We propose a method to easily modify existing offline Recommender Systems to run online using Transfer Learning. Online Learning for Recommender Systems has two main advantages: quality and scale. Like many Machine Learning algorithms in production if not regularly retrained will suffer from Concept Drift. A policy that is updated frequently online can adapt to drift faster than a batch system. This is especially true for user-interaction systems like recommenders where the underlying distribution can shift drastically to follow user behaviour. As a platform grows rapidly like Grubhub, the cost of running batch training jobs becomes material. A shift from stateless batch learning offline to stateful incremental learning online can recover, for example, at Grubhub, up to a 45x cost savings and a +20% metrics increase. There are a few challenges to overcome with the transition to online stateful learning, namely convergence, non-stationary embeddings and off-policy evaluation, which we explore from our experiences running this system in production.

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Ensuring the health of a modern large-scale recommendation system is a very challenging problem. To address this, we need to put in place proper logging, sophisticated exploration policies, develop ML-interpretability tools or even train new ML models to predict/detect issues of the main production model. In this talk, we shine a light on this less-discussed but important area and share some of the best practices, called RecSysOps, that we’ve learned while operating our increasingly complex recommender systems at Netflix. RecSysOps is a set of best practices for identifying issues and gaps as well as diagnosing and resolving them in a large-scale machine-learned recommender system. RecSysOps helped us to 1) reduce production issues and 2) increase recommendation quality by identifying areas of improvement and 3) make it possible to bring new innovations faster to our members by enabling us to spend more of our time on new innovations and less on debugging and firefighting issues.

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