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DOI: 10.4230/LIPIcs.OPODIS.2020.9

ACE: Abstract Consensus Encapsulation for Liveness Boosting of State Machine Replication

Authors: Alexander Spiegelman, Arik Rinberg, and Dahlia Malkhi

Published in: LIPIcs, Volume 184, 24th International Conference on Principles of Distributed Systems (OPODIS 2020)

Abstract

With the emergence of attack-prone cross-organization systems, providing asynchronous state machine replication (SMR) solutions is no longer a theoretical concern. This paper presents ACE, a framework for the design of such fault tolerant systems. Leveraging a known paradigm for randomized consensus solutions, ACE wraps existing practical solutions and real-life systems, boosting their liveness under adversarial conditions and, at the same time, promoting load balancing and fairness. Boosting is achieved without modifying the overall design or the engineering of these solutions. ACE is aimed at boosting the prevailing approach for practical fault tolerance. This approach, often named partial synchrony, is based on a leader-based paradigm: a good leader makes progress and a bad leader does no harm. The partial synchrony approach focuses on safety and forgoes liveness under targeted and dynamic attacks. Specifically, an attacker might block specific leaders, e.g., through a denial of service, to prevent progress. ACE provides boosting by running waves of parallel leaders and selecting a winning leader only retroactively, achieving boosting at a linear communication cost increase. ACE is agnostic to the fault model, inheriting it s failure model from the wrapped solution assumptions. As our evaluation shows, an asynchronous Byzantine fault tolerance (BFT) replication system built with ACE around an existing partially synchronous BFT protocol demonstrates reasonable slow-down compared with the base BFT protocol during faultless synchronous scenarios, yet exhibits significant speedup while the system is under attack.

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Alexander Spiegelman, Arik Rinberg, and Dahlia Malkhi. ACE: Abstract Consensus Encapsulation for Liveness Boosting of State Machine Replication. In 24th International Conference on Principles of Distributed Systems (OPODIS 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 184, pp. 9:1-9:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{spiegelman_et_al:LIPIcs.OPODIS.2020.9,
  author =	{Spiegelman, Alexander and Rinberg, Arik and Malkhi, Dahlia},
  title =	{{ACE: Abstract Consensus Encapsulation for Liveness Boosting of State Machine Replication}},
  booktitle =	{24th International Conference on Principles of Distributed Systems (OPODIS 2020)},
  pages =	{9:1--9:18},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-176-4},
  ISSN =	{1868-8969},
  year =	{2021},
  volume =	{184},
  editor =	{Bramas, Quentin and Oshman, Rotem and Romano, Paolo},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2020.9},
  URN =		{urn:nbn:de:0030-drops-134948},
  doi =		{10.4230/LIPIcs.OPODIS.2020.9},
  annote =	{Keywords: Framework, Asynchronous, Consensus boosting, State Machine Replication}
}

Document

DOI: 10.4230/LIPIcs.DISC.2020.2

Intermediate Value Linearizability: A Quantitative Correctness Criterion

Authors: Arik Rinberg and Idit Keidar

Published in: LIPIcs, Volume 179, 34th International Symposium on Distributed Computing (DISC 2020)

Abstract

Big data processing systems often employ batched updates and data sketches to estimate certain properties of large data. For example, a CountMin sketch approximates the frequencies at which elements occur in a data stream, and a batched counter counts events in batches. This paper focuses on correctness criteria for concurrent implementations of such objects. Specifically, we consider quantitative objects, whose return values are from a totally ordered domain, with a particular emphasis on (ε,δ)-bounded objects that estimate a numerical quantity with an error of at most ε with probability at least 1 - δ. The de facto correctness criterion for concurrent objects is linearizability. Intuitively, under linearizability, when a read overlaps an update, it must return the object’s value either before the update or after it. Consider, for example, a single batched increment operation that counts three new events, bumping a batched counter’s value from 7 to 10. In a linearizable implementation of the counter, a read overlapping this update must return either 7 or 10. We observe, however, that in typical use cases, any intermediate value between 7 and 10 would also be acceptable. To capture this additional degree of freedom, we propose Intermediate Value Linearizability (IVL), a new correctness criterion that relaxes linearizability to allow returning intermediate values, for instance 8 in the example above. Roughly speaking, IVL allows reads to return any value that is bounded between two return values that are legal under linearizability. A key feature of IVL is that we can prove that concurrent IVL implementations of (ε,δ)-bounded objects are themselves (ε,δ)-bounded. To illustrate the power of this result, we give a straightforward and efficient concurrent implementation of an (ε, δ)-bounded CountMin sketch, which is IVL (albeit not linearizable). Finally, we show that IVL allows for inherently cheaper implementations than linearizable ones. In particular, we show a lower bound of Ω(n) on the step complexity of the update operation of any wait-free linearizable batched counter from single-writer objects, and propose a wait-free IVL implementation of the same object with an O(1) step complexity for update.

Cite as

Arik Rinberg and Idit Keidar. Intermediate Value Linearizability: A Quantitative Correctness Criterion. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 2:1-2:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{rinberg_et_al:LIPIcs.DISC.2020.2,
  author =	{Rinberg, Arik and Keidar, Idit},
  title =	{{Intermediate Value Linearizability: A Quantitative Correctness Criterion}},
  booktitle =	{34th International Symposium on Distributed Computing (DISC 2020)},
  pages =	{2:1--2:17},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-168-9},
  ISSN =	{1868-8969},
  year =	{2020},
  volume =	{179},
  editor =	{Attiya, Hagit},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.2},
  URN =		{urn:nbn:de:0030-drops-130801},
  doi =		{10.4230/LIPIcs.DISC.2020.2},
  annote =	{Keywords: concurrency, concurrent objects, linearizability}
}

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ACE: Abstract Consensus Encapsulation for Liveness Boosting of State Machine Replication

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Intermediate Value Linearizability: A Quantitative Correctness Criterion

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