Lazy State Determination for SQL databases

Transactional systems have seen various efforts to increase their throughput, mainly by making use of parallelism and efficient Concurrency Control techniques. Most approaches optimize the systems’ behaviour when under high contention. In this work, we strive towards reducing the system’s overall contention through Lazy State Determination (LSD). LSD is a new transactional API that leverages on futures to delay the accesses to the Database as much as possible, reducing the amount of time that transactions require to operate under isolation and, thus, reducing the contention window. LSD was shown to be a promising solution for Key-Value Stores. Now, our focus turns to Relational Database Management Systems, as we attempt to implement and evaluate LSD in this new setting. This implementation was done through a custom JDBC driver to minimize required modifications to any external platform. Results show that the reduction of the contention window effectively improves the success rate of transactional applications. However, our current implementation exhibits some performance issues that must be further investigated and addressed.Os sistemas transacionais têm sido alvo de esforços variados para aumentar a sua velocidade de processamento, principalmente através de paralelismo e de técnicas de controlo de concorrência mais eficazes. A maior parte das soluções propostas visam a otimização do comportamento destes sistemas em ambientes de elevada contenção. Neste trabalho, nós iremos reduzir a contenção no sistema recorrendo ao Lazy State Determination (LSD). O LSD é uma nova API transacional que promove a utilização de futuros para adiar o máximo os acessos à Base de Dados, reduzindo assim o tempo que cada transação requer para executar em isolamento e, por consequência, reduzindo também a janela de contenção. O LSD tem-se mostrado uma solução promissora para bases de dados Chave-Valor. O nosso foco foi agora redirecionado para Sistemas de Gestão de Bases de Dados Relacionais, com uma tentativa de implementação e avaliação do LSD neste novo contexto. Este objetivo foi concretizado através da implementação de um controlador JDBC para minimizar quaisquer alterações a plataformas externas. Os resultados mostram que a redução da janela de contenção efetivamente melhora a taxa de sucesso de aplicações transacionais. No entanto, a nossa implementação atual tem alguns problemas de desempenho que necessitam de ser investigados e endereçados

Transactional concurrency control for resource constrained applications

PhD ThesisTransactions have long been used as a mechanism for ensuring the consistency of databases. Databases, and associated transactional approaches, have always been an active area of research as different application domains and computing architectures have placed ever more elaborate requirements on shared data access. As transactions typically provide consistency at the expense of timeliness (abort/retry) and resource (duplicate shared data and locking), there has been substantial efforts to limit these two aspects of transactions while still satisfying application requirements. In environments where clients are geographically distant from a database the consistency/performance trade-off becomes acute as any retrieval of data over a network is not only expensive, but relatively slow compared to co-located client/database systems. Furthermore, for battery powered clients the increased overhead of transactions can also be viewed as a significant power overhead. However, for all their drawbacks transactions do provide the data consistency that is a requirement for many application types. In this Thesis we explore the solution space related to timely transactional systems for remote clients and centralised databases with a focus on providing a solution, that, when compared to other's work in this domain: (a) maintains consistency; (b) lowers latency; (c) improves throughput. To achieve this we revisit a technique first developed to decrease disk access times via local caching of state (for aborted transactions) to tackle the problems prevalent in real-time databases. We demonstrate that such a technique (rerun) allows a significant change in the typical structure of a transaction (one never before considered, even in rerun systems). Such a change itself brings significant performance success not only in the traditional rerun local database solution space, but also in the distributed solution space. A byproduct of our improvements also, one can argue, brings about a "greener" solution as less time coupled with improved throughput affords improved battery life for mobile devices