,
Pasin Manurangsi
Creative Commons Attribution 4.0 International license
A common problem in private data analysis is the partition selection problem, where each user holds a set of partitions (e.g. keys in a GROUP BY operation) from a possibly unbounded set. The challenge here is in maximizing the set of released partitions while respecting a differential privacy constraint. Previous work [Desfontaines et al., 2021] presented an optimal (ε, δ)-DP algorithm when each user submits only a single partition. We generalize this approach to find the optimal algorithm under δ-approximate (α, ε)-Rényi differential privacy (RDP), which allows much tighter analysis under composition. Motivated by the non-existence of a general optimality result in the case where users submit multiple partitions each, we present an extension of our optimal algorithm tuned for L² bounded weighted partition selection which can be used as a drop-in improvement over the Gaussian mechanism any time the partition frequency is not also needed. We show that our primitive can be easily plugged into state of the art partition selection algorithms (PolicyGaussian from [Gopi et al., 2020] and MAD2R from [Justin Y. Chen et al., 2025]), improving performance both for parallel and sequential adaptive algorithms. Finally, we show that there is an inherent cost to algorithms which do support releasing the frequency as well as the partitions. Specifically, we formulate a basic notion of optimal approximate RDP algorithm for partition selection using additive noise, and show that there is a numerical separation between additive and non-additive noise mechanisms for this problem.
@InProceedings{harrison_et_al:LIPIcs.FORC.2026.16,
author = {Harrison, Charlie and Manurangsi, Pasin},
title = {{Optimal Partition Selection with R\'{e}nyi Differential Privacy}},
booktitle = {7th Symposium on Foundations of Responsible Computing (FORC 2026)},
pages = {16:1--16:22},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-419-2},
ISSN = {1868-8969},
year = {2026},
volume = {368},
editor = {Lin, Huijia (Rachel)},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FORC.2026.16},
URN = {urn:nbn:de:0030-drops-259894},
doi = {10.4230/LIPIcs.FORC.2026.16},
annote = {Keywords: Differentially Privacy, Partition Selection, Renyi Differentially Privacy}
}