Time to replace the hit ratio with something more intuitive?

Michael Fischer michael at dynamine.net
Tue Jan 19 22:50:53 CET 2010


On Tue, Jan 19, 2010 at 1:40 PM, Rob S <rtshilston at gmail.com> wrote:

> Michael Fischer wrote:
>
>  On Tue, Jan 19, 2010 at 12:09 PM, Nils Goroll <slink at schokola.de <mailto:
>> slink at schokola.de>> wrote:
>>
>>    I am suggesting to amend (or replace ?) this figure by a ratio of
>>    client
>>    requests being handled by the cache by total number of requests.
>>    In other words,
>>    a measure for how many of the client requests do not result in a
>>    backend request.
>>
>>
>> I vote for the replacement option.  In my view, the ratio should be (total
>> requests)/(requests satisfied from cache).
>>
> That'd give odd figures (eg 1.25), when you'd expect to see 0.8.  Can we
> flip it the other way up?
>

Oops!  Yes.

I'd also caution against replacing, as people may have monitoring against
> the old figures...
>

Well, under the current regime, the figures may lead to a false sense of
complacency since the hit ratio may be falsely high.  If changing it causes
additional alerts to be raised, they probably needed to know all along. :)

--Michael
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