Top-K Off-Policy Correction for a REINFORCE Recommender System
Abstract
Industrial recommender systems deal with extremely large action
spaces – many millions of items to recommend. Moreover, they
need to serve billions of users, who are unique at any point in
time, making a complex user state space. Luckily, huge quantities
of logged implicit feedback (e.g., user clicks, dwell time) are available
for learning. Learning from the logged feedback is however
subject to biases caused by only observing feedback on recommendations
selected by the previous versions of the recommender. In
this work, we present a general recipe of addressing such biases in
a production top-K recommender system at YouTube, built with a
policy-gradient-based algorithm, i.e. REINFORCE [48]. The contributions
of the paper are: (1) scaling REINFORCE to a production
recommender system with an action space on the orders of millions;
(2) applying off-policy correction to address data biases in learning
from logged feedback collected from multiple behavior policies; (3)
proposing a novel top-K off-policy correction to account for our
policy recommending multiple items at a time; (4) showcasing the
value of exploration. We demonstrate the efficacy of our approaches
through a series of simulations and multiple live experiments on
YouTube.
Research Areas
