why different db cache hit ratios?

the calculation of db cache hit ratios using following methods produce different results?

1- using v$sysstat:
SELECT 100*(1- ((p.value - l.value - d.value) / s.value)) "Buffer Cache Hit Ratio"
FROM v$sysstat s, v$sysstat l, v$sysstat d, v$sysstat p WHERE s.name = 'session logical reads'

AND d.name = 'physical reads direct'
AND l.name = 'physical reads direct (lob)'
AND p.name = 'physical reads';

2- using v$buffer_pool_statistics

select (1-(physical_reads/(db_block_gets+consistent_gets)))*100 cache_hit_ratio
from v$buffer_pool_statistics;

• So which v$ table has more accurate stats or more reliable ?

Thanks,
i.d. Received on Tue Dec 23 2003 - 10:15:08 CST