  Federated learning (FL) enhanced by differential privacy has emerged as a
popular approach to better safeguard the privacy of client-side data by
protecting clients' contributions during the training process. Existing
solutions typically assume a uniform privacy budget for all records and provide
one-size-fits-all solutions that may not be adequate to meet each record's
privacy requirement. In this paper, we explore the uncharted territory of
cross-silo FL with record-level personalized differential privacy. We devise a
novel framework named \textit{rPDP-FL}, employing a two-stage hybrid sampling
scheme with both uniform client-level sampling and non-uniform record-level
sampling to accommodate varying privacy requirements.
  A critical and non-trivial problem is how to determine the ideal per-record
sampling probability $q$ given the personalized privacy budget $\varepsilon$.
We introduce a versatile solution named \textit{Simulation-CurveFitting},
allowing us to uncover a significant insight into the nonlinear correlation
between $q$ and $\varepsilon$ and derive an elegant mathematical model to
tackle the problem. Our evaluation demonstrates that our solution can provide
significant performance gains over the baselines that do not consider
personalized privacy preservation.
