Determine if the DATA_BLOCK_BUFFERS is set high enough

Question

Hello,
I am currently tuning my database for optimal performance. (some
of my users are complaining about performance problem at high
load)
I wanted to check if my DATA_BLOCK_BUFFERS has been set high
enough.
Anyone please guide me through.
NB. I have tried to run the following query but the results are
not too clear to me:
prompt "Determining if the Data Block buffers is set high enough"
select 1-(sum(decode(name, 'physical reads', value,0))/
(sum(decode(name, 'db block gets', value,0)) +
(sum(decode(name, 'consistent gets', value,0))))) * 100
"Read Hit Ratio"
from v$sysstat;
Read Hit Ratio
-7.201386
Thanks in Advance
Yogeeraj

Answer 1

Hi,
Your query needs 2 extra brackets to give the correct result :
select (1-(sum(decode(name, 'physical reads', value,0))/
(sum(decode(name, 'db block gets', value,0)) +
(sum(decode(name, 'consistent gets', value,0)))))) * 100
"Read Hit Ratio"
from v$sysstat
You will get a hitrate of about 92% which is rather low.
Instead of raising your db_block_buffers parameter you should
consider splitting your tables up between the recycle and keep
buffer pool.
Large tables that are frequently accessed in a random way should
be put in the 'recycle' pool while the others can be put in
the 'keep' pool.
See the oracle docs for more info on this.
Regards,
Roger.