Make remote FeatureGenerators

[matt-gardner]

With large graphs (such as Freebase), it can take upwards of 10 minutes just to load the graph from disk and create the graph object. Maybe there are some things I can do in code to make that a bit quicker, but it still would be nice to only have it done once and be able to reuse a running graph server.

[matt-gardner]

As of 1/21/16, this actually works, but it's incredibly slow. I did a bunch of work trying to optimize graph loading, and the way the graph is stored in memory. So that should help a bit. There is one more optimization I want to try for loading the graph (store a binary file, and load that, instead of the GraphChi ascii version I currently use), but that doesn't help the server any. To make the server idea really feasible, I need to offload more of the computation to the graph, having the graph object compute paths and such. That would be a pretty big refactoring of the code, so I'm not going to do it any time soon.

[matt-gardner]

Actually, to implement what I want to do, I just need to make a FeatureGeneratorServer, instead of a GraphServer. You issue a query about a node pair to the server, it does the graph computation, and responds with a list of features. This is definitely feasible. I just don't have a particular need for it at the moment.