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DOI: 10.4230/LIPIcs.OPODIS.2025.22

Making Democracy Work: Fixing and Simplifying Egalitarian Paxos

Authors: Fedor Ryabinin, Alexey Gotsman, and Pierre Sutra

Published in: LIPIcs, Volume 361, 29th International Conference on Principles of Distributed Systems (OPODIS 2025)

Abstract

Classical state-machine replication protocols, such as Paxos, rely on a distinguished leader process to order commands. Unfortunately, this approach makes the leader a single point of failure and increases the latency for clients that are not co-located with it. As a response to these drawbacks, Egalitarian Paxos [Iulian Moraru et al., 2013] introduced an alternative, leaderless approach, that allows replicas to order commands collaboratively. Not relying on a single leader allows the protocol to maintain non-zero throughput with up to f crashes of any processes out of a total of n = 2f+1. The protocol furthermore allows any process to execute a command c fast, in 2 message delays, provided no more than e = ⌈(f+1)/2⌉ other processes fail, and all concurrently submitted commands commute with c; the latter condition is often satisfied in practical systems. Egalitarian Paxos has served as a foundation for many other replication protocols. But unfortunately, the protocol is very complex, ambiguously specified and suffers from nontrivial bugs. In this paper, we present EPaxos* - a simpler and correct variant of Egalitarian Paxos. Our key technical contribution is a simpler failure-recovery algorithm, which we have rigorously proved correct. Our protocol also generalizes Egalitarian Paxos to cover the whole spectrum of failure thresholds f and e such that n ≥ max{2e+f-1, 2f+1} - the number of processes that we show to be optimal.

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Fedor Ryabinin, Alexey Gotsman, and Pierre Sutra. Making Democracy Work: Fixing and Simplifying Egalitarian Paxos. In 29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, pp. 22:1-22:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{ryabinin_et_al:LIPIcs.OPODIS.2025.22,
  author =	{Ryabinin, Fedor and Gotsman, Alexey and Sutra, Pierre},
  title =	{{Making Democracy Work: Fixing and Simplifying Egalitarian Paxos}},
  booktitle =	{29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
  pages =	{22:1--22:19},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-409-3},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{361},
  editor =	{Arusoaie, Andrei and Onica, Emanuel and Spear, Michael and Tucci-Piergiovanni, Sara},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2025.22},
  URN =		{urn:nbn:de:0030-drops-251955},
  doi =		{10.4230/LIPIcs.OPODIS.2025.22},
  annote =	{Keywords: Consensus, state-machine replication, fault tolerance}
}

Document

DOI: 10.4230/LIPIcs.CSL.2021.13

Reachability in Distributed Memory Automata

Authors: Benedikt Bollig, Fedor Ryabinin, and Arnaud Sangnier

Published in: LIPIcs, Volume 183, 29th EACSL Annual Conference on Computer Science Logic (CSL 2021)

Abstract

We introduce Distributed Memory Automata, a model of register automata suitable to capture some features of distributed algorithms designed for shared-memory systems. In this model, each participant owns a local register and a shared register and has the ability to change its local value, to write it in the global memory and to test atomically the number of occurrences of its value in the shared memory, up to some threshold. We show that the control-state reachability problem for Distributed Memory Automata is Pspace-complete for a fixed number of participants and is in Pspace when the number of participants is not fixed a priori.

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Benedikt Bollig, Fedor Ryabinin, and Arnaud Sangnier. Reachability in Distributed Memory Automata. In 29th EACSL Annual Conference on Computer Science Logic (CSL 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 183, pp. 13:1-13:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{bollig_et_al:LIPIcs.CSL.2021.13,
  author =	{Bollig, Benedikt and Ryabinin, Fedor and Sangnier, Arnaud},
  title =	{{Reachability in Distributed Memory Automata}},
  booktitle =	{29th EACSL Annual Conference on Computer Science Logic (CSL 2021)},
  pages =	{13:1--13:16},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-175-7},
  ISSN =	{1868-8969},
  year =	{2021},
  volume =	{183},
  editor =	{Baier, Christel and Goubault-Larrecq, Jean},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CSL.2021.13},
  URN =		{urn:nbn:de:0030-drops-134472},
  doi =		{10.4230/LIPIcs.CSL.2021.13},
  annote =	{Keywords: Distributed algorithms, Atomic snapshot objects, Register automata, Reachability}
}

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Documents authored by Ryabinin, Fedor

Making Democracy Work: Fixing and Simplifying Egalitarian Paxos

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Reachability in Distributed Memory Automata

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