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Calculating cache hit and cache miss rate

EXPERT RESPONSE FROM: Paul Baumgartel

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QUESTION POSED ON: 23 June 2004
How can I calculate the cache hit and cache miss rate in 9i?

EXPERT RESPONSE
Here's a query that will give you the hit ratio. The miss rate is just 100 minus the hit rate.

select 1-(PHY.VALUE - LOB.VALUE - DIR.VALUE)/SES.VALUE "CACHE HIT RATIO"
FROM V$SYSSTAT SES, V$SYSSTAT LOB, V$SYSSTAT DIR, V$SYSSTAT PHY
WHERE SES.NAME ='session logical reads'
and DIR.NAME ='physical reads direct'
and LOB.NAME ='physical reads direct (lob)'
and PHY.NAME ='physical reads';

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