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Revising 1-Copy Equivalence in Replicated Databases with Snapshot Isolation*
Francesc D. Muñoz-Escoí1, Josep M. Bernabé-Gisbert1, Ruben de Juan-Marín1, Jose Enrique Armendáriz-Íñigo2, and Jose Ramon González De Mendívil2
1Instituto Tecnológico de Informática, Univ. Politécnica de Valencia, Camino de Vera, s/n, 46022 Valencia, Spain
fmunyoz@iti.upv.es
jbgisber@iti.upv.es
rjuan@iti.upv.es
2Depto. de Ing. Matemática e Informática, Univ. Pública de Navarra, Campus de Arrosadía, s/n, 31006 Pamplona, Spain
enrique.armendariz@unavarra.es
mendivil@unavarra.es
Abstract. Multiple database replication protocols have used replicas supporting the snapshot isolation level. They have provided some kind of one-copy equivalence, but such concept was initially conceived for serializable databases. In the snapshot isolation case, due to its reliance on multi-versioned concurrency control that never blocks read accesses, such one-copy equivalence admits two different variants. The first one consists in relying on sequential replica consistency, but it does not guarantee that the snapshot used by each transaction holds the updates of the last committed transactions in the whole replicated system, but only those of the last locally committed transaction. Thus, a single user might see inconsistent results when two of her transactions have been served by different delegate replicas: the updates of the first one might not be in the snapshot of the second. The second variant avoids such problem, but demands atomic replica consistency, blocking the start (i.e., in many cases, read accesses) of new transactions. Several protocols of each kind exist nowadays, and most of them have given different names to their intended correctness criterion. We survey such previous works and propose uniform names to these criteria, justifying some of their properties.
*This work has been partially supported by EU FEDER and the Spanish MEC under grant TIN2006-14738-C02, by EU FEDER and the Spanish MICINN under grant TIN2009-14460-C03 and by IMPIVA under grant IMIDIC/2007/68.
LNCS 5870, p. 467 ff.
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© Springer-Verlag Berlin Heidelberg 2009