
Accessing RAM sometimes costs extra log(N) - Tojot
http://arxiv.org/abs/1212.0703
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Tojot
In response to "The Myth of RAM"
[https://news.ycombinator.com/item?id=12383012](https://news.ycombinator.com/item?id=12383012)

It so happens that a large part of my PhD was on this very subject. The result
I've got N log(N), this is more visible when you get to larger RAM (I had 0,5
TB RAM at the time). We have an empirical result, a justification and a
rigorous predictive model.

The reason has to do with hashing, but a different type: TLB.

Feel free to take a look at a free copy at
[http://arxiv.org/abs/1212.0703](http://arxiv.org/abs/1212.0703) where we
establish the VAT cost model.

~~~
corysama
Very interesting and informative. I would have expected a TLB to incur an
additional cost beyond exhausting the cache hierarchy. But, I would have
expected it to be a single additional cliff around a gig at most.

Shame there's no discussion here. I've x-posted to
[https://www.reddit.com/r/programming/comments/509qhd/randoml...](https://www.reddit.com/r/programming/comments/509qhd/randomly_accessing_n_items_in_dram_is_on_in/)
Maybe that will drum up a bit more conversation.

~~~
Tojot
Thanks! Looks like it worked.

