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Documents authored by Lesani, Mohsen

Document
Brief Announcement
DOI: 10.4230/LIPIcs.DISC.2024.52
Brief Announcement: Reconfigurable Heterogeneous Quorum Systems

Authors: Xiao Li and Mohsen Lesani

Published in: LIPIcs, Volume 319, 38th International Symposium on Distributed Computing (DISC 2024)

Abstract
In contrast to proof-of-work replication, Byzantine quorum systems maintain consistency across replicas with higher throughput, modest energy consumption, and deterministic liveness guarantees. If complemented with heterogeneous trust and open membership, they have the potential to serve as blockchains backbone. This paper presents a general model of heterogeneous quorum systems where each participant can declare its own quorums, and captures the consistency, availability and inclusion properties of these systems. In order to support open membership, it then presents reconfiguration protocols for heterogeneous quorum systems including joining and leaving of a process, and adding and removing of a quorum, and further, proves their correctness in the face of Byzantine attacks. The design of the protocols is informed by the trade-offs that the paper proves for the properties that reconfigurations can preserve. The paper further presents a graph characterization of heterogeneous quorum systems, and its application for reconfiguration optimization.
Cite as

Xiao Li and Mohsen Lesani. Brief Announcement: Reconfigurable Heterogeneous Quorum Systems. In 38th International Symposium on Distributed Computing (DISC 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 319, pp. 52:1-52:8, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{li_et_al:LIPIcs.DISC.2024.52,
  author =	{Li, Xiao and Lesani, Mohsen},
  title =	{{Brief Announcement: Reconfigurable Heterogeneous Quorum Systems}},
  booktitle =	{38th International Symposium on Distributed Computing (DISC 2024)},
  pages =	{52:1--52:8},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-352-2},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{319},
  editor =	{Alistarh, Dan},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2024.52},
  URN =		{urn:nbn:de:0030-drops-212804},
  doi =		{10.4230/LIPIcs.DISC.2024.52},
  annote =	{Keywords: Quorum Systems, Reconfiguration, Heterogeneity}
}
Document
DOI: 10.4230/LIPIcs.DISC.2023.28
Quorum Subsumption for Heterogeneous Quorum Systems

Authors: Xiao Li, Eric Chan, and Mohsen Lesani

Published in: LIPIcs, Volume 281, 37th International Symposium on Distributed Computing (DISC 2023)

Abstract
Byzantine quorum systems provide higher throughput than proof-of-work and incur modest energy consumption. Further, their modern incarnations incorporate personalized and heterogeneous trust. Thus, they are emerging as an appealing candidate for global financial infrastructure. However, since their quorums are not uniform across processes anymore, the properties that they should maintain to support abstractions such as reliable broadcast and consensus are not well-understood. It has been shown that the two properties quorum intersection and availability are necessary. In this paper, we prove that they are not sufficient. We then define the notion of quorum subsumption, and show that the three conditions together are sufficient: we present reliable broadcast and consensus protocols, and prove their correctness for quorum systems that provide the three properties.
Cite as

Xiao Li, Eric Chan, and Mohsen Lesani. Quorum Subsumption for Heterogeneous Quorum Systems. In 37th International Symposium on Distributed Computing (DISC 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 281, pp. 28:1-28:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{li_et_al:LIPIcs.DISC.2023.28,
  author =	{Li, Xiao and Chan, Eric and Lesani, Mohsen},
  title =	{{Quorum Subsumption for Heterogeneous Quorum Systems}},
  booktitle =	{37th International Symposium on Distributed Computing (DISC 2023)},
  pages =	{28:1--28:19},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-301-0},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{281},
  editor =	{Oshman, Rotem},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2023.28},
  URN =		{urn:nbn:de:0030-drops-191541},
  doi =		{10.4230/LIPIcs.DISC.2023.28},
  annote =	{Keywords: Distributed Systems, Impossibility Results, Byzantine fault tolerance}
}
Document
DOI: 10.4230/LIPIcs.DISC.2019.34
Polynomial-Time Fence Insertion for Structured Programs

Authors: Mohammad Taheri, Arash Pourdamghani, and Mohsen Lesani

Published in: LIPIcs, Volume 146, 33rd International Symposium on Distributed Computing (DISC 2019)

Abstract
To enhance performance, common processors feature relaxed memory models that reorder instructions. However, the correctness of concurrent programs is often dependent on the preservation of the program order of certain instructions. Thus, the instruction set architectures offer memory fences. Using fences is a subtle task with performance and correctness implications: using too few can compromise correctness and using too many can hinder performance. Thus, fence insertion algorithms that given the required program orders can automatically find the optimum fencing can enhance the ease of programming, reliability, and performance of concurrent programs. In this paper, we consider the class of programs with structured branch and loop statements and present a greedy and polynomial-time optimum fence insertion algorithm. The algorithm incrementally reduces fence insertion for a control-flow graph to fence insertion for a set of paths. In addition, we show that the minimum fence insertion problem with multiple types of fence instructions is NP-hard even for straight-line programs.
Cite as

Mohammad Taheri, Arash Pourdamghani, and Mohsen Lesani. Polynomial-Time Fence Insertion for Structured Programs. In 33rd International Symposium on Distributed Computing (DISC 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 146, pp. 34:1-34:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@InProceedings{taheri_et_al:LIPIcs.DISC.2019.34,
  author =	{Taheri, Mohammad and Pourdamghani, Arash and Lesani, Mohsen},
  title =	{{Polynomial-Time Fence Insertion for Structured Programs}},
  booktitle =	{33rd International Symposium on Distributed Computing (DISC 2019)},
  pages =	{34:1--34:17},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-126-9},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{146},
  editor =	{Suomela, Jukka},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2019.34},
  URN =		{urn:nbn:de:0030-drops-113412},
  doi =		{10.4230/LIPIcs.DISC.2019.34},
  annote =	{Keywords: Fence Insertion, Synchronization, Concurrent Programming}
}
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