Optimizing the Pinning Process
Late today I was talking with Phil, a co-worker, and he had placed some New Relic instrumentation in the code and with the results we obtained from a few runs, it was clear that the way in which we were pinning the demand points to the merchants was a real problem. Like the singularly largest time spent in the code. And in a way, it makes sense - we're scanning all demand points for each of several thousand merchants, and that's going to take some time.
What's the better solution? Well… indexes, of course!
What we decided to do was something like what we'd done in a different part of the code, and I decided that I wanted to do it. The plan was to index all the demand data very much like a HashMap does - but the key for each 'bin' is the same values that we are trying to match in the scanning code.
For example, if we're matching the City, State, and Service, then we make the key:
key = [city, state, service]
and then use that as the key in a Hash to hold an array of all the demand points that have those three values. Of course, for a demand point with multiple services, we'll have multiple entries in the indexing data, but that's OK, as Ruby does all this with references and not deep copies.
I'm just getting started, and I'm planning on working on it this weekend, but it's looking very exciting, and I'm really happy the direction this is going.
UPDATE: I'm happy to say that I got a lot of good work done on the train. I still need to finish a lot of loose ends, but the bulk of the work should be ready to go. Lots of testing to do, but it's looking good.