How are Reddit and Hacker News ranking algorithms used?

Question

I\'ve been looking at ranking algorithms recently, specifically those used by Reddit and Hacker News. The algorithms themselves are simple enough, but I don\'t quite understand

Answer 1

Reddit uses Pyrex, the sort algorithm is a Python C extension to improve performance.

So, you can do the same in SQL when the record is updated, pex: when is up or down voted.

The pseudocode you must to translate to your SQL engine syntax:

function hot(ups, downs, date){
    score = ups - downs;
    order = log(max(abs(score), 1), 10);
    if (score>0){
        sign = 1;
    } else {
        if (score<0){
            sign = -1;
        } else {
            sign = 0;
        }
    }
    td = date - datetime(1970,1,1);
    seconds = td.days * 86400 + td.seconds + (float(td.microseconds) / 1000000) - 1134028003;

    return round(order + sign * seconds / 45000, 7);
}

So you must to store in the post table the ups, downs, date and the hot function result. And then you can make a sort in the hot column.

You can see the Reddit source code here: http://code.reddit.com/

Answer 2

I implemented an SQL version of Reddit's ranking algorithm for a video aggregator like so:

SELECT id, title
FROM videos
ORDER BY 
    LOG10(ABS(cached_votes_total) + 1) * SIGN(cached_votes_total)   
    + (UNIX_TIMESTAMP(created_at) / 300000) DESC
LIMIT 50

cached_votes_total is updated by a trigger whenever a new vote is cast. It runs fast enough on our current site, but I am planning on adding a ranking value column and updating it with the same trigger as the cached_votes_total column. After that optimization, it should be fast enough for most any size site.

edit: More information at Reddit Hotness Algorithm in SQL