Approximate number of zappers in ~5k. Registered users are more like 30k. The ItemAct table has almost 6m rows (roughly half are zaps).

I would guess a zap or downzap from a new zapper creates 20-100 pairs. 

k00b

What are you working on this week?

woot, I'm looking forward to that!  I have some ideas regarding trust graph i wanted to test out.

By the way, I was meaning to ask: I know the number of items is around 900,000, but what's approximately the number of users, and just as importantly, what's the approximate size of the ItemAct table?  i.e. What percent of all potential user-item pairs are populated by an action like a zap or downzap?

I discovered some [collaborative filtering](https://en.wikipedia.org/wiki/Collaborative_filtering) [algorithms](http://yifanhu.net/PUB/cf.pdf) that look promising, but need to get a sense of their scalability in this context. 

(I'm also not convinced yet they're the right way to go for SN, will provide a write up soon-ish)