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Buffer cache hit ratio


How is calculated the buffer cache hit ratio showed on Spotlight on Oracle? It doesn’t match the value calculated from v$sysstat: 1 - ((‘physical reads cache’) / (‘consistent gets from cache’ + ‘db block gets from cache’))



Hi Ezio,

Spotlight is using the Delta value to calculate the ratio, that is say the value increased in the last data refresh interval (by default 15 secords), and also averaged the ratio value over 30 seconds (by default) to prevent Spotlight from reporting alarms for such spikes if they do not persist.


Hi Kevin,
Thx for an answer.

Delta value to calculate the ratio
Could you elaborate a little better this. I had also several customer asking that but couldn’t get an answer, which I now have a chnace if you decribe just a little bit … is some number example is possible…great.


Like first time Spotlight get the value of “physical reads cache” from the database is 10000, and the second time it increase to 10180, then the value for Spotlight calculate is 180, same to ‘db block gets from cache’ and ‘consistent gets from cache’,


Hi Kevin
Thx for an answer. All clear now.