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POPL 2019
Sun 13 - Sat 19 January 2019 Cascais, Portugal
Tue 15 Jan 2019 16:00 - 16:30 at Sala III - Networks and Concurrency Chair(s): Cezara Drăgoi

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.

Tue 15 Jan
Times are displayed in time zone: Greenwich Mean Time : Belfast change

16:00 - 17:30
Networks and ConcurrencyVMCAI at Sala III
Chair(s): Cezara DrăgoiINRIA, ENS, CNRS
On the Semantics of Snapshot Isolation
Azalea RaadMPI-SWS, Germany, Ori LahavTel Aviv University, Viktor VafeiadisMPI-SWS, Germany
Fast BGP Simulation of Large Datacenters
Nuno P. LopesMicrosoft Research, Andrey RybalchenkoMicrosoft Research
Parametric Timed Broadcast Protocols
Étienne AndréLIPN, CNRS UMR 7030, Université Paris 13, Benoit Delahaye, Paulin Fournier, Didier Lime
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