> 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.

FWIW, a few years back I did some in-depth data gathering on this score using 
"real world" websites. I found that, for encoded data, hit rate in the cache 
increased exponentially as cache size increased up to ~4MB, increased linearly 
as cache size increased above ~4MB, and increased not at all as cache size 
increased above ~100MB (since all resources that were eligible for caching and 
not expired were already in the cache). My guess is that the inflection points 
in the graph have moved out to ~8MB or ~16MB in the past few years.

Note that these numbers do not correspond precisely to WebCore cache sizes, 
since the WebCore cache size includes both encoded and decoded data.

Of course, the precise hit rates you'll see depend on the content you're 
browsing, and it's possible to hand-craft content that shows benefits up to 
arbitrarily large cache sizes, or shows no benefits down to arbitrarily small 
cache sizes. 

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