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Documents authored by Sanders, Peter

Document
DOI: 10.4230/LIPIcs.ESA.2024.69
PHOBIC: Perfect Hashing With Optimized Bucket Sizes and Interleaved Coding

Authors: Stefan Hermann, Hans-Peter Lehmann, Giulio Ermanno Pibiri, Peter Sanders, and Stefan Walzer

Published in: LIPIcs, Volume 308, 32nd Annual European Symposium on Algorithms (ESA 2024)

Abstract
A minimal perfect hash function (or MPHF) maps a set of n keys to [n] : = {1, …, n} without collisions. Such functions find widespread application e.g. in bioinformatics and databases. In this paper we revisit PTHash - a construction technique particularly designed for fast queries. PTHash distributes the input keys into small buckets and, for each bucket, it searches for a hash function seed that places its keys in the output domain without collisions. The collection of all seeds is then stored in a compressed way. Since the first buckets are easier to place, buckets are considered in non-increasing order of size. Additionally, PTHash heuristically produces an imbalanced distribution of bucket sizes by distributing 60% of the keys into 30% of the buckets. Our main contribution is to characterize, up to lower order terms, an optimal choice for the expected bucket sizes, improving construction throughput for space efficient configurations both in theory and practice. Further contributions include a new encoding scheme for seeds that works across partitions of the data structure and a GPU parallelization. Compared to PTHash, PHOBIC is 0.17 bits/key more space efficient for same query time and construction throughput. For a configuration with fast queries, our GPU implementation can construct an MPHF at 2.17 bits/key in 28 ns/key, which can be queried in 37 ns/query on the CPU.
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Stefan Hermann, Hans-Peter Lehmann, Giulio Ermanno Pibiri, Peter Sanders, and Stefan Walzer. PHOBIC: Perfect Hashing With Optimized Bucket Sizes and Interleaved Coding. In 32nd Annual European Symposium on Algorithms (ESA 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 308, pp. 69:1-69:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{hermann_et_al:LIPIcs.ESA.2024.69,
  author =	{Hermann, Stefan and Lehmann, Hans-Peter and Pibiri, Giulio Ermanno and Sanders, Peter and Walzer, Stefan},
  title =	{{PHOBIC: Perfect Hashing With Optimized Bucket Sizes and Interleaved Coding}},
  booktitle =	{32nd Annual European Symposium on Algorithms (ESA 2024)},
  pages =	{69:1--69:17},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-338-6},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{308},
  editor =	{Chan, Timothy and Fischer, Johannes and Iacono, John and Herman, Grzegorz},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ESA.2024.69},
  URN =		{urn:nbn:de:0030-drops-211405},
  doi =		{10.4230/LIPIcs.ESA.2024.69},
  annote =	{Keywords: Compressed Data Structures, Minimal Perfect Hashing, GPU}
}
Document
DOI: 10.4230/LIPIcs.ESA.2024.83
Scalable Distributed String Sorting

Authors: Florian Kurpicz, Pascal Mehnert, Peter Sanders, and Matthias Schimek

Published in: LIPIcs, Volume 308, 32nd Annual European Symposium on Algorithms (ESA 2024)

Abstract
String sorting is an important part of tasks such as building index data structures. Unfortunately, current string sorting algorithms do not scale to massively parallel distributed-memory machines since they either have latency (at least) proportional to the number of processors p or communicate the data a large number of times (at least logarithmic). We present practical and efficient algorithms for distributed-memory string sorting that scale to large p. Similar to state-of-the-art sorters for atomic objects, the algorithms have latency of about p^{1/k} when allowing the data to be communicated k times. Experiments indicate good scaling behavior on a wide range of inputs on up to 49152 cores. Overall, we achieve speedups of up to 4.9 over the current state-of-the-art distributed string sorting algorithms.
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Florian Kurpicz, Pascal Mehnert, Peter Sanders, and Matthias Schimek. Scalable Distributed String Sorting. In 32nd Annual European Symposium on Algorithms (ESA 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 308, pp. 83:1-83:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{kurpicz_et_al:LIPIcs.ESA.2024.83,
  author =	{Kurpicz, Florian and Mehnert, Pascal and Sanders, Peter and Schimek, Matthias},
  title =	{{Scalable Distributed String Sorting}},
  booktitle =	{32nd Annual European Symposium on Algorithms (ESA 2024)},
  pages =	{83:1--83:17},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-338-6},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{308},
  editor =	{Chan, Timothy and Fischer, Johannes and Iacono, John and Herman, Grzegorz},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ESA.2024.83},
  URN =		{urn:nbn:de:0030-drops-211541},
  doi =		{10.4230/LIPIcs.ESA.2024.83},
  annote =	{Keywords: sorting, strings, distributed-memory computing, distributed membership filters, scalability}
}
Document
DOI: 10.4230/LIPIcs.SEA.2024.20
Targeted Branching for the Maximum Independent Set Problem Using Graph Neural Networks

Authors: Kenneth Langedal, Demian Hespe, and Peter Sanders

Published in: LIPIcs, Volume 301, 22nd International Symposium on Experimental Algorithms (SEA 2024)

Abstract
Identifying a maximum independent set is a fundamental NP-hard problem. This problem has several real-world applications and requires finding the largest possible set of vertices not adjacent to each other in an undirected graph. Over the past few years, branch-and-bound and branch-and-reduce algorithms have emerged as some of the most effective methods for solving the problem exactly. Specifically, the branch-and-reduce approach, which combines branch-and-bound principles with reduction rules, has proven particularly successful in tackling previously unmanageable real-world instances. This progress was largely made possible by the development of more effective reduction rules. Nevertheless, other key components that can impact the efficiency of these algorithms have not received the same level of interest. Among these is the branching strategy, which determines which vertex to branch on next. Until recently, the most widely used strategy was to choose the vertex of the highest degree. In this work, we present a graph neural network approach for selecting the next branching vertex. The intricate nature of current branch-and-bound solvers makes supervised and reinforcement learning difficult. Therefore, we use a population-based genetic algorithm to evolve the model’s parameters instead. Our proposed approach results in a speedup on 73% of the benchmark instances with a median speedup of 24%.
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Kenneth Langedal, Demian Hespe, and Peter Sanders. Targeted Branching for the Maximum Independent Set Problem Using Graph Neural Networks. In 22nd International Symposium on Experimental Algorithms (SEA 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 301, pp. 20:1-20:21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{langedal_et_al:LIPIcs.SEA.2024.20,
  author =	{Langedal, Kenneth and Hespe, Demian and Sanders, Peter},
  title =	{{Targeted Branching for the Maximum Independent Set Problem Using Graph Neural Networks}},
  booktitle =	{22nd International Symposium on Experimental Algorithms (SEA 2024)},
  pages =	{20:1--20:21},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-325-6},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{301},
  editor =	{Liberti, Leo},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SEA.2024.20},
  URN =		{urn:nbn:de:0030-drops-203853},
  doi =		{10.4230/LIPIcs.SEA.2024.20},
  annote =	{Keywords: Graphs, Independent Set, Vertex Cover, Graph Neural Networks, Branch-and-Reduce}
}
Document
DOI: 10.4230/LIPIcs.ESA.2023.19
High Performance Construction of RecSplit Based Minimal Perfect Hash Functions

Authors: Dominik Bez, Florian Kurpicz, Hans-Peter Lehmann, and Peter Sanders

Published in: LIPIcs, Volume 274, 31st Annual European Symposium on Algorithms (ESA 2023)

Abstract
A minimal perfect hash function (MPHF) bijectively maps a set S of objects to the first |S| integers. It can be used as a building block in databases and data compression. RecSplit [Esposito et al., ALENEX'20] is currently the most space efficient practical minimal perfect hash function. It heavily relies on trying out hash functions in a brute force way. We introduce rotation fitting, a new technique that makes the search more efficient by drastically reducing the number of tried hash functions. Additionally, we greatly improve the construction time of RecSplit by harnessing parallelism on the level of bits, vectors, cores, and GPUs. In combination, the resulting improvements yield speedups up to 239 on an 8-core CPU and up to 5438 using a GPU. The original single-threaded RecSplit implementation needs 1.5 hours to construct an MPHF for 5 Million objects with 1.56 bits per object. On the GPU, we achieve the same space usage in just 5 seconds. Given that the speedups are larger than the increase in energy consumption, our implementation is more energy efficient than the original implementation.
Cite as

Dominik Bez, Florian Kurpicz, Hans-Peter Lehmann, and Peter Sanders. High Performance Construction of RecSplit Based Minimal Perfect Hash Functions. In 31st Annual European Symposium on Algorithms (ESA 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 274, pp. 19:1-19:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{bez_et_al:LIPIcs.ESA.2023.19,
  author =	{Bez, Dominik and Kurpicz, Florian and Lehmann, Hans-Peter and Sanders, Peter},
  title =	{{High Performance Construction of RecSplit Based Minimal Perfect Hash Functions}},
  booktitle =	{31st Annual European Symposium on Algorithms (ESA 2023)},
  pages =	{19:1--19:16},
  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 =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ESA.2023.19},
  URN =		{urn:nbn:de:0030-drops-186728},
  doi =		{10.4230/LIPIcs.ESA.2023.19},
  annote =	{Keywords: compressed data structure, parallel perfect hashing, bit parallelism, GPU, SIMD, parallel computing, vector instructions}
}
Document
DOI: 10.4230/LIPIcs.ESA.2023.46
Learned Monotone Minimal Perfect Hashing

Authors: Paolo Ferragina, Hans-Peter Lehmann, Peter Sanders, and Giorgio Vinciguerra

Published in: LIPIcs, Volume 274, 31st Annual European Symposium on Algorithms (ESA 2023)

Abstract
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.
Cite as

Paolo Ferragina, Hans-Peter Lehmann, Peter Sanders, and Giorgio Vinciguerra. Learned Monotone Minimal Perfect Hashing. In 31st Annual European Symposium on Algorithms (ESA 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 274, pp. 46:1-46:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{ferragina_et_al:LIPIcs.ESA.2023.46,
  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 =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ESA.2023.46},
  URN =		{urn:nbn:de:0030-drops-186990},
  doi =		{10.4230/LIPIcs.ESA.2023.46},
  annote =	{Keywords: compressed data structure, monotone minimal perfect hashing, retrieval}
}
Document
DOI: 10.4230/LIPIcs.ESA.2023.51
A Sweep-Plane Algorithm for Calculating the Isolation of Mountains

Authors: Daniel Funke, Nicolai Hüning, and Peter Sanders

Published in: LIPIcs, Volume 274, 31st Annual European Symposium on Algorithms (ESA 2023)

Abstract
One established metric to classify the significance of a mountain peak is its isolation. It specifies the distance between a peak and the closest point of higher elevation. Peaks with high isolation dominate their surroundings and provide a nice view from the top. With the availability of worldwide Digital Elevation Models (DEMs), the isolation of all mountain peaks can be computed automatically. Previous algorithms run in worst case time that is quadratic in the input size. We present a novel sweep-plane algorithm that runs in time 𝒪(nlog n+pT_NN) where n is the input size, p the number of considered peaks and T_NN the time for a 2D nearest-neighbor query in an appropriate geometric search tree. We refine this to a two-level approach that has high locality and good parallel scalability. Our implementation reduces the time for calculating the isolation of every peak on Earth from hours to minutes while improving precision.
Cite as

Daniel Funke, Nicolai Hüning, and Peter Sanders. A Sweep-Plane Algorithm for Calculating the Isolation of Mountains. In 31st Annual European Symposium on Algorithms (ESA 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 274, pp. 51:1-51:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{funke_et_al:LIPIcs.ESA.2023.51,
  author =	{Funke, Daniel and H\"{u}ning, Nicolai and Sanders, Peter},
  title =	{{A Sweep-Plane Algorithm for Calculating the Isolation of Mountains}},
  booktitle =	{31st Annual European Symposium on Algorithms (ESA 2023)},
  pages =	{51:1--51:17},
  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 =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ESA.2023.51},
  URN =		{urn:nbn:de:0030-drops-187040},
  doi =		{10.4230/LIPIcs.ESA.2023.51},
  annote =	{Keywords: computational geometry, Geo-information systems, sweepline algorithms}
}
Document
DOI: 10.4230/LIPIcs.ESA.2023.60
Pareto Sums of Pareto Sets

Authors: Demian Hespe, Peter Sanders, Sabine Storandt, and Carina Truschel

Published in: LIPIcs, Volume 274, 31st Annual European Symposium on Algorithms (ESA 2023)

Abstract
In bi-criteria optimization problems, the goal is typically to compute the set of Pareto-optimal solutions. Many algorithms for these types of problems rely on efficient merging or combining of partial solutions and filtering of dominated solutions in the resulting sets. In this paper, we consider the task of computing the Pareto sum of two given Pareto sets A, B of size n. The Pareto sum contains all non-dominated points of the Minkowski sum M = {a+b|a ∈ A, b ∈ B}. Since the Minkowski sum has a size of n², but the Pareto sum C can be much smaller, the goal is to compute C without having to compute and store all of M. We present several new algorithms for efficient Pareto sum computation, including an output-sensitive one with a running time of 𝒪(n log n + nk) and a space consumption of 𝒪(n+k) for k = |C|. We also describe suitable engineering techniques to improve the practical running times of our algorithms and provide a comparative experimental study. As one showcase application, we consider preprocessing-based methods for bi-criteria route planning in road networks. Pareto sum computation is a frequent task in the preprocessing phase. We show that using our algorithms with an output-sensitive space consumption allows to tackle larger instances and reduces the preprocessing time compared to algorithms that fully store M.
Cite as

Demian Hespe, Peter Sanders, Sabine Storandt, and Carina Truschel. Pareto Sums of Pareto Sets. In 31st Annual European Symposium on Algorithms (ESA 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 274, pp. 60:1-60:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{hespe_et_al:LIPIcs.ESA.2023.60,
  author =	{Hespe, Demian and Sanders, Peter and Storandt, Sabine and Truschel, Carina},
  title =	{{Pareto Sums of Pareto Sets}},
  booktitle =	{31st Annual European Symposium on Algorithms (ESA 2023)},
  pages =	{60:1--60:17},
  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 =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ESA.2023.60},
  URN =		{urn:nbn:de:0030-drops-187132},
  doi =		{10.4230/LIPIcs.ESA.2023.60},
  annote =	{Keywords: Minkowski sum, Skyline, Successive Algorithm}
}
Document
DOI: 10.4230/LIPIcs.SEA.2023.20
Efficient Yao Graph Construction

Authors: Daniel Funke and Peter Sanders

Published in: LIPIcs, Volume 265, 21st International Symposium on Experimental Algorithms (SEA 2023)

Abstract
Yao graphs are geometric spanners that connect each point of a given point set to its nearest neighbor in each of k cones drawn around it. Yao graphs were introduced to construct minimum spanning trees in d dimensional spaces. Moreover, they are used for instance in topology control in wireless networks. An optimal 𝒪(n log n)-time algorithm to construct Yao graphs for a given point set has been proposed in the literature but - to the best of our knowledge - never been implemented. Instead, algorithms with a quadratic complexity are used in popular packages to construct these graphs. In this paper we present the first implementation of the optimal Yao graph algorithm. We engineer the data structures required to achieve the 𝒪(n log n) time bound and detail algorithmic adaptations necessary to take the original algorithm from theory to practice. We propose a priority queue data structure that separates static and dynamic events and might be of independent interest for other sweepline algorithms. Additionally, we propose a new Yao graph algorithm based on a uniform grid data structure that performs well for medium-sized inputs. We evaluate our implementations on a wide variety of synthetic and real-world datasets and show that our implementation outperforms current publicly available implementations by at least an order of magnitude.
Cite as

Daniel Funke and Peter Sanders. Efficient Yao Graph Construction. In 21st International Symposium on Experimental Algorithms (SEA 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 265, pp. 20:1-20:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{funke_et_al:LIPIcs.SEA.2023.20,
  author =	{Funke, Daniel and Sanders, Peter},
  title =	{{Efficient Yao Graph Construction}},
  booktitle =	{21st International Symposium on Experimental Algorithms (SEA 2023)},
  pages =	{20:1--20:20},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-279-2},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{265},
  editor =	{Georgiadis, Loukas},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SEA.2023.20},
  URN =		{urn:nbn:de:0030-drops-183706},
  doi =		{10.4230/LIPIcs.SEA.2023.20},
  annote =	{Keywords: computational geometry, geometric spanners, Yao graphs, sweepline algorithms, optimal algorithms}
}
Document
DOI: 10.4230/LIPIcs.SEA.2022.4
Fast Succinct Retrieval and Approximate Membership Using Ribbon

Authors: Peter C. Dillinger, Lorenz Hübschle-Schneider, Peter Sanders, and Stefan Walzer

Published in: LIPIcs, Volume 233, 20th International Symposium on Experimental Algorithms (SEA 2022)

Abstract
A retrieval data structure for a static function f: S → {0,1}^r supports queries that return f(x) for any x ∈ S. Retrieval data structures can be used to implement a static approximate membership query data structure (AMQ), i.e., a Bloom filter alternative, with false positive rate 2^{-r}. The information-theoretic lower bound for both tasks is r|S| bits. While succinct theoretical constructions using (1+o(1))r|S| bits were known, these could not achieve very small overheads in practice because they have an unfavorable space-time tradeoff hidden in the asymptotic costs or because small overheads would only be reached for physically impossible input sizes. With bumped ribbon retrieval (BuRR), we present the first practical succinct retrieval data structure. In an extensive experimental evaluation BuRR achieves space overheads well below 1% while being faster than most previously used retrieval data structures (typically with space overheads at least an order of magnitude larger) and faster than classical Bloom filters (with space overhead ≥ 44%). This efficiency, including favorable constants, stems from a combination of simplicity, word parallelism, and high locality. We additionally describe homogeneous ribbon filter AMQs, which are even simpler and faster at the price of slightly larger space overhead.
Cite as

Peter C. Dillinger, Lorenz Hübschle-Schneider, Peter Sanders, and Stefan Walzer. Fast Succinct Retrieval and Approximate Membership Using Ribbon. In 20th International Symposium on Experimental Algorithms (SEA 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 233, pp. 4:1-4:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{dillinger_et_al:LIPIcs.SEA.2022.4,
  author =	{Dillinger, Peter C. and H\"{u}bschle-Schneider, Lorenz and Sanders, Peter and Walzer, Stefan},
  title =	{{Fast Succinct Retrieval and Approximate Membership Using Ribbon}},
  booktitle =	{20th International Symposium on Experimental Algorithms (SEA 2022)},
  pages =	{4:1--4:20},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-251-8},
  ISSN =	{1868-8969},
  year =	{2022},
  volume =	{233},
  editor =	{Schulz, Christian and U\c{c}ar, Bora},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SEA.2022.4},
  URN =		{urn:nbn:de:0030-drops-165385},
  doi =		{10.4230/LIPIcs.SEA.2022.4},
  annote =	{Keywords: AMQ, Bloom filter, dictionary, linear algebra, randomized algorithm, retrieval data structure, static function data structure, succinct data structure, perfect hashing}
}
Document
DOI: 10.4230/LIPIcs.SEA.2022.5
Parallel Flow-Based Hypergraph Partitioning

Authors: Lars Gottesbüren, Tobias Heuer, and Peter Sanders

Published in: LIPIcs, Volume 233, 20th International Symposium on Experimental Algorithms (SEA 2022)

Abstract
We present a shared-memory parallelization of flow-based refinement, which is considered the most powerful iterative improvement technique for hypergraph partitioning at the moment. Flow-based refinement works on bipartitions, so current sequential partitioners schedule it on different block pairs to improve k-way partitions. We investigate two different sources of parallelism: a parallel scheduling scheme and a parallel maximum flow algorithm based on the well-known push-relabel algorithm. In addition to thoroughly engineered implementations, we propose several optimizations that substantially accelerate the algorithm in practice, enabling the use on extremely large hypergraphs (up to 1 billion pins). We integrate our approach in the state-of-the-art parallel multilevel framework Mt-KaHyPar and conduct extensive experiments on a benchmark set of more than 500 real-world hypergraphs, to show that the partition quality of our code is on par with the highest quality sequential code (KaHyPar), while being an order of magnitude faster with 10 threads.
Cite as

Lars Gottesbüren, Tobias Heuer, and Peter Sanders. Parallel Flow-Based Hypergraph Partitioning. In 20th International Symposium on Experimental Algorithms (SEA 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 233, pp. 5:1-5:21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{gottesburen_et_al:LIPIcs.SEA.2022.5,
  author =	{Gottesb\"{u}ren, Lars and Heuer, Tobias and Sanders, Peter},
  title =	{{Parallel Flow-Based Hypergraph Partitioning}},
  booktitle =	{20th International Symposium on Experimental Algorithms (SEA 2022)},
  pages =	{5:1--5:21},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-251-8},
  ISSN =	{1868-8969},
  year =	{2022},
  volume =	{233},
  editor =	{Schulz, Christian and U\c{c}ar, Bora},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SEA.2022.5},
  URN =		{urn:nbn:de:0030-drops-165393},
  doi =		{10.4230/LIPIcs.SEA.2022.5},
  annote =	{Keywords: multilevel hypergraph partitioning, shared-memory algorithms, maximum flow}
}
Document
DOI: 10.4230/LIPIcs.ESA.2021.48
Deep Multilevel Graph Partitioning

Authors: Lars Gottesbüren, Tobias Heuer, Peter Sanders, Christian Schulz, and Daniel Seemaier

Published in: LIPIcs, Volume 204, 29th Annual European Symposium on Algorithms (ESA 2021)

Abstract
Partitioning a graph into blocks of "roughly equal" weight while cutting only few edges is a fundamental problem in computer science with a wide range of applications. In particular, the problem is a building block in applications that require parallel processing. While the amount of available cores in parallel architectures has significantly increased in recent years, state-of-the-art graph partitioning algorithms do not work well if the input needs to be partitioned into a large number of blocks. Often currently available algorithms compute highly imbalanced solutions, solutions of low quality, or have excessive running time for this case. This is due to the fact that most high-quality general-purpose graph partitioners are multilevel algorithms which perform graph coarsening to build a hierarchy of graphs, initial partitioning to compute an initial solution, and local improvement to improve the solution throughout the hierarchy. However, for large number of blocks, the smallest graph in the hierarchy that is used for initial partitioning still has to be large. In this work, we substantially mitigate these problems by introducing deep multilevel graph partitioning and a shared-memory implementation thereof. Our scheme continues the multilevel approach deep into initial partitioning - integrating it into a framework where recursive bipartitioning and direct k-way partitioning are combined such that they can operate with high performance and quality. Our integrated approach is stronger, more flexible, arguably more elegant, and reduces bottlenecks for parallelization compared to existing multilevel approaches. For example, for large number of blocks our algorithm is on average at least an order of magnitude faster than competing algorithms while computing partitions with comparable solution quality. At the same time, our algorithm consistently produces balanced solutions. Moreover, for small number of blocks, our algorithms are the fastest among competing systems with comparable quality.
Cite as

Lars Gottesbüren, Tobias Heuer, Peter Sanders, Christian Schulz, and Daniel Seemaier. Deep Multilevel Graph Partitioning. In 29th Annual European Symposium on Algorithms (ESA 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 204, pp. 48:1-48:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{gottesburen_et_al:LIPIcs.ESA.2021.48,
  author =	{Gottesb\"{u}ren, Lars and Heuer, Tobias and Sanders, Peter and Schulz, Christian and Seemaier, Daniel},
  title =	{{Deep Multilevel Graph Partitioning}},
  booktitle =	{29th Annual European Symposium on Algorithms (ESA 2021)},
  pages =	{48:1--48:17},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-204-4},
  ISSN =	{1868-8969},
  year =	{2021},
  volume =	{204},
  editor =	{Mutzel, Petra and Pagh, Rasmus and Herman, Grzegorz},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ESA.2021.48},
  URN =		{urn:nbn:de:0030-drops-146298},
  doi =		{10.4230/LIPIcs.ESA.2021.48},
  annote =	{Keywords: graph partitioning, graph algorithms, multilevel, shared-memory, parallel}
}
Document
DOI: 10.4230/LIPIcs.ESA.2021.81
Engineering MultiQueues: Fast Relaxed Concurrent Priority Queues

Authors: Marvin Williams, Peter Sanders, and Roman Dementiev

Published in: LIPIcs, Volume 204, 29th Annual European Symposium on Algorithms (ESA 2021)

Abstract
Priority queues with parallel access are an attractive data structure for applications like prioritized online scheduling, discrete event simulation, or greedy algorithms. However, a classical priority queue constitutes a severe bottleneck in this context, leading to very small throughput. Hence, there has been significant interest in concurrent priority queues with relaxed semantics. We investigate the complementary quality criteria rank error (how close are deleted elements to the global minimum) and delay (for each element x, how many elements with lower priority are deleted before x). In this paper, we introduce MultiQueues as a natural approach to relaxed priority queues based on multiple sequential priority queues. Their naturally high theoretical scalability is further enhanced by using three orthogonal ways of batching operations on the sequential queues. Experiments indicate that MultiQueues present a very good performance-quality tradeoff and considerably outperform competing approaches in at least one of these aspects. We employ a seemingly paradoxical technique of "wait-free locking" that might be of more general interest to convert sequential data structures to relaxed concurrent data structures.
Cite as

Marvin Williams, Peter Sanders, and Roman Dementiev. Engineering MultiQueues: Fast Relaxed Concurrent Priority Queues. In 29th Annual European Symposium on Algorithms (ESA 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 204, pp. 81:1-81:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{williams_et_al:LIPIcs.ESA.2021.81,
  author =	{Williams, Marvin and Sanders, Peter and Dementiev, Roman},
  title =	{{Engineering MultiQueues: Fast Relaxed Concurrent Priority Queues}},
  booktitle =	{29th Annual European Symposium on Algorithms (ESA 2021)},
  pages =	{81:1--81:17},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-204-4},
  ISSN =	{1868-8969},
  year =	{2021},
  volume =	{204},
  editor =	{Mutzel, Petra and Pagh, Rasmus and Herman, Grzegorz},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ESA.2021.81},
  URN =		{urn:nbn:de:0030-drops-146627},
  doi =		{10.4230/LIPIcs.ESA.2021.81},
  annote =	{Keywords: concurrent data structure, priority queues, randomized algorithms, wait-free locking}
}
Document
Complete Volume
DOI: 10.4230/LIPIcs.ESA.2020
LIPIcs, Volume 173, ESA 2020, Complete Volume

Authors: Fabrizio Grandoni, Grzegorz Herman, and Peter Sanders

Published in: LIPIcs, Volume 173, 28th Annual European Symposium on Algorithms (ESA 2020)

Abstract
LIPIcs, Volume 173, ESA 2020, Complete Volume
Cite as

28th Annual European Symposium on Algorithms (ESA 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 173, pp. 1-1598, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@Proceedings{grandoni_et_al:LIPIcs.ESA.2020,
  title =	{{LIPIcs, Volume 173, ESA 2020, Complete Volume}},
  booktitle =	{28th Annual European Symposium on Algorithms (ESA 2020)},
  pages =	{1--1598},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-162-7},
  ISSN =	{1868-8969},
  year =	{2020},
  volume =	{173},
  editor =	{Grandoni, Fabrizio and Herman, Grzegorz and Sanders, Peter},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ESA.2020},
  URN =		{urn:nbn:de:0030-drops-128651},
  doi =		{10.4230/LIPIcs.ESA.2020},
  annote =	{Keywords: LIPIcs, Volume 173, ESA 2020, Complete Volume}
}
Document
Front Matter
DOI: 10.4230/LIPIcs.ESA.2020.0
Front Matter, Table of Contents, Preface, Conference Organization

Authors: Fabrizio Grandoni, Grzegorz Herman, and Peter Sanders

Published in: LIPIcs, Volume 173, 28th Annual European Symposium on Algorithms (ESA 2020)

Abstract
Front Matter, Table of Contents, Preface, Conference Organization
Cite as

28th Annual European Symposium on Algorithms (ESA 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 173, pp. 0:i-0:xx, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{grandoni_et_al:LIPIcs.ESA.2020.0,
  author =	{Grandoni, Fabrizio and Herman, Grzegorz and Sanders, Peter},
  title =	{{Front Matter, Table of Contents, Preface, Conference Organization}},
  booktitle =	{28th Annual European Symposium on Algorithms (ESA 2020)},
  pages =	{0:i--0:xx},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-162-7},
  ISSN =	{1868-8969},
  year =	{2020},
  volume =	{173},
  editor =	{Grandoni, Fabrizio and Herman, Grzegorz and Sanders, Peter},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ESA.2020.0},
  URN =		{urn:nbn:de:0030-drops-128669},
  doi =		{10.4230/LIPIcs.ESA.2020.0},
  annote =	{Keywords: Front Matter, Table of Contents, Preface, Conference Organization}
}
Document
DOI: 10.4230/LIPIcs.SEA.2020.15
Concurrent Expandable AMQs on the Basis of Quotient Filters

Authors: Tobias Maier, Peter Sanders, and Robert Williger

Published in: LIPIcs, Volume 160, 18th International Symposium on Experimental Algorithms (SEA 2020)

Abstract
A quotient filter is a cache efficient Approximate Membership Query (AMQ) data structure. Depending on the fill degree of the filter most insertions and queries only need to access one or two consecutive cache lines. This makes quotient filters very fast compared to the more commonly used Bloom filters that incur multiple independent memory accesses depending on the false positive rate. However, concurrent Bloom filters are easy to implement and can be implemented lock-free while concurrent quotient filters are not as simple. Usually concurrent quotient filters work by using an external array of locks - each protecting a region of the table. Accessing this array incurs one additional memory access per operation. We propose a new locking scheme that has no memory overhead. Using this new locking scheme we achieve 1.6× times higher insertion performance and over 2.1× higher query performance than with the common external locking scheme. Another advantage of quotient filters over Bloom filters is that a quotient filter can change its capacity when it is becoming full. We implement this growing technique for our concurrent quotient filters and adapt it in a way that allows unbounded growing while keeping a bounded false positive rate. We call the resulting data structure a fully expandable quotient filter. Its design is similar to scalable Bloom filters, but we exploit some concepts inherent to quotient filters to improve the space efficiency and the query speed. Additionally, we propose several quotient filter variants that are aimed to reduce the number of status bits (2-status-bit variant) or to simplify concurrent implementations (linear probing quotient filter). The linear probing quotient filter even leads to a lock-free concurrent filter implementation. This is especially interesting, since we show that any lock-free implementation of other common quotient filter variants would incur significant overheads in the form of additional data fields or multiple passes over the accessed data. The code produced as part of this submission can be found at https://www.github.com/Toobiased/lpqfilter.
Cite as

Tobias Maier, Peter Sanders, and Robert Williger. Concurrent Expandable AMQs on the Basis of Quotient Filters. In 18th International Symposium on Experimental Algorithms (SEA 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 160, pp. 15:1-15:13, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{maier_et_al:LIPIcs.SEA.2020.15,
  author =	{Maier, Tobias and Sanders, Peter and Williger, Robert},
  title =	{{Concurrent Expandable AMQs on the Basis of Quotient Filters}},
  booktitle =	{18th International Symposium on Experimental Algorithms (SEA 2020)},
  pages =	{15:1--15:13},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-148-1},
  ISSN =	{1868-8969},
  year =	{2020},
  volume =	{160},
  editor =	{Faro, Simone and Cantone, Domenico},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SEA.2020.15},
  URN =		{urn:nbn:de:0030-drops-120890},
  doi =		{10.4230/LIPIcs.SEA.2020.15},
  annote =	{Keywords: Quotient filter, Concurrent data structures, Locking}
}
Document
DOI: 10.4230/OASIcs.ATMOS.2019.10
More Hierarchy in Route Planning Using Edge Hierarchies

Authors: Demian Hespe and Peter Sanders

Published in: OASIcs, Volume 75, 19th Symposium on Algorithmic Approaches for Transportation Modelling, Optimization, and Systems (ATMOS 2019)

Abstract
A highly successful approach to route planning in networks (particularly road networks) is to identify a hierarchy in the network that allows faster queries after some preprocessing that basically inserts additional "shortcut"-edges into a graph. In the past there has been a succession of techniques that infer a more and more fine grained hierarchy enabling increasingly more efficient queries. This appeared to culminate in contraction hierarchies that assign one hierarchy level to each vertex. In this paper we show how to identify an even more fine grained hierarchy that assigns one level to each edge of the network. Our findings indicate that this can lead to considerably smaller search spaces in terms of visited edges. Currently, this rarely implies improved query times so that it remains an open question whether edge hierarchies can lead to consistently improved performance. However, we believe that the technique as such is a noteworthy enrichment of the portfolio of available techniques that might prove useful in the future.
Cite as

Demian Hespe and Peter Sanders. More Hierarchy in Route Planning Using Edge Hierarchies. In 19th Symposium on Algorithmic Approaches for Transportation Modelling, Optimization, and Systems (ATMOS 2019). Open Access Series in Informatics (OASIcs), Volume 75, pp. 10:1-10:14, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@InProceedings{hespe_et_al:OASIcs.ATMOS.2019.10,
  author =	{Hespe, Demian and Sanders, Peter},
  title =	{{More Hierarchy in Route Planning Using Edge Hierarchies}},
  booktitle =	{19th Symposium on Algorithmic Approaches for Transportation Modelling, Optimization, and Systems (ATMOS 2019)},
  pages =	{10:1--10:14},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-95977-128-3},
  ISSN =	{2190-6807},
  year =	{2019},
  volume =	{75},
  editor =	{Cacchiani, Valentina and Marchetti-Spaccamela, Alberto},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.ATMOS.2019.10},
  URN =		{urn:nbn:de:0030-drops-114228},
  doi =		{10.4230/OASIcs.ATMOS.2019.10},
  annote =	{Keywords: shortest path, hierarchy, road networks, preprocessing}
}
Document
DOI: 10.4230/LIPIcs.ESA.2019.59
Parallel Weighted Random Sampling

Authors: Lorenz Hübschle-Schneider and Peter Sanders

Published in: LIPIcs, Volume 144, 27th Annual European Symposium on Algorithms (ESA 2019)

Abstract
Data structures for efficient sampling from a set of weighted items are an important building block of many applications. However, few parallel solutions are known. We close many of these gaps both for shared-memory and distributed-memory machines. We give efficient, fast, and practicable algorithms for sampling single items, k items with/without replacement, permutations, subsets, and reservoirs. We also give improved sequential algorithms for alias table construction and for sampling with replacement. Experiments on shared-memory parallel machines with up to 158 threads show near linear speedups both for construction and queries.
Cite as

Lorenz Hübschle-Schneider and Peter Sanders. Parallel Weighted Random Sampling. In 27th Annual European Symposium on Algorithms (ESA 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 144, pp. 59:1-59:24, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@InProceedings{hubschleschneider_et_al:LIPIcs.ESA.2019.59,
  author =	{H\"{u}bschle-Schneider, Lorenz and Sanders, Peter},
  title =	{{Parallel Weighted Random Sampling}},
  booktitle =	{27th Annual European Symposium on Algorithms (ESA 2019)},
  pages =	{59:1--59:24},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-124-5},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{144},
  editor =	{Bender, Michael A. and Svensson, Ola and Herman, Grzegorz},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ESA.2019.59},
  URN =		{urn:nbn:de:0030-drops-111800},
  doi =		{10.4230/LIPIcs.ESA.2019.59},
  annote =	{Keywords: categorical distribution, multinoulli distribution, parallel algorithm, alias method, PRAM, communication efficient algorithm, subset sampling, reservoir sampling}
}
Document
DOI: 10.4230/LIPIcs.SEA.2018.1
Network Flow-Based Refinement for Multilevel Hypergraph Partitioning

Authors: Tobias Heuer, Peter Sanders, and Sebastian Schlag

Published in: LIPIcs, Volume 103, 17th International Symposium on Experimental Algorithms (SEA 2018)

Abstract
We present a refinement framework for multilevel hypergraph partitioning that uses max-flow computations on pairs of blocks to improve the solution quality of a k-way partition. The framework generalizes the flow-based improvement algorithm of KaFFPa from graphs to hypergraphs and is integrated into the hypergraph partitioner KaHyPar. By reducing the size of hypergraph flow networks, improving the flow model used in KaFFPa, and developing techniques to improve the running time of our algorithm, we obtain a partitioner that computes the best solutions for a wide range of benchmark hypergraphs from different application areas while still having a running time comparable to that of hMetis.
Cite as

Tobias Heuer, Peter Sanders, and Sebastian Schlag. Network Flow-Based Refinement for Multilevel Hypergraph Partitioning. In 17th International Symposium on Experimental Algorithms (SEA 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 103, pp. 1:1-1:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{heuer_et_al:LIPIcs.SEA.2018.1,
  author =	{Heuer, Tobias and Sanders, Peter and Schlag, Sebastian},
  title =	{{Network Flow-Based Refinement for Multilevel Hypergraph Partitioning}},
  booktitle =	{17th International Symposium on Experimental Algorithms (SEA 2018)},
  pages =	{1:1--1:19},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-070-5},
  ISSN =	{1868-8969},
  year =	{2018},
  volume =	{103},
  editor =	{D'Angelo, Gianlorenzo},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SEA.2018.1},
  URN =		{urn:nbn:de:0030-drops-89368},
  doi =		{10.4230/LIPIcs.SEA.2018.1},
  annote =	{Keywords: Multilevel Hypergraph Partitioning, Network Flows, Refinement}
}
Document
DOI: 10.4230/LIPIcs.SEA.2018.27
Real-Time Traffic Assignment Using Fast Queries in Customizable Contraction Hierarchies

Authors: Valentin Buchhold, Peter Sanders, and Dorothea Wagner

Published in: LIPIcs, Volume 103, 17th International Symposium on Experimental Algorithms (SEA 2018)

Abstract
Given an urban road network and a set of origin-destination (OD) pairs, the traffic assignment problem asks for the traffic flow on each road segment. A common solution employs a feasible-direction method, where the direction-finding step requires many shortest-path computations. In this paper, we significantly accelerate the computation of flow patterns, enabling interactive transportation and urban planning applications. We achieve this by revisiting and carefully engineering known speedup techniques for shortest paths, and combining them with customizable contraction hierarchies. In particular, our accelerated elimination tree search is more than an order of magnitude faster for local queries than the original algorithm, and our centralized search speeds up batched point-to-point shortest paths by a factor of up to 6. These optimizations are independent of traffic assignment and can be generally used for (batched) point-to-point queries. In contrast to prior work, our evaluation uses real-world data for all parts of the problem. On a metropolitan area encompassing more than 2.7 million inhabitants, we reduce the flow-pattern computation for a typical two-hour morning peak from 76.5 to 10.5 seconds on one core, and 4.3 seconds on four cores. This represents a speedup of 18 over the state of the art, and three orders of magnitude over the Dijkstra-based baseline.
Cite as

Valentin Buchhold, Peter Sanders, and Dorothea Wagner. Real-Time Traffic Assignment Using Fast Queries in Customizable Contraction Hierarchies. In 17th International Symposium on Experimental Algorithms (SEA 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 103, pp. 27:1-27:15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{buchhold_et_al:LIPIcs.SEA.2018.27,
  author =	{Buchhold, Valentin and Sanders, Peter and Wagner, Dorothea},
  title =	{{Real-Time Traffic Assignment Using Fast Queries in Customizable Contraction Hierarchies}},
  booktitle =	{17th International Symposium on Experimental Algorithms (SEA 2018)},
  pages =	{27:1--27:15},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-070-5},
  ISSN =	{1868-8969},
  year =	{2018},
  volume =	{103},
  editor =	{D'Angelo, Gianlorenzo},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SEA.2018.27},
  URN =		{urn:nbn:de:0030-drops-89623},
  doi =		{10.4230/LIPIcs.SEA.2018.27},
  annote =	{Keywords: traffic assignment, equilibrium flow pattern, customizable contraction hierarchies, batched shortest paths}
}
Document
DOI: 10.4230/LIPIcs.ESA.2017.9
In-Place Parallel Super Scalar Samplesort (IPSSSSo)

Authors: Michael Axtmann, Sascha Witt, Daniel Ferizovic, and Peter Sanders

Published in: LIPIcs, Volume 87, 25th Annual European Symposium on Algorithms (ESA 2017)

Abstract
We present a sorting algorithm that works in-place, executes in parallel, is cache-efficient, avoids branch-mispredictions, and performs work O(n log n) for arbitrary inputs with high probability. The main algorithmic contributions are new ways to make distribution-based algorithms in-place: On the practical side, by using coarse-grained block-based permutations, and on the theoretical side, we show how to eliminate the recursion stack. Extensive experiments shw that our algorithm IPSSSSo scales well on a variety of multi-core machines. We outperform our closest in-place competitor by a factor of up to 3. Even as a sequential algorithm, we are up to 1.5 times faster than the closest sequential competitor, BlockQuicksort.
Cite as

Michael Axtmann, Sascha Witt, Daniel Ferizovic, and Peter Sanders. In-Place Parallel Super Scalar Samplesort (IPSSSSo). In 25th Annual European Symposium on Algorithms (ESA 2017). Leibniz International Proceedings in Informatics (LIPIcs), Volume 87, pp. 9:1-9:14, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2017)

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@InProceedings{axtmann_et_al:LIPIcs.ESA.2017.9,
  author =	{Axtmann, Michael and Witt, Sascha and Ferizovic, Daniel and Sanders, Peter},
  title =	{{In-Place Parallel Super Scalar Samplesort (IPSSSSo)}},
  booktitle =	{25th Annual European Symposium on Algorithms (ESA 2017)},
  pages =	{9:1--9:14},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-049-1},
  ISSN =	{1868-8969},
  year =	{2017},
  volume =	{87},
  editor =	{Pruhs, Kirk and Sohler, Christian},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ESA.2017.9},
  URN =		{urn:nbn:de:0030-drops-78542},
  doi =		{10.4230/LIPIcs.ESA.2017.9},
  annote =	{Keywords: shared memory, parallel sorting, in-place algorithm, comparison-based sorting, branch prediction}
}
Document
DOI: 10.4230/LIPIcs.ESA.2017.58
Dynamic Space Efficient Hashing

Authors: Tobias Maier and Peter Sanders

Published in: LIPIcs, Volume 87, 25th Annual European Symposium on Algorithms (ESA 2017)

Abstract
We consider space efficient hash tables that can grow and shrink dynamically and are always highly space efficient, i.e., their space consumption is always close to the lower bound even while growing and when taking into account storage that is only needed temporarily. None of the traditionally used hash tables have this property. We show how known approaches like linear probing and bucket cuckoo hashing can be adapted to this scenario by subdividing them into many subtables or using virtual memory overcommitting. However, these rather straightforward solutions suffer from slow amortized insertion times due to frequent reallocation in small increments. Our main result is DySECT (Dynamic Space Efficient Cuckoo Table) which avoids these problems. DySECT consists of many subtables which grow by doubling their size. The resulting inhomogeneity in subtable sizes is equalized by the flexibility available in bucket cuckoo hashing where each element can go to several buckets each of which containing several cells. Experiments indicate that DySECT works well with load factors up to 98%. With up to 2.7 times better performance than the next best solution.
Cite as

Tobias Maier and Peter Sanders. Dynamic Space Efficient Hashing. In 25th Annual European Symposium on Algorithms (ESA 2017). Leibniz International Proceedings in Informatics (LIPIcs), Volume 87, pp. 58:1-58:14, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2017)

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@InProceedings{maier_et_al:LIPIcs.ESA.2017.58,
  author =	{Maier, Tobias and Sanders, Peter},
  title =	{{Dynamic Space Efficient Hashing}},
  booktitle =	{25th Annual European Symposium on Algorithms (ESA 2017)},
  pages =	{58:1--58:14},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-049-1},
  ISSN =	{1868-8969},
  year =	{2017},
  volume =	{87},
  editor =	{Pruhs, Kirk and Sohler, Christian},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ESA.2017.58},
  URN =		{urn:nbn:de:0030-drops-78487},
  doi =		{10.4230/LIPIcs.ESA.2017.58},
  annote =	{Keywords: Dynamic data structures, open addressing, closed hashing, cuckoo hashing, space efficiency}
}
Document
Invited Talk
DOI: 10.4230/LIPIcs.STACS.2015.10
Parallel Algorithms Reconsidered (Invited Talk)

Authors: Peter Sanders

Published in: LIPIcs, Volume 30, 32nd International Symposium on Theoretical Aspects of Computer Science (STACS 2015)

Abstract
Parallel algorithms have been a subject of intensive algorithmic research in the 1980s. This research almost died out in the mid 1990s. In this paper we argue that it is high time to reconsider this subject since a lot of things have changed. First and foremost, parallel processing has moved from a niche application to something mandatory for any performance critical computer applications. We will also point out that even very fundamental results can still be obtained. We give examples and also formulate some open problems.
Cite as

Peter Sanders. Parallel Algorithms Reconsidered (Invited Talk). In 32nd International Symposium on Theoretical Aspects of Computer Science (STACS 2015). Leibniz International Proceedings in Informatics (LIPIcs), Volume 30, pp. 10-18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2015)

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@InProceedings{sanders:LIPIcs.STACS.2015.10,
  author =	{Sanders, Peter},
  title =	{{Parallel Algorithms Reconsidered}},
  booktitle =	{32nd International Symposium on Theoretical Aspects of Computer Science (STACS 2015)},
  pages =	{10--18},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-939897-78-1},
  ISSN =	{1868-8969},
  year =	{2015},
  volume =	{30},
  editor =	{Mayr, Ernst W. and Ollinger, Nicolas},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.STACS.2015.10},
  URN =		{urn:nbn:de:0030-drops-49572},
  doi =		{10.4230/LIPIcs.STACS.2015.10},
  annote =	{Keywords: parallel algorithm, algorithm engineering, communication efficient algorithm, polylogarithmic time algorithm, parallel machine model}
}
Document
DOI: 10.4230/DagSemProc.10261.1
10261 Abstracts Collection – Algorithm Engineering

Authors: Giuseppe F. Italiano, David S. Johnson, Petra Mutzel, and Peter Sanders

Published in: Dagstuhl Seminar Proceedings, Volume 10261, Algorithm Engineering (2010)

Abstract
From June 27 to July 2, the Dagstuhl Seminar 10261 ``Algorithm Engineering '' was held in Schloss Dagstuhl~--~Leibniz Center for Informatics. During the seminar, several participants presented their current research, and ongoing work and open problems were discussed. Abstracts of the presentations given during the seminar as well as abstracts of seminar results and ideas are put together in this paper. The first section describes the seminar topics and goals in general. Links to extended abstracts or full papers are provided, if available.
Cite as

Giuseppe F. Italiano, David S. Johnson, Petra Mutzel, and Peter Sanders. 10261 Abstracts Collection – Algorithm Engineering. In Algorithm Engineering. Dagstuhl Seminar Proceedings, Volume 10261, pp. 1-10, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2010)

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@InProceedings{italiano_et_al:DagSemProc.10261.1,
  author =	{Italiano, Giuseppe F. and Johnson, David S. and Mutzel, Petra and Sanders, Peter},
  title =	{{10261 Abstracts Collection – Algorithm Engineering}},
  booktitle =	{Algorithm Engineering},
  pages =	{1--10},
  series =	{Dagstuhl Seminar Proceedings (DagSemProc)},
  ISSN =	{1862-4405},
  year =	{2010},
  volume =	{10261},
  editor =	{Giuseppe F. Italiano and David S. Johnson and Petra Mutzel and Peter Sanders},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DagSemProc.10261.1},
  URN =		{urn:nbn:de:0030-drops-28179},
  doi =		{10.4230/DagSemProc.10261.1},
  annote =	{Keywords: Experimental algorithmics, Game theory, Parallel and distributed algorithms, Multi-core}
}
Document
DOI: 10.4230/DagSemProc.10261.2
10261 Executive Summary – Algorithm Engineering

Authors: Giuseppe F. Italiano, David S. Johnson, Petra Mutzel, and Peter Sanders

Published in: Dagstuhl Seminar Proceedings, Volume 10261, Algorithm Engineering (2010)

Abstract
Algorithm engineering (AE) consists of the design, theoretical analysis, implementation, and experimental evaluation of algorithms, with the aim of bridging the gap between theory and practice in the area of algorithms. In the last decade, this approach to algorithmic research has gained increasing attention. The aim of this seminar was to bring together researchers with different backgrounds, e.g., from combinatorial optimization, algorithmic theory, and algorithm engineering, in order to strengthen and foster collaborations in the area of algorithm engineering and to identify key research directions for the future.
Cite as

Giuseppe F. Italiano, David S. Johnson, Petra Mutzel, and Peter Sanders. 10261 Executive Summary – Algorithm Engineering. In Algorithm Engineering. Dagstuhl Seminar Proceedings, Volume 10261, pp. 1-2, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2010)

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@InProceedings{italiano_et_al:DagSemProc.10261.2,
  author =	{Italiano, Giuseppe F. and Johnson, David S. and Mutzel, Petra and Sanders, Peter},
  title =	{{10261 Executive Summary – Algorithm Engineering}},
  booktitle =	{Algorithm Engineering},
  pages =	{1--2},
  series =	{Dagstuhl Seminar Proceedings (DagSemProc)},
  ISSN =	{1862-4405},
  year =	{2010},
  volume =	{10261},
  editor =	{Giuseppe F. Italiano and David S. Johnson and Petra Mutzel and Peter Sanders},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DagSemProc.10261.2},
  URN =		{urn:nbn:de:0030-drops-27966},
  doi =		{10.4230/DagSemProc.10261.2},
  annote =	{Keywords: Experimental algorithmics, Game theory, Parallel and distributed algorithms, Multi-core}
}
Document
DOI: 10.4230/OASIcs.ATMOS.2010.74
Engineering Time-Dependent Many-to-Many Shortest Paths Computation

Authors: Robert Geisberger and Peter Sanders

Published in: OASIcs, Volume 14, 10th Workshop on Algorithmic Approaches for Transportation Modelling, Optimization, and Systems (ATMOS'10) (2010)

Abstract
Computing distance tables is important for many logistics problems like the vehicle routing problem (VRP). While shortest distances from all source nodes in S to all target nodes in T are time-independent, travel times are not. We present the first efficient algorithms to compute time-dependent travel time tables in large time-dependent road networks. Our algorithms are based on time-dependent contraction hierarchies (TCH), currently the fastest time-dependent speed-up technique. The computation of a table is inherently in Theta(|S|*|T|), and therefore inefficient for large tables. We provide one particular algorithm using only Theta(|S|+|T|) time and space, being able to answer queries two orders of magnitude faster than the basic TCH implementation. If small errors are acceptable, approximate versions of our algorithms are further orders of magnitude faster.
Cite as

Robert Geisberger and Peter Sanders. Engineering Time-Dependent Many-to-Many Shortest Paths Computation. In 10th Workshop on Algorithmic Approaches for Transportation Modelling, Optimization, and Systems (ATMOS'10). Open Access Series in Informatics (OASIcs), Volume 14, pp. 74-87, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2010)

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@InProceedings{geisberger_et_al:OASIcs.ATMOS.2010.74,
  author =	{Geisberger, Robert and Sanders, Peter},
  title =	{{Engineering Time-Dependent Many-to-Many Shortest Paths Computation}},
  booktitle =	{10th Workshop on Algorithmic Approaches for Transportation Modelling, Optimization, and Systems (ATMOS'10)},
  pages =	{74--87},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-939897-20-0},
  ISSN =	{2190-6807},
  year =	{2010},
  volume =	{14},
  editor =	{Erlebach, Thomas and L\"{u}bbecke, Marco},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.ATMOS.2010.74},
  URN =		{urn:nbn:de:0030-drops-27511},
  doi =		{10.4230/OASIcs.ATMOS.2010.74},
  annote =	{Keywords: time-dependent, travel time table, algorithm engineering, vrp}
}
Document
DOI: 10.4230/OASIcs.ATMOS.2010.88
Fast Detour Computation for Ride Sharing

Authors: Robert Geisberger, Dennis Luxen, Sabine Neubauer, Peter Sanders, and Lars Volker

Published in: OASIcs, Volume 14, 10th Workshop on Algorithmic Approaches for Transportation Modelling, Optimization, and Systems (ATMOS'10) (2010)

Abstract
Ride sharing becomes more and more popular not least because internet services help matching offers and request. However, current systems use a rather simple-minded functionality allowing to search for the origin and destination city, sometimes enriched with radial search around the cities. We show that theses services can be substantially improved using innovative route planning algorithms. More concretely, we generalize previous static algorithms for many-to-many routing to a dynamic setting and develop an additional pruning strategy. With these measures it becomes possible to match each request to $n$ offers using $2n+1$ exact travel time computations in a large road network in a fraction of a microsecond per offer. For requests spread over Germany according to population density, we are able to reduce the number of failing entries substantially. We are able to find a reasonable match for more than 60% of the failing entries left by contemporary matching strategies. Additionally, we halve the average waste of resources in the matches found compared to radial search.
Cite as

Robert Geisberger, Dennis Luxen, Sabine Neubauer, Peter Sanders, and Lars Volker. Fast Detour Computation for Ride Sharing. In 10th Workshop on Algorithmic Approaches for Transportation Modelling, Optimization, and Systems (ATMOS'10). Open Access Series in Informatics (OASIcs), Volume 14, pp. 88-99, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2010)

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@InProceedings{geisberger_et_al:OASIcs.ATMOS.2010.88,
  author =	{Geisberger, Robert and Luxen, Dennis and Neubauer, Sabine and Sanders, Peter and Volker, Lars},
  title =	{{Fast Detour Computation for Ride Sharing}},
  booktitle =	{10th Workshop on Algorithmic Approaches for Transportation Modelling, Optimization, and Systems (ATMOS'10)},
  pages =	{88--99},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-939897-20-0},
  ISSN =	{2190-6807},
  year =	{2010},
  volume =	{14},
  editor =	{Erlebach, Thomas and L\"{u}bbecke, Marco},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.ATMOS.2010.88},
  URN =		{urn:nbn:de:0030-drops-27525},
  doi =		{10.4230/OASIcs.ATMOS.2010.88},
  annote =	{Keywords: ride sharing, algorithm engineering, carpool}
}
Document
DOI: 10.4230/DagSemProc.09491.1
09491 Abstracts Collection – Graph Search Engineering

Authors: Lubos Brim, Stefan Edelkamp, Eric A. Hansen, and Peter Sanders

Published in: Dagstuhl Seminar Proceedings, Volume 9491, Graph Search Engineering (2010)

Abstract
From the 29th November to the 4th December 2009, the Dagstuhl Seminar 09491 ``Graph Search Engineering '' was held in Schloss Dagstuhl~--~Leibniz Center for Informatics. During the seminar, several participants presented their current research, and ongoing work and open problems were discussed. Abstracts of the presentations given during the seminar as well as abstracts of seminar results and ideas are put together in this paper. The first section describes the seminar topics and goals in general. Links to extended abstracts or full papers are provided, if available.
Cite as

Lubos Brim, Stefan Edelkamp, Eric A. Hansen, and Peter Sanders. 09491 Abstracts Collection – Graph Search Engineering. In Graph Search Engineering. Dagstuhl Seminar Proceedings, Volume 9491, pp. 1-31, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2010)

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@InProceedings{brim_et_al:DagSemProc.09491.1,
  author =	{Brim, Lubos and Edelkamp, Stefan and Hansen, Eric A. and Sanders, Peter},
  title =	{{09491 Abstracts Collection – Graph Search Engineering}},
  booktitle =	{Graph Search Engineering},
  pages =	{1--31},
  series =	{Dagstuhl Seminar Proceedings (DagSemProc)},
  ISSN =	{1862-4405},
  year =	{2010},
  volume =	{9491},
  editor =	{Lubos Brim and Stefan Edelkamp and Erik A. Hansen and Peter Sanders},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DagSemProc.09491.1},
  URN =		{urn:nbn:de:0030-drops-24315},
  doi =		{10.4230/DagSemProc.09491.1},
  annote =	{Keywords: Model Checking, Artificial Intelligence, AI Planning, State Explosion Problem, Error Detection, Protocol Analysis, Software Verification and Validation, Heuristics, Pattern/Abstraction Databases, I/O Efficient Search, Solid State Disks, GPU}
}
Document
DOI: 10.4230/DagSemProc.05031.22
Online Scheduling with Bounded Migration

Authors: Peter Sanders, Naveen Sivadasan, and Martin Skutella

Published in: Dagstuhl Seminar Proceedings, Volume 5031, Algorithms for Optimization with Incomplete Information (2005)

Abstract
Consider the classical online scheduling problem where jobs that arrive one by one are assigned to identical parallel machines with the objective of minimizing the makespan. We generalize this problem by allowing the current assignment to be changed whenever a new job arrives, subject to the constraint that the total size of moved jobs is bounded by~$\beta$ times the size of the arriving job. Our main result is a linear time `online approximation scheme', that is, a family of online algorithms with competitive ratio~$1+\epsilon$ and constant migration factor~$\beta(\epsilon)$, for any fixed~$\epsilon>0$. This result is of particular importance if considered in the context of sensitivity analysis: While a newly arriving job may force a complete change of the entire structure of an optimal schedule, only very limited `local' changes suffice to preserve near-optimal solutions. We believe that this concept will find wide application in its own right. We also present simple deterministic online algorithms with migration factors~$\beta=2$ and~$\beta=4/3$, respectively. Their competitive ratio~$3/2$ beats the lower bound on the performance of any online algorithm in the classical setting without migration. We also present improved algorithms and similar results for closely related problems. In particular, there is a short discussion of corresponding results for the objective to maximize the minimum load of a machine. The latter problem has an application for configuring storage servers that was the original motivation for this work.
Cite as

Peter Sanders, Naveen Sivadasan, and Martin Skutella. Online Scheduling with Bounded Migration. In Algorithms for Optimization with Incomplete Information. Dagstuhl Seminar Proceedings, Volume 5031, pp. 1-3, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2005)

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@InProceedings{sanders_et_al:DagSemProc.05031.22,
  author =	{Sanders, Peter and Sivadasan, Naveen and Skutella, Martin},
  title =	{{Online Scheduling with Bounded Migration}},
  booktitle =	{Algorithms for Optimization with Incomplete Information},
  pages =	{1--3},
  series =	{Dagstuhl Seminar Proceedings (DagSemProc)},
  ISSN =	{1862-4405},
  year =	{2005},
  volume =	{5031},
  editor =	{Susanne Albers and Rolf H. M\"{o}hring and Georg Ch. Pflug and R\"{u}diger Schultz},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DagSemProc.05031.22},
  URN =		{urn:nbn:de:0030-drops-707},
  doi =		{10.4230/DagSemProc.05031.22},
  annote =	{Keywords: scheduling, sensitivity analysis, online algorithm}
}
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