Nice work and some thoughs

My %Wins is a bit of a cheat. It is just 1 point per PL win, divided by bots in rumble. I prefer it to PL because it is not dependant on the number of bots in the rumble. So if Combat was doing well in PL, it should do well in %Win.

I'm still not using my Backend for anything, so I was thinking that once a day I could use it to generate some sort of pseudo-problembot stats stuff. ELO/Glicko is nice, but it is really designed for being good approximations when pairings are missing. In our case, the pairings are fairly easy to fill, so that isn't a problem; APS tends to converge to the same ranking order, and it isn't full of voodoo that makes it difficult to comprehend. It is also possible to correct APS easily if results get lost due to being in memcache =)

One ranking idea I had an idea for was doing a The Best Bot calculation (get a point for being the best against any competitor). It would increase my number of database writes in the only reasonably robust/non-batch way I can think of, which is what is holding me back at the moment. I could use a Backend for calculating it once or twice a day, I guess, or make it expire once every 6 hours and be triggered by a page load. It needs n*n runtime. Maybe I can fit it into the regular rankings calculations.

The hardest part is getting the rumble to stay in the free tier. I think it will be limited to about 6 melee clients in total, or maybe 12 1v1 clients instead (less pairings per battle in 1v1).

The last time I checked, App Engine offered about 1GB database in the free tier. Which is enough to store all pairings and all uploaded battles, as long as you delete data from retired bots once in a while.

As for the amount of clients the server can handle, it should not really be an issue, since there are usually 3 to 4 simultaneous clients at most.

If you want to use some batch processing, adding a Ranked Pairs ranking would make my day. I has O(n^4) complexity, but I think it can still fit inside the 10 minutes window from cron, so no need for a backend.

The problem isn't so much total storage space, but that I'm limited at 50k writes per day. Each bot counts as 2 writes, so effectively I have 25k updates I can do. I've figured out a caching scheme so that each melee battle comes out to 10 updates (1 per bot) instead of 45 updates (1 per pairing). I also need to update the total rumble battles count and the user upload count, so that leaves a bit of overhead, meaning I can have ~2000 melee battles per day uploaded.

I'l see what ratings systems are feasible..

I've actually figured out a sort of temporary caching between requests where I wait for bots to accumulate a certain number of pairings before pushing them to disk. I don't think it's necessary to re-work the rumble upload protocol yet. One thing I would like the rumble to tell me is how many bots are in a melee battle though. Right now I just have it hardcoded at 10. It would help with my caching if I knew how many they were uploading per battle.

Flush them to the database on a period basis (constant number of commits regardless of number of uploads) instead of being per number of uploads?