Finbarr Timbers

How I designed my machine learning app

Introduction

Approximately ten thousand years ago, during undergrad, I made what was probably the best decision of my academic career and took Russ Greiner's CMPUT 466 class at the University of Alberta. As a math major, it took some convincing to let the CS department allow me into the course, as I was missing approximately every prerequisite for the class, but convince them I did, and I was introduced to the body of techniques known as machine learning. The course required me to complete a group project, and my group worked on the problem of bug report deduplication.

Inspiration

Managing the flood of bug reports that pour in is a problem for any sizable software project. Android has some 53 636 bug reports as of the time of writing, and if you search "bug report triage" in Google Scholar, you get almost 4000 results for academic work. The cost of managing bug reports is huge, too— if each bug report takes a quarter of an hour to administer (read, compare to previous bug reports, link them, and assign to a developer), then the Android community has spent 13 409 hours, or 32 work years managing bug reports. That ignores the number of internal bug reports that Google's QA staff would have found and reported. If we assume a typical Software Engineer costs $100 000 annually, that's $3.2 million that the Android community has dedicated to bug triage.

The project that my team worked on focused on analysing the text of the bug reports and using features generated from those to classify the bug reports. We developed a series of features that used reference material (textbooks, manuals, documentation) to create subject specific word lists, from which we generated numerical comparison scores. From this, we were able to get a series of subject scores (e.g. Android security: 0.2). The work proved remarkably successful, almost matching the performance of word lists that were manually extracted. With very little tuning, we were able to correctly classify 97% of bug reports, and I suspect that with some modelling effort (hyperparameter optimization, investigating some more complicated models) that could be improved on.

That was several years ago. The code that performed the bug report deduplication has been sitting around on Github for a few years, untouched. It seemed to me that bug report deduplication was a problem with a clear solution that hadn't been implemented by anyone. I've been looking for a side project to do that will let me learn more about product development and deploying machine learning in production environments, instead of just academic experimental settings, so I took it upon myself to turn the academic code into a web app. I was able to recruit a few of my friends to help, and we built BugDedupe. It's still in a very early stage, so I'm looking for feedback and feature requests. The goal is to have the site be free for open source repositories and small (private) side projects, charging larger repositories to recoup my costs. If you have feedback or feature requests, or just want to chat, shoot me an email at [email protected]

When I started building BugDedupe, I hadn't seen many posts about how teams designed their machine learning web apps, so I wanted to write about how we approached ours, to get feedback and to help others doing the same.

Myself

I'm a stats/ML guy who does a lot of number crunching in Python at my day job (Numpy/sklearn/SciPy). I've been wanting to learn more about the whole Python stack, and particularly web dev, so that I can learn how to make products from end-to-end. As a consultant, I get all of my projects to the MVP stage and then have to start again on the next one for a new client. I wanted to work on something that I could polish and grow, and given my stats background, BugDedupe seemed like a great opportunity.

Background:

We developed an automated method of predicting whether or not two bug reports are duplicates of each other. We did this by analysing the text of the bug report and comparing it to each other, and to reference texts (e.g. we had bug reports for a Java project, and we compared them to different chapters of a Java textbook to get subject scores— allowing us to say that a given report is 30\% cryptography and 45\% networking). This gave us a number of features that we could run through a machine learning classifier. We used a number of different ones and got really high results— 97\%. The method worked, and we tested it on real world data— the bug reports from Android, and Eclipse, among others. The only remaining problem was figuring out how to make the service available online.

Layout

At the start of the project, I was pretty confused about how to develop the site. I've been a fan of functional programming for a long time, and try to develop all of my projects in a functional manner.In that light, I decided to use a stateless architecture for the app. All of the state of the app (users, data, etc.) would be stored in the MySQL database, and the server would exist only to render it onto the web; similarly, the machine learning processes would interact uniquely with the database. As a result, we can have anything except the database crash at any time, and we won't lose any data. The database is regularly backed up, and as we're using Google Cloud SQL, it's in good hands. If, god willing, we run into scaling problems, we feel that our architecture will also allow us to focus only on optimizing the specific parts that are bottlenecking our performance, as everything is logically separated.

Hosting

I've been using Docker at work and like it a lot. I decided to encapsulate each separate component in a container, and run them on Google Cloud Platform, as I like what Google's doing with Kubernetes. Once I had the components in Docker, it was straightforwardt to launch them on Google Container Engine.

I found it surprisingly easy. It sucked getting started, but now that everything's set up, it's super easy to work with, and kubernetes makes a lot of the administrative tasks go away (e.g. managing secrets/environment variables, restarting Python, scaling).

Conclusion

While some things surprised me (particularly the latency of APIs- I was using Stormpath for authentication, and it started adding up to 6 seconds per request), overall, I'm extremely happy with how the program turned out. I think that having everything interact only with the database and itself managed to reduce complexity significantly, so that I only had to think about how the current component interacted with the database, instead of having to worry about how it fit in with all of the other components of the stack. The test now is to get more users, and see how we perform at scale. The more users we get, the more accurate our classifier will be, and the more useful our service will be, so we need to get that flywheel rolling as fast as we can.

If you found this useful, or if you have any feedback, please send me an email at [email protected] I'd love to hear what you think of our architecture.