On the semantics of snapshot isolation

Azalea Raad, Ori Lahav, Viktor Vafeiadis

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

Abstract

Snapshot isolation (SI) is a standard transactional consistency model used in databases, distributed systems and software transactional memory (STM). Its semantics is formally defined both declaratively as an acyclicity axiom, and operationally as a concurrent algorithm with memory bearing timestamps. We develop two simpler equivalent operational definitions of SI as lock-based reference implementations that do not use timestamps. Our first locking implementation is prescient in that requires a priori knowledge of the data accessed by a transaction and carries out transactional writes eagerly (in-place). Our second implementation is non-prescient and performs transactional writes lazily by recording them in a local log and propagating them to memory at commit time. Whilst our first implementation is simpler and may be better suited for developing a program logic for SI transactions, our second implementation is more practical due to its non-prescience. We show that both implementations are sound and complete against the declarative SI specification and thus yield equivalent operational definitions for SI. We further consider, for the first time formally, the use of SI in a context with racy non-transactional accesses, as can arise in STM implementations of SI. We introduce robust snapshot isolation (RSI), an adaptation of SI with similar semantics and guarantees in this mixed setting. We present a declarative specification of RSI as an acyclicity axiom and analogously develop two operational models as lock-based reference implementations (one eager, one lazy). We show that these operational models are both sound and complete against the declarative RSI model.

Original languageEnglish
Title of host publicationVerification, Model Checking, and Abstract Interpretation - 20th International Conference, VMCAI 2019, Proceedings
EditorsRuzica Piskac, Constantin Enea
PublisherSpringer Verlag
Pages1-23
Number of pages23
ISBN (Print)9783030112448
DOIs
StatePublished - 2019
Event20th International Conference on Verification, Model Checking, and Abstract Interpretation, VMCAI 2019 - Cascais, Portugal
Duration: 13 Jan 201915 Jan 2019

Publication series

NameLecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)
Volume11388 LNCS
ISSN (Print)0302-9743
ISSN (Electronic)1611-3349

Conference

Conference20th International Conference on Verification, Model Checking, and Abstract Interpretation, VMCAI 2019
Country/TerritoryPortugal
CityCascais
Period13/01/1915/01/19

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