This is a very quick and easy fix that has made latency on Ubuntu servers I maintain go from three to four seconds to instantaneous. If you’ve noticed that you have high latency on ssh or scp (or even other software like remctl), and you have control over your server, try this on the server: aptitude remove libnss-mdns. It turns out that multicast DNS on Ubuntu has a longstanding bug on Ubuntu where they didn’t correctly tune the timeouts, which results in extremely bad performance on reverse DNS lookups when an IP has no name.
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If you haven’t noticed, these are coming in the order of the visit days.
Whereas the weather at UPenn was nice and sunny, the NJ Transit dinghy rolled into a very misty Princeton. Fortunately, I had properly registered for this visit day, so the hotel was in order. I was a bit early, so I met up with an old friend who had recently penned this short story and we talked about various bits and bobs (“I hear you’re up for a Hugo!”) before I meandered over to the computer science building.
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Note: this is not a discussion of Hilbert’s formalism versus Brouwer’s intuitionism; I’m using formalism and intuition in a more loose sense, where formalism represents symbols and formal systems which we use to rigorously define arguments (though not logic: a sliding scale of rigor is allowed here), while intuition represents a hand-wavy argument, the mental model mathematicians actually carry in their head.
Formalism and intuition should be taught together.
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I’m hoping that this will be the beginning of a series of posts describing all of the visit days/open houses that I attended over the past month. Most of the information is being sucked out of the notes I took during the visits, so it’s very stream of consciousness style. It’s kind of personal, and I won’t be offended if you decide not to read. You’ve been warned!
I arrive at the Inn at Penn shortly before midnight, and check in. Well, attempt it; they appear to have no reservation on hand. It appears that I hadn’t actually registered for the visit weekend. Oops.
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Suppose that you have k sorted arrays, each of size n. You would like to search for single element in each of the k arrays (or its predecessor, if it doesn’t exist).
Obviously you can binary search each array individually, resulting in a $O(k\lg n)$ runtime. But we might think we can do better that: after all, we’re doing the same search k times, and maybe we can “reuse” the results of the first search for later searches.
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