Re: Cache Hit Ratio?

No, slight problem with the formula:

Cache Hit Ratio = (1-(Physical Reads/(db block gets + consistent gets))) * 100

BUT... In our system, 7x24 shop with lots of reads, the internal counters in the V$STATS overflow and go negative, so this formula if fairly useless.

Instead, I worked up the following that gives you an 'instantaneous' efficiency rating:

 select 'DB Block Efficiency (should be >= 95%) ..... ' ||

        round(100*(sum(e.block_gets)+sum(e.consistent_gets)
                                    -sum(e.physical_reads))/
        (sum(e.block_gets)+sum(e.consistent_gets)),2)
dbratio               from v$sess_io e;

-- 
R. Wayne Linton, I.S.P.
Database & Systems Management
Shell Canada Ltd.


SatarNag wrote:


> 

> Is this Right?

> 

> Cache Hit Ratio = (1-(Physical Reads/(db block gets = consistent gets))) *

> 100

> 

> I know the variables are right, but is that the correct formula?

> 

> Satar Naghshineh

> SatarNag_at_aol.com