Values for buffer cache are zeros so they appear disabled.
The metric is enabled, its just that the primary metric which is used to display the Buffer Cache Hit Ratio does not have thresholds associated, there are other metrics used to show an alarm.
We derive the delta from the following calculation.
The metric Systat.hitratio
Hitratio = 100 - SysStat.MissRatio
Missratio is defined as:
MissRatio = 100 * (SysStat.PhysReadsCacheD / SysStat.LogicalReadsCacheD)
PhysReadsCacheD is basically the delta of physical reads cache:
PhysReadsCacheD = lookupkey(SysStat.DeltaValue, physical reads cache, 0)
LogicalReadsCacheD is the summation of the delta of consistent gets from cache and db block gets from cache:
lookupkey(SysStat.DeltaValue, consistent gets from cache,0) + lookupkey(SysStat.DeltaValue, db block gets from cache,0)
As you can see from the above we use delta to calculate the Buffer Cache Hit Ratio and not realtime data.
