Estimating the branching factor

[Rob]

Hello

I would like to know if there should be an estimation of the branching factor to pursuit a certain number of nodes. How can someone know if the tree/number of nodes is big/small enough?

Thank you.

[Bartholomew Furrow]

If you aren't going to get many write QPS on the ranker, it probably doesn't matter.

More levels means fewer transactional collisions, but also more nodes per lookup.

More nodes per lookup, as long as the number is reasonably small (<20?), isn't really a problem for SetScore and FindRank, but it is for FindScore, which can end up doing serial lookups proportional to the depth of the tree.

Fewer transactional collisions is important if you're going to end up with a lot of writes (SetScore).

So as with all things, it's a tradeoff.  We found that a depth of 5 and a branching factor of 101 (scores 0-9999, penalty times 0-999999 seconds) worked pretty well for Code Jam, which has a lot of reads per write.

I hope that helps!

Bartholomew

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