On Wed, Oct 10, 2012 at 12:04 AM, Maciej Stachowiak <m...@apple.com> wrote:
> On Oct 9, 2012, at 1:50 PM, Adam Barth <aba...@webkit.org> wrote:
>> That raises the question of what the cache-size to hit-rate curve
>> looks like.  I don't think that's something we've ever measured for
>> the MemoryCache, but it would be interesting to know, for example,
>> whether increasing the cache size by 4% increases the cache hit rate
>> by more or less than 4%.
>
> My guess is that frequency of hits on given cache items approximately follows 
> a power law distribution, and therefore increasing cache size gives 
> diminishing returns. The question you raise is ceratainly an interesting one 
> to study to determine the optimum cache size, and to revisit when 
> improvements are made to cache efficiency.
>
> But with respect to the proposed improvement under discussion:
>
> If you imagine this as a curve with hit rate on the Y axis and cache size 
> required to achieve that hit rate on the X axis, then the potential 
> improvement under discussion would shift the curve down (assuming the 4% 
> redundancy level holds across the typical user's working set). In economic 
> terms, you can think of this as shifting the supply curve down (more hit rate 
> can be supplied at any given cost in memory), rather than movement along the 
> supply curve. Which is pretty good for you regardless of your demand curve 
> (your willingness to pay memory use for cache hit rate).

Yes, but depending on the slope of the curve, you can be introducing
all this complexity for, e.g., a 1% increase in the cache hit rate.

Adam
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