Oracle Buffer Utilisation is very low

Question

Hi,
Below are the values of buffer cache. Can some body suggest how to improve the buffer hit ratio. For my database it is under 80%.
NAME TYPE VALUE
db_cache_size big integer 654311424
SQL> show parameter db_block_size
NAME TYPE VALUE
db_block_size integer 8192
Thanks
VAS

Answer 1

VAS wrote:
Hi,
Below are the values of buffer cache. Can some body suggest how to improve the buffer hit ratio. For my database it is under 80%. You don't say what an improvement would be, though it sounds like you want to raise it. The easiest way to achieve your stated goal would be to do a bunch of useless indexed work - handily http://www.oracledba.co.uk/tips/choose.htm will do this for you and you can have whatever hit ratio short of 100 you desire (assuming you've got some time to waste). Of course your actual goal may be to improve the performance of something or other rather than to do a bunch of useless work - the code on my link above won't help you there. For that you'll have to
1) define what it is you wish to improve in specific terms
2) define what acceptable improvement is
3) determine how you are going to measure the performance of the thing you are interested in
4) measure it
5) work out if it is unacceptable
6) work out why it isn't meeting your acceptability criteria
7) fix the major contributor
8) return to step 4
9) repeat until step 5 shows your performance is now acceptable.
of course this takes more effort than modifying some cache parameters or running a script from the intertubes, but it s more satisfying (unless you're paid a bonus based on your hit ratio in which case go for the script.
Niall Litchfield
http://www.orawin.info/