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Documents authored by Petruschka, Asaf

Document
DOI: 10.4230/LIPIcs.ITCS.2024.88
Color Fault-Tolerant Spanners

Authors: Asaf Petruschka, Shay Sapir, and Elad Tzalik

Published in: LIPIcs, Volume 287, 15th Innovations in Theoretical Computer Science Conference (ITCS 2024)

Abstract
We initiate the study of spanners in arbitrarily vertex- or edge-colored graphs (with no "legality" restrictions), that are resilient to failures of entire color classes. When a color fails, all vertices/edges of that color crash. An f-color fault-tolerant (f-CFT) t-spanner of an n-vertex colored graph G is a subgraph H that preserves distances up to factor t, even in the presence of at most f color faults. This notion generalizes the well-studied f-vertex/edge fault-tolerant (f-V/EFT) spanners. The size (number of edges) of an f-V/EFT spanner crucially depends on the number f of vertex/edge faults to be tolerated. In the colored variants, even a single color fault can correspond to an unbounded number of vertex/edge faults. The key conceptual contribution of this work is in showing that the size required by an f-CFT spanner is in fact comparable to its uncolored counterpart, with no dependency on the size of color classes. We provide optimal bounds on the size required by f-CFT (2k-1)-spanners, as follows: - When vertices have colors, we show an upper bound of O(f^{1-1/k} n^{1+1/k}) edges. This precisely matches the (tight) bounds for (2k-1)-spanners resilient to f individual vertex faults [Bodwin et al., SODA 2018; Bodwin and Patel, PODC 2019]. - For colored edges, we show that O(f n^{1+1/k}) edges are always sufficient. Further, we prove this is tight, i.e., we provide an Ω(f n^{1+1/k}) (worst-case) lower bound. The state-of-the-art bounds known for the corresponding uncolored setting of edge faults are (roughly) Θ(f^{1/2} n^{1+1/k}) [Bodwin et al., SODA 2018; Bodwin, Dinitz and Robelle, SODA 2022]. - We also consider a mixed model where both vertices and edges are colored. In this case, we show tight Θ(f^{2-1/k} n^{1+1/k}) bounds. Thus, CFT spanners exhibit an interesting phenomenon: while (individual) edge faults are "easier" than vertex faults, edge-color faults are "harder" than vertex-color faults. Our upper bounds are based on a generalization of the blocking set technique of [Bodwin and Patel, PODC 2019] for analyzing the (exponential-time) greedy algorithm for FT spanners. We complement them by providing efficient constructions of CFT spanners with similar size guarantees, based on the algorithm of [Dinitz and Robelle, PODC 2020].
Cite as

Asaf Petruschka, Shay Sapir, and Elad Tzalik. Color Fault-Tolerant Spanners. In 15th Innovations in Theoretical Computer Science Conference (ITCS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 287, pp. 88:1-88:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{petruschka_et_al:LIPIcs.ITCS.2024.88,
  author =	{Petruschka, Asaf and Sapir, Shay and Tzalik, Elad},
  title =	{{Color Fault-Tolerant Spanners}},
  booktitle =	{15th Innovations in Theoretical Computer Science Conference (ITCS 2024)},
  pages =	{88:1--88:17},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-309-6},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{287},
  editor =	{Guruswami, Venkatesan},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ITCS.2024.88},
  URN =		{urn:nbn:de:0030-drops-196160},
  doi =		{10.4230/LIPIcs.ITCS.2024.88},
  annote =	{Keywords: Fault tolerance, Graph spanners}
}
Document
DOI: 10.4230/LIPIcs.DISC.2022.31
Near-Optimal Distributed Computation of Small Vertex Cuts

Authors: Merav Parter and Asaf Petruschka

Published in: LIPIcs, Volume 246, 36th International Symposium on Distributed Computing (DISC 2022)

Abstract
We present near-optimal algorithms for detecting small vertex cuts in the {CONGEST} model of distributed computing. Despite extensive research in this area, our understanding of the vertex connectivity of a graph is still incomplete, especially in the distributed setting. To this date, all distributed algorithms for detecting cut vertices suffer from an inherent dependency in the maximum degree of the graph, Δ. Hence, in particular, there is no truly sub-linear time algorithm for this problem, not even for detecting a single cut vertex. We take a new algorithmic approach for vertex connectivity which allows us to bypass the existing Δ barrier. - As a warm-up to our approach, we show a simple Õ(D)-round randomized algorithm for computing all cut vertices in a D-diameter n-vertex graph. This improves upon the O(D+Δ/log n)-round algorithm of [Pritchard and Thurimella, ICALP 2008]. - Our key technical contribution is an Õ(D)-round randomized algorithm for computing all cut pairs in the graph, improving upon the state-of-the-art O(Δ ⋅ D)⁴-round algorithm by [Parter, DISC '19]. Note that even for the considerably simpler setting of edge cuts, currently Õ(D)-round algorithms are currently known only for detecting pairs of cut edges. Our approach is based on employing the well-known linear graph sketching technique [Ahn, Guha and McGregor, SODA 2012] along with the heavy-light tree decomposition of [Sleator and Tarjan, STOC 1981] . Combining this with a careful characterization of the survivable subgraphs, allows us to determine the connectivity of G ⧵ {x,y} for every pair x,y ∈ V, using Õ(D)-rounds. We believe that the tools provided in this paper are useful for omitting the Δ-dependency even for larger cut values.
Cite as

Merav Parter and Asaf Petruschka. Near-Optimal Distributed Computation of Small Vertex Cuts. In 36th International Symposium on Distributed Computing (DISC 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 246, pp. 31:1-31:21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{parter_et_al:LIPIcs.DISC.2022.31,
  author =	{Parter, Merav and Petruschka, Asaf},
  title =	{{Near-Optimal Distributed Computation of Small Vertex Cuts}},
  booktitle =	{36th International Symposium on Distributed Computing (DISC 2022)},
  pages =	{31:1--31:21},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-255-6},
  ISSN =	{1868-8969},
  year =	{2022},
  volume =	{246},
  editor =	{Scheideler, Christian},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2022.31},
  URN =		{urn:nbn:de:0030-drops-172223},
  doi =		{10.4230/LIPIcs.DISC.2022.31},
  annote =	{Keywords: Vertex-connectivity, Congest, Graph Sketches}
}
Document
DOI: 10.4230/LIPIcs.DISC.2022.32
Õptimal Dual Vertex Failure Connectivity Labels

Authors: Merav Parter and Asaf Petruschka

Published in: LIPIcs, Volume 246, 36th International Symposium on Distributed Computing (DISC 2022)

Abstract
In this paper we present succinct labeling schemes for supporting connectivity queries under vertex faults. For a given n-vertex graph G, an f-VFT (resp., EFT) connectivity labeling scheme is a distributed data structure that assigns each of the graph edges and vertices a short label, such that given the labels of a vertex pair u and v, and the labels of at most f failing vertices (resp., edges) F, one can determine if u and v are connected in G ⧵ F. The primary complexity measure is the length of the individual labels. Since their introduction by [Courcelle, Twigg, STACS '07], FT labeling schemes have been devised only for a limited collection of graph families. A recent work [Dory and Parter, PODC 2021] provided EFT labeling schemes for general graphs under edge failures, leaving the vertex failure case fairly open. We provide the first sublinear f-VFT labeling schemes for f ≥ 2 for any n-vertex graph. Our key result is 2-VFT connectivity labels with O(log³ n) bits. Our constructions are based on analyzing the structure of dual failure replacement paths on top of the well-known heavy-light tree decomposition technique of [Sleator and Tarjan, STOC 1981]. We also provide f-VFT labels with sub-linear length (in |V|) for any f = o(log log n), that are based on a reduction to the existing EFT labels.
Cite as

Merav Parter and Asaf Petruschka. Õptimal Dual Vertex Failure Connectivity Labels. In 36th International Symposium on Distributed Computing (DISC 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 246, pp. 32:1-32:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{parter_et_al:LIPIcs.DISC.2022.32,
  author =	{Parter, Merav and Petruschka, Asaf},
  title =	{{\~{O}ptimal Dual Vertex Failure Connectivity Labels}},
  booktitle =	{36th International Symposium on Distributed Computing (DISC 2022)},
  pages =	{32:1--32:19},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-255-6},
  ISSN =	{1868-8969},
  year =	{2022},
  volume =	{246},
  editor =	{Scheideler, Christian},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2022.32},
  URN =		{urn:nbn:de:0030-drops-172239},
  doi =		{10.4230/LIPIcs.DISC.2022.32},
  annote =	{Keywords: Fault-Tolerance, Heavy-Light Decomposition, Labeling Schemes}
}
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