RE: Cache hit ratio?

From: Cary Millsap <cary.millsap_at_hotsos.com>
Date: Wed, 09 Oct 2002 18:18:33 -0800
Message-ID: <F001.004E52BC.20021009181833@fatcity.com>

...and a high cache hit ratio (>99%) is usually an indication of a serious problem as well.

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

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-----Original Message-----

WILLIAMS
Sent: Wednesday, October 09, 2002 5:04 PM To: Multiple recipients of list ORACLE-L

Seema

1. How low is too low? Basically, different applications will tend to have different BHR values (Buffer Hit Ratio).
2. BHR varies over time, and will depend a lot on the lengths of time you sample it, and what type of processing was running.
3. A low BHR can lead you to a problem. Other indicators like waits can also lead you to the same problems. But the point is that you need to investigate what the problem actually is, rather than just increase the buffer cache size.
4. Changing the db_block_buffer size may increase the BHR. Sometimes it doesn't affect the BHR at all.
5. Get a copy of the book Oracle Performance Tuning 101 and you will learn more about Oracle tuning and why you don't just want to focus on the BHR and increasing the buffer cache size.

Dennis Williams
DBA
Lifetouch, Inc.
dwilliams_at_lifetouch.com

-----Original Message-----

Sent: Wednesday, October 09, 2002 4:14 PM To: Multiple recipients of list ORACLE-L

Hi
One of my database Cache Hit Ratio is low.I adjusted db_block_buffer and I
have noticed after week again cache hit ratio became low. Can u please suggest what other things I can do to fix this problem? Thx
-Seema

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Author: Cary Millsap
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