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    <p>On Hacker News, only the 210 newest stories and 210 most popular stories are paginated (7 pages worth * 30 stories each). My guess is that the reason for the limit (at least in part) is this problem.</p> <p>Why not drop all the fancy SQL for the most popular stories and just keep a running list instead? Once you've established a list of the top 210 stories you only need to worry about reordering when a new vote comes in since relative order is maintained over time. And when a new vote does come in, you only need to worry about reordering the story that received the vote.</p> <p>If the story that received the vote is not on the list, calculate the score of that story, plus the least popular story that <em>is</em> on the list. If the story that received the vote is lower, you're done. If it's higher, calculate the current score for the second-to-least most popular (story 209) and compare again. Continue working up until you find a story with a higher score and then place the newly-voted-upon story right below that one in the rankings. Unless, of course, it reaches #1.</p> <p>The benefit of this approach is that it limits the set of stories you have to look at to figure out the top stories list. In the absolute worst case scenario, you have to calculate the ranking for 211 stories. So it's very efficient unless you have to establish the list from an existing data set - but that's just a one-time penalty assuming you cache the list someplace.</p> <p>Downvotes are another issue, but I can only upvote (at my karma level, anyway).</p>
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    1. POImplementing a popularity algorithm in Django
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    1. COThat's a pretty nifty idea. I never expect this site to get very large so there would have to be some major tweaking of those numbers but I like where it's going.
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    2. COA few months late but i'm back at it. You wouldn't mind elaborating on this further would you? How would you keep track of your running list? Another database table? Would it be calculated on the fly on every Http Request? Don't worry about the downvotes, I've come to the conclusion that downvoting is a bad idea in most cases. buildingreputation.com has some great reads.
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