License: Creative Commons Attribution 4.0 International license (CC BY 4.0)
When quoting this document, please refer to the following
DOI: 10.4230/LIPIcs.ESA.2023.46
URN: urn:nbn:de:0030-drops-186990
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Ferragina, Paolo ; Lehmann, Hans-Peter ; Sanders, Peter ; Vinciguerra, Giorgio

Learned Monotone Minimal Perfect Hashing

LIPIcs-ESA-2023-46.pdf (1.0 MB)


A Monotone Minimal Perfect Hash Function (MMPHF) constructed on a set S of keys is a function that maps each key in S to its rank. On keys not in S, the function returns an arbitrary value. Applications range from databases, search engines, data encryption, to pattern-matching algorithms.
In this paper, we describe LeMonHash, a new technique for constructing MMPHFs for integers. The core idea of LeMonHash is surprisingly simple and effective: we learn a monotone mapping from keys to their rank via an error-bounded piecewise linear model (the PGM-index), and then we solve the collisions that might arise among keys mapping to the same rank estimate by associating small integers with them in a retrieval data structure (BuRR). On synthetic random datasets, LeMonHash needs 34% less space than the next larger competitor, while achieving about 16 times faster queries. On real-world datasets, the space usage is very close to or much better than the best competitors, while achieving up to 19 times faster queries than the next larger competitor. As far as the construction of LeMonHash is concerned, we get an improvement by a factor of up to 2, compared to the competitor with the next best space usage.
We also investigate the case of keys being variable-length strings, introducing the so-called LeMonHash-VL: it needs space within 13% of the best competitors while achieving up to 3 times faster queries than the next larger competitor.

BibTeX - Entry

  author =	{Ferragina, Paolo and Lehmann, Hans-Peter and Sanders, Peter and Vinciguerra, Giorgio},
  title =	{{Learned Monotone Minimal Perfect Hashing}},
  booktitle =	{31st Annual European Symposium on Algorithms (ESA 2023)},
  pages =	{46:1--46:17},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-295-2},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{274},
  editor =	{G{\o}rtz, Inge Li and Farach-Colton, Martin and Puglisi, Simon J. and Herman, Grzegorz},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{},
  URN =		{urn:nbn:de:0030-drops-186990},
  doi =		{10.4230/LIPIcs.ESA.2023.46},
  annote =	{Keywords: compressed data structure, monotone minimal perfect hashing, retrieval}

Keywords: compressed data structure, monotone minimal perfect hashing, retrieval
Collection: 31st Annual European Symposium on Algorithms (ESA 2023)
Issue Date: 2023
Date of publication: 30.08.2023
Supplementary Material: Software (Source Code): archived at:

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