Dinesh Babu Verma (2/8/2012)
In case no data in data cache, the physical read will be equal to number of logical read.
Not necessarily, because a query could request the same page more than once. If the page doesn't start in cache, the first will be a physical read, the others will not.
Buffer Cash Hit Ratio
Buffer hit ratio will be calculated based on these two kinds of read as the following formula: (logical reads – physical reads)/logical read * 100%. The high buffer hit ratio (if possible to near 100%) indicates good database performance on SQL Server level. So use information from physical read and buffer hit ratio to measure performance in server level and logical read to measure individual query level
Buffer cache hit ratio is a near-useless counter. By the time it drops significantly the server would have been having severe problems for a while.
p.s. Over 3 year old thread.
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability