Computing graph spanners in small memory: fault-tolerance and streaming

  • Authors:
  • Giorgio Ausiello;Paolo G. Franciosa;Giuseppe F. Italiano;Andrea Ribichini

  • Affiliations:
  • Dipartimento di Informatica e Sistemistica, Sapienza Università di Roma, Roma, Italy;Dipartimento di Statistica, Probabilità e Statistiche Applicate, Sapienza Università di Roma, Roma, Italy;Dipartimento di Informatica, Sistemi e Produzione, Università di Roma "Tor Vergata", Roma, Italy;Dipartimento di Informatica e Sistemistica, Sapienza Università di Roma, Roma, Italy

  • Venue:
  • COCOON'10 Proceedings of the 16th annual international conference on Computing and combinatorics
  • Year:
  • 2010

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Abstract

Let G be an undirected graph with m edges and n vertices. A spanner of G is a subgraph which preserves approximate distances between all pairs of vertices. An f-vertex fault-tolerant spanner is a subgraph which preserves approximate distances, under the failure of any set of at most f vertices. The contribution of this paper is twofold: we present algorithms for computing fault-tolerant spanners, and propose streaming algorithms for computing spanners in very small internal memory. In particular, we give algorithms for computing f-vertex faulttolerant (3,2)- and (2,1)-spanners of G with the following bounds: our (3,2)-spanner contains O(f4/3n4/3) edges and can be computed in time Õ (f2m), while our (2,1)-spanner contains O(fn3/2) edges and can be computed in time Õ (fm). Both algorithms improve significantly on previously known bounds. Assume that the graph G is presented as an input stream of edges, which may appear in any arbitrary order, and that we do not know in advance m and n. We show how to compute efficiently (3,2)- and (2,1)- spanners of G, using only very small internal memory and a slow access external memory device. Our spanners have asymptotically optimal size and the I/O complexity of our algorithms for computing such spanners is optimal up to a polylogarithmic factor. Our f-vertex fault-tolerant (3,2)- and (2,1)-spanners can also be computed efficiently in the same computational model described above.