cache hit rate/ratio

Timothy Holtzen tah at NebrWesleyan.edu
Tue Feb 23 14:42:29 UTC 2010


I have seen references out there about cache hit rates of 50-70% being
normal.  However I'm confused as to how to measure/calculate hit ratio?
 I can't seem to find any good references on how to find it.  The only
thing I've been able to find is to do

 ("responses sent") - ("queries caused recursion")

but this would include queries for local authoritative zones.  In our
particular case if I divide by the total number of queries I end up with
a number around 66%.  Is this the correct way?  In our particular case I
suspect that the majority of those responses are for local authoritative
zones.  Wouldn't a more accurate way to measure cache performance be to
take

("non authoritative answer")-("queries caused recursion")/Total Queries?  

In our case calculating this way would yield a number closer to 13%
which looks low when compared to the "normal" range listed above.  How
are others calculating hit rate/ratio and what do you tend to see as
"normal"?  Obviously normal can vary wildly depending on configuration
and what kind of queries a system receives.  I'm just trying to get a
handle on how our cache is performing and what I should expect.  Cache
hit rate seems to be an important metric when considering overall DNS
performance.

-- 
Timothy A. Holtzen
Campus Network Administrator
Nebraska Wesleyan University




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