Offline Retraining for Online RL: Decoupled Policy Learning to Mitigate
  Exploration Bias
Max Sobol Mark Archit Sharma Fahim Tajwar Rafael Rafailov Sergey Levine Chelsea Finn
It is desirable for policies to optimistically explore new states and
behaviors during online reinforcement learning (RL) or fine-tuning, especially
when prior offline data does not provide enough state coverage. However,
exploration bonuses can bias the learned policy, and our experiments find that
naive, yet standard use of such bonuses can fail to recover a performant
policy. Concurrently, pessimistic training in offline RL has enabled recovery
of performant policies from static datasets. Can we leverage offline RL to
recover better policies from online interaction? We make a simple observation
that a policy can be trained from scratch on all interaction data with
pessimistic objectives, thereby decoupling the policies used for data
collection and for evaluation. Specifically, we propose offline retraining, a
policy extraction step at the end of online fine-tuning in our
Offline-to-Online-to-Offline (OOO) framework for reinforcement learning (RL).
An optimistic (exploration) policy is used to interact with the environment,
and a separate pessimistic (exploitation) policy is trained on all the observed
data for evaluation. Such decoupling can reduce any bias from online
interaction (intrinsic rewards, primacy bias) in the evaluation policy, and can
allow more exploratory behaviors during online interaction which in turn can
generate better data for exploitation. OOO is complementary to several
offline-to-online RL and online RL methods, and improves their average
performance by 14% to 26% in our fine-tuning experiments, achieves
state-of-the-art performance on several environments in the D4RL benchmarks,
and improves online RL performance by 165% on two OpenAI gym environments.
Further, OOO can enable fine-tuning from incomplete offline datasets where
prior methods can fail to recover a performant policy. Implementation:
https://github.com/MaxSobolMark/OOO