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Title
Database Health Check displays a negative Buffer cache hit ratio -
Description
The Database Health Check displays a negative Buffer cache hit ratio.
What does this mean? -
Resolution
At times when a database has been up for a longer time, some of the statistical values get larger than the display fields that hold and handle them.When this occurs, it wraps around to negative. User should not be alarmed about these values.
For 10g, Toad uses the following query:
SELECT ROUND (100 * (1 - (physical_reads / (db_block_gets + consistent_gets))),4)FROM v$buffer_pool_statistics -
Attachments
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Additional Information
As for the positive ratio 85%, this has been proven to be a used metric. More detailed information from the attached article: Why a 99%+ Database Buffer Cache Hit Ratio is Not Ok below.