Credit-assigned Policy Gradient for Early Stage Retrieval in Two-stage Ranking
Large-scale search, recommendation, and retrieval-augmented generation (RAG) systems typically employ a two-stage architecture: an early-stage ranker (ESR) generates a candidate set, which is subsequently re-ranked by a late-stage ranker (LSR). While there are many reinforcement learning (RL) methods for training the LSR, end-to-end training of the ESR has proven challenging. In particular, naive application of "vanilla" policy gradient (V-PG) is not scalable for candidate-set sizes relevant for practical use due to exploding variance. This issue arises because V-PG propagates the gradient to the joint probability of the candidate sets, ignoring the contribution of each specific item in t...
| Authors | Haruka Kiyohara, Mihaela Curmei, Ariel Evnine et al. |
|---|---|
| Primary category | cs.IR |
| Published | 25 May 2026 |
| Last updated at source | 25 May 2026 |
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