_at_ucdavis.edu

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-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.com
-- 
Author: Cary Millsap
  INET: cary.millsap_at_hotsos.com

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Received on Wed Jul 03 2002 - 18:13:21 CDT

Original text of this message

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