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Bug in bot selection algorithm on server?

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Bug in bot selection algorithm on server?

Postby BenJackson » Sat Nov 12, 2011 8:24 pm

I've noticed that my most recent submission has played a lot of pairs of games. If the "time" in the game list is the end time it's possible that each time it is actually starting two games near simultaneously. The last two actually have adjacent game numbers. I'm wondering if the "countdown to selection" is letting multiple threads pick my bot when it reaches the front of the queue before some mechanism (is it completing the game?) sends it to the back of the list:

http://aichallenge.org/visualizer.php?game=80546
http://aichallenge.org/visualizer.php?game=80543

http://aichallenge.org/visualizer.php?game=83502
http://aichallenge.org/visualizer.php?game=83511

http://aichallenge.org/visualizer.php?game=88151
http://aichallenge.org/visualizer.php?game=88156

http://aichallenge.org/visualizer.php?game=89019
http://aichallenge.org/visualizer.php?game=89020

Those intervals are 3, 9, 5 and 1 games.

(for comparison the typical interval between games looks like about 900-1000)

Obviously I don't mind playing more games! But it's possible that the lack of atomicity in the "select/send to back of list" is causing everyone's plays to be more lumpy and unevenly distributed.
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Re: Bug in bot selection algorithm on server?

Postby Janzert » Sun Nov 13, 2011 1:11 am

Hmm, yes there is actually a bug/race condition. The bad news is that it probably can't be easily eliminated completely. The good news is that it only effects roughly 2% of games. The first example you have (games 80546 and 80543) happens to be one of them, but the rest are all legitimate games for you. In fact you're not even the seed in either of the games 88151 and 88156 (i.e. you weren't at the top of the queue for either one).

The primary reason for multiple games within a short period of time is because players that are good opponents for you are also good opponents for each other and anyone that plays together will be next to each other in the game queue. Meaning that often around the same time you are seeded for a game you are also likely to be pulled into a game (or sometimes even multiple games).
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